Epitaxial oxide materials, structures, and devices

Abstract

The semiconductor structure may include two or more epitaxial oxide materials with different properties such as composition, crystal symmetry, band gap, etc. The semiconductor structure may include one or more epitaxial oxide layers formed on a compatible substrate with in-plane lattice parameters and atomic positions that provide a suitable template for the growth of the epitaxial oxide materials. The epitaxial oxide material or materials may be strained. The epitaxial oxide material or materials may be doped n-type or p-type. The semiconductor structure may include a superlattice with the epitaxial oxide materials. The semiconductor structure may include a chirped layer with the epitaxial oxide materials. The semiconductor structure may be part of a semiconductor device such as an optoelectronic device, a light emitting diode, a laser diode, a photodetector, a solar cell, a high power diode, a high power transistor, a transducer, or a high electron mobility transistor.

Description

[Technical Field]

[0001] Related Applications This application claims priority to International Application No. PCT / IB2021 / 060414, filed November 10, 2021, entitled "Ultrawide Bandgap Semiconductor Devices Including Magnesium Germanium Oxides," International Application No. PCT / IB2021 / 060413, filed November 10, 2021, entitled "Epitaxial Oxide Materials, Structures and Devices," and International Application No. PCT / IB2021 / 060427, filed November 10, 2021, entitled "Epitaxial Oxide Materials, Structures, and Devices," all of which are incorporated herein by reference for all purposes.

[0002] This application is related to U.S. Non-Provisional Patent Application No. 16 / 990,349, filed August 11, 2020, and entitled "Metal Oxide Semiconductor-Based Light Emitting Device," all of which are incorporated herein by reference for all purposes.

[0003] The following publications are referenced in this application, the contents of which are incorporated herein by reference in their entireties: U.S. Patent No. 9,412,911, entitled "OPTICAL TUNING OF LIGHT EMITTING SEMICONDUCTOR JUNCTIONS," issued August 9, 2016, and is assigned to the present applicant. U.S. Patent No. 9,691,938, entitled "ADVANCED ELECTRONIC DEVICE STRUCTURES USING SEMICONDUCTOR STRUCTURES AND SUPERLATTICES," issued June 27, 2017, and is assigned to the present applicant. U.S. Patent No. 10,475,956, entitled "OPTOELECTRONIC DEVICE," issued November 12, 2019, and is assigned to the present applicant.

[0004] The contents of each of the above publications are expressly incorporated by reference in their entirety. [Background technology]

[0005] Electronic and optoelectronic devices such as diodes, transistors, photodetectors, LEDs, and lasers can use epitaxial semiconductor structures to control the transport of free carriers, detect light, or generate light. Wide bandgap semiconductor materials, such as those with a bandgap greater than about 4 eV, are useful for several applications, such as high-power and optoelectronic devices that detect or emit light in ultraviolet (UV) wavelengths.

[0006] For example, UV light-emitting devices (UVLEDs) have many applications in medicine, medical diagnostics, water purification, food processing, sterilization, aseptic packaging, and deep submicron lithography processes. Emerging applications in biosensing, communications, pharmaceutical processing, and materials manufacturing are also enabled by providing ultrashort wavelength light sources in compact, lightweight packages with high electrical conversion efficiency, such as UVLEDs. Highly efficient electro-optical conversion of electrical energy to discrete optical wavelengths has generally been achieved using semiconductors with the necessary properties to achieve spatial recombination of electron and hole charge carriers to emit light at the required wavelength. When UV light is required, UVLEDs have been developed almost exclusively using gallium-indium-aluminum-nitride (GaInAlN) compositions, which form a wurtzite crystal structure.

[0007] In another example, high-power RF switches are used in transceivers in wireless communication systems to separate, amplify, and filter transmit and receive signals. A requirement for the transistor devices that make up such RF switches is that they can handle high voltages without damage. Typical RF switches use transistor devices employing low-bandgap semiconductors (e.g., Si or GaAs) with relatively low breakdown voltages (e.g., less than approximately 3 V), and therefore many transistor devices are connected in series to withstand the required voltages. To reduce the number of transistor devices connected in series and improve the maximum voltage limits of RF switches, wider-bandgap semiconductors (e.g., GaN) with higher breakdown voltages are being used. An additional advantage of using wider-bandgap semiconductors such as GaN in RF switches is that they simplify impedance matching with microwave circuits. Summary of the Invention [Means for solving the problem]

[0008] In some embodiments, the semiconductor structure includes an epitaxial oxide material. In some embodiments, the semiconductor structure includes two or more epitaxial oxide materials with different properties, such as composition, crystal symmetry, or bandgap. The semiconductor structure may include one or more epitaxial oxide layers formed on a compatible substrate with in-plane lattice parameters and atomic positions that provide a suitable template for growth of the epitaxial oxide materials. In some embodiments, one or more of the epitaxial oxide materials is strained. In some embodiments, one or more of the epitaxial oxide materials is doped n-type or p-type. In some embodiments, the semiconductor structure includes a superlattice with epitaxial oxide materials. In some embodiments, the semiconductor structure includes a chirped layer with epitaxial oxide materials.

[0009] The semiconductor structures described herein can be part of semiconductor devices such as optoelectronic devices, light emitting diodes, laser diodes, photodetectors, solar cells, high power diodes, high power transistors, transducers, or high electron mobility transistors, having wavelengths from infrared to deep ultraviolet. In some embodiments, the semiconductor devices have high breakdown voltages due to the properties of the epitaxial oxide material therein. In some embodiments, the semiconductor devices use an impact ionization mechanism for carrier multiplication.

[0010] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a process flow diagram for constructing a metal oxide semiconductor-based LED according to an exemplary embodiment of the present disclosure. [Figure 2] 1A and 1B illustrate schematic diagrams of two classes of LED devices based on vertical and waveguide light confinement and emission disposed on a substrate, according to exemplary embodiments of the present disclosure. [Figure 3A] 1A-1C are schematic diagrams of different LED device configurations according to exemplary embodiments of the present disclosure including multiple regions. [Figure 3B] 1A-1C are schematic diagrams of different LED device configurations according to exemplary embodiments of the present disclosure including multiple regions. [Figure 3C] 1A-1C are schematic diagrams of different LED device configurations according to exemplary embodiments of the present disclosure including multiple regions. [Figure 3D] 1A-1C are schematic diagrams of different LED device configurations according to exemplary embodiments of the present disclosure including multiple regions. [Figure 3E] 1A-1C are schematic diagrams of different LED device configurations according to exemplary embodiments of the present disclosure including multiple regions. [Figure 4] 10A-B schematically illustrate injection of oppositely charged carriers from a physically separated region into a recombination region, according to an exemplary embodiment of the present disclosure. [Figure 5]1 illustrates possible light emission directions from the light emitting area of ​​an LED, according to an exemplary embodiment of the present disclosure. [Figure 6] 10 illustrates an opening through an opaque region that allows light to be emitted from an LED, according to an exemplary embodiment of the present disclosure. [Figure 7] 1 illustrates exemplary selection criteria for constructing a metal oxide semiconductor structure according to exemplary embodiments of the present disclosure. [Figure 8] FIG. 1 is an exemplary process flow diagram for selecting and epitaxially depositing a metal oxide structure according to an exemplary embodiment of the present disclosure. [Figure 9] Summary of technologically relevant semiconductor band gaps as a function of electron affinity, showing relative band lineups. [Figure 10] 1 is an exemplary schematic process flow for depositing multiple layers that form multiple regions containing LEDs, according to an exemplary embodiment of the present disclosure. [Figure 11] 1 is a ternary alloy photonic bandgap tuning curve for a gallium oxide-based metal oxide semiconductor ternary composition according to an exemplary embodiment of the present disclosure. [Figure 12] 1 is a ternary alloy photonic bandgap tuning curve for an aluminum oxide-based metal oxide semiconductor ternary composition according to an exemplary embodiment of the present disclosure. [Figure 13A] 1 is a representation of electron energy versus crystal momentum for a metal oxide-based optoelectronic semiconductor exhibiting a direct bandgap, according to an exemplary embodiment of the present disclosure. [Figure 13B] 1 is a representation of electron energy versus crystal momentum for a metal oxide-based optoelectronic semiconductor exhibiting an indirect bandgap, according to an exemplary embodiment of the present disclosure. [Figure 13C] 1 is a representation of electron energy versus crystal momentum showing allowed optical emission and absorption transitions at k=0 with respect to the Ga2O3 monoclinic crystal symmetry axis, according to an exemplary embodiment of the present disclosure. [Figure 13D]1 is a representation of electron energy versus crystal momentum showing allowed optical emission and absorption transitions at k=0 with respect to the Ga2O3 monoclinic crystal symmetry axis, according to an exemplary embodiment of the present disclosure. [Figure 13E] 1 is a representation of electron energy versus crystal momentum showing allowed optical emission and absorption transitions at k=0 with respect to the Ga2O3 monoclinic crystal symmetry axis, according to an exemplary embodiment of the present disclosure. [Figure 14] 1A and 1B illustrate the sequential deposition of multiple dissimilar metal oxide semiconductor layers with different crystal symmetry types to embed a light emitting region, according to an exemplary embodiment of the present disclosure. [Figure 15] FIG. 1 is a schematic diagram of an atomic deposition tool for creating a multilayer metal oxide semiconductor film including multiple material compositions, according to an exemplary embodiment of the present disclosure. [Figure 16] 1A-1C depict sequential deposition of layers and regions having similar crystal symmetry types that match a substrate, according to an exemplary embodiment of the present disclosure. [Figure 17] 1 illustrates the sequential deposition of regions having different crystal symmetries relative to a first surface of an underlying substrate, showing surface modifications to the substrate, according to an exemplary embodiment of the present disclosure. [Figure 18] 1 shows a buffer layer deposited with the same crystal symmetry as the underlying substrate to enable subsequent heterosymmetric deposition of oxide materials, according to an exemplary embodiment of the present disclosure. [Figure 19] 1 shows a structure including multiple heterosymmetric regions deposited sequentially as a function of growth direction, according to an exemplary embodiment of the present disclosure. [Figure 20A] 1 illustrates a crystal symmetry transition region linking two deposited crystal symmetry types, according to an exemplary embodiment of the present disclosure. [Figure 20B] 1 shows the change in specific crystal surface energy as a function of crystal surface orientation for corundum sapphire and monoclinic gallia single crystal oxide materials, according to an exemplary embodiment of the present disclosure. [Figure 21] 1A-C illustrate schematic diagrams of the change in electronic energy configuration or band structure of a metal oxide semiconductor under the influence of biaxial strain applied to the crystalline unit cell, according to exemplary embodiments of the present disclosure. [Figure 22] 1A and 1B illustrate schematic diagrams of the change in band structure of a metal oxide semiconductor under the influence of uniaxial strain applied to the crystalline unit cell, according to an exemplary embodiment of the present disclosure. [Figure 23] 1A-C illustrate the effect on the band structure of monoclinic gallium oxide as a function of uniaxial strain applied to the crystalline unit cell, according to exemplary embodiments of the present disclosure. [Figure 24] A and B show the Ek electron configurations of two different binary metal oxides according to exemplary embodiments of the present disclosure, one with a wide direct bandgap material and the other with a narrow indirect bandgap material. [Figure 25] 1A-C illustrate the effect of valence band mixing of two dissimilar binary metal oxide materials that together form a ternary metal oxide alloy, according to an exemplary embodiment of the present disclosure. [Figure 26] 1A and 1B illustrate schematic diagrams of a portion of the energy versus crystal momentum of the coherent valence bands provided by two bulk metal oxide semiconductor materials up to the first Brillouin zone, according to exemplary embodiments of the present disclosure. [Figure 27A] 1 illustrates the effect of a one-dimensional superlattice (SL) on the Ek configuration for a layered structure with a superlattice period equal to approximately twice the bulk lattice constant of the host metal oxide semiconductor, and demonstrates the creation of a superlattice Brillouin zone that opens an artificial bandgap at the zone center, according to an exemplary embodiment of the present disclosure. [Figure 27B] 1 illustrates the effect of a one-dimensional superlattice (SL) on the Ek configuration for a layered structure with a superlattice period equal to approximately twice the bulk lattice constant of the host metal oxide semiconductor, and demonstrates the creation of a superlattice Brillouin zone that opens an artificial bandgap at the zone center, according to an exemplary embodiment of the present disclosure. [Figure 27C] The digital alloy exhibits a two-layer binary superlattice comprising multiple thin epitaxial layers of Al2O3 and Ga2O3 repeating in a fixed unit cell period that simulates an equivalent ternary AlxGa1-xO3 bulk alloy according to the constituent layer thickness ratios of the superlattice period, in accordance with an exemplary embodiment of the present disclosure. [Figure 27D]The digital alloy represents another two-layer binary superlattice comprising multiple thin epitaxial layers of NiO and GaO repeated in a fixed unit cell period that simulates an equivalent ternary (NiO)(GaO) bulk alloy according to the constituent layer thickness ratios of the superlattice period, in accordance with exemplary embodiments of the present disclosure. [Figure 27E] Figure 1 shows yet another ternary material binary superlattice comprising multiple thin epitaxial layers of MgO, NiO repeated in a fixed unit cell period, where the digital alloy simulates an equivalent ternary bulk alloy (NiO)x(MgO)1-x depending on the constituent layer thickness ratio of the superlattice period, and the binary metal oxides used in the repeating units are each selected to vary in thickness between 1 and 10 unit cells, which together constitute a unit cell of the SL according to an exemplary embodiment of the present disclosure. [Figure 27F] Figure 1 shows yet another possible four-material binary superlattice comprising multiple thin epitaxial layers of MgO, NiO, and GaO repeated in a fixed unit cell period, where the binary metal oxides used in the repeating units are each selected to vary in thickness from 1 to 10 unit cells, simulating the equivalent quaternary bulk alloy (NiO)x(GaO3)y(MgO)z depending on the constituent layer thickness ratios of the superlattice period comprising the unit cell of the SL according to an exemplary embodiment of the present disclosure. [Figure 28] 1 shows a chart of ternary metal oxide combinations that may be employed in forming optoelectronic devices according to various exemplary embodiments of the present disclosure. [Figure 29] FIG. 10 is an exemplary design flow diagram for tailoring and building optoelectronic functionality of an LED region, according to an exemplary embodiment of the present disclosure. [Figure 30] 1 illustrates the heterojunction band lineup of binary Al2O3, ternary alloy (Al,Ga)O3, and binary Ga2O3 semiconductor oxides according to exemplary embodiments of the present disclosure. [Figure 31] 1 illustrates a three-dimensional crystal unit cell of the corundum symmetric crystal structure (alpha phase) Al2O3 used to calculate the Ek band structure, according to an exemplary embodiment of the present disclosure. [Figure 32] 1A and 1B show calculated energy-momentum configurations of alpha Al2O3 near the Brillouin zone center, according to exemplary embodiments of the present disclosure. [Figure 33] 1 illustrates a three-dimensional crystal unit cell of Al2O3 with monoclinic symmetry crystal structure used to calculate the Ek band structure, according to an exemplary embodiment of the present disclosure. [Figure 34] 1A and 1B show calculated energy-momentum configurations of theta-Al2O3 near the Brillouin zone center, according to exemplary embodiments of the present disclosure. [Figure 35] 1 illustrates a three-dimensional crystal unit cell of the corundum-symmetric crystal structure (alpha phase) Ga2O3 used to calculate the Ek band structure, according to an exemplary embodiment of the present disclosure. [Figure 36] 1A and 1B show calculated energy-momentum configurations of corundum alpha Ga2O3 near the Brillouin zone center, according to exemplary embodiments of the present disclosure. [Figure 37] 1 illustrates a three-dimensional crystal unit cell of monoclinic symmetry crystal structure (beta phase) Ga2O3 used to calculate the Ek band structure, according to an exemplary embodiment of the present disclosure. [Figure 38] 1A and 1B show calculated energy-momentum configurations of beta-Ga2O3 near the center of the Brillouin zone, according to exemplary embodiments of the present disclosure. [Figure 39] 1 illustrates a three-dimensional crystal unit cell of the orthorhombic symmetric crystal structure of a bulk ternary alloy of (Al,Ga)O3 used to calculate the Ek band structure, according to an exemplary embodiment of the present disclosure. [Figure 40] 1 shows the calculated energy-momentum configuration of (Al,Ga)O 3 near the center of the Brillouin zone, exhibiting a direct bandgap, according to an exemplary embodiment of the present disclosure. [Figure 41] FIG. 1 is a process flow diagram for forming an optoelectronic semiconductor device according to an exemplary embodiment of the present disclosure. [Figure 42]1 shows a cross-sectional portion of an (Al,Ga)O3 ternary structure formed by sequentially depositing Al-O-Ga-O-...-O-Al epilayers along the growth direction according to an exemplary embodiment of the present disclosure. [Figure 43A] The selection of substrate crystals for depositing metal oxide structures according to various exemplary embodiments of the present disclosure is shown in Table I. [Figure 43B] The unit cell parameters of a selection of metal oxides according to various exemplary embodiments of the present disclosure, illustrating the lattice constant mismatch between Al2O3 and Ga2O3, are shown in Table II. [Figure 44A] 1 shows the calculated energy of formation of aluminum-gallium-oxide ternary alloys as a function of composition and crystal symmetry, according to an exemplary embodiment of the present disclosure. [Figure 44B] 1 shows experimental high-resolution X-ray diffraction (HRXRD) of two different compositional example high-quality single-crystalline ternary (AlxGa1-x)2O3 epitaxially deposited on a bulk (010)-oriented Ga2O3 substrate, according to an exemplary embodiment of the present disclosure. [Figure 44C] 1 shows experimental HRXRD and grazing incidence X-ray reflectivity (GIXR) of an exemplary superlattice comprising two repeating unit cells selected from [(AlxGa1-x)2O3 / Ga2O3] elastically strained on a β-Ga2O3 (010) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44D] 1 shows experimental HRXRD and GIXR of two exemplary different compositions of high-quality single-crystalline ternary (AlxGa1-x)2O3 layers epitaxially deposited on bulk (001)-oriented Ga2O3 substrates, according to exemplary embodiments of the present disclosure. [Figure 44E] 1 shows experimental HRXRD and GIXR of a superlattice containing two layers of repeating unit cells selected from [(AlxGa1-x)2O3 / Ga2O3] elastically strained on a β-Ga2O3 (001) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44F] 1 shows experimental HRXRD and GIXR of a cubic crystal symmetry binary nickel oxide (NiO) epilayer elastically strained on a monoclinic crystal symmetry β-GaO(001) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44G] 1 shows experimental HRXRD and GIXR of an elastically strained monoclinic crystal symmetry Ga2O3 (100) oriented epilayer on a cubic crystal symmetry MgO (100) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44H] Figure 1 shows experimental HRXRD and GIXR of a superlattice containing two layers of repeating unit cells selected from [(AlxEr1-x)2O3 / Al2O3] elastically strained on a corundum crystal symmetric α-Al2O3 (001) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44I] FIG. 1 shows the distortion-free energy-crystal momentum (Ek) dispersion near the Brillouin zone center for ternary aluminum-erbium-oxide (AlxEr1-x)2O3 exhibiting a direct bandgap at Γ(k=0), in accordance with an exemplary embodiment of the present disclosure. [Figure 44J] Experimental HRXRD and GIXR of a superlattice consisting of two-layer unit cells of monoclinic crystal symmetry Ga2O3(100) oriented films bonded to a cubic (spinel) crystal symmetry ternary composition of magnesium-gallium-oxide, MgxGa2(1-x)O3-2x, where the SL is epitaxially deposited on a monoclinic Ga2O3(010) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44K] Figure 1 shows the distortion-free energy-crystal momentum (Ek) dispersion near the Brillouin zone center for ternary magnesium-gallium-oxides MgxGa2(1-x)O3-2x, which exhibit a direct bandgap at Γ(k=0), according to an exemplary embodiment of the present disclosure. [Figure 44L] 1 shows experimental HRXRD and GIXR of an elastically strained orthorhombic GaO epilayer on a cubic crystal symmetry magnesium-aluminum-oxide MgAlO (100) oriented substrate according to an exemplary embodiment of the present disclosure. [Figure 44M] 1 shows experimental HRXRD of an elastically strained ternary zinc-gallium-oxide ZnGa2O4 epilayer on a wurtzite zinc oxide ZnO layer deposited on a monoclinic crystal symmetry gallium oxide (-201) oriented substrate according to an exemplary embodiment of the present disclosure. [Figure 44N]Figure 1 shows the distortion-free energy-crystal momentum (Ek) dispersion near the Brillouin zone center for ternary cubic zinc-gallium-oxide ZnxGa2(1-x)O3-2x (x=0.5) exhibiting an indirect bandgap at Γ(k=0), in accordance with an exemplary embodiment of the present disclosure. [Figure 44O] 1 illustrates an epitaxial layer stack deposited along the growth direction for an orthorhombic GaO crystalline symmetric film using an intermediate layer and a prepared substrate surface according to an exemplary embodiment of the present disclosure. [Figure 44P] 1 shows experimental HRXRD of two distinctly different crystal symmetry binary GaO compositions deposited on rhomboidal sapphire α-AlO(0001) oriented substrates controlled by growth conditions, according to exemplary embodiments of the present disclosure. [Figure 44Q] FIG. 1 illustrates distortion-free energy-crystal momentum (Ek) dispersion near the Brillouin zone center for binary orthorhombic gallium-oxide exhibiting a direct bandgap at Γ(k=0), according to an exemplary embodiment of the present disclosure. [Figure 44R] 1 shows experimental HRXRD and GIXR of two exemplary different compositions of high-quality single-crystal corundum symmetric ternary (AlxGa1-x)2O3 epitaxially deposited on a bulk (1-100) oriented corundum crystalline symmetric Al2O3 substrate, according to exemplary embodiments of the present disclosure. [Figure 44S] 1 shows experimental HRXRD of a monoclinic top active GaO epilayer deposited on a ternary erbium-gallium-oxide (ErGa)O transition layer deposited on a single-crystal silicon (111) oriented substrate, according to an exemplary embodiment of the present disclosure. [Figure 44T] 1 shows experimental HRXRD and GIXR of an exemplary high-quality single-crystal corundum symmetry binary GaO epitaxially deposited on a bulk (11-20) oriented corundum crystalline symmetry AlO substrate, where two thicknesses of GaO are shown to be pseudomorphically strained (i.e., elastic deformation of the bulk GaO unit cell) relative to the underlying AlO substrate, according to an exemplary embodiment of the present disclosure. [Figure 44U]Experimental HRXRD and GIXR are shown for an exemplary high-quality single-crystal corundum symmetry superlattice comprising two layers of binary pseudomorphic GaO and AlO epitaxially deposited on a bulk (11-20) oriented corundum crystalline symmetry AlO substrate, where the superlattice [AlO / GaO] demonstrates the unique properties of corundum crystalline symmetry, according to an exemplary embodiment of the present disclosure. [Figure 44V] 1 shows an experimental transmission electron micrograph (TEM) of a high-quality single crystal superlattice made of SL[Al2O3 / Ga2O3] deposited on a corundum Al2O3 substrate exhibiting low dislocation defect density, according to an exemplary embodiment of the present disclosure. [Figure 44W] 1 shows experimental HRXRD of a corundum crystal symmetric top active (AlxGa1-x)2O3 epilayer deposited on a single corundum Al2O3 (1-102) oriented substrate according to an exemplary embodiment of the present disclosure. [Figure 44X] We present experimental HRXRD and GIXR of an exemplary high-quality single-crystal corundum symmetric superlattice comprising two layers of ternary pseudomorphic (AlxGa1-x)2O3 and Al2O3 epitaxially deposited on a bulk (1-102)-oriented corundum crystalline symmetry Al2O3 substrate according to an exemplary embodiment of the present disclosure, and the superlattice [Al2O3 / (AlxGa1-x)2O3] demonstrates the unique properties of corundum crystalline symmetry. [Figure 44Y] 1 shows experimental wide-angle HRXRD of a cubic crystal symmetry top active magnesium oxide MgO epilayer deposited on a single crystal cubic (spinel) magnesium-aluminum-oxide MgAl2O4 (100) oriented substrate according to an exemplary embodiment of the present disclosure. [Figure 44Z] Figure 1 shows the distortion-free energy-crystal momentum (Ek) dispersion near the Brillouin zone center for ternary magnesium-aluminum-oxide MgxAl2(1-x)O3-2x (x=0.5) exhibiting a direct bandgap at Γ(k=0), in accordance with an exemplary embodiment of the present disclosure. [Figure 45]1A and 1B illustrate schematic diagrams of epitaxial regions of metal oxide UV LEDs with pin heterojunction diodes and multiple quantum wells for tuning emission energy, according to exemplary embodiments of the present disclosure. [Figure 46] FIG. 46 is an energy band diagram versus growth direction for the epitaxial metal oxide UV LED structure shown in FIG. 45, where the k=0 representation of the band structure is plotted according to an exemplary embodiment of the present disclosure. [Figure 47] 47 illustrates a spatial carrier confinement structure of a multiple quantum well (MQW) region of FIG. 46, in which the MQW region has a narrow band gap material including Ga2O3, with quantized electron and hole wave functions that spatially recombine within the MQW region to produce a predetermined emitted photon energy determined by their respective quantized states in the conduction and valence bands, according to an exemplary embodiment of the present disclosure. [Figure 48] 48 shows a calculated optical absorption spectrum for the device structure of FIG. 47 in which the lowest energy electron-hole recombination is determined by quantized energy levels within the MQW, resulting in sharp, discrete absorption / emission energies, according to an exemplary embodiment of the present disclosure. [Figure 49] 1 is an energy band diagram versus growth direction of an epitaxial metal oxide UV LED structure in which the MQW region has a narrow band gap material including (Al0.05Ga0.95)2O3, according to an exemplary embodiment of the present disclosure. [Figure 50] 49A and 49B show calculated optical absorption spectra for the device structure of FIG. 49, in which the lowest energy electron-hole recombination is determined by quantized energy levels within the MQW, resulting in sharp, discrete absorption / emission energies, according to an exemplary embodiment of the present disclosure. [Figure 51] 1 is an energy band diagram versus growth direction of an epitaxial metal oxide UV LED structure in which the MQW region has a narrow band gap material comprising (Al0.1Ga0.9)2O3, according to an exemplary embodiment of the present disclosure. [Figure 52]49A and 49B show calculated optical absorption spectra for the device structure of FIG. 49, in which the lowest energy electron-hole recombination is determined by quantized energy levels within the MQW, resulting in sharp, discrete absorption / emission energies, according to an exemplary embodiment of the present disclosure. [Figure 53] 1 is an energy band diagram versus growth direction of an epitaxial metal oxide UV LED structure in which the MQW region has a narrow band gap material comprising (Al 0.2 Ga 0.8) 2 O 3 according to an exemplary embodiment of the present disclosure. [Figure 54] 54 shows a calculated optical absorption spectrum for the device structure of FIG. 53 in which the lowest energy electron-hole recombination is determined by quantized energy levels within the MQW, resulting in sharp, discrete absorption / emission energies, according to an exemplary embodiment of the present disclosure. [Figure 55] 1 is a plot of the work function energies of pure metals, sorted from high to low work function for application in p-type and n-type ohmic contacts to metal oxides according to an exemplary embodiment of the present disclosure. [Figure 56] 1 is a reciprocal lattice map dual-axis X-ray diffraction pattern of pseudomorphic ternary (AlGa)O on an A-plane AlO substrate, according to an exemplary embodiment of the present disclosure. [Figure 57] 1 is a dual-axis X-ray diffraction pattern of pseudomorphic 10-period SL[Al2O3 / Ga2O3] on an A-plane Al2O3 substrate showing in-plane lattice matching throughout the structure, according to an exemplary embodiment of the present disclosure. [Figure 58] 1A and 1B show the optical mode structure and threshold gain of a slab of metal oxide semiconductor material according to an exemplary embodiment of the present disclosure. [Figure 59] 1A and 1B show the optical mode structure and threshold gain of a slab of metal oxide semiconductor material according to another exemplary embodiment of the present disclosure. [Figure 60] 1 illustrates an optical cavity formed using an optical gain medium embedded between two optical reflectors, according to an exemplary embodiment of the present disclosure. [Figure 61]1 illustrates an optical cavity formed using an optical gain medium embedded between two optical reflectors, according to an exemplary embodiment of the present disclosure, showing that two optical wavelengths can be supported by the gain medium and cavity length. [Figure 62] 1 illustrates an optical cavity formed using an optical gain medium of finite thickness embedded between two optical reflectors and positioned at the peak electric field strength of the fundamental wavelength mode, showing that only one optical wavelength can be supported by the gain medium and cavity length, according to an exemplary embodiment of the present disclosure. [Figure 63] 1 illustrates an optical cavity formed using two optical gain media of finite thickness embedded between two optical reflectors and positioned at the peak electric field strength of the shorter wavelength mode, showing that only one optical wavelength can be supported by the gain media and cavity length, according to an exemplary embodiment of the present disclosure. [Figure 64] 1A and 1B show a single quantum well structure comprising a metal oxide ternary material with quantized electron and hole states according to an exemplary embodiment of the present disclosure showing two different quantum well thicknesses. [Figure 65] 1A and 1B are diagrams illustrating a single quantum well structure including a metal oxide ternary material with quantized electron and hole states according to an exemplary embodiment of the present disclosure, showing two different quantum well thicknesses. [Figure 66] 64A, 64B, 65A and 65B show spontaneous emission spectra from the disclosed quantum well structures. [Figure 67] 1A and 1B show the spatial energy band structure and associated energy-crystal momentum band structure of a metal oxide quantum well according to an exemplary embodiment of the present disclosure. [Figure 68] A and B show the electron and hole population inversion mechanism in the quantum well band structure and the resulting gain spectrum of the quantum well. [Figure 69] A and B show the energy states of electrons and holes in the filled conduction and valence bands in energy momentum space for direct and pseudo-direct band gap metal oxide structures according to exemplary embodiments of the present disclosure. [Figure 70] 1A and 1B illustrate the metal oxide injected hot electron impact ionization process resulting in pair creation according to an exemplary embodiment of the present disclosure. [Figure 71] 1A and 1B illustrate a metal oxide injected hot electron impact ionization process resulting in pair creation according to another exemplary embodiment of the present disclosure. [Figure 72] 10A and 10B show the effect of an electric field applied to a metal oxide to generate multiple impact ionization events, according to another exemplary embodiment of the present disclosure. [Figure 73] 1 illustrates a vertical ultraviolet laser structure according to an exemplary embodiment of the present disclosure, in which a reflector forms part of the cavity and the electrical circuit. [Figure 74] 1 illustrates a vertical ultraviolet laser structure according to an exemplary embodiment of the present disclosure, in which the reflector forming the optical cavity is isolated from the electrical circuitry. [Figure 75] 1 illustrates a waveguide-type ultraviolet laser structure according to an exemplary embodiment of the present disclosure, in which the reflector forming the optical cavity is decoupled from the electrical circuitry, and the optical gain medium embedded within the lateral cavity can have a length optimized for low threshold gain. [Figure 76A-1] A table showing the crystal symmetry (or space group), lattice constants ('a', 'b' and 'c' for different crystal directions, in Angstroms), band gap (minimum band gap energy, in eV), and wavelength of light ('λ_g', in nm) corresponding to the band gap energy of various materials is shown. [Figure 76A-2] A table showing the crystal symmetry (or space group), lattice constants ('a', 'b' and 'c' for different crystal directions, in Angstroms), band gap (minimum band gap energy, in eV), and wavelength of light ('λ_g', in nm) corresponding to the band gap energy of various materials is shown. [Figure 76B]1 shows a chart of the band gap (minimum band gap energy, in eV) versus, and in some cases, the crystal symmetry (e.g., α-, β-, γ-, and κ-AlxGa1-xOy) versus the lattice constant (in Angstroms) of the epitaxial oxide material for several epitaxial oxide materials. [Figure 76C] The chart shown in Figure 76B further illustrates the lattice constant size classification of epitaxial oxides. [Figure 76D] 1 shows a plot of lattice constant "a" versus lattice constant "b" for selected epitaxial oxides. [Figure 76E] 1 shows a chart of the calculated band gaps (minimum band gap energy, in eV) of several epitaxial oxide materials. [Figure 76F] 1 shows a chart of the calculated band gaps (minimum band gap energy, in eV) of several epitaxial oxide materials. [Figure 76G] 1 shows a chart of the calculated band gaps (minimum band gap energy, in eV) of several epitaxial oxide materials. [Figure 76H] 1 shows a chart of the calculated band gaps (minimum band gap energy, in eV) of several epitaxial oxide materials. [Figure 77] FIG. 76A is a flowchart illustrating a process for forming epitaxial materials described in the present disclosure, including those in the tables of FIGS. 76A-1 and 76A-2. [Figure 78] FIG. 1 is a schematic diagram using the metaphor of a seesaw to illustrate what happens when elements are added to an epitaxial oxide. [Figure 79] 1 is a plot of shear modulus (in GPa) versus bulk modulus (in GPa) for several example epitaxial oxide materials. [Figure 80] 1 is a plot of Poisson's ratio for several epitaxial oxide materials. [Figure 81A] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81B] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81C] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81D] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81E] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81F] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81G] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81H] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81I] 1 illustrates an example of a semiconductor structure that includes epitaxial oxide material in a layer or region. [Figure 81J] Additional examples of semiconductor structures that include epitaxial oxide materials in layers or regions are provided. [Figure 81K] Additional examples of semiconductor structures that include epitaxial oxide materials in layers or regions are provided. [Figure 81L] Additional examples of semiconductor structures that include epitaxial oxide materials in layers or regions are provided. [Figure 82A] 1 is a schematic diagram of an example of a semiconductor structure including an epitaxial oxide layer on a suitable substrate. [Figure 82B] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82C] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82D]1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82E] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82F] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82G] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82H] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 82I] 1 is a plot showing electron energy (y-axis) versus growth direction (x-axis) for an embodiment of an epitaxial oxide heterostructure including a layer of a heterogeneous epitaxial oxide material. [Figure 83A] The relationship between electron energy and growth direction for three different example digital alloys is shown, along with examples of the wave functions of the confined electrons and holes in each case. [Figure 83B] The relationship between electron energy and growth direction for three different example digital alloys is shown, along with examples of the wave functions of the confined electrons and holes in each case. [Figure 83C] The relationship between electron energy and growth direction for three different example digital alloys is shown, along with examples of the wave functions of the confined electrons and holes in each case. [Figure 84] FIG. 83C is a chart showing a plot of effective band gap versus average composition (x) for the digital alloys shown in FIGS. 83A-83C. [Figure 85]1 shows a chart of several DFT-calculated epitaxial oxide materials' band gaps (minimum band gap energy in eV) versus, and in some cases, crystal symmetry versus lattice constants of, the epitaxial oxide materials. [Figure 86] FIG. 1 shows a schematic diagram illustrating how epitaxial oxide materials with monoclinic unit cells are compatible with epitaxial oxide materials with cubic unit cells. [Figure 87] Shown is a chart of several DFT calculated band gaps (minimum band gap energy in eV) versus lattice constants for epitaxial oxide materials, and in some cases, crystal symmetry versus lattice constants for epitaxial oxide materials, further illustrating groupings where epitaxial oxide materials within each group are compatible with other materials within the group. [Figure 88A] Shown is a chart of band gap (minimum band gap energy, in eV) versus lattice constant for several DFT-calculated epitaxial oxide materials, all of which have tetragonal crystalline symmetry with Fd3m or Fm3m space groups. [Figure 88B-1] 1 is a schematic diagram illustrating how an epitaxial oxide material having cubic symmetry with a relatively small lattice constant (e.g., equal to about 4 Angstroms) can be lattice matched (or have a small lattice mismatch) with an epitaxial oxide material with a relatively large lattice constant (e.g., equal to about 8 Angstroms). [Figure 88B-2] The crystal structure of NiAl2O4 with the Fd3m space group is shown. [Figure 88C] FIG. 88A shows a chart with lines connecting subsets of epitaxial oxide materials having composition (NixMgyZn1-xy)(AlqGa1-q)2O4, where 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0≦q≦1, or composition (NixMgyZn1-xy)GeO4, where 0≦x≦1, 0≦y≦1, and 0≦z≦1, and the shaded area is the convex hull of the connected materials shown on the plot. [Figure 88D]FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including MgAl2O4, ZnAl2O4, NiAl2O4, and some alloys thereof. [Figure 88E] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including "2ax MgO," γ-Ga2O3, MgAl2O4, ZnAl2O4, NiAl2O4, and some alloys thereof. [Figure 88F] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including MgAl2O4, MgGa2O4, ZnGa2O4, and some alloys thereof. [Figure 88G] Figure 88A shows a chart with lines connecting a subset of epitaxial oxide materials including "2ax NiO" (NiO where the plotted lattice constant is twice that of the NiO unit cell), "2ax MgO," γ-Al2O3, γ-Ga2O3, MgAl2O4, and some alloys thereof. [Figure 88H] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga 2 O 3 , MgGa 2 O 4 , Mg 2 GeO 4 , and some alloys thereof. [Figure 88I] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga2O3, MgGa2O4, "2ax MgO," and some alloys thereof. [Figure 88J] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga2O3, Mg2GeO4, "2ax MgO," and some alloys thereof. [Figure 88K] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including Ni2GeO4, Mg2GeO4, (Mg0.5Zn0.5)2GeO4, Zn(Al0.5Ga0.5)2O4, Mg(Al0.5Ga0.5)2O4, "2ax MgO," and some alloys thereof. [Figure 88L]FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga 2 O 3 , γ-Al 2 O 3 , MgAl 2 O 4 , ZnAl 2 O 4 , and some alloys thereof. [Figure 88M] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga2O3, γ-Al2O3, MgAl2O4, ZnAl2O4, "2ax MgO," and some alloys thereof, with the bulk alloy γ-(AlxGa1-x)2O3 shown along one of the lines. [Figure 88N] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including γ-Ga2O3, γ-Al2O3, MgAl2O4, ZnAl2O4, "2ax MgO," and some alloys thereof, where the digital alloy composition including a layer of (MgO)z((AlxGa1-x)2O3)1-z material is shown within the shaded area surrounded by the line. [Figure 88O] FIG. 88A shows a chart with lines connecting a subset of epitaxial oxide materials including MgGa2O4, ZnGa2O4, (Mg0.5Zn0.5)Ga2O4, (Mg0.5Ni0.5)Ga2O4, (Zn0.5Ni0.5)Ga2O4, "2ax NiO", "2ax MgO", and some alloys thereof. [Figure 89A] Shown is a chart of band gap (minimum band gap energy, in eV) versus lattice constant for several DFT-calculated epitaxial oxide materials, with lattice constants ranging from approximately 4.5 Å to 5.3 Å, and materials with non-cubic symmetries such as hexagonal and orthorhombic. [Figure 89B] Table showing DFT calculated properties of Li(AlxGa1-x)O2 films: space group ("SG"), lattice constants ("a" and "b") in Angstroms, and lattice mismatch ("%Δa" and "%Δb") between the LiGaO2 film and the listed possible substrates ("sub"). [Figure 90A] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of LiAlO2 with the P41212 space group is shown. [Figure 90B] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Li(Al0.5Ga0.5)O2 with the Pna21 space group is shown. [Figure 90C] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of LiGaO2 with Pna21 space group is shown. [Figure 90D] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of ZnAl2O4 with Fd3m space group is shown. [Figure 90E] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of ZnGa2O4 with Fd3m space group is shown. [Figure 90F] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of MgGa2O4 with Fd3m space group is shown. [Figure 90G] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of GeMg2O4 with the Fd3m space group. [Figure 90H] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of NiO with Fm3m space group is shown. [Figure 90I] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of MgO with Fm3m space group is shown. [Figure 90J] Calculated energy-crystal momentum (Ek) dispersion plots around the Brillouin zone center of SiO2 with the P3221 space group are shown. [Figure 90K] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of NiAl2O4 with the Imma space group. [Figure 90L] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of α-Al2O3 with the R3c space group. [Figure 90M]Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of α(Al0.75Ga0.25)2O3 with R3c space group. [Figure 90N] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of α(Al0.5Ga0.5)2O3 with the R3c space group. [Figure 90O] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of α(Al0.25Ga0.75)2O3 with the R3c space group. [Figure 90P] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of α-Ga2O3 with the R3c space group. [Figure 90Q] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of κGa2O3 with the Pna21 space group is shown. [Figure 90R] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of κ(Al0.5Ga0.5)2O3 with the Pna21 space group. [Figure 90S] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of κ-Al2O3 with the Pna21 space group. [Figure 90T] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of γGa2O3 with the Fd3m space group. [Figure 90U] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of MgAl2O4 with the Fd3m space group. [Figure 90V] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of NiAl2O4 with Fd3m space group is shown. [Figure 90W] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of MgNi2O4 with the Fd3m space group. [Figure 90X] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of GeNi2O4 with Fd3m space group is shown. [Figure 90Y] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Li2O with Fm3m space group is shown. [Figure 90Z] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Al2Ge2O7 with C2c space group is shown. [Figure 90AA] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Ga4Ge1O8 with C2m space group is shown. [Figure 90BB] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of NiGa2O4 with Fd3m space group is shown. [Figure 90CC] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Ga3N1O3 with R3m space group is shown. [Figure 90DD] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Ga3N1O3 with C2m space group is shown. [Figure 90EE] Calculated energy-crystal momentum (Ek) dispersion plots around the Brillouin zone center of MgF2 with the P42mnm space group are shown. [Figure 90FF] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of NaCl with Fm3m space group is shown. [Figure 90GG] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Mg0.75Zn0.25O with Fd3m space group is shown. [Figure 90HH] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of ErAlO3 with the P63mcm space group. [Figure 90II]Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Zn2Ge1O4 with R3 space group is shown. [Figure 90JJ] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of LiNi2O4 with the P4332 space group is shown. [Figure 90KK] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of GeLi4O4 with Cmcm space group is shown. [Figure 90LL] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of GeLi2O3 with the Cmc21 space group. [Figure 90MM] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Zn(Al0.5Ga0.5)2O4 with Fd3m space group is shown. [Figure 90NN] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Mg(Al0.5Ga0.5)2O4 with the Fd3m space group. [Figure 90OO] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of (Mg0.5Zn0.5)Al2O4 with the Fd3m space group. [Figure 90PP] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of (Mg0.5Ni0.5)Al2O4 with Fd3m space group is shown. [Figure 90QQ] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(AlGa1.0)2O3 (i.e., β(Ga2O3)) with the C2m space group. [Figure 90RR] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(Al0.125Ga0.875)2O3 with the C2m space group. [Figure 90SS]Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(Al0.25Ga0.75)2O3 with the C2m space group. [Figure 90TT] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(Al0.375Ga0.625)2O3 with the C2m space group. [Figure 90UU] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(Al0.5Ga0.5)2O3 with the C2m space group. [Figure 90VV] Figure 1 shows a calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of β(Al1.0Ga0.0)2O3 (i.e., θ-aluminum oxide) with C2m space group. [Figure 90WW] Calculated energy-crystal momentum (Ek) dispersion plots around the Brillouin zone center of GeO2 with the P42mnm space group are shown. [Figure 90XX] The calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of Ge(Mg0.5Zn0.5)2O4 (with the Fd3m space group) is shown. [Figure 90YY] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of (Ni0.5Zn0.5)Al2O4 with Fd3m space group is shown. [Figure 90ZZ] Calculated energy-crystal momentum (Ek) dispersion plot around the Brillouin zone center of LiF with the Fm3m space group is shown. [Figure 91] 1 shows the atomic crystal structure of the heterojunction between MgGa2O4 and MgAl2O4 epitaxial oxide materials. [Figure 92A] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [MgAl2O4]1|[MgGa2O4]1 with the Fd3m space group in the unit cell. [Figure 92B]Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [MgAl2O4]1|[Mg(Al0.5Ga0.5)2O4]1 with the Fd3m space group in the unit cell. [Figure 92C] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [MgAl2O4]1|[ZnAl2O4]1 with the Fd3m space group in the unit cell. [Figure 92D] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [MgGa2O4]1|[(Mg0.5Zn0.5)O]1 with the Fd3m space group in the unit cell. [Figure 92E] The calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [αAl2O3]2|[αGa2O3]2 with an R3c space group in the unit cell and A-plane growth direction is shown. [Figure 92F] The calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [αAl2O3]1|[αGa2O3]1 with an R3c space group in the unit cell and A-plane growth direction is shown. [Figure 92G] Figure 1 shows the calculated energy-crystal momentum (Ek) dispersion plot near the Brillouin zone center of a superlattice containing [GeMg2O4]1|[MgO]1 with the Fd3m / Fd3m space group in the unit cell. [Figure 93] The atomic crystal structure of β-(Al0.5Ga0.5)2O3 with space group C2m is shown. [Figure 94] The energy-crystal momentum (Ek) dispersion plots calculated by DFT around the Brillouin zone center of the superlattices with β-(Al0.5Ga0.5)2O3 and β-Ga2O3 are shown. [Figure 95A] Schematic of a coherently (and pseudomorphically) strained β-Ga2O3(100) film on an MgO(100) substrate, showing the in-plane unit cell alignment (along the “b” and “c” directions in the plan view). [Figure 95B] Schematic of a coherently (and pseudomorphically) strained β-Ga2O3(100) film on an MgO(100) substrate, showing the unit cell alignment along the growth direction ("a"), where the film lattice is rotated 45° relative to the substrate lattice. [Figure 96] The energy-crystal momentum (Ek) dispersion plot calculated by DFT around the Brillouin zone center of β-Ga2O3 pseudomorphically distorted on a 45° rotated MgO lattice is shown. [Figure 97] A schematic diagram of a superlattice formed from alternating layers of β-Ga2O3 and MgO (each layer having one or more unit cells) is shown, where the β-Ga2O3 layers are pseudomorphically distorted relative to the lattice of MgO rotated by 45°. [Figure 98A] 1 is a table of crystalline structure properties of exemplary epitaxial films and substrates compatible with Mg2GeO4. [Figure 98B] 1 is a table showing the compatibility of β-Ga2O3 with various heterostructure materials. [Figure 99] 1 is a table illustrating a selection of possible oxide material compositions including the constituent elements (Mg, Zn, Al, Ga, O). [Figure 100] 99 shows a schematic diagram of an epitaxial layer structure formed from at least two different materials further selected from the categories of Oxide_type_A and Oxide_type_B shown in FIG. [Figure 101] The single crystal orientation of an ultrawide bandgap cubic oxide composition containing ZnGa2O4 (ZGO) epitaxially deposited on the smaller bandgap wurtzite surface of SiC-4H is shown. [Figure 102] The atomic arrangement of the ZnGa2O4(111) surface is shown in the shaded triangular area. [Figure 103] A and B show experimental XRD and XRR data of ZGa2O4 (111) oriented films epitaxially grown on prepared SiC-4H (0001) surfaces. [Figure 104A]1 shows a schematic diagram of a large lattice constant cubic oxide represented by ZnGa2O4 formed on a smaller cubic lattice constant oxide represented by MgO. [Figure 104B] 104B shows the proposed crystal structure of the epitaxial growth surface for the structure in FIG. 104A, including the top and bottom atomic structures of MgO(100) and ZnGa2O4(100), respectively. [Figure 105] A and B show experimental XRD data of high structural quality epilayers of ZnGa2O4 films deposited on MgO substrates. [Figure 106] Experimental XRD data of high structural quality epilayers of NiO films deposited on MgO substrates are presented. [Figure 107] 1 shows a schematic diagram of a large cubic lattice constant oxide, represented by MgGa2O4, formed on a smaller cubic lattice constant oxide, represented by MgO. [Figure 108] A and B show experimental XRD data for the formation of ultrawide bandgap cubic MgGa2O4 (100) oriented epilayers on prepared MgO(100) substrates. [Figure 109] We present a further epilayer structure comprising two UWBG large lattice constant cubic oxide layers integrated into a heterogeneous bandgap oxide structure deposited on a large lattice constant cubic MgAl2O4 (100) oriented substrate. [Figure 110] A and B show experimental XRD data of MgO, ZnAl2O4, and ZnGa2O4 cubic oxide films on MgAl2O4 (100) oriented substrates. [Figure 111] The surface atomic arrangements of the cubic LiF(111) oriented surface and the cubic γGa2O3(111) oriented surface are shown. [Figure 112] A and B show experimental XRD data for gallium oxide showing the crystal symmetry group of the epilayer controlled by the symmetry of the underlying substrate or seed surface. [Figure 113] The epitaxial structure of Ga2O3 grown on a cubic MgO substrate is shown. [Figure 114]A and B show experimental XRD data of low growth temperature (LT) and high growth temperature (HT) Ga2O3 film formation on prepared MgO(100) oriented substrates, respectively. [Figure 115] We show complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 116] A and B show experimental XRD data of SL structures formed using MgGa2O4 and ZnGa2O4 layers deposited on an MgO(100) substrate but with different periodicity. [Figure 117] A and B show experimentally determined grazing incidence XRR data demonstrating the extremely high crystalline structural quality of the SL[MgGa2O4 / ZnGa2O4] / / MgO(100) structure shown in Figures 116A and 116B, respectively. [Figure 118] Another example shows complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 119] A and B show experimental XRD and XRR data of the epitaxial SL structure forming the SL [MgAl2O4 / MgO] / / MgAl2O4(100) described in Figure 118. [Figure 120] As a further example, we show complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 121] We present experimental XRD data for Fd3m crystal structure GeMg2O4 deposited as a high-quality bulk layer on a Fm3m MgO(100) substrate and further including an MgO cap. [Figure 122] Experimental XRD data for Fd3m crystal structure GeMg2O4 when incorporated as an SL structure with 20x periodicity SL [GeMg2O4 / MgO] on an Fm3m MgO(100) substrate are presented. [Figure 123] Another example shows complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 124] Representation of the (100) crystallographic plane of the Fd3m cubic symmetry unit cell of GeMg2O4 and MgGa2O4 is shown. [Figure 125] Experimental XRD data of an SL structure containing 20x periodic SL [Mg2GeO4 / MgGa2O4] on an MgO(100) substrate are shown. [Figure 126] Experimental XRD data of an SL structure containing 10x periodic SL [Mg2GeO4 / MgGa2O4] on an MgO(100) substrate is shown. [Figure 127] As a further example, we show complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 128] A and B show experimental XRD data for a superlattice structure containing SL[GeMg2O4 / γGa2O3] / / MgOsub(100). [Figure 129] Another example shows complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 130] A and B show experimental XRD and XRR data for heterostructures and superlattice structures including SL[ZnGa2O4 / MgO] / / MgOsub(100). [Figure 131] Another example shows complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 132] A and B show experimental XRD data for a superlattice structure containing SL[MgGa2O4 / MgO] / / MgOsub(100). [Figure 133] It shows a complex epilayer structure in which different cubic oxide layers are integrated to form heterostructures and SLs, including SL[Ga2O3 / MgO] / / MgOsub(100). [Figure 134] 13A and 13B show experimental XRD data for the SL structure of FIG. 133, where the growth temperature was selected to achieve cubic phase γGa 2 O 3 during the MBE deposition process. [Figure 135] As a further example, we show complex epilayer structures of heterogeneous cubic oxide layers integrated into superlattice or multiple heterojunction structures. [Figure 136]Experimental XRD data of pseudomorphically strained bulk RS-Mg0.9Zn0.1O epilayers on cubic Fm3m MgO(100) oriented substrates are presented. [Figure 137] 13 shows experimental XRD data for the bulk RS-Mg0.9Zn0.1O composition shown in FIG. 136 incorporated into a digital alloy in the form SL[RS-Mg0.9Zn0.1O / MgO] / / MgOsub(100). [Figure 138A] 1 shows a plot of the minimum bandgap energy versus the small lattice constant for monoclinic β(AlxGa1-x)2O3. [Figure 138B] 1 shows a plot of the minimum band gap energy versus the small lattice constant for hexagonal α(AlxGa1-x)2O3. [Figure 138C] Examples of R3c α(AlxGa1-x)2O3 epitaxial structures that can be formed are shown. [Figure 139A] An epilayer structure is shown that incrementally adjusts the effective alloy composition of each SL region along the growth direction. [Figure 139B] 139A shows experimental XRD data for a step-graded SL (SGSL) structure using a digital alloy containing a bilayer of αGa2O3 and αAl2O3 deposited on (110)-oriented sapphire (zero miscut). [Figure 140] In one example, we show another step-graded SL structure that can be used to form a pseudo-substrate with tailored in-plane lattice constant for subsequent high-quality, near-lattice-matched active layers. [Figure 141A] We present another step-graded SL structure containing highly complex digital alloy grading interleaved by wide bandgap spacers. [Figure 141B] 141B shows experimental high-resolution XRD data for a step-graded (ie, chirped) SL structure with an interposer as shown in FIG. 141A. [Figure 141C] 141B shows high resolution XRD data for a step-graded (ie, chirped) SL structure with an interposer as shown in FIG. 141A. [Figure 142A] 1 shows the electronic band diagram as a function of growth direction for chirped layer structures. [Figure 142B] 1 shows the electronic band diagram as a function of growth direction for chirped layer structures. [Figure 142C] 1 shows the electronic band diagram as a function of growth direction for chirped layer structures. [Figure 142D] 142A-142C are wavelength spectra of oscillator strengths of electric dipole transitions between the conduction band and valence band of the chirped layer modeled in FIGS. 142A-142C. [Figure 143A] 1 shows an example of the full Ek band structure of an epitaxial oxide material, derived from the atomic structure of the crystal. [Figure 143B] A simplified band structure showing the minimum band gap of a material with space (z) as the x-axis rather than wave vector as in the Ek diagram of Figure 143A is shown. [Figure 144A] 1 shows a simplified band structure of a homojunction device including a pin structure with an epitaxial oxide layer. [Figure 144B] 1 shows a simplified band structure of a homojunction device including an nin structure with an epitaxial oxide layer. [Figure 145A] 1 shows a simplified band structure of a heterojunction pin device including an epitaxial oxide layer. [Figure 145B] FIG. 1 shows a band structure diagram for a double heterojunction device including an epitaxial oxide layer. [Figure 145C] 1 shows a simplified band structure of a multiple heterojunction pin device including an epitaxial oxide layer. [Figure 146] 1 shows a band structure diagram for a metal-insulator-semiconductor (MIS) structure containing an epitaxial oxide layer. [Figure 147A] 1 shows a simplified band structure of another example pin structure having a superlattice in the i-region. [Figure 147B] A single quantum well of the structure shown in Figure 147A is shown. [Figure 148] 1 shows a simplified band structure of another example of a pin structure having a superlattice in the n-layer, i-layer, and p-layer. [Figure 149]148 shows a simplified band structure of another example of a pin structure having a superlattice in the n-layer, i-layer, and p-layer, similar to the structure in FIG. [Figure 150A] 1 illustrates an example of a semiconductor structure that includes an epitaxial oxide layer. [Figure 150B] The structure of Figure 150A is shown with layers etched to allow contact to any layer of the semiconductor structure. [Figure 150C] The structure of Figure 150B is shown with an additional contact area that contacts the backside of the substrate (opposite the epitaxial oxide layer). [Figure 151] 1 illustrates a multilayer structure used to form an electronic device having distinct regions that include at least one layer of MgaGebOc. [Figure 152] FIG. 1 is a diagram showing examples of materials that can be combined with MgaGebOc to form a heterostructure. [Figure 153] 1 is a plot of bandgap energy as a function of lattice constant for example materials that may be used in heterostructures of semiconductor structures. [Fig. 154] 1 is a schematic cross-sectional view of an in-plane conduction device including an insulating substrate and a semiconductor layer region formed on the substrate with electrical contacts disposed on the upper semiconductor layer of the device. [Figure 155] 1 is a schematic cross-sectional view of a vertical conduction device including a conductive substrate and a semiconductor layer region formed on the substrate with electrical contacts disposed above and below the device. [Figure 156A] FIG. 156 is a schematic cross-sectional view of a vertical conduction device for emitting light, having the electrical contact configuration shown in FIG. 155 and configured as a planar parallel waveguide for the emitted light. [Figure 156B] 156 is a schematic cross-sectional view of a light emitting vertical conduction device having the electrical contact configuration shown in FIG. 155 and configured as a vertical light emitting device. [Figure 157A] 155 is a schematic cross-sectional view of an in-plane conduction device for light detection having the electrical contact configuration shown in FIG. 154 and configured to receive light passing through a semiconductor layer region and / or substrate. [Figure 157B]155 is a schematic cross-sectional view of a planar conduction device for emitting light having the electrical contact configuration shown in FIG. 154 and configured to emit light vertically or in planarly. [Figure 158A] A semiconductor structure that can be used as part of a light emitting device. [Figure 158B] 158B is a schematic cross-sectional view of a light-emitting device that can be formed using the semiconductor structure of FIG. 158A. [Figure 159A] A semiconductor structure that can be used as part of a light emitting device. [Figure 159B] 159B is a schematic cross-sectional view of a light-emitting device that can be formed using the semiconductor structure of FIG. 159A. [Figure 160] FIG. 1 is a schematic cross-sectional view of an in-plane surface metal-semiconductor-metal (MSM) conductive device having a semiconductor layer region including a substrate and a plurality of semiconductor layers, the top layer including a pair of planar interdigitated electrical contacts. [Figure 161A] FIG. 1 illustrates a top view of an in-plane dual metal MSM conductive device with a first electrical contact formed of a first metal material interdigitated with a second electrical contact formed of a second metal material. [Figure 161B] FIG. 64B is a schematic cross-sectional view of an in-plane dual metal MSM conductive device formed from the substrate and semiconductor layer regions shown in FIG. 64A and showing the unit cell arrangement. [Figure 162] FIG. 1 is a schematic cross-sectional view of a multi-layer semiconductor device having a first electrical contact formed on a mesa surface and a second electrical contact spaced horizontally and vertically from the first electrical contact. [Figure 163] FIG. 163 is a schematic cross-sectional view of an in-plane MSM conduction device in which a device is formed by laterally arranging multiple unit cells of the mesa structure shown in FIG. 162. [Fig. 164] 1 is a schematic cross-sectional view of a multi-electrical terminal device having multiple mesa structures. [Figure 165A]1 is a schematic cross-sectional view of a planar field effect transistor (FET) including source, gate, and drain electrical contacts, the source and drain electrical contacts being formed on a semiconductor layer region formed on an insulating substrate, and the gate electrical contact being formed on a gate layer formed on the semiconductor layer region. [Figure 165B] FIG. 165B is a top view of the planar FET shown in FIG. 165A showing the distance between the source to gate electrical contact and the drain to gate electrical contact. [Figure 166A] 165A and 165B, except that the source electrical contact is embedded in the substrate through the semiconductor layer region and the drain electrical contact is embedded only in the semiconductor layer region, according to some embodiments. [Figure 166B] FIG. 166B is a top view of the planar FET shown in FIG. 166A. [Figure 167] FIG. 166B is a top view of a planar FET including multiple interconnected unit cells of the planar FET shown in FIG. 165A or FIG. 166A. [Figure 168] FIG. 1 is a process flow diagram for forming a conductive device including regrown isotropic semiconductor layer regions on exposed etched mesa sidewalls. [Figure 169A] 1 is a chart illustrating center frequencies of RF operating bands that may be used in various applications. [Figure 169B] The circuit diagram of a typical RF switch is shown below. [Figure 170A] 1 shows a circuit diagram and an equivalent circuit diagram of a FET having a source terminal ("S"), a drain terminal ("D"), and a gate terminal ("G"); [Figure 170B] The circuit diagram and equivalent circuit diagram of an RF switch that uses multiple FETs in series to achieve high breakdown voltage are shown below. [Figure 170C] The circuit diagram and equivalent circuit diagram of an RF switch that uses multiple FETs in series to achieve high breakdown voltage are shown below. [Figure 170D]The circuit diagram and equivalent circuit diagram of an RF switch that uses multiple FETs in series to achieve high breakdown voltage are shown below. [Figure 171] 1 shows a chart of the calculated specific on-resistance of an RF switch and the calculated breakdown voltages associated with the various semiconductors that make up the RF switch. [Figure 172A] A circuit diagram of multiple Si-based FETs connected in series to achieve high breakdown voltage is shown. [Figure 172B] A circuit diagram of a single Ga2O3-based FET that can achieve a high breakdown voltage equivalent to that of the series Si-based FET shown in Figure 172A is shown. [Figure 173] 1 is a chart of calculated off-state FET capacitance (in F) versus calculated specific on-resistance (RON) for Si (low bandgap material) and epitaxial oxide materials with high bandgaps. [Fig. 174] 1 is a chart of the fully depleted layer thickness (tFD) of the channel of a FET containing α-Ga2O3 versus the doping density of α-Ga2O3 in the channel (ND CH). [Figure 175] 1 shows a schematic diagram of an example of a FET including epitaxial oxide material. [Figure 176A] FIG. 1 is an Ek diagram showing the calculated band structure of epitaxial oxide materials that can be used in the FETs and RF switches of the present disclosure, showing that in this example α-Al2O3 can be used as a gate layer or additional oxide encapsulation. [Figure 176B] FIG. 1 is an Ek diagram showing the calculated band structure of epitaxial oxide materials that can be used in the FETs and RF switches of the present disclosure, showing that in this example, α-Ga2O3 can be used as the channel layer. [Figure 177] 1 shows a chart of calculated minimum band gap energy (in eV) versus lattice constant (in Angstroms) for α- and κ-(AlxGa1-x)2O3 materials compatible with sapphire (α-Al2O3) substrates. [Figure 178] 1 shows a schematic diagram of a portion of a FET and a chart of energy versus distance along the channel (in the "x" direction). [Figure 179] To illustrate the operation of a FET using epitaxial oxide materials, a schematic diagram of a portion of a FET and a chart of energy versus distance along the channel (in the "z" direction) are shown. [Figure 180] 1 shows a schematic diagram of a portion of a FET and a chart of energy versus distance along the channel (in the "z" direction). [Figure 181] A schematic diagram of the atomic surface of α-Al2O3 oriented in the A plane (i.e., the (110) plane) is shown. [Figure 182] 1 shows a schematic diagram of an example FET including epitaxial oxide material and an integrated phase shifter. [Figure 183] 18A and 18B show schematic diagrams of a system including one or more switches (eg, including the FETs of FIG. 182) with integrated phase shifters. [Figure 184] 1 shows a schematic diagram of an example FET including epitaxial oxide material and an epitaxial oxide buried ground plane. [Figure 185] FIGS. 179A and 179B are energy band diagrams along the gate stack direction ("z" as shown in the schematic diagram of FIG. 179) for an example FET having a structure like the FET of FIG. 184, with layers formed of α-(AlxGa1-x)2O3 and α-Al2O3. [Figure 186] 1 illustrates several RF waveguide structures that can be formed using a buried ground plane that includes epitaxial oxide material. [Figure 187] 1 shows a schematic diagram of an example FET including an epitaxial oxide material and a field shield on the gate electrode. [Figure 188] 1 shows a schematic diagram of the epitaxial oxide and dielectric materials forming the integrated FET and coplanar (CP) waveguide structure. [Figure 189] 1 shows a schematic diagram of an example FET including epitaxial oxide material and an integrated phase shifter. [Figure 190] 178A to 178C show energy band diagrams along the channel direction ("x" as shown in FIG. 178) of the S tunnel junction and D tunnel junction described with respect to the FET shown in FIG. [Figure 191A] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191B] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191C] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191D] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191E] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191F] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 191G] FIG. 189 is a schematic diagram of an example process flow for fabricating a FET including epitaxial oxide material, such as the FET shown in FIG. 189. [Figure 192] Figure 1 shows the DFT-calculated atomic structure of κ-Ga2O3 (i.e., Ga2O3 with the Pna21 space group). [Figure 193A] The DFT-calculated band structures of κ-(AlxGa1-x)2O3, x = 1, 0.5, and 0 are shown. [Figure 193B] The DFT-calculated band structures of κ-(AlxGa1-x)2O3, x = 1, 0.5, and 0 are shown. [Figure 193C] The DFT-calculated band structures of κ-(AlxGa1-x)2O3, x = 1, 0.5, and 0 are shown. [Figure 193D] The DFT-calculated minimum band gap energies for κ-(AlxGa1-x)2O3, x = 1, 0.5, and 0 are shown. [Figure 194A]Schematic diagram and calculated band diagrams (conduction and valence band edges), calculated electron wave functions, and calculated electron densities of energy versus growth direction “z” for κ-(AlxGa1-x)2O3 / κ-Ga2O3 heterostructures. [Figure 194B] Schematic diagram and calculated band diagrams (conduction and valence band edges), calculated electron wave functions, and calculated electron densities of energy versus growth direction “z” for κ-(AlxGa1-x)2O3 / κ-Ga2O3 heterostructures. [Figure 194C] Schematic diagram and calculated band diagrams (conduction and valence band edges), calculated electron wave functions, and calculated electron densities of energy versus growth direction “z” for κ-(AlxGa1-x)2O3 / κ-Ga2O3 heterostructures. [Figure 194D] Figure 1 shows the electron density in a thin layer within a confined energy well formed in a κ-(AlxGa1-x)2O3 / κ-Ga2O3 heterostructure, x=0.3, 0.5, and 1. [Figure 194E] Figure 1 shows the electron density in a thin layer within a confined energy well formed in a κ-(AlxGa1-x)2O3 / κ-Ga2O3 heterostructure, x=0.3, 0.5, and 1. [Figure 195] The band structure of Li-doped κ-Ga2O3 calculated by DFT is shown. [Figure 196] A chart summarizing the DFT-calculated band structure results for (Al,Ga)xOy doped with different dopants is shown. [Figure 197A] An example of a pin structure having multiple quantum wells in the n-layer, i-layer, and p-layer is shown (similar to the structure shown in FIG. 149). [Figure 197B] 197A shows the calculated band diagram and confined electron and hole wave functions (similar to those in the examples of FIGS. 194B and 194C) for a portion of the superlattice in the n region of a structure like that of FIG. 197A. [Figure 197C]197A shows the calculated band diagram and confined electron and hole wave functions (similar to those in the examples of FIGS. 194B and 194C) for a portion of the superlattice in the n region of a structure like that of FIG. 197A. [Figure 198A] A structure is shown having a crystalline substrate with a particular orientation (hkl) relative to the growth direction, and an epitaxial layer ("film epilayer") with an orientation (h'k'l'). [Figure 198B] 1 is a table showing some substrates compatible with κ-AlxGa1-xOy epitaxial layers, the space group ("SG") of the substrate, the orientation of the substrate, the orientation of the κ-AlxGa1-xOy film grown on the substrate, and the mismatch elastic strain energy. [Figure 199] An example is shown including a substrate (C-face α-Al2O3) and a template (low-temperature "LT" grown Al(111)) structure used to match the in-plane lattice constant to κ-AlxGa1-xOy ("Pna21 AlGaO"). [Figure 200] In various examples, we present several DFT-calculated epitaxial oxide materials with lattice constants between about 4.8 Å and about 5.3 Å that can serve as substrates for κ-AlxGa1-xOy and / or form heterostructures with κ-AlxGa1-xOy. [Figure 201] In various examples, we present several additional DFT-calculated epitaxial oxide materials with possible in-plane lattice constants between about 4.8 Å and about 5.3 Å that can serve as substrates for κ-AlxGa1-xOy and / or form heterostructures with κ-AlxGa1-xOy. [Figure 202A] The rectangular arrangement of atoms within the unit cell of the (001) surface of κ-Ga2O3 is shown. [Figure 202B] The surface of α-SiO2 is shown, superimposed on a rectangular unit cell of κ-Ga2O3(001). [Figure 202C] The surface of LiGaO2(011) is shown, superimposed on a rectangular unit cell of κ-Ga2O3(001). [Figure 202D]The Al(111) surface is shown superimposed on a rectangular unit cell of κ-Ga2O3(001). [Figure 202E] The surface of α-Al2O2(001) (i.e., C-plane sapphire) is shown superimposed on a rectangular unit cell of κ-Ga2O3(001). [Figure 203] 1 shows a flowchart of an example method for forming a semiconductor structure including κ-AlxGa1-xOy. [Figure 204A] Two overlaid experimental XRD scans are shown, one of κ-Al2O3 grown on an Al(111) template and the other of κ-Al2O3 grown on a Ni(111) template. [Figure 204B] Two overlaid experimental XRD scans (shifted in the y-axis) of the shown structure are shown, one containing a κ-Ga2O3 layer grown on an α-Al2O3 substrate with an Al(111) template layer, and the other containing a β-Ga2O3 layer grown on an α-Al2O3 substrate without a template layer. [Figure 204C] Two overlaid scans are shown in Figure 204B at high resolution, where fringes due to layer enhancement are observed. [Figure 205] 2A and 2B show simplified Ek diagrams near the Brillouin zone center of epitaxial oxide materials such as those shown in FIGS. 28, 76A-1, 76A-2, and 76B, illustrating the process of impact ionization. [Figure 206A] A plot of energy versus band gap for epitaxial oxide materials (including the conduction band edge, Ec, and valence band edge, Ev) is shown, with the dotted line indicating the approximate threshold energy required for hot electrons to create excess electron-hole pairs through the impact ionization process. [Figure 206B] An example using α-Ga2O3 with a band gap of approximately 5 eV is shown. [Figure 207A] 1 shows a schematic diagram of an epitaxial oxide material with two planar contact layers (e.g., a metal or heavily doped semiconductor contact material and a metal contact) coupled to an applied voltage Va. [Figure 207B] 207B shows the band diagram for the structure shown in FIG. 207A along the growth direction ("z" direction) of the epitaxial oxide material. [Figure 207C] 207A shows a band diagram along the growth (“z”) direction of the epitaxial oxide material of the structure shown in FIG. 207A, where the epitaxial oxide has a bandgap gradient (i.e., a graded bandgap), Ec(z), in the growth “z” direction. [Figure 208] 1 shows a schematic diagram of an example electroluminescent device including a high work function metal ("Metal #1"), an ultra-high band gap ("UWBG") layer, a wide band gap ("WBG") epitaxial oxide layer, and a second metal contact ("Metal #2"). [Figure 209] 1A and 1B show schematic diagrams of an example electroluminescent device that is a p-i-n diode that includes a p-type semiconductor layer, an epitaxial oxide layer that is not intentionally doped (NID) and includes an impact ionization region (IIR), and an n-type semiconductor layer. DETAILED DESCRIPTION OF THE INVENTION

[0012] Disclosed herein are embodiments of epitaxial oxide materials, including structures and electronic devices that include the epitaxial oxide materials. Some embodiments disclose optoelectronic semiconductor light emitting devices that can be configured to emit light having a wavelength in the range of about 150 nm to about 280 nm. The devices include a metal oxide substrate having at least one epitaxial semiconductor metal oxide layer disposed thereon. The substrate can be selected from a group consisting of Al2O3, Ga2O3, MgO, LiF, MgAl2O4, MgGa2O4, LiGaO2, LiAlO2, (Al x Ga 1-x )2O3, MgF2, LaAlO3, TiO2, or quartz. In certain embodiments, one or more of the at least one semiconductor layer comprises at least one of Al2O3 and Ga2O3.

[0013] In a first aspect, the present disclosure provides an optoelectronic semiconductor light emitting device configured to emit light having a wavelength in a range from about 150 nm to about 280 nm, the device comprising: a substrate having at least one epitaxial semiconductor layer disposed thereon, wherein each of the one or more epitaxial semiconductor layers comprises a metal oxide.

[0014] In another embodiment, the metal oxide of each of the one or more semiconductor layers is selected from the group consisting of Al2O3, Ga2O 3、 It is selected from the group consisting of MgO, NiO, Li2O, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, IrO2, and any combination of the aforementioned metal oxides.

[0015] In another form, at least one of the one or more semiconductor layers is single crystalline.

[0016] In another form, at least one of the one or more semiconductor layers has rhombohedral, hexagonal, or monoclinic crystal symmetry.

[0017] In another form, at least one of the one or more semiconductor layers is comprised of a binary metal oxide, the metal oxide being selected from Al2O3 and Ga2O3.

[0018] In another form, at least one of the one or more semiconductor layers is comprised of a ternary metal oxide composition including at least one of Al2O3 and Ga2O3, and optionally a metal oxide selected from MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, and IrO2.

[0019] In another form, at least one of the one or more semiconductor layers is (Al x Ga 1-x )2O3 ternary metal oxide composition, where 0 <x<1である。

[0020] In another form, at least one of the one or more semiconductor layers includes a uniaxially deformed unit cell.

[0021] In another form, at least one of the one or more semiconductor layers includes a biaxially deformed unit cell.

[0022] In another form, at least one of the one or more semiconductor layers includes a triaxially deformed unit cell.

[0023] In another form, at least one of the one or more semiconductor layers is composed of a quaternary metal oxide composition, and the quaternary metal oxide composition includes either (i) a metal oxide selected from Ga2O3, Al2O3, MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, IrO2, or (ii) a metal oxide selected from Al2O3, Ga2O3, MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, and IrO2.

[0024] In another form, at least one of the one or more semiconductor layers is a quaternary metal oxide composition (Ni x Mg 1-x ) y Ga 2(1-y) O 3-2y composed of, where 0 < x < 1 and 0 < y < 1.

[0025] In another form, the surface of the substrate is configured to enable lattice matching of the crystal symmetry of at least one semiconductor layer.

[0026] In another form, the substrate is a single crystal substrate.

[0027] In another form, the substrate is selected from Al2O3, Ga2O3, MgO, LiF, MgAl2O4, MgGa2O4, LiGaO2, LiAlO2, MgF2, LaAlO3, TiO2, and quartz.

[0028] In another form, the surface of the substrate has a crystal symmetry and in-plane lattice parameter matching to allow homoepitaxy or heteroepitaxy of at least one semiconductor layer.

[0029] In another form, one or more of the at least one semiconductor layer is direct bandgap.

[0030] In a second aspect, the present disclosure provides an optoelectronic semiconductor device for generating light of a predetermined wavelength, comprising: a substrate; and a light emitting region having a light emitting region band structure configured to generate light of the predetermined wavelength, the light emitting region comprising one or more epitaxial metal oxide layers supported by the substrate.

[0031] In another form, configuring the light emitting region band structure to produce light of the predetermined wavelength includes selecting the one or more epitaxial metal oxide layers to have a light emitting region band gap energy capable of producing light of the predetermined wavelength.

[0032] In another aspect, selecting one or more epitaxial metal oxide layers to have a light emitting region band gap energy capable of producing light of a predetermined wavelength can include selecting an epitaxial metal oxide layer having a metal species (A) and oxygen (O) combined in relative proportions x and y. x O y forming one or more epitaxial metal oxide layers comprising a binary metal oxide in the form of

[0033] In another form, the binary metal oxide is Al2O3.

[0034] In another embodiment, the binary metal oxide is Ga2O3.

[0035] In another embodiment, the binary metal oxide is selected from the group consisting of MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, and IrO2.

[0036] In another form, selecting one or more epitaxial metal oxide layers to have a light-emitting region bandgap energy capable of generating light of a predetermined wavelength includes forming one or more epitaxial metal oxide layers of a ternary metal oxide.

[0037] In another form, the ternary metal oxide includes metal species (A) and (B) bonded to oxygen (O) in relative ratios x, y, and n, A x B y O n is a ternary metal oxide bulk alloy in the form of.

[0038] In another form, the relative ratio of metal species B to metal species A ranges from a minority relative ratio to a majority relative ratio.

[0039] In another form, the ternary metal oxide is A x B 1-x O n is in the form of, where 0 < x < 1.0.

[0040] In another form, metal species A is Al, and metal species B is selected from the group consisting of Zn, Mg, Ga, Ni, rare earths, Ir, Bi, and Li.

[0041] In another form, metal species A is Ga, and metal species B is selected from the group consisting of Zn, Mg, Ni, Al, rare earths, Ir, Bi, and Li.

[0042] In another form, the ternary metal oxide is (Al x Ga 1-x )2O3 is in the form of, where 0 < x < 1. In other forms, x is about 0.1, or about 0.3, or about 0.5.

[0043] In another form, the ternary metal oxide is formed by continuous deposition of unit cells formed along the unit cell direction and includes an alternating arrangement layer of metal species A and metal species B having an intermediate O layer to form a ternary metal oxide regular alloy structure in the form of a metal oxide regular alloy such as A-O-B-O-A-O-B-.

[0044] In another embodiment, metal species A is Al and metal species B is Ga, and the ordered ternary metal oxide alloy is of the form Al-O-Ga-O-Al-, etc.

[0045] In another form, the ternary metal oxide is in the form of a host binary metal oxide crystal having crystal-modifying species.

[0046] In another form, the host binary metal oxide crystal is selected from the group consisting of Ga2O3, Al2O3, MgO, NiO, ZnO, Bi2O3, r-GeO2, Ir2O3, RE2O3, and Li2O, and the crystal modifier is selected from the group consisting of Ga, Al, Mg, Ni, Zn, Bi, Ge, Ir, RE, and Li.

[0047] In another form, selecting the one or more epitaxial metal oxide layers to have a light emitting region band gap energy capable of producing light of the predetermined wavelength includes forming the one or more epitaxial metal oxide layers as a superlattice including two or more metal oxide layers that form a unit cell and repeat with a fixed unit cell period along the growth direction.

[0048] In another form, the superlattice is a bilayer superlattice that includes repeating layers that include two different metal oxides.

[0049] In another embodiment, the two different metal oxides include a first binary metal oxide and a second binary metal oxide.

[0050] In another form, the first binary metal oxide is Al2O3 and the second binary metal oxide is Ga2O3.

[0051] In another embodiment, the first binary metal oxide is NiO and the second binary metal oxide is Ga2O3.

[0052] In another embodiment, the first binary metal oxide is MgO and the second binary metal oxide is NiO.

[0053] In another embodiment, the first binary metal oxide is Al2O3, Ga2O 3、 The second binary metal oxide is selected from the group consisting of Al2O3, Ga2O3, MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2, absent the first selected binary metal oxide.

[0054] In another embodiment, the two different metal oxides include a binary metal oxide and a ternary metal oxide.

[0055] In another embodiment, the binary metal oxide is Ga2O3 and the ternary metal oxide is (Al x Ga 1-x )2O3, where 0 <x<1.0である。

[0056] In another embodiment, the binary metal oxide is Ga2O3 and the ternary metal oxide is Al x Ga 1-x O3, where 0 <x<1.0である。

[0057] In another embodiment, the binary metal oxide is Ga2O3 and the ternary metal oxide is Mg x Ga 2(1-x) O 3-2x where 0 <x<1.0である。

[0058] In another embodiment, the binary metal oxide is Al2O3 and the ternary metal oxide is (Al x Ga 1-x )2O3, where 0 <x<1.0である。

[0059] In another form, the binary metal oxide is Al2O3 and the ternary metal oxide is Al x Ga 1-x O3, where 0 <x<1.0である。

[0060] In another embodiment, the binary metal oxide is Al2O3 and the ternary metal oxide is (Al x Er 1-x )2O3.

[0061] In another form, the ternary metal oxide is (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1.0である。

[0062] In another embodiment, the binary metal oxide is Al2O3, Ga2O 3、 It is selected from the group consisting of MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2.

[0063] In another form, the two different metal oxides include a first ternary metal oxide and a second ternary metal oxide.

[0064] In another form, the first ternary metal oxide is Al x Ga 1-x O, and the second ternary metal oxide is (Al x Ga 1-x )2O3 or Al y Ga 1-y O3, where 0 < x < 1 and 0 < y < 1.

[0065] In another form, the first ternary metal oxide is (Al x Ga 1-x )2O3, and the second ternary metal oxide is (Al y Ga 1-y )2O3, where 0 < x < 1 and 0 < y < 1. <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​)2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 and the second ternary metal oxide is free of the first selected ternary metal oxide, (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 , and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1.0である。

[0067] In another form, the superlattice is a three-layer superlattice that includes repeating layers of three different metal oxides.

[0068] In another embodiment, the three different metal oxides include a first binary metal oxide, a second binary metal oxide, and a third binary metal oxide.

[0069] In another embodiment, the first binary metal oxide is MgO, the second binary metal oxide is NiO, and the third binary metal oxide is Ga2O3.

[0070] In another embodiment, the first binary metal oxide is Al2O3, Ga2O 3、 the second binary metal oxide is selected from the group consisting of Al2O3, Ga2O3, MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2, absent the first selected binary metal oxide; and the third binary metal oxide is selected from the group consisting of Al2O3, Ga2O3, MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2, absent the first and second selected binary metal oxides. 3、 It is selected from the group consisting of Gd2O3, PdO, Bi2O3 and IrO2.

[0071] In another embodiment, the three different metal oxides include a first binary metal oxide, a second binary metal oxide, and a ternary metal oxide.

[0072] In another embodiment, the first binary metal oxide is Al2O3, Ga2O 3、 The second binary metal oxide is selected from the group consisting of MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, and IrO2, and the first selected binary metal oxide is free of Al2O3, Ga2O 3、 The ternary metal oxide is selected from the group consisting of MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2, and the ternary metal oxide is (Ga2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1である。

[0073] In another embodiment, the three different metal oxides include a binary metal oxide, a first ternary metal oxide, and a second ternary metal oxide.

[0074] In another embodiment, the binary metal oxide is Al2O3, Ga2O 3、 The first ternary metal oxide is selected from the group consisting of MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3 and IrO2, and the first ternary metal oxide is (Ga 2x Ni 1-x )O 2x+1 , (Al2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 and the second ternary metal oxide is free of the first selected ternary metal oxide, (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Alx Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1である。

[0075] In another embodiment, the three different metal oxides include a first ternary metal oxide, a second ternary metal oxide, and a third ternary metal oxide.

[0076] In another embodiment, the first ternary metal oxide is (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al xIr 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 and the second ternary metal oxide is free of the first selected ternary metal oxide, (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x .Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 and the third ternary metal oxide is free of the first and second selected ternary metal oxides, (Ga2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1である。

[0077] In another form, the superlattice is a four-layer superlattice that includes repeating layers of at least three different metal oxides.

[0078] In another form, the superlattice is a four-layer superlattice comprising repeating layers of three different metal oxides, where selected metal oxide layers of the three different metal oxides are repeated in the four-layer superlattice.

[0079] In another embodiment, the three different metal oxides include a first binary metal oxide, a second binary metal oxide, and a third binary metal oxide.

[0080] In another form, the first binary metal oxide is MgO, the second binary metal oxide is NiO, and the third binary metal oxide is GaO forming a four-layer superlattice including a MgO—GaO—NiO—GaO layer.

[0081] In another form, the three different metal oxides are Al2O3, Ga2O 3、 MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, IrO 2、 (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1.0である。

[0082] In another form, the superlattice is a four-layer superlattice that includes repeating layers of four different metal oxides.

[0083] In another form, the four different metal oxides are Al2O3, Ga2O 3、 MgO, NiO, LiO2, ZnO, SiO2, GeO2, Er2O3, Gd2O3, PdO, Bi2O3, IrO 2、 (Ga 2x Ni 1-x )O 2x+1 , (Al 2x Ni 1-x )O 2x+1 , (Al 2x Mg 1-x )O 2x+1 , (Ga 2x Mg 1-x )O 2x+1 , (Al 2x Zn 1-x )O 2x+1 , (Ga 2x Zn 1-x )O 2x+1 , (Ga x Bi 1-x )2O3, (Al x Bi 1-x )2O3, (Al 2x Ge 1-x )O 2+x , (Ga 2x Ge 1-x )O 2+x , (Al x Ir 1-x )2O3, (Ga x Ir 1-x )2O3, (Ga x RE 1-x )O3, (Al x RE 1-x )O3, (Al 2x Li 2(1-x) )O 2x+1 and (Ga 2x Li 2(1-x) )O 2x+1 wherein 0 is selected from the group consisting of <x<1.0である。

[0084] In another form, each individual layer of the two or more metal oxide layers forming a unit cell of the superlattice has a thickness that is less than or about equal to the electron de Broglie wavelength in that each individual layer.

[0085] In another form, configuring the light emitting region band structure to generate light of a predetermined wavelength includes modifying the initial light emitting region band structure of one or more epitaxial metal oxide layers in forming the optoelectronic device.

[0086] In another form, modifying the initial light-emitting region band structure of one or more epitaxial metal oxide layers in forming an optoelectronic device comprises introducing a predetermined strain into the one or more epitaxial metal oxide layers during epitaxial deposition of the one or more epitaxial metal oxide layers.

[0087] In another form, a predetermined strain is introduced to modify the initial light-emitting region band structure from an indirect bandgap to a direct bandgap.

[0088] In another form, a predetermined strain is introduced to modify the initial band gap energy of the initial light emitting region band structure.

[0089] In another form, a predetermined strain is introduced to modify the initial valence band structure of the initial light-emitting region band structure.

[0090] In another form, modifying the initial valence band structure includes raising or lowering selected valence bands relative to the Fermi energy level of the light emitting region.

[0091] In another form, modifying the initial valence band structure includes modifying the shape of the valence band structure to modify the localization characteristics of holes formed in the light emitting region.

[0092] In another form, introducing the predetermined strain into the one or more epitaxial metal oxide layers includes selecting a strained metal oxide layer having a composition and crystal symmetry type that, when epitaxially formed on an underlayer having the underlayer composition and crystal symmetry type, introduces the predetermined strain into the strained metal oxide layer.

[0093] In another form, the predetermined strain is a biaxial strain.

[0094] In another form, the underlayer is a metal oxide having a first crystal symmetry type, and the strained metal oxide layer also has the first crystal symmetry type but has a different lattice constant to introduce biaxial strain into the strained metal oxide layer.

[0095] In another embodiment, the metal oxide underlayer is Ga2O3, the strained metal oxide layer is Al2O3, and biaxial compression is induced in the Al2O3 layer.

[0096] The metal oxide underlayer is Al2O3, the strained metal oxide layer is Ga2O3, and biaxial tension is introduced into the Ga2O3 layer.

[0097] In another form, the predetermined strain is a uniaxial strain.

[0098] In another form, the underlayer has a first crystal symmetry type having an asymmetric unit cell.

[0099] In another embodiment, the strained metal oxide layer is monoclinic GaO 3、 Al x Ga 1-x O or Al2O3, where x<0<1.

[0100] In another embodiment, the underlayer and the strained layer form layers of a superlattice.

[0101] In another form, modifying the initial light emitting region band structure of one or more epitaxial metal oxide layers in forming an optoelectronic device comprises introducing a predetermined strain into the one or more epitaxial metal oxide layers after epitaxial deposition of the one or more epitaxial metal oxide layers.

[0102] In another form, an optoelectronic device comprises a first conductivity type region including one or more epitaxial metal oxide layers having a first conductivity type region band structure configured to operate in combination with a light emitting region to generate light of a predetermined wavelength.

[0103] In another form, configuring the first conductivity type region band structure to operate in combination with the light emitting region to produce light of the predetermined wavelength includes selecting the first conductivity type region energy band gap greater than the light emitting region energy band gap.

[0104] In another form, configuring the first conductivity type region band structure to operate in combination with the light emitting region to produce light of the predetermined wavelength includes selecting the first conductivity type region to have an indirect bandgap.

[0105] In another aspect, configuring the band structure of the first conductivity type region includes one or more of selecting an appropriate metal oxide material or materials consistent with the principles and techniques contemplated herein in connection with the light emitting region, forming a superlattice consistent with the principles and techniques contemplated herein in connection with the light emitting region, and / or modifying the band structure of the first conductivity type region by applying strain consistent with the principles and techniques contemplated herein in connection with the light emitting region.

[0106] In another form, the first conductivity type region is an n-type region.

[0107] In another form, an optoelectronic device comprises a second conductivity type region including one or more epitaxial metal oxide layers having a second conductivity type region band structure configured to operate in combination with the light emitting region and the first conductivity type region to generate light of a predetermined wavelength.

[0108] In another form, configuring the second conductivity type region band structure to operate in combination with the light emitting region to produce light of the predetermined wavelength includes selecting the second conductivity type region energy band gap greater than the light emitting region energy band gap.

[0109] In another form, configuring the second conductivity type region band structure to operate in combination with the light emitting region to produce light of the predetermined wavelength includes selecting the second conductivity type region to have an indirect bandgap.

[0110] In another aspect, configuring the band structure of the second conductivity type region includes one or more of selecting an appropriate metal oxide material or materials consistent with the principles and techniques contemplated herein in connection with the light emitting region, forming a superlattice consistent with the principles and techniques contemplated herein in connection with the light emitting region, and / or modifying the band structure of the first conductivity type region by applying strain consistent with the principles and techniques contemplated herein in connection with the light emitting region.

[0111] In another form, the second conductivity type region is a p-type region.

[0112] In another form, the substrate is formed from a metal oxide.

[0113] In another embodiment, the metal oxide is Al2O3, Ga2O3, MgO, LiF, MgAl2O4, MgGa2O4, LiGaO2, LiAlO2, (Al x Ga 1-x )2O3, LaAlO3, TiO2 and quartz.

[0114] In another form, the substrate is formed from a metal fluoride.

[0115] In another embodiment, the metal fluoride is MgF2 or LiF.

[0116] In another embodiment, the predetermined wavelength is in the wavelength range of 150 nm to 700 nm.

[0117] In another embodiment, the predetermined wavelength is in the wavelength range of 150 nm to 280 nm.

[0118] In a third aspect, the present disclosure provides a method for forming an optoelectronic semiconductor device configured to emit light having a wavelength in a range of about 150 nm to about 280 nm, the method including providing a metal oxide substrate having an epitaxial growth surface; oxidizing the epitaxial growth surface to form an activated epitaxial growth surface; and exposing the activated epitaxial growth surface to one or more atomic beams each comprising high-purity metal atoms and one or more atomic beams comprising oxygen atoms under conditions to deposit two or more epitaxial metal oxide films.

[0119] In another embodiment, the metal oxide substrate comprises an Al or Ga metal oxide substrate.

[0120] In another embodiment, the one or more atomic beams each containing high purity metal atoms are selected from the group consisting of Al, Ga 、 Mg, Ni, Li, Zn, Si, Ge, Er, Y, La, Pr, Gd, Pd, Bi, Ir 、 and any combination of the foregoing metals.

[0121] In another embodiment, the one or more atomic beams each containing high purity metal atoms include any one or more metals selected from the group consisting of Al and Ga, and the epitaxial metal oxide film is formed by depositing (Al x Ga 1-x )2O3, where 0≦x≦1.

[0122] In another form, the conditions for depositing two or more epitaxial metal oxide films include exposing the activated epitaxial growth surface to an atomic beam comprising high purity metal atoms and an atomic beam comprising oxygen atoms, with an oxygen:total metal flux ratio >1.

[0123] In another form, at least one of the two or more epitaxial metal oxide films provides a first conductivity type region comprising one or more epitaxial metal oxide layers, and at least another of the two or more epitaxial metal oxide films provides a second conductivity type region comprising one or more epitaxial metal oxide layers.

[0124] In another embodiment, two or more epitaxial (Al x Ga 1-x At least one of the epitaxial (Al)2O3 films is x Ga 1-x a first conductivity type region including two or more epitaxial (Al)2O3 layers; x Ga 1-x At least one other of the 2O3 films is formed by one or more epitaxial (Al x Ga 1-x a second conductivity type region comprising a SiO layer;

[0125] In another form, the substrate is heated in an ultra-high vacuum chamber (5 × 10 -10 The epitaxial growth surface is then treated by high temperature (>800°C) desorption in less than 1000 Torr to form an atomically flat epitaxial growth surface.

[0126] In another aspect, the method further includes monitoring the surface in real time to assess atomic surface quality.

[0127] In another form, the surface is monitored in real time by reflection high-energy electron diffraction (RHEED).

[0128] In another form, oxidizing the epitaxial growth surface comprises exposing the epitaxial growth surface to an oxygen source under conditions that oxidize the epitaxial growth surface.

[0129] In another aspect, the oxygen source is selected from one or more of the group consisting of oxygen plasma, ozone, and nitrous oxide.

[0130] In another embodiment, the oxygen source is a radio frequency inductively coupled plasma (RF-ICP).

[0131] In another aspect, the method further includes monitoring the surface in real time to assess the oxygen density of the surface.

[0132] In another embodiment, the surface is monitored in real time by RHEED.

[0133] In another form, atomic beams containing high purity Al atoms and / or high purity Ga atoms are each provided by an effusion cell containing an inert ceramic crucible emitted and heated by a filament and controlled by feedback sensing that monitors the metal melt temperature within the crucible.

[0134] In another embodiment, high purity elemental metals with a purity of 6N to 7N or higher are used.

[0135] In another aspect, the method further includes measuring the beam fluxes of the Al and / or Ga and oxygen atomic beams to determine a relative flux ratio, and then exposing the activated epitaxial growth surface to the atomic beams at the determined relative flux ratio.

[0136] In another form, the method further includes rotating the substrate as the activated epitaxial growth surface is exposed to the atomic beam to accumulate a uniform amount of the atomic beam intersecting the substrate surface for a given deposition time.

[0137] In another form, the method further comprises heating the substrate as the activated epitaxial growth surface is exposed to the atomic beam.

[0138] In another form, the substrate is radiatively heated from behind using a blackbody emissivity that matches the absorption below the bandgap of the metal oxide substrate.

[0139] In another embodiment, the activated epitaxial growth surface is about 1×10 -6 Torr ~ approx. 1 × 10 -5 It is exposed to an atomic beam in a vacuum of 100 Torr.

[0140] In another embodiment, the atomic beam flux of Al and Ga at the substrate surface is about 1×10 -8 Torr ~ approx. 1 × 10 -6 It's Torr.

[0141] In another embodiment, the oxygen atomic beam flux at the substrate surface is about 1×10 -7 Torr to approximately 1×10 -5 It's Torr.

[0142] In another embodiment, the Al or Ga metal oxide substrate is A-plane sapphire.

[0143] In another embodiment, the Al or Ga metal oxide substrate is monoclinic Ga2O3.

[0144] In another embodiment, two or more epitaxial (Al x Ga 1-x The AlGaO film contains corundum-type AlGaO.

[0145] In another embodiment, two or more epitaxial (Al x Ga 1-x )2O3 films, x≦0.5.

[0146] In a fourth aspect, the present disclosure provides a method of forming a multi-layer semiconductor device, comprising: forming a first layer having a first crystal symmetry type and a first composition; and depositing, in a non-equilibrium environment, a metal oxide layer on the first layer having a second crystal symmetry type and a second composition, wherein depositing the second layer on the first layer comprises initially matching the second crystal symmetry type to the first crystal symmetry type.

[0147] In another form, initially matching the second crystal symmetry type to the first crystal symmetry type comprises matching a first lattice arrangement of the first crystal symmetry type with a second lattice arrangement of the second crystal symmetry type at a horizontal planar growth interface.

[0148] In another form, matching the first and second crystal symmetry types includes substantially matching the end facet lattice constants of each of the first and second lattice configurations.

[0149] In another form, the first layer is corundum Al2O3 (sapphire) and the metal oxide layer is corundum Ga2O3.

[0150] In another form, the first layer is monoclinic Al2O3 and the metal oxide layer is monoclinic Ga2O3.

[0151] In another form, the first layer is R-plane corundum Al2O3 (sapphire) prepared under O-rich growth conditions, and the metal oxide layer is corundum AlGaO3 selectively grown at low temperature (<550°C).

[0152] In another form, the first layer is M-plane corundum Al2O3 (sapphire) and the metal oxide layer is corundum AlGaO3.

[0153] In another form, the first layer is A-plane corundum Al2O3 (sapphire) and the metal oxide layer is corundum AlGaO3.

[0154] In another form, the first layer is corundum Ga2O3 and the metal oxide layer is corundum Al2O3.

[0155] In another form, the first layer is monoclinic Ga2O3 and the metal oxide layer is monoclinic Al2O3 (sapphire).

[0156] In another embodiment, the first layer is (-201) oriented monoclinic Ga2O3 and the metal oxide layer is (-201) oriented monoclinic AlGaO3.

[0157] In another embodiment, the first layer is (010) oriented monoclinic Ga2O3 and the metal oxide layer is (010) oriented monoclinic AlGaO3.

[0158] In another embodiment, the first layer is (001) oriented monoclinic Ga2O3 and the metal oxide layer is (001) oriented monoclinic AlGaO3.

[0159] In another form, the first and second crystal symmetry types are different, and matching the first and second lattice configurations includes reorienting the metal oxide layer to substantially match in-plane atomic arrangements at the horizontal planar growth interface.

[0160] In another form, the first layer is C-plane corundum Al2O3 (sapphire) and the metal oxide layer is one of monoclinic, triclinic, or hexagonal AlGaO3.

[0161] In another form, C-plane corundum Al2O3 (sapphire) is prepared under O-rich growth conditions to selectively grow hexagonal AlGaO3 at lower growth temperatures (<650°C).

[0162] In another form, C-plane corundum Al2O3 (sapphire) is prepared under O-rich growth conditions to selectively grow monoclinic AlGaO3 at higher growth temperatures (>650 °C) with Al% limited to about 45-50%.

[0163] In another form, R-plane corundum Al2O3 (sapphire) is prepared under O-rich growth conditions to selectively grow monoclinic AlGaO3 with Al% <50% at growth temperatures (>700°C).

[0164] In another form, the first layer is A-plane corundum Al2O3 (sapphire) and the metal oxide layer is (110) oriented monoclinic Ga2O3.

[0165] In another form, the first layer is (110) oriented monoclinic Ga2O3 and the metal oxide layer is corundum AlGaO3.

[0166] In another embodiment, the first layer is (010) oriented monoclinic Ga2O3 and the metal oxide layer is (111) oriented cubic MgGa2O4.

[0167] In another embodiment, the first layer is (100) oriented cubic MgO and the metal oxide layer is (100) oriented monoclinic AlGaO3.

[0168] The first layer is (100) oriented cubic NiO, and the metal oxide layer is (100) oriented monoclinic AlGaO3.

[0169] In another form, initially matching the second crystal symmetry type to the first crystal symmetry type includes depositing a buffer layer between the first layer and the metal oxide layer in a non-equilibrium environment, the buffer layer having the same crystal symmetry type as the first crystal symmetry type to provide an atomically flat layer for seeding the metal oxide layer having the second crystal symmetry type.

[0170] In another form, the buffer layer includes an O-terminated template for seeding the metal oxide layer.

[0171] In another form, the buffer layer includes a metal termination template for seeding the metal oxide layer.

[0172] In another aspect, the first and second crystal symmetry types are selected from the group consisting of cubic, hexagonal, orthorhombic, trigonal, rhomboidal, and monoclinic.

[0173] In another form, a first crystal symmetry type and a first composition of the first layer and a second crystal symmetry type and a second composition of the second layer are selected to introduce a predetermined strain in the second layer.

[0174] In another embodiment, the first layer is a metal oxide layer.

[0175] In another form, the first and second layers form unit cells that are repeated with a fixed unit cell period to form a superlattice.

[0176] In another form, the first and second layers are configured to have substantially equal but opposite strains to facilitate the formation of a defect-free superlattice.

[0177] In another aspect, the method includes depositing, in a non-equilibrium environment, an additional metal oxide layer having a third crystal symmetry type and a third composition onto the metal oxide layer.

[0178] In another aspect, the third crystalline form is selected from the group consisting of cubic, hexagonal, orthorhombic, trigonal, rhomboidal, and monoclinic.

[0179] In another form, the multi-layer semiconductor device is an optoelectronic semiconductor device that produces light of a predetermined wavelength.

[0180] In another embodiment, the predetermined wavelength is in the wavelength range of 150 nm to 700 nm.

[0181] In another embodiment, the predetermined wavelength is in the wavelength range of 150 nm to 280 nm.

[0182] In a fifth aspect, the present disclosure provides a method of forming an optoelectronic semiconductor device that generates light of a predetermined wavelength, the method including: introducing a substrate; depositing, in a non-equilibrium environment, a first conductivity type region comprising one or more epitaxial layers of a metal oxide; depositing, in a non-equilibrium environment, a light emitting region comprising one or more epitaxial layers of a metal oxide and comprising a light emitting region band structure configured to generate light of the predetermined wavelength; and depositing, in a non-equilibrium environment, a second conductivity type region comprising one or more epitaxial layers of a metal oxide.

[0183] In another embodiment, the predetermined wavelength is in the wavelength range of about 150 nm to about 700 nm. In another embodiment, the predetermined wavelength is in the wavelength range of about 150 nm to about 425 nm. In one example, bismuth oxide can be used to produce wavelengths up to about 425 nm.

[0184] In another embodiment, the predetermined wavelength is in the wavelength range of about 150 nm to about 280 nm.

[0185] In yet another aspect, the luminous efficiency is controlled by the selection of the crystal symmetry type of the light-emitting region. The optical selection rules for electric dipole luminescence are governed by the symmetry of the conduction and valence band states and the crystal symmetry type. Light-emitting regions having crystal structures with point group symmetry can possess either inversion centrosymmetry or non-inversion symmetry characteristics. Advantageous selection of crystal symmetry to promote electric dipole or magnetic dipole optical transitions is claimed herein for application to the light-emitting region. Conversely, advantageous selection of crystal symmetry to suppress electric dipole or magnetic dipole optical transitions can also promote optically non-absorbing regions of the device.

[0186] As an overview, FIG. 1 is a process flow diagram for constructing an optoelectronic semiconductor optoelectronic device according to an exemplary embodiment. In one example, the optoelectronic semiconductor device is a UV LED, and in a further example, the UV LED is configured to generate a predetermined wavelength in the wavelength range of about 150 nm to about 280 nm. In this example, the construction process first involves (i) selecting a desired operating wavelength (e.g., a UVC wavelength or lower) in step 10 and (ii) selecting an optical configuration for the device in step 60 (e.g., a vertical-emitting device 70 in which the light output vector or direction is substantially perpendicular to the plane of the epilayers, or a waveguide device 75 in which the light output vector is substantially parallel to the plane of the epilayers). The light-emitting characteristics of the device are implemented in part by the selection of semiconductor material 20 and optical material 30.

[0187] Taking the example of a UV LED, an optoelectronic semiconductor device constructed according to the process shown in Figure 1 includes a light emitting region based on a selected light emitting region material 35 in which photons are generated by favorable spatial recombination of electrons in the conduction band and holes in the valence band. In one example, the light emitting region includes one or more metal oxide layers.

[0188] The light emitting region may have a direct bandgap band structure configuration. This may be an inherent property of the selected material(s) or may be tailored using one or more of the techniques of this disclosure. The light recombination or light emitting region may be clad with electron and hole reservoirs including n-type and p-type conduction regions. The n-type and p-type conduction regions are selected from electron and hole injection materials 45 that may have a larger bandgap than the light emitting region material 35 or may include an indirect bandgap structure that limits light absorption at the operating wavelength. In one example, the n-type and p-type conduction regions are formed from one or more metal oxide layers.

[0189] Impurity doping of Ga2O3 and low Al% AlGaO3 is possible for both n-type and p-type materials. N-type doping is particularly favorable for Ga2O3 and AlGaO3, while p-type doping is more difficult but possible. Suitable impurities for n-type doping are Si, Ge, Sn, and rare earths (e.g., erbium (Er) and gadolinium (Gd)). The use of a Ge flux for codeposition doping control is particularly suitable. For p-type co-doping with group III metals, the Ga site is doped with magnesium (Mg 2+ ), zinc (Zn 2+ ) and atomic nitrogen (N for O sites) 3- Further improvements can be achieved using iridium (Ir), bismuth (Bi), nickel (Ni), and palladium (Pd).

[0190] Digital alloys using NiO, Bi2O3, Ir2O3, and PdO can also be used in some embodiments to advantageously support p-type formation in Ga2O3-based materials. While p-type doping of AlGaO3 is possible, cubic crystal symmetry metal oxides (e.g., Li-doped NiO or Ni-vacancy NiO) are not. x>1 ) and alternative doping strategies using wurtzite p-type Mg:GaN are also possible.

[0191] Yet another opportunity is the ability to form highly polar morphologies with hexagonal symmetry and epsilon-phase Ga2O3 directly integrated into AlGaO3, thereby inducing polarization according to the principles and techniques described and referenced in U.S. Patent No. 9,691,938. The optical materials 30 required to confine light within the device as a differential change in refractive index also need to be selected. For the deep or vacuum ultraviolet, the choice of optically transparent materials ranges from MgO to metal fluorides such as MgF2, LiF, etc. In accordance with the present disclosure, single-crystal LiF and MgO substrates have been found to be advantageous for UV LED implementation.

[0192] The electrical materials 50 that form contacts to the electron and hole injector regions are selected from low and high work function metals, respectively. In one example, metal ohmic contacts are formed in situ directly on the final metal oxide surface, thereby reducing any intermediate level traps / defects that occur at the semiconductor oxide-metal interface. The device is then constructed in step 80.

[0193] 2A and 2B schematically illustrate a vertical emission device 110 and a waveguide emission device 140 according to exemplary embodiments. Device 110 includes a substrate 105 and a light-emitting structure 135. Similarly, device 140 includes a substrate 155 and a light-emitting structure 145. Light 125 and 130 from device 110 and light 150 from device 140 are generated in a light-generating region 120, propagate from region 120 through the device, and are confined by an optical escape cone defined by the difference in refractive index at the semiconductor-to-air interface. Metal-oxide semiconductors have significantly lower refractive indices than III-N materials due to their large bandgap energy. Therefore, the use of metal-oxide materials provides an improved optical escape cone and, therefore, higher light output coupling efficiency compared to conventional light-emitting devices. Waveguide devices operating in both single and multimode modes are also possible.

[0194] Broad-area stripe waveguides can also utilize elemental Al or Mg metals to form ultraviolet plasmon guides directly at the semiconductor-metal interface. This is an efficient method for forming waveguide structures. The E band structures of Al, Mg, and Ni are discussed below. Once the desired material selections are available, the process for constructing a semiconductor optoelectronic device can occur in step 80 (see FIG. 1).

[0195] FIG. 3A illustrates functional areas of an epitaxial structure of an optoelectronic semiconductor device 160 for generating light of a predetermined wavelength, according to an example embodiment.

[0196] Substrate 170 is provided with favorable crystal symmetry and in-plane lattice constant matching at the surface to enable subsequent homoepitaxy or heteroepitaxy of first conductivity type region 175 with non-absorbing spacer region 180, light emitting region 185, optional second spacer region 190, and second conductivity type region 195. In one example, the in-plane lattice constant and lattice shape / configuration are matched to modify (i.e., reduce) lattice defects. Electrical excitation is provided by source 200 connected to the electron injection and hole injection regions of first conductivity type region 175 and second conductivity type region 195. Ohmic metal contacts and low bandgap or semimetallic zero bandgap oxide semiconductors are shown in FIG. 3B as regions 196, 197, and 198 in another exemplary embodiment.

[0197] First and second conductivity type regions 175 and 195 are formed, in one example, using a wide bandgap metal oxide and are electrically contacted using ohmic contact regions 197, 198, and 196, as described herein. In the case of an insulating-type substrate 170, electrical contact is made via ohmic contact region 198 and first conductivity type region 175 for one conductivity type (i.e., electrons or holes) and via ohmic contact region 196 and second conductivity type region 195 for the other. Ohmic contact region 198 may optionally be made on exposed portions of first conductivity type region 175. Insulating substrate 170 may also be transparent or opaque to the operating wavelength, so that in the case of a transparent substrate, lower ohmic contact region 197 may be utilized as an optical reflector as part of an optical cavity in another embodiment.

[0198] For vertical conduction devices, substrate 170 is conductive and may be either transparent or opaque to the operating wavelength. Electrical or ohmic contact regions 197 and 198 are advantageously positioned to allow both electrical connection and optical propagation within the device.

[0199] 3C schematically illustrates a further possible electrical arrangement of electrical contact regions 196 and 198, showing portions of the mesa etched to expose lower conductivity type regions 175 and 198. Ohmic contact region 196 may be further patterned to expose portions of the device for light extraction.

[0200] 3D shows yet another electrical configuration in which an insulating substrate 170 is used such that first conductivity type region 175 is exposed and electrical contact is made to the partially exposed portion of first conductivity type region 175. In the case of a conductive, transparent substrate contact, ohmic contact region 198 is not required and spatially spaced electrical contact regions 197 are used.

[0201] Figure 3E further illustrates possible placement of optical apertures 199 partially or completely etched into optically opaque substrate 170 for optical coupling of light generated from light emitting region 185. Optical apertures can similarly be utilized with the previous embodiments of Figures 3A-3D.

[0202] 4 schematically illustrates the operation of optoelectronic semiconductor device 160, where an exemplary configuration includes electron injection region 180 and hole injection region 190 with an electrical bias 200 to transport and direct mobile electrons 230 and holes 225 toward recombination region 220. The resulting recombination of electrons and holes forms spatial light-emitting region 185.

[0203] Very large energy band gap (E G ) metal oxide semiconductor (E G >4 eV) may exhibit low mobility hole-type carriers and may even be highly spatially localized, thereby limiting the spatial extent of hole injection. The regions near the hole injection region 190 and the recombination region 220 may then be favorable for the recombination process. Furthermore, the hole injection region 190 itself may be a favorable region for injecting electrons such that the recombination region 220 is located within a portion of the hole injection region 190.

[0204] 5, light or luminescence is generated within device 160 by the selective spatial recombination of electrons and holes to generate high energy photons 240, 245, and 250 of predetermined wavelengths determined by the band structure configuration of the metal oxide layers that form light emitting region 185, as described below. Both the electrons and holes instantly annihilate, generating photons that are characteristic of the band structure of the selected metal oxide.

[0205] Light generated in the light-emitting region 185 can propagate within the device according to the crystal symmetry of the metal oxide host region. The crystal symmetry group of the host metal oxide semiconductor has a well-defined energy and crystal momentum dispersion, known as the Ek configuration, that characterizes the band structure of the various regions comprising the light-emitting region 185. The nontrivial Ek dispersion is fundamentally determined by the physical atomic arrangement underlying the well-defined crystal symmetry of the host medium. In general, the possible polarizations, emission energies, and intensity of the light-emitting oscillator are directly related to the valence band dispersion of the host crystal. According to the present disclosure, embodiments advantageously configure the band structure, including the valence band dispersion, of a selected metal oxide semiconductor for application in optoelectronic semiconductor devices, such as, for example, UV LEDs.

[0206] Vertically generated light 240 and 245 must satisfy the optical selection rules of the underlying band structure. Similarly, there are optical selection rules for lateral light 250 generation. These optical selection rules can be achieved by advantageously arranging the crystal symmetry type and physical spatial orientation of the crystals for each of the regions within the UV LED. The advantageous orientation of the constituent metal oxide crystals as a function of growth direction is beneficial for optimal operation of the UV LEDs of the present disclosure. Additionally, the selection of optical properties 30 in the process flow diagram shown in FIG. 1, such as refractive index, to form a waveguide-type device is indicated for optical confinement and low loss.

[0207] For the sake of completeness, FIG. 6 further illustrates another embodiment including an optical aperture 260 disposed within the optoelectronic semiconductor device 160 to allow for the use of a material 195 that is opaque to the operating wavelength to provide light output coupling from the light emitting region 185.

[0208] FIG. 7 outlines selection criteria 270 for one or more metal oxide crystal compositions, according to an exemplary embodiment. First, a semiconductor material 275 is selected. The semiconductor material 275 may include a metal oxide semiconductor 280, which may be one or more of a binary oxide, a ternary oxide, or a quaternary oxide. The recombination region 220 (see, e.g., FIG. 5 ), which forms the light-emitting region 185 of the optoelectronic semiconductor device 160, is selected to exhibit efficient electron-hole recombination, while the conduction-type region is selected for its ability to provide a source of electrons and holes. Metal oxide semiconductors can also be selectively created from multiple possible crystal symmetry types, even if the constituent metal species are the same. A metal oxide semiconductor containing one metal species may be selected. x O y may be used, where a metal species (A) is bonded to oxygen (O) in relative ratios of x and y. Even with the same relative ratios of x and y, multiple crystal structure configurations are possible with widely different crystal symmetry groups.

[0209] As explained below, the compositions Ga2O3 and Al2O3 exhibit several advantageous and well-defined crystal symmetries (e.g., monoclinic, rhombohedral, triclinic, and hexagonal), but caution is warranted regarding their usefulness in incorporating and constructing UV LEDs. Other advantageous metal oxide compositions, such as MgO and NiO, exhibit less variation in the crystal structure that is practically achievable, i.e., cubic.

[0210] The addition of a beneficial second heterometallic species (B) enhances the host binary metal oxide crystal structure, resulting in A x B y O nTernary metal oxides of the form: ##STR1## can also be produced. Ternary metal oxides range from dilute additions of B species to large relative proportions. As discussed below, ternary metal oxides can be advantageously employed to form direct bandgap light-emitting structures in various embodiments. Additionally, quaternary compositions A and B can be produced. x B y C z O n Further materials can be designed that contain three different cationic atomic species bonded to oxygen forming

[0211] In general, while it is theoretically possible to incorporate more dissimilar metal atoms (>4) to form complex oxide materials, they rarely produce high crystalline quality with well-defined crystal symmetry structures. Such complex oxides are generally polycrystalline or amorphous and therefore lack optimal utility for optoelectronic device applications. As will become apparent, the present disclosure, in various examples, seeks substantially single-crystalline, low-defect density compositions for utilizing band structures to form UV LED epitaxially formed devices. Some embodiments involve achieving the desired Ek composition through the addition of additional, different metal species.

[0212] The selection of the desired bandgap structure for each of the UVLED regions of the optoelectronic semiconductor device 160 can also involve the integration of different crystal symmetry types. For example, monoclinic and cubic crystal symmetry host regions can be utilized to comprise a portion of the UVLED. The epitaxial formation relationship then requires attention to the formation of low-defect layer formation. The type of layer formation step is then classified as homo-symmetric and hetero-symmetric formation 285. Band structure modifiers 290, such as digital alloys with biaxial strain, uniaxial strain, and superlattice formation, can be utilized to achieve the goal of providing materials that form the epilayer structure.

[0213] The epitaxy process 295 is then defined by the type and order of material compositions required for deposition. This disclosure describes new processes and compositions to achieve this goal.

[0214] FIG. 8 illustrates the formation steps of the epitaxy process 300. In step 310, a film-forming substrate for supporting the light-emitting region is selected to have the desired crystal symmetry type characteristics, as well as optical and electrical properties. In one example, the substrate is selected to be optically transparent to the operating wavelength and to have a crystal symmetry that matches the required epitaxial crystal symmetry type. While comparable crystal symmetries of both the substrate and epitaxial film(s) can be used, there is also optimization 315 to match in-plane atomic arrangements, such as in-plane lattice constants or favorable co-incidence of in-plane shapes of respective crystal planes from dissimilar crystal symmetry types.

[0215] Substrate surfaces have a well-defined two-dimensional crystalline arrangement of terminated surface atoms. In vacuum-prepared surfaces, this discontinuity in the well-defined crystalline structure minimizes the surface energy of the dangling bonds of the terminated atoms. For example, in one embodiment, a metal oxide surface can be prepared as an oxygen-terminated surface, or in another embodiment, as a metal-terminated surface. Metal oxide semiconductors can have complex crystal symmetries, and care must be taken when terminating pure species. For example, both Ga2O3 and Al2O3 can be O-terminated by high-temperature annealing in vacuum followed by sustained exposure to atomic or molecular oxygen at high temperatures.

[0216] The substrate's crystal surface orientation 320 can also be selected to achieve selective film formation crystal symmetry of the epitaxial metal oxide. For example, A-plane sapphire can be used to advantageously select (110)-oriented alpha-phase-forming high-quality epitaxial Ga2O3, AlGaO3, and Al2O3, while C-plane sapphire produces hexagonal and monoclinic Ga2O3 and AlGaO3 films. Ga2O3-oriented surfaces can also be selectively used to select AlGaO3 crystal symmetry for film formation.

[0217] The growth conditions 325 are then optimized for the relative proportions of elemental metal and activated oxygen necessary to achieve the desired material properties. The growth temperature also plays an important role in determining the possible crystal structure symmetry types. The judicious selection of the substrate surface energy along with the appropriate crystal surface orientation also determines the temperature process window of the epitaxial process over which the epitaxial structure 330 is deposited.

[0218] A materials selection database 350 for UV LED-based optoelectronic device applications is disclosed in Figure 9. Metal oxide materials 380 are plotted as a function of their electron affinity energy 375 relative to vacuum. As ordered from left to right, the semiconductor materials have increasing optical bandgaps, making them more useful for UV LEDs operating at shorter wavelengths. Using lithium fluoride (LiF) as an example in this graph, LiF has a bandgap 370 (represented as a box for each material), which is the energy difference in electron volts between the conduction band minimum 360 and the valence band maximum 365. The absolute energy positions, represented by the conduction band minimum 360 and the valence band maximum 365, are plotted against vacuum energy. Narrow bandgap materials, such as rare earth nitrides (RE-N), germanium (Ge), palladium oxide (PdO), and silicon (Si), do not provide suitable host properties for the light-emitting region but can be advantageously used to form electrical contacts. The use of the intrinsic electron affinity of a given material can be used to form ohmic contacts and metal-insulator-semiconductor junctions as needed.

[0219] A desirable combination of materials for use as a substrate is bismuth oxide (Bi2O3), nickel oxide (NiO), and germanium oxide (GeO x~2), gallium oxide (GaO), lithium oxide (LiO), magnesium oxide (MgO), aluminum oxide (AlO), single crystal quartz SiO, and finally lithium fluoride 355 (LiF). Specifically, AlO (sapphire), GaO, MgO, and LiF are available as large, high-quality single crystal substrates and can be used in some embodiments as substrates for UV LED-type optoelectronic devices. Additional substrate embodiments for UV LED applications also include single crystal cubic symmetry magnesium aluminate (MgAlO) and magnesium gallate (MgGaO). In some embodiments, the ternary form AlGaO can be arranged as bulk substrates with monoclinic (high Ga%) and corundum (high Al%) crystal symmetry using large-area formation methods such as Czochralski (CZ) and edge-fed growth (EFG).

[0220] Considering the host metal oxide semiconductors of Ga2O3 and Al2O3, in some embodiments alloying and / or doping via elements selected from database 350 is advantageous for film forming properties.

[0221] Therefore, elements selected from silicon (Si), germanium (Ge), Er (erbium), Gd (gadolinium), Pd (palladium), Bi (bismuth), Ir (iridium), Zn (zinc), Ni (nickel), Li (lithium), and magnesium (Mg) are desirable crystal modifiers for forming ternary crystal structures or dilute additions to Al2O3, AlGaO3, or Ga2O3 host crystals (see semiconductor 280 in Figure 7).

[0222] Further embodiments include selection from the group of crystal modifiers selected from the group Bi, Ir, Ni, Mg, Li.

[0223] In applications to host crystals Al2O3, AlGaO3, or Ga2O3, possible multivalent states can be added using Bi and Ir, enabling p-type impurity doping. Adding Ni and Mg cations also allows substitutional doping of p-type impurities at Ga or Al crystal sites. In one embodiment, lithium can be used as a crystal modifier to increase the bandgap and potentially modify the crystal symmetry, ultimately leading to lithium gallate (LiGaO2) with orthorhombic symmetry and aluminum gallate (LiAlO2) with tetragonal symmetry. For n-type doping, Si and Ge can be used as impurity dopants, with Ge providing an improved growth process for film formation.

[0224] Although other materials are possible, database 350 provides advantageous properties for UV LED applications.

[0225] FIG. 10 illustrates a sequential epitaxial layer formation process flow 400 utilized to epitaxially integrate defined material regions within an optoelectronic semiconductor device 160 according to an exemplary embodiment.

[0226] A substrate 405 is prepared with a surface 410 configured to receive a first conductivity type crystalline structure layer(s) 415, which may include multiple epitaxial layers. Next, a first spacer region composition layer(s) 420, which may include multiple epitaxial layers, is formed on layer 415. A light-emitting region 425 is then formed on layer 420, which may include multiple epitaxial layers. A second spacer region 430, which may include multiple epitaxial layers, is then deposited on region 425. A second conductivity type cap region 435, which may include multiple epitaxial layers, then completes the majority of the UV LED epitaxial structure. Other layers, such as ohmic metal layers and passive optical layers, such as optical confinement or antireflection layers, may be added to complete the optoelectronic semiconductor device.

[0227] Referring to Figure 11, a possible selection of ternary metal oxide semiconductors 450 is shown for gallium oxide-based (GaOx-based) compositions 485. Ternary Oxide Alloy A x B 1-x The optical band gap 480 for various values ​​of x in O is plotted. As previously mentioned, metal oxides can exhibit several stable forms with more complex crystal symmetry structures through the addition of other species to form ternaries. However, exemplary general trends can be found by selectively incorporating or alloying atoms of aluminum, group II cations (Mg, Ni, Zn), iridium, erbium, and gadolinium, as well as lithium atoms, advantageously into Ga-oxide. Ni and Ir typically form deep d-bands, but useful optical structures can be formed with high Ga %. Ir is capable of multiple valence states, and in some embodiments, the Ir2O3 form is utilized.

[0228] X = one of {Ir, Ni, Zn, Bi} with Ga x X 1-x Alloying with O reduces the available optical bandgap (see curves labeled 451, 452, 453, and 454). Conversely, alloying with one of Y = {Al, Mg, Li, RE} reduces the available optical bandgap. x Y 1-x The available band gap of O increases (see curves 456, 457, 458, 459).

[0229] Thus, FIG. 11 can be understood in its application to forming emissive and conductive regions in accordance with the present disclosure.

[0230] Similarly, Figure 12 discloses a possible choice of ternary metal oxide semiconductor 490 for an aluminum oxide-based (AlOx-based) composition 485 in terms of optical bandgap 480. Inspection of the curves reveals that one of X = {Ir, Ni, Zn, Mg, Bi, Ga, RE, Li} is replaced by Al. x X 1-xIt can be seen that alloying with O reduces the available optical bandgap. The group Y={Ni, Mg, Zn} forms a spinel crystal structure, but all are ternary Al x Y 1-x 12 also shows the energy gap 502 of alpha-phase aluminum oxide (Al2O3), which has rhombohedral crystal symmetry.

[0231] Figure 12 can thus be understood in its application to the formation of emissive and conductive regions in accordance with the present disclosure. Shown in Figure 28 is a chart 2800 of potential ternary oxide combinations (0 < x < 1) that may be employed in accordance with the present disclosure. Chart 2800 shows crystal growth modifiers down the left column and host crystals across the top of the chart.

[0232] 13A and 13B are representations of electron energy versus crystal momentum for possible metal oxide-based semiconductors exhibiting direct (FIG. 13A) and indirect (FIG. 13B) bandgaps, illustrating concepts relevant to the formation of optoelectronic devices according to the present disclosure. It is known by researchers in the fields of quantum mechanics and crystal structure design that symmetry directly determines the electronic configuration or band structure of a single crystal structure.

[0233] Generally, when applied to light-emitting crystal structures, there are two classes of electronic band structures, as shown in Figures 13A and 13B. The fundamental process utilized in the optoelectronic devices of the present disclosure is the recombination of physical (bulk) electron and hole particle-like charge carriers, which are a manifestation of allowed energy and crystal momentum. The recombination process can occur with the conservation of crystal momentum of the incident carriers from the initial state to the final state.

[0234] Achieving a final state in which the electron and hole annihilate to form a massless photon (i.e., the momentum k of the final state massless photon) γ ga k γ= 0) requires the special E band structure shown in Figure 13A. Metal-oxide-semiconductor structures with pure crystalline symmetry can be calculated using a variety of computational techniques. One such method is density functional theory, which uses first principles to construct atomic structures including differentiated pseudopotentials associated with each constituent atom comprising the structure. An iterative computational scheme of ab initio total energy calculations using a plane wave basis can be used to calculate the band structure resulting from the symmetry and spatial geometry of the crystal.

[0235] Figure 13A shows the reciprocal space energy versus crystal momentum or band structure 520 of a crystal structure.

number

number

number

[0236] Dispersions 525 and 535 are the electron energy in electron volts (increasing direction 530, decreasing direction 585) and the crystal momentum in reciprocal space units (positive K BZ 545 and negative K BZThe band structure 520 is plotted with respect to the conduction band minimum 565. The band structure 520 is shown at the point of highest symmetry of the crystal, labeled as the Γ point, which represents the band structure at k=0. The band gap is defined by the energy difference between the minimum and maximum values, 525 and 535, respectively. Electrons propagating through the crystal minimize their energy and relax to the conduction band minimum 565. Similarly, holes relax to the lowest energy state 580.

[0237] If 565 and 580 are simultaneously located at k=0, then the electron and hole can annihilate, and a direct recombination process can occur that generates a new massless photon 570 with energy approximately equal to the bandgap energy 560. That is, an electron and hole at k=0 can recombine and preserve their crystal momenta to create a massless particle called a "direct" bandgap material. As will be disclosed, this situation is rare in practice, and only a small subset of all crystal symmetry semiconductors exhibit this advantageous configuration.

[0238] Referring now to the crystal structure 590 of FIG. 13B, if the first-order bands 525 and 620 of the band structure do not have their respective minimum 565 and maximum 610 at k=0, this is referred to as an "indirect" configuration. The minimum bandgap energy 600 is still defined as the energy difference between the conduction band minimum and valence band maximum occurring at the same wave vector, known as the indirect bandgap energy 600. The light emission process is clearly unfavorable because crystal momentum cannot be conserved in recombination events and secondary particles are required to conserve crystal momentum, such as crystal vibrational quantum phonons. In metal oxides, the longitudinal optical phonon energy is proportional to the bandgap and is very large compared to the energies found in, for example, GaAs, Si, etc.

[0239] Therefore, it is difficult to use the indirect Ek configuration for the purpose of emitting light. This disclosure describes methods for manipulating the otherwise indirect band gap of a particular crystal symmetry structure to convert or modify the zone-centered k=0 characteristic of the band structure to a direct band gap dispersion suitable for light emission. These methods are disclosed herein for application to the fabrication of optoelectronic devices, specifically UV LEDs.

[0240] Even when direct bandgap configurations exist, design choices are faced with the specific crystal symmetry of a given metal oxide, with electric dipole selection rules governed by the symmetry characteristic groups assigned to each energy band. In the case of Ga2O3 and Al2O3, optical absorption is governed between the lowest conduction band and the three topmost valence bands.

[0241] 13C-13E show the emission and absorption transitions at k=0 for GaO monoclinic symmetry. vi 13C shows the optically allowed electric dipole transitions for electron 566 and hole 624 for optical polarization vectors in the a-axis and c-axis of the monoclinic unit cell. In terms of reciprocal space Ek, this corresponds to wave vector 627 of the Γ-Y ​​branch. Similarly, the electric dipole transition between electron 566 and hole 625 in FIG. 13D is allowed for polarization along the c-axis 628 of the crystal unit cell. Furthermore, the higher energy transition between electron 566 and hole 626 in FIG. 13E is allowed for an optical polarization field along the b-axis 629 of the unit cell, corresponding to the Ek(Γ-X) branch.

[0242] Clearly, the magnitudes of energy transitions 630, 631, and 632 in Figures 13C, 13D, and 13E, respectively, are increased only at the lowest energy transitions favorable for light emission. However, the Fermi energy level ( EF ) but the lowest valence band 621 is E F Higher, 622 is E FIf configured to be lower, emission can occur at energy 631. These selection rules are particularly useful when designing waveguide devices that are optically polarization dependent for specific TE, TM, and TEM modes of operation.

[0243] With reference to the discussion above related to band structure, reference is now made to Figures 14A and 14B, which illustrate how these complex elements can be incorporated into a device structure 160. Each functional region of a UV LED has a specific Ek dispersion with both indirect and direct materials, which can be attributed to dramatically different crystal symmetry types. This then allows the light-emitting region to be advantageously embedded within the device.

[0244] 14A and 14B show representations of composite Ek materials by a single block 633 defined by layer thicknesses 655, 660, and 665, and fundamental bandgap energies 640, 645, and 650, respectively. The relative alignment of the conduction and valence band edges is indicated in block 633. FIG. 14B plots electron energy 670 versus spatial growth direction 635 for three distinct materials with bandgap energies 640, 645, and 650. For example, a first region deposited along growth direction 635 using an indirect crystallization is possible, but with a final surface lattice constant geometry that can otherwise accommodate subsequent mechanical and elastic deformation of crystal 645. For example, this can occur when growing AlGaO directly on GaO.

[0245] Epitaxial manufacturing method

[0246] Non-equilibrium growth techniques are known in the prior art and are referred to as atomic and molecular beam epitaxy, chemical vapor phase epitaxy, or physical vapor phase epitaxy. Atomic and molecular beam epitaxy utilizes atomic beams of spatially separated elements directed at the growth surface, as shown in Figure 15. While molecular beams are also used, it is the combination of molecular and atomic beams that can be used in accordance with the present disclosure.

[0247] One guiding principle is to use pure component sources that can be multiplied at the growth surface through favorable condensation and kinetically favorable growth conditions to physically build crystalline atomic layers, layer by layer. While the growing crystal can essentially self-assemble, the control of this method also allows for atomic-level intervention, depositing atomically thick epilayers of a single species. Unlike equilibrium growth techniques that rely on the thermodynamic chemical potential of bulk crystal formation, this technique allows for the deposition of very thin atomic layers with growth parameters far removed from the equilibrium growth temperature of the bulk crystal.

[0248] In one example, Al2O3 films are formed at film formation temperatures in the range of 300-800°C, while conventional bulk equilibrium growth of Al2O3 (sapphire) is produced at temperatures well above 1500°C and requires a melt reservoir containing Al and O liquids that can be configured to place a solid seed crystal in close proximity to the melt surface. Careful positioning of the seed crystal orientation places it in contact with the melt and forms a recrystallized portion in the vicinity of the melt. When the seed and partially solidified recrystallized portion are pulled away from the melt, a continuous crystalline boule is formed.

[0249] Such equilibrium growth methods for metal oxides limit the possible combinations of metals and the complexity of discontinuous regions possible for heteroepitaxial formation of complex structures. The non-equilibrium growth techniques disclosed herein can operate with growth parameters far enough away from the melting point of the target metal oxide that the atomic species present in a single atomic layer of the crystalline unit cell can even be modulated along a preselected growth direction. Such non-equilibrium growth methods are not constrained by equilibrium phase diagrams. In one example, the method utilizes an evaporation source material that is ultra-pure and includes a beam that impinges on the growth surface in a substantially charge-neutral manner. Charged ions may be generated, but these should be minimized as much as possible.

[0250] For metal oxide growth, the component source beams can be varied in their relative proportions in known ways. For example, oxygen-rich and metal-rich growth conditions can be achieved by controlling the relative beam fluxes measured at the growth surface. While almost all metal oxides grow optimally under oxygen-rich growth conditions similar to the arsenic-rich growth of gallium arsenide (GaAs), some materials differ. For example, GaN and AlN require metal-rich growth conditions with very narrow growth windows, which is one of the biggest limitations for mass production.

[0251] Metal oxides favor oxygen-rich growth over a wide growth window, but there is an opportunity to intervene and create intentional metal-deficient growth conditions. For example, both Ga2O3 and NiO favor cation vacancies for the generation of active hole conduction. Physical cation vacancies can generate electron-carrier holes, thus favoring p-type conductivity.

[0252] 41, there is shown, in summary, a process flow diagram 4100 of a method for forming an optoelectronic semiconductor device according to the present disclosure. In one example, the optoelectronic semiconductor device is configured to emit light at a wavelength between about 150 nm and about 280 nm.

[0253] In step 4110, a metal oxide substrate having an epitaxial growth surface is provided. In step 4120, the epitaxial growth surface is oxidized to form an activated epitaxial growth surface. In step 4130, the activated epitaxial growth surface is exposed to one or more atomic beams each containing high purity metal atoms and one or more atomic beams containing oxygen atoms under conditions to deposit two or more epitaxial metal oxide films or layers.

[0254] Referring again to FIG. 15, in one example, an epitaxial deposition system 680 is shown for providing atomic and molecular beam epitaxy according to the method 4100 referenced in FIG.

[0255] In one example, substrate 685 rotates about axis AX and is radiatively heated by heater 684, which has an emissivity designed to match the absorption of the metal oxide substrate. High vacuum chamber 682 has multiple element sources 688, 689, 690, 691, 692 that can generate atomic or molecular species as beams of pure atomic components. Also shown is plasma or gas source 693, and gas feed 694, which is a connection to gas source 693.

[0256] For example, sources 689-692 may include jet-type sources of liquid Ga, Al, and Ge or precursor-based gases. Activated oxygen sources 687 and 688 may be provided via plasma-excited molecular oxygen (forming atomic O and O*), ozone (O), nitrous oxide (NO), etc. In some embodiments, plasma-activated oxygen is used as a controllable source of atomic oxygen. Multiple gases can be injected via sources 695, 696, and 697 to provide a mixture of different species for growth. For example, atomic nitrogen and excited molecular nitrogen enable the production of n-type, p-type, and semi-insulating conductivity films with Ga-oxide-based materials. Vacuum pump 681 maintains the vacuum, and a mechanical shutter intersecting atomic beam 686 modulates the respective beam flux to provide line-of-sight to the substrate deposition surface.

[0257] This deposition method has proven particularly useful in allowing flexibility in incorporating elemental species into Ga-oxide and Al-oxide based materials.

[0258] FIG. 16 illustrates an embodiment of an epitaxial process 700 for constructing a UV LED as a function of growth direction 705. A homosymmetric layer 735 can be formed using a native substrate 710. The substrate 710 and the crystalline epitaxial layer 735 are homosymmetric, labeled Type 1 herein. For example, a corundum-type sapphire substrate can be used to deposit layers 715, 720, 725, and 730 with corundum crystal symmetry. Yet another example is using monoclinic substrate crystal symmetry to form monoclinic crystal symmetry layers 715-730. This is readily possible using native substrates for the growth of target materials disclosed herein (see, e.g., Table I in FIG. 43A). Of particular interest is the growth of epitaxial layers, such as corundum-AlGaO, with multiple compositions for layers 715-730. Alternatively, a monoclinic GaO substrate 710 can be used to form multiple monoclinic AlGaO compositions for layers 715-730.

[0259] 17 , a further epitaxial process 740 is illustrated that uses a substrate 710 having a crystal symmetry that is essentially foreign to the crystal type of the target epitaxial metal oxide epilayer of layers 745, 750, 755, 760. That is, the substrate 710 is of crystal symmetry type 1 that is heterosymmetric to the crystal structure epitaxy 765 consisting of layers 745, 750, 755, 760, which are all of type 2.

[0260] For example, C-plane corundum sapphire can be used as a substrate to deposit at least one of monoclinic, triclinic, or hexagonal AlGaO3 structures. Another example is to use a (110)-oriented monoclinic Ga2O3 substrate to epitaxially deposit a corundum AlGaO3 structure. Yet another example is to use a (100)-oriented cubic symmetric MgO substrate to epitaxially deposit a (100)-oriented monoclinic AlGaO3 film.

[0261] Process 740 can also be used to produce a corundum GaO-modified surface 742 by selectively diffusing Ga atoms into the surface structure provided by the AlO substrate. This can be done by increasing the growth temperature of the substrate 710 and exposing the AlO surface to excess Ga while also providing an O atom mixture. Under Ga-rich conditions and high temperatures, Ga adatoms selectively attach to the O sites, forming volatile suboxides, GaO, while the excess Ga further diffuses Ga adatoms to the AlO surface. Under appropriate conditions, a corundum GaO surface structure can be obtained, allowing for lattice matching of Ga-rich AlGaO structures or thicker layers to provide monoclinic AlGaO crystal symmetry.

[0262] FIG. 18 illustrates yet another embodiment of a process 770 in which a buffer layer 775 is deposited on a substrate 710, the buffer layer 775 having the same crystal symmetry type (type 1) as the substrate 710, thereby allowing atomically flat layers to seed alternate crystal symmetry types of layers 780, 785, 790 (types 2, 3, ... N). For example, a monoclinic buffer 775 is deposited on a monoclinic bulk GaO substrate 710. Cubic MgO and NiO layers 780-790 are then formed. In this figure, the heterosymmetric crystal structure epitaxy with a homosymmetric buffer layer is labeled as structure 800.

[0263] FIG. 19 further illustrates a further embodiment of process 805, showing sequential variation along the growth direction 705 of multiple crystal symmetry types. For example, a corundum Al2O3 substrate 710 (type 1) produces an O-terminated template 810, which then seeds a corundum AlGaO3 layer 815 of type 2 crystal symmetry. A hexagonal AlGaO3 layer 820 of type 3 crystal symmetry can then be formed, followed by a cubic crystal symmetry type (type N), such as an MgO or NiO layer 830. Layers 815, 820, 825, and 830 are collectively labeled heterosymmetric crystal structure epitaxy 835 in this illustration. Such crystal growth matching is possible using layers of very different crystal symmetry types when a co-incident geometry of the in-plane lattice can occur. Although rare, this is the case for (100)-oriented cubic MgO. x Ni 1-x It has been found possible in the present disclosure with 0 (0≦x≦1) and monoclinic AlGaO compositions. This procedure can then be repeated along the growth direction.

[0264] Yet another embodiment is shown in FIG. 20A, in which a substrate 710 of type 1 crystal symmetry has a prepared surface (template 810) that seeds a first crystal symmetry type 815 (type 2), which can then be designed to transition to another symmetry type 845 (transition type 2-3) over a given layer thickness. An optional layer 850 can then be grown in yet another crystal symmetry type (type N). For example, a C-plane sapphire substrate 710 forms a corundum GaO layer 815, which is then relaxed to a hexagonal GaO or monoclinic crystal symmetry type. Further growth of layer 850 can then be used to form a high-quality relaxed layer with high crystal structure quality. Layers 815, 845, and 850 are collectively labeled heterosymmetric crystal structure epitaxy 855 in this figure.

[0265] 20B, there is shown a chart 860 of the variation of specific crystalline surface energy 865 as a function of crystalline surface orientation 870 for corundum-sapphire 880 and monoclinic gallium single crystal oxide material 875. In accordance with the present disclosure, it has been discovered that the crystalline surface energies of the technically relevant corundum Al2O3 880 and monoclinic substrates can be used to selectively form AlGaO3 crystalline symmetry types.

[0266] For example, C-plane sapphire can be prepared under O-rich growth conditions to selectively grow hexagonal AlGaO3 at lower growth temperatures (<650°C) and monoclinic AlGaO3 at higher temperatures (>650°C). Monoclinic AlGaO3 is limited to an Al content of approximately 45–50% due to its monoclinic crystal symmetry, which has approximately 50% tetrahedrally coordinated bonds (TCB) and 50% octahedral coordinated bonds (OCB). Ga can accommodate both TCB and OCB sites, while Al preferentially seeks OCB sites. R-plane sapphire can accommodate corundum AlGaO3 compositions ranging from 0–100% Al, grown at low temperatures below approximately 550°C under O-rich conditions, and monoclinic AlGaO3 with Al <50% at high temperatures >700°C.

[0267] M-plane sapphire surprisingly offers a more stable surface, providing an atomically flat surface, on which only corundum AlGaO3 compositions with Al%=0-100% can be grown.

[0268] Even more surprising is the discovery of a very low defect density corundum-AlGaO3 composition and the A-plane sapphire surface presented for AlGaO3, which allows for superlattices (see discussion below). This result is fundamentally due to the fact that both corundum-GaO3 and corundum-AlO3 share an exclusive crystal symmetry structure formed by OCB. This translates into very stable growth conditions in the growth temperature window ranging from room temperature to 800°C. This clearly demonstrates the importance of crystal symmetry engineering, which can generate new structural morphologies applicable to LEDs, including UV LEDs.

[0269] Similarly, a native monoclinic Ga2O3 substrate with a (-201) oriented surface can only accommodate monoclinic AlGaO3 compositions. The Al% in a (-201) oriented film is significantly lower due to the TCB presented by the growing crystal surface. This does not favor a large Al fraction, but it can be used to form very shallow MQWs of AlGaO3 / Ga2O3.

[0270] Surprisingly, the (010) and (001) oriented surfaces of monoclinic Ga2O3 can accommodate monoclinic AlGaO3 structures with very high crystalline quality. The main limitation of Al% in AlGaO3 is the accumulation of biaxial strain. Through careful strain management using AlGaO3 / Ga2O3 superlattices, we have found a limit of Al% < 40%, achieving higher quality films using (001) oriented Ga2O3 substrates. Furthermore, a further example of (010) oriented monoclinic Ga2O3 substrates is the very high quality lattice match of MgGa2O4 (111) oriented films with cubic crystal symmetry.

[0271] Similarly, the crystal symmetry of MgAl2O4 is compatible with the corundum AlGaO3 composition. (100)-oriented Ga2O3 has also been found experimentally in accordance with the present disclosure to provide a nearly perfect lattice match to cubic MgO(100) and NiO(100) films. Even more surprising is the utility of (110)-oriented monoclinic Ga2O3 substrates for the epitaxial growth of corundum AlGaO3.

[0272] These unique properties provide many advantages in the manufacture of LEDs, particularly UV LEDs, by way of example only, through the selective use of crystalline surface orientation, providing the selective utility of Al2O3 and Ga2O3 crystal symmetric substrates.

[0273] In some embodiments, conventional bulk crystal growth techniques can be employed to form corundum-AlGaO3 composition bulk substrates having corundum and monoclinic crystal symmetry types. These ternary AlGaO3 substrates may also be valuable for UV LED device applications.

[0274] Band Structure Modifier

[0275] Optimization of the AlGaO3 band structure can be achieved by paying attention to structural variations of a given crystal symmetry type. For solid-state, specifically semiconductor-based, electro-optically driven ultraviolet light-emitting devices, the valence band structure (VBS) is crucial. It is the VBS-k dispersion that typically determines the effectiveness of direct electron-hole recombination to generate light emission. Therefore, attention has been focused on valence band tuning options to achieve one exemplary UV LED operation.

[0276] Band structure construction by biaxial strain

[0277] In some embodiments, selective epitaxial deposition of AlGaO crystalline structures can be formed under elastic structural deformation by using compositional control or by using surface crystal geometries that can epitaxially register AlGaO films while still maintaining elastic deformation of the AlGaO unit cell.

[0278] For example, Figures 21A-21C show the change in the E band structure near the Brillouin zone center (k = 0), which favors e-h recombination to generate bandgap energy photons under the influence of biaxial strain applied to the crystal unit cell. The band structures of both corundum and monoclinic Al2O3 are direct. Deposition of Al2O3, Ga2O3, or AlGaO3 thin films onto suitable surfaces where the in-plane lattice constant of the film can be elastically strained can be achieved and engineered according to the present disclosure.

[0279] The lattice parameter mismatch between Al2O3 and Ga2O3 is shown in Table II of Figure 43B. Ternary alloys can be roughly interpolated between the endpoint binaries of the same crystal symmetry type. In general, Al2O3 films deposited on Ga2O3 substrates that preserve crystal orientation produce Al2O3 films in biaxial tension, while Ga2O3 films deposited on Al2O3 substrates with the same orientation produce Al2O3 films in compression.

[0280] Monoclinic and corundum crystals have nontrivial geometries with relatively complex strain tensors compared to conventional cubic, zinc blende, and even wurtzite crystals. The general trends observed for E dispersion near the BZ center are illustrated in Figures 21A and 21B. For example, diagram 890 in Figure 21A depicts a c-plane corundum crystal unit cell 894 with strain-free (σ = 0) E dispersion, with a conduction band 891 and a valence band 892 separated by a band gap 893. Biaxial compression of the unit cell 899 in diagram 895 in Figure 21B alters the dispersion by hydrostatically lifting the conduction band and distorting the E curvature of the valence band 897, e.g., see conduction band 896. Under compressive strain (σ < 0), the band gap 898 generally increases as follows:

number

[0281] Conversely, as shown in diagram 900 of FIG. 21C, biaxial tension applied to unit cell 904 causes band gap 903

number

[0282] Band structure due to uniaxial strain

[0283] Of particular interest is the possibility of using uniaxial strain to advantageously modify the valence band structure, as shown in Figures 22A and 22B, where the reference numbers in Figure 22A correspond to those in Figure 21A. For example, in-plane uniaxial deformation of unit cell 894 substantially along one crystallographic direction, as shown in unit cell 909, asymmetrically deforms valence band 907, as shown in diagram 905, which also shows conduction band 906 and band gap 908.

[0284] Similar behavior occurs for monoclinic and corundum crystalline symmetric films, with Al2O3 / Ga2O3, Al x Ga 1-x O3 / Ga2O3 and Al x Ga 1-x This can be demonstrated by elastically strained superlattice structures containing Ga2O3 / Al2O3. Such structures have been grown in connection with this disclosure, and the critical layer thickness (CLT) was found to be in the range of 1-2 nm to about 50 nm for binary Ga2O3 on sapphire, depending on the surface orientation of the substrate. x Ga 1-x O 3x , for x<10%, the CLT can exceed 100 nm on Ga2O3.

[0285] Uniaxial strain can be achieved by growth on symmetric crystal surfaces with surface geometries that have asymmetric surface unit cells. This has been achieved for both corundum and monoclinic crystals under various surface orientations, as illustrated in Figure 20B, but other surface orientations and crystals are also possible, such as MgO(100), MgAl2O4(100), 4H-SiC(0001), ZnO(111), Er2O3(222), and AlN(0002).

[0286] Figure 22B shows the advantageous deformation of the valence band structure for the direct bandgap case. For indirect bandgap Ek dispersions, such as those for thin monolayer monoclinic Ga2O3, the valence band dispersion can be adjusted from indirect to direct bandgap, as shown by the transition from Figure 23A or 23B to Figure 23C. Consider the unstrained band structure 915 of Figure 23B, with a conduction band 916, a valence band 917, a band gap 918, and a valence band maximum 919. Similarly, the compressive structure 910 of Figure 23A shows a conduction band 911, a valence band 912, a band gap 913, and a valence band maximum 914. The tensile structure 920 of Figure 23C shows a conduction band 921, a valence band 922, a band gap 923, and a valence band maximum 924. Detailed calculations and experimental angle-resolved photoemission spectroscopy (ARPES) can show that compressive and tensile strain applied to thin films of GaO can warp the valence bands, as shown in structures 910 and 920 for the case of compressive (valence band 912) and tensile (valence band 922) uniaxial strain applied along the b-axis or c-axis of the monoclinic GaO unit cell.

[0287] As shown in these figures, strain plays a key role and typically requires the management of complex epitaxy structures. Unmanaged strain accumulation can relax the elastic energy within the unit cell by creating dislocations and crystallographic defects that reduce the efficiency of UV LEDs.

[0288] Band structure construction by post-growth stress application

[0289] While the above techniques involve introducing stress in the form of uniaxial or biaxial strain during the formation of the layers, in other embodiments, external stress can be applied following the formation or growth of the metal oxide layer or layers to shape the band structure as needed. Exemplary techniques that can be employed to introduce these stresses are disclosed in U.S. Pat. No. 9,412,911.

[0290] Band structure construction by selecting alloy composition

[0291] Yet another mechanism utilized in this disclosure and applied to light-emitting metal oxide-based UV LEDs is the use of compositional alloying to form ternary crystal structures with desirable direct bandgaps. Generally, two different binary oxide material compositions are shown in Figures 24A and 24B. Band structure 925 includes a metal oxide AO, having a crystalline structure material 930 constructed from metal atoms 928 and oxygen atoms 929 with a conduction band 926, valence band dispersion 927, and direct bandgap 931. Another binary metal oxide BO, having a crystalline structure material 940 constructed from different metal cations 938 and oxygen atoms 939 of type B, has an indirect band structure 935 with a conduction band 936, bandgap 941, and valence band dispersion 937. In this example, the common anion is oxygen, and both AO and BO have the same basic crystal symmetry type.

[0292] Mixing metal atoms A and B with cation sites in an otherwise similar oxygen matrix (AO) x (BO) 1-x If a ternary alloy can be formed by forming A, this has the same fundamental crystal symmetry. x B 1-x 0 composition. Based on this, it is then possible to form a ternary metal oxide with valence band mixing effects, as shown in FIG. 25B (Note: FIGS. 25A and 25C reproduce FIGS. 24A and 24B). Direct valence band dispersion 927 of AO crystalline structure material 930 alloyed with BO crystalline structure material 940 having indirect valence band dispersion 937 can produce ternary material 948 with improved valence band dispersion 947, conduction band 946, and band gap 949. That is, atomic species A of material 930 incorporated into the B site of material 940 can increase the dispersion of the valence band. Atomistic density functional theory calculations can be used to simulate this concept, fully accounting for the pseudopotentials, strain energies, and crystal symmetries of the constituent atoms.

[0293] Thus, alloying corundum Al2O3 and Ga2O3 can result in a direct band gap in the band structure of the ternary metal oxide alloy and can also improve the valence band curvature of the monoclinic symmetry composition.

[0294] Band structure construction by digital alloy fabrication selection

[0295] While ternary alloy compositions such as AlGaO are desirable, an equivalent method for producing ternary alloys is through the use of digital alloying, employing superlattices (SLs) constructed from periodic repeats of at least two different materials. If each layer constituting the repeating unit cell of the SL is less than the electron de Broglie wavelength (typically about 0.1 to several tens of nanometers), then the periodicity of the superlattice creates a "mini-Brillouin zone" within the crystalline band structure, as shown in Figure 27A. In effect, a new periodicity is superimposed on the intrinsic crystalline structure by the formation of a given SL structure. The SL periodicity is typically one-dimensional, in the growth direction of epitaxial film formation.

[0296] In graph 950 of Figure 26, consider valence band states 953 inherent to material 955 and valence band states 954 from material 956. The Ek dispersion shows the energy gap 957 along energy axis 951 in region 958 and the first Brillouin zone edge 959 for k = 0. Region 958 is the forbidden energy gap (ΔE) between energy band states 953 and 954, which is the bulk-like energy band of materials 955 and 956. Materials A and B form a superlattice 968 as shown in Figure 27B, with an SL periodicity L SL is the average lattice constant a of A and B AB multiples of (e.g., L S L=2a AB), new states 961, 962, 963, and 964 are then generated, as shown in FIG. 27A. Thus, the superlattice energy potential generates an SL band gap 967 at k=0. This effectively folds the energy band 953 from the first bulk Brillouin zone edge 959 to k=0. That is, when the superlattice is made into ultrathin layers (thicknesses 970 and 971, respectively) using two materials 955 and 956, a periodic repeat unit 969 is formed, and the original bulk-like valence band states 953 and 954 are folded into new energy band states 961, 962, 963, and 964. In other words, the superlattice potential generates a new energy dispersion structure containing band states 961, 962, 963, and 964. When the superlattice period imposes a new spatial potential, the Brillouin zone collapses to wave vector 975.

[0297] This type of SL structure in Figure 27B is a different example of Al x Ga 1-x O / Ga2O3, Al x Ga 1-x O3 / Al2O3, Al2O3 / Ga2O3 and Al x Ga 1-x O3 / Al y Ga 1-y It can be generated using a two-layer pair containing O3.

[0298] The general use of SL to construct optoelectronic devices is disclosed in US Pat. No. 10,475,956.

[0299] FIG. 27C shows the SL structure for a digital binary metal oxide including Al2O3 layers 983 and Ga2O3 layers 984. The structure is shown in terms of electron energy 981 as a function of epitaxial growth direction 982. The periods of the SL forming the repeating unit cell 980 are repeated in integer or half-integer repeats. For example, the number of repeats can vary from 3 or more periods to 100 or 1000 or more periods. The equivalent digital alloy Al x Ga 1-xThe average Al% content of O is

number

number

number

[0300] Further examples of possible SL structures are shown in Figures 27D-27F.

[0301] The digital alloy concept can be extended to other different crystal symmetry types, e.g., cubic NiO987 and monoclinic Ga2O3986, as shown in Figure 27D, where digital alloy 985 is an equivalent ternary (NiO) x (Ga2O3) 1-x It simulates a bulk alloy.

[0302] Yet another example is shown in digital alloy 990 in Figure 27E, which uses a cubic MgO layer 991 and a cubic NiO layer 992 to form the SL. In this example, MgO and NiO have a very close lattice match, unlike Al2O3 and Ga2O3, which have a large lattice mismatch.

[0303] A four-layer periodic SL 996 is shown in digital alloy 995 of FIG. 27F, where cubic MgO and NiO grown oriented along (100) can be lattice matched to (100)-oriented monoclinic Ga2O3. x Ni y Mg z O n It has an effective quaternary composition of

[0304] Band structure of Al-Ga oxides

[0305] The UV LED component is made of binary or ternary Al, either in bulk or digitally alloyed. x Ga 1-x The O3 composition can be used to select the band gap. As mentioned above, advantageous valence band tuning using biaxial or uniaxial strain is also possible. An exemplary process flow 1000 describing possible selection criteria for selecting at least one of the crystal modification methods for forming the band gap region of a UV LED is shown in Figure 29.

[0306] In step 1005, the bandgap energy, E, is determined, whether the bandgap is direct or indirect. fermi The band structure configuration is selected, including, but not limited to, band structure properties such as carrier mobility, doping, and polarization. In step 1010, it is determined whether a binary oxide is suitable, and further in step 1015, whether the band structure of the binary oxide can be modified (i.e., tailored) to meet the requirements. If the binary oxide material meets the requirements, this material is selected for the relevant layer of the optoelectronic device in step 1045. If the binary oxide is not suitable, it is determined in step 1025 whether a ternary oxide is suitable, and further in step 1030, whether the band structure of the ternary oxide can be modified to meet the requirements. If the ternary oxide meets the requirements, this material is selected for the relevant layer in step 1045.

[0307] If a ternary oxide is not suitable, then in step 1035 it is determined whether a digital alloy is suitable, and whether the band structure of the digital alloy can be modified to meet the requirements in step 1040. If the digital alloy meets the requirements, then this material is selected for the associated layer in step 1045. Following the determination of the layer in this manner, an optoelectronic device stack is fabricated in step 1048.

[0308] Ternary alloy Al x Ga 1-xOne embodiment of the energy band lineup of Al2O3 and Ga2O3 with respect to O3 is shown in diagram 1050 of Figure 30, which varies with the offset of the conduction and valence bands for corundum and monoclinic crystal symmetries. In diagram 1050, the y-axis is electron energy 1051, and the x-axis is the different material types 1053 (Al2O3 1054, (Ga1Al)O3 1055, and Ga2O3 1056). While both the corundum and monoclinic heterojunctions appear to have Type I and Type II offsets, Figure 30 simply plots the band alignment using known values ​​for the electron affinity of each material.

[0309] Theoretical electronic band structures for the corundum and monoclinic bulk crystal forms of Al2O3 and Ga2O3 are known in the prior art. However, the application of strain to thin epitaxial films is underdeveloped and is the subject of this disclosure. By referencing the bulk band structures of Ga2O3 1056 and Al2O3 1054, embodiments of the present disclosure exploit how strain engineering can be advantageously applied for UV LED applications. Understanding how the valence bands are affected requires the incorporation of a kp-like Hamiltonian into the monoclinic and triclinic strain tensors. Prior art kp crystal models applied to zincblende and wurtzite crystal symmetry systems lack maturity for simulation of both monoclinic and trigonal systems. Current efforts are focused on this centered point group C2 h The present work is directed to carrying out this calculation in the second-order approximation of the valence band Hamiltonian at the centre of the Brillouin zone of a material with symmetry of

[0310] Single Crystal Aluminum Oxide

[0311] Two main crystal forms, having monoclinic (C2m) and corundum (R3c) crystal symmetries, are described herein for both Al2O3 and Ga2O3, although other crystal symmetries, such as triclinic and hexagonal, are possible. Other crystal symmetries can also be applied in accordance with the principles described in this disclosure.

[0312] (a) Corundum symmetric Al2O3

[0313] The crystal structure of trigonal Al2O3 (corundum) 1060 is shown in Figure 31. The larger spheres represent Al atoms 1064, and the smaller spheres represent oxygen 1063. The unit cell 1062 has a crystallographic axis 1061. Along the c-axis are layers of Al and O atoms. This crystal structure has a calculated band structure 1065, as shown in Figures 32A and 32B. The electronic energy 1066 is plotted as a function of the crystal wave vector 1067 within the Brillouin zone. High symmetry points within the Brillouin zone, near the center of the zone k=0, are labeled as shown, which can be applied to understanding the luminescence properties of the material.

[0314] The direct bandgap has a valence band maximum 1068 and a conduction band minimum 1069 at k=0. A detailed view of the valence bands in Figure 32B shows the complex dispersion of the two top valence bands. If electrons and holes can indeed be injected simultaneously into the Al2O3 band structure, the top valence band will determine the emission properties.

[0315] (b) Monoclinic symmetry Al2O3

[0316] The crystal structure 1070 of monoclinic Al2O3 is shown in Figure 33. The larger spheres represent Al atoms 1064 and the smaller spheres represent oxygen 1063. The unit cell 1072 has crystallographic axes 1071. This crystal structure has a calculated band structure 1075, as shown in Figures 34A and 34B, with Figure 34B showing a detailed view of the valence band. Figure 34A also shows the conduction band 1076. High symmetry points within the Brillouin zone are labeled as shown near the center of the zone, k=0, which can be applied to understanding the luminescence properties of the material.

[0317] The monoclinic crystal structure 1070 is relatively more complex than trigonal symmetry, and has a lower density and smaller bandgap than the corundum sapphire 1060 form shown in FIG.

[0318] The monoclinic Al2O3 form also has a direct band gap with a well-defined split highest valence band 1077 that has lower curvature for the Ek dispersion along the GX and GN wave vectors. The monoclinic band gap is approximately 1.4 eV smaller than the corundum form. The second highest valence band 1078 is symmetrically split from the topmost valence band.

[0319] Single crystal gallium oxide

[0320] (a) Corundum symmetry Ga2O3

[0321] The crystal structure of trigonal Ga2O3 (corundum) 1080 is shown in Figure 35. The larger spheres represent Ga atoms 1084 and the smaller spheres represent oxygen 1083. The unit cell 1082 has crystallographic axes 1081. Corundum (trigonal crystal symmetry) is also known as the alpha phase. The crystal structure is identical to sapphire 1060 in Figure 31. The lattice constants define the unit cell 1082 shown in Table II in Figure 43B. The Ga2O3 unit cell 1082 is larger than Al2O3. Corundum crystals have octahedrally bonded Ga atoms.

[0322] The calculated band structure 1085 for corundum Ga2O3 is shown in Figures 36A and 36B, which shows the valence band maximum Value and Zone center k=0 The valence band energy of The conduction band 1086 is also shown in Figure 36A.

[0323] Biaxial and uniaxial strain applied to corundum Ga2O3 using the methods described above can then be used to modify the band structure and valence band directly into the band gap. Indeed, applying tensile strain along the crystallographic b-axis and / or c-axis can shift the valence band maximum to the zone center. It is estimated that approximately 5% tensile strain can be accommodated within a thin Ga2O3 layer containing an Al2O3 / Ga2O3 SL.

[0324] (b) Monoclinic symmetry Ga2O3

[0325] The crystal structure of monoclinic Ga2O3 (corundum) 1090 is shown in Figure 37. The larger spheres represent Ga atoms 1084 and the smaller spheres represent oxygen 1083. The unit cell 1092 has crystallographic axes 1091. This crystal structure has a calculated band structure 1095, as shown in Figures 38A and 38B. High symmetry points within the Brillouin zone are labeled as shown near the center of the zone, k=0, which can be applied to understanding the luminescence properties of the material. The conduction band 1096 is also shown in Figure 38A.

[0326] Monoclinic Ga2O3 has a top valence of 1097 with a relatively flat Ek distribution. Close inspection reveals that the actual maximum of the valence band is several eV (thermal energy k B It becomes clear that there is a dispersion of T (less than about 25 meV). The relatively small valence dispersion provides insight into the fact that monoclinic Ga2O3 has a relatively large hole effective mass, which can lead to low mobility and is relatively localized. Therefore, strain can be used advantageously to improve the band structure, specifically the valence band dispersion.

[0327] Ternary aluminum-gallium oxide

[0328] Yet another example of the unique properties of the AlGaO3 material system is demonstrated by the crystal structure 1100 shown in Figure 39, having crystallographic axes 1101 and unit cell 1102. The ternary alloy includes a 50% Al composition.

[0329] (Al x Ga 1-x )2O3, where x=0.5, can be modified into substantially different crystal symmetry forms with a rhombic structure. Ga atoms 1084 and Al atoms 1064 are arranged in the crystal as shown by oxygen atoms 1083. Of particular interest are layered structures of Al and Ga atomic planes. This type of structure can also be constructed using atomic layer techniques to form the ordered alloys described throughout this disclosure.

[0330] The calculated band structure of 1105 is shown in Figure 40. The conduction band minimum 1106 and valence band maximum 1107 indicate a direct band gap.

[0331] Ordered ternary AlGaO3 alloy

[0332] Atomic layer epitaxy can also be used to create new types of crystalline symmetry structures. For example, some embodiments include ultrathin epilayers containing alternating sequences along the growth direction in the form [Al-O-Ga-O-Al-...]. Structure 1110 in Figure 42 illustrates one possible extreme case in which alternating sequences 1115 and 1120 are used to create an ordered ternary alloy. In the context of this disclosure, it has been demonstrated that growth conditions can be created in which self-ordering of Al and Ga can occur. This condition can occur even when Al and Ga fluxes are simultaneously incident on the growth surface, resulting in a self-organized ordered alloy. Alternatively, a predetermined modulation of the Al and Ga fluxes reaching the surface of the epilayer can also produce an ordered alloy structure.

[0333] The ability to configure the band structure of optoelectronic devices, specifically UV LEDs, by selecting from bulk metal oxides, ternary compositions, or even digital alloys are all considered within the scope of this disclosure.

[0334] Yet another example is the use of biaxial and uniaxial strain to modify the band structure, one example being the use of strained layer epitaxy on Al2O3 or Ga2O3 substrates (Al x Ga 1-x )2O3 material system.

[0335] Substrate selection for AlGaO-based UV LEDs

[0336] The choice of native metal oxide substrate is based on strained layer epitaxy on Al2O3 or Ga2O3 substrates (Al x Ga1-x This is one advantage of the present disclosure as it applies to epitaxy in the .)2O3 material system.

[0337] Examples of substrates are listed in Table I of Figure 43A. In some embodiments, intermediate AlGaO3 bulk substrates can also be utilized and are advantageous for UV LED applications.

[0338] The beneficial utility of monoclinic Ga2O3 bulk substrates is limited by strain accumulation, as is the monoclinic (Al) with a high Ga% (e.g., about 30-40%). x Ga 1-x )2O3 structure can be formed. This allows for a conductive substrate, making vertical devices possible. Conversely, when a corundum Al2O3 substrate is used, a corundum epitaxial film (Al x Ga 1-x )2O3 becomes possible.

[0339] Other substrates such as MgO(100), MgAl2O4, and MgGa2O4 are also suitable for epitaxial growth of metal oxide UV LED structures.

[0340] Selection and action of crystal growth modifiers.

[0341] Examples of metal oxide structures are described herein for optoelectronic applications, specifically for the fabrication of UV LEDs. The structures disclosed in Figures 44A-44Z, which are subsequently described, demonstrate that possible crystal structure modifiers are the crystalline structure modifiers of the given metal oxides MO (where M = Al, Ga), binary Ga2O3, ternary (Al x Ga 1-x )2O3 and binary Al2O3, and may be selected from any of the elemental cation and anion configurations, but are not limited thereto.

[0342] It has been found theoretically and experimentally in accordance with the present disclosure that the cationic seed modifier to the above-defined MO may be selected from at least one of the following:

[0343] Germanium (Ge)

[0344] Ge is beneficially supplied as a pure elemental species to incorporate via codeposition of MO species during the non-equilibrium crystal formation process. In some embodiments, an elementally pure ballistic beam of atomic Ga and Ge is co-deposited with an activated oxygen beam impinging on the growth surface. For example, Ge has a valence of +4 and is introduced in a dilute atomic ratio by substitution into the metal cation M site of the MO host crystal, forming (Ge +4 O2) m (Ga2O3) n =(Ge +4 O2) m / (m+n) (Ga2O3) n / (m+n) =(Ge +4 O2) x (Ga2O3) 1-x =Ge x Ga 2(1-x) O 3-x It is possible to form a stoichiometry of the form where x<0.1 for dilute Ge plasticity.

[0345] According to the present disclosure, when x<0.1, the dilute ratio of Ge is F It has been found that sufficient electronic modification of the intrinsic MOs can be achieved to manipulate the Ge content, thereby increasing the available electron free carrier concentration and altering the crystal lattice structure to impart favorable strain during epitaxial growth. For dilute compositions, the host MO physical unit cell remains substantially unperturbed. Further increases in Ge concentration can alter the host Ga2O3 crystal structure through lattice expansion or even result in new material compositions.

[0346] For example, when x≦1 / 3, the monoclinic crystal structure of the host Ga2O3 unit cell can be maintained. For example, when x=0.25, the monoclinic Ge 0.25 Ga 1.50 O 2.75 =GeGaO 11 Advantageously, it is possible to form monoclinic Ge x Ga 2(1-x) O 3-xThe (x=1 / 3) crystal exhibits an excellent direct bandgap exceeding 5 eV. Lattice deformation by introducing Ge increases the monoclinic unit cell preferentially along the b- and c-axes while preserving the a-axis lattice parameter compared to unstrained monoclinic Ga2O3.

[0347] The lattice constants of monoclinic Ga2O3 are (a=3.08A, b=5.88A, c=6.41A), and monoclinic Ge1Ga6O 11 (a=3.04A, b=6.38A, c=7.97A). Therefore, the introduction of Ge results in a biaxial expansion of the free-standing unit cell along the b-axis and c-axis. x Ga 2(1-x) O 3-x is epitaxially deposited on a bulk monoclinic GaO surface oriented along the b-axis and c-axis (i.e., deposited along the a-axis), then, as described herein, Ge x Ga 2(1-x) O 3-x Thin films of can be elastically deformed to induce biaxial compression and thus favorably warp the valence band Ek dispersion.

[0348] Above x>1 / 3, the higher the Ge %, the more the crystal structure changes to cubic, e.g., GeGa2O5.

[0349] In some embodiments, Al2O3 and (Al x Ga 1-x Incorporation of Ge into )2O3 is also possible.

[0350] For example, direct bandgap Ge x Al 2(1-x) O 3-x The ternary system can also be formed epitaxially by co-deposition of the elements Al and Ge with active oxygen to form thin films with monoclinic symmetry. In accordance with the present disclosure, it has been found that the monoclinic structure is stabilized at a Ge % of x about 0.6, producing a free-standing lattice with large relative expansion along the a- and c-axes but a modest reduction along the b-axis when compared to monoclinic Al2O3.

[0351] The lattice parameters of monoclinic Ge2Al2O7 are (a = 5.34 Å, b = 5.34 Å, c = 9.81 Å) and those of monoclinic Al2O3 are (a = 2.94 Å, b = 5.671 Å, c = 6.14 Å). Therefore, Ge deposited along a growth direction oriented along the b axis and further deposited on the monoclinic Al2O3 surface x Al 2(1-x) O3 is subjected to biaxial tension when the membrane is thin enough to sustain elastic deformation.

[0352] Silicon (Si)

[0353] Elemental Si may also be supplied as a pure elemental species for incorporation via codeposition of MO species during the non-equilibrium crystal formation process. In some embodiments, elementally pure ballistic beams of atomic Ga and Si are co-deposited with an activated oxygen beam impinging on the growth surface. For example, Si has a valence of +4 and is introduced in a dilute atomic ratio by substitution into the metal cation M site of the MO host crystal, forming (Si +4 O2) m (Ga2O3) n =(Si +4 O2) m / (m+n) (Ga2O3) n / (m+n) =(Si +4 O2) x (Ga2O3) 1-x =Si x Ga 2(1-x) O 3-x where x<0.1 for dilute Si compositions.

[0354] According to the present disclosure, when Si is <0.1, the dilute ratio of Si is FIt has been found that sufficient electronic modification of the intrinsic MOs can be achieved to manipulate the Si content, thereby increasing the available electron free carrier concentration and altering the crystal lattice structure to impart favorable strain during epitaxial growth. For dilute compositions, the host MO physical unit cell remains substantially unperturbed. Further increases in Si concentration can alter the host Ga2O3 crystal structure through lattice expansion or even result in new material compositions.

[0355] For example, when Si is x≦1 / 3, the monoclinic crystal structure of the host Ga2O3 unit cell can be maintained. For example, when Si%x=0.25, the monoclinic Si 0.25 Ga 1.50 O 2.75 =SiGaO 11 The lattice distortion by introducing Si increases the monoclinic unit cell preferentially along the b- and c-axes while preserving the a-axis lattice parameter compared to unstrained monoclinic Ga2O3. 11 The lattice parameters are (a=6.40A, b=6.40A, c=9.40A) compared to (a=3.08A, b=5.88A, c=6.41A) for monoclinic Ga2O3.

[0356] Therefore, the introduction of Si results in a biaxial expansion of the free-standing unit cell along all of the a-, b-, and c-axes. x Ga 2(1-x) O 3-x is epitaxially deposited on a bulk monoclinic GaO surface oriented along the b-axis and c-axis (i.e., deposited along the a-axis), then, as described herein, Si x Ga 2(1-x) O 3-x Thin films of can be elastically deformed to induce asymmetric biaxial compression and thus favorably warp the valence band Ek dispersion.

[0357] Above x>1 / 3, the higher the Si%, the more the crystal structure changes to cubic, e.g., SiGa2O5.

[0358] In some embodiments, Si, Al2O3, and (Al x Ga 1-x )2O3 is also possible. For example, +4 O2) x (Al2O3) 1-x =Si x Al 2(1-x) O 3-x This is possible by codepositing elemental Si and Al directly onto the deposition surface with an active oxygen flux. If the deposition surface is selected from available trigonal α-Al2O3 surfaces (e.g., A-plane, R-plane, M-plane), then it is possible to form orthorhombic symmetry Al2SiO5 (i.e., x = 0.5), which reports a large direct bandgap at the Brillouin zone center. The lattice parameters for orthorhombic Al2SiO5 are (a = 5.61 Å, b = 7.88 Å, c = 7.80 Å), while for trigonal (R3c) Al2O3 they are (a = 4.75 Å, b = 4.75 Å, c = 12.982 Å).

[0359] Therefore, deposition of oriented Al2SiO5 films on Al2O3 can result in large biaxial compression for elastically strained films. Exceeding the elastic energy limit creates harmful crystal misfit dislocations and should generally be avoided. In particular, to achieve elastically deformed films on Al2O3, films less than approximately 10 nm thick are preferred.

[0360] Magnesium (Mg)

[0361] Some embodiments involve incorporating Mg elemental species into Ga2O3 and Al2O3 host crystals, with Mg being selected as the preferred Group II metal species. x Ga 1-x )2O3, and the incorporation of quaternary Mg x (Al, Ga) y O z It can be used up to the formation of Mg x Ga 2(1-x) O 3-2x A particularly useful composition of Ga2O3 and (Al x Ga 1-xThe electronic structure of the Ga 2O 3 host is 3+ Mg cation site 2+ By substituting with cations, it is possible to make it p-type conductive. (Al y Ga 1-y In the case of )2O3, the band gap is approximately 6.0 eV when y=0.3, and Mg can be incorporated up to y=0.05 to 0.1, changing the host conductivity type from the inherent weak excess electron n-type to excess hole p-type.

[0362] Mg x Ga 2(1-x) O 3-2x and Mg x Al 2(1-x) O 3-2x and (Ni x Mg 1-x Ternary compounds of the type )O are also exemplary embodiments of active region materials for light-emitting UV LEDs.

[0363] In some embodiments, Mg with x=0.5 yields a cubic crystal symmetry structure. x Ga 2(1-x) O 3-2x and Mg x Al 2(1-x) O 3-2x Both stoichiometries exhibit favorable direct bandgap Ek dispersion and are suitable for the emission region.

[0364] Furthermore, according to the present disclosure, Mg x Ga 2(1-x) O 3-2x and Mg x Al 2(1-x) O 3-2x The composition was found to be epitaxially compatible with cubic MgO and Ga2O3 in monoclinic, corundum, and hexagonal crystal symmetry forms.

[0365] The use of non-equilibrium growth techniques allows for a large miscibility range of Mg, from MgO to the respective M-O2 elements, within both Ga2O3 and Al2O3 hosts, in contrast to equilibrium growth techniques such as CZ, where phase separation occurs due to volatile Mg species.

[0366] For example, Mg where x is approximately 0.5 x Ga 2(1-x) O 3-2x The lattice constants of the cubic and monoclinic forms of Mg are (a=b=c=8.46 Å) and (a=10.25 Å, b=5.98 Å, c=14.50 Å), respectively. x Ga 2(1-x) O 3-2x It was found that the morphology can be oriented as thin films with (100) and (111) orientation on monoclinic Ga2O3 (100) and Ga2O3 (001) substrates. x Ga 2(1-x) O 3-2x Thin epitaxial films of MgO with 0≦x≦1 can be deposited on MgO substrates. x Ga 2(1-x) O 3-2x The films can be deposited directly onto MgAl2O4 (100) spinel crystal symmetric substrates.

[0367] In a further embodiment, Mg x Al 2(1-x) O 3-2x and Mg x Ga 2(1-x) O 3-2x High-quality (i.e., low defect density) epitaxial films of both can be deposited directly on lithium fluoride (LiF) substrates.

[0368] Zinc (Zn)

[0369] Some embodiments include the incorporation of Zn elemental species into Ga2O3 and Al2O3 host crystals, with Zn being another preferred Group II metal species. x Ga 1-x )2O3, and the quaternary Zng x (Al, Ga) y O z It can be used up to the formation of

[0370] Furthermore, further quaternary compositions that are advantageous for tailoring the direct band gap structure are compounds of the most common form: (Mg x Zn 1-x ) z (Al y Ga 1-y ) 2(1-z) O 3-2z , where 0≦x, y, z≦1.

[0371] In accordance with the present disclosure, it has been discovered that cubic crystal symmetry compositions with z of about 0.5 can be advantageously used for a given fixed y composition between Al and Ga. By varying the ratio x of Mg to Zn, the direct band gap can be adjusted to about 4 eV≦E G The bandgap (x) can be tuned from <7 eV. This can be advantageously achieved by providing separately controllable fluxes of pure elemental beams of Al, Ga, Mg, and Zn, and providing an activated oxygen flux for the anionic species. Generally, an excess of atomic oxygen relative to the total impinging metal flux is desired. The Al:Ga flux ratio and Mg:Zn ratio reaching the growth surface can then be controlled to preselect the desired composition for bandgap tuning in the UV LED region.

[0372] Surprisingly, zinc oxide (ZnO) generally has a wurtzite hexagonal crystal symmetry structure, whereas (Mg x Zn 1-x ) z (Al y Ga 1-y ) 2(1-z) O 3-2z When introduced into the Brillouin zone, cubic and spinel crystal symmetries are readily possible using the non-equilibrium growth methods described herein. The bandgap characteristics of the Brillouin zone center can be tuned by the alloy composition (x, y, z) ranging from indirect to direct characteristics. This is advantageous for applications in substantially non-absorbing electrical injection and light-emitting regions, respectively. Furthermore, bandgap modulation is possible for bandgap-engineered structures such as superlattices and quantum wells described herein.

[0373] Nickel (Ni)

[0374] The incorporation of Ni elemental species into Ga2O3 and Al2O3 host crystals is yet another preferred group II metal species. Further, the incorporation of Ni into (Al x Ga 1-x )2O3 is available up to the formation of the quaternary Ni x (Al, Ga) y O z .

[0375] Furthermore, additional quaternary compositions advantageous for tuning the direct bandgap structure are the most common form of compounds: (Mg x Ni 1-x ) z (Al y Ga 1-y ) 2(1-z) O 3-2z , where 0 ≦ x, y, z ≦ 1.

[0376] According to the present disclosure, it has been found that cubic crystal symmetry compositions with z of about 0.5 can be advantageously used for a given fixed y composition between Al and Ga. By varying the ratio x of Mg to Ni, the direct bandgap can be tuned from about 4.9 eV ≦ E G (x) < 7 eV. This can be achieved advantageously by arranging the fluxes of the pure elemental beams of Al, Ga < Mg and Ni to be separately controllable advantageously and providing an activated oxygen flux to the anion species. Then, the Al:Ga flux ratio and the Mg:Ni ratio reaching the growth surface can be controlled to pre-select the desired composition for bandgap tuning in the UVLED region.

[0377] Very useful herein is the specific band structure and intrinsic conductivity type of cubic NiO. Nickel oxide (NiO) exhibits a native p-type conductivity due to Ni d-orbital electrons. The general cubic crystal symmetry form (Mg x Ni 1-x ) z (Al y Ga 1-y ) 2(1-z) O 3-2z is possible using the non-equilibrium growth method described herein.

[0378] Ni z Ga 2(1-z) O 3-2z and Ni z Al 2(1-z) O 3-2z Both are advantageous for application in UV LED formation. Dilute compositions with z<0.1 have been found to be advantageous for producing p-type conductivity in accordance with the present disclosure, and ternary cubic crystal symmetry compounds with z about 0.5 also exhibit a direct bandgap at the center of the Brillouin zone.

[0379] Lanthanides

[0380] Binary Ga2O3, ternary (Al x Ga 1-x There is a large selection of available lanthanide metal atomic species that can be incorporated into GaO and binary AlO. The lanthanide group of metals ranges from 15 elements starting with lanthanum (Z=57) through lutetium (Z=71). In some embodiments, gadolinium Gd (Z=64) and erbium Er (Z=68) are utilized due to their distinct 4f shell configuration and ability to form advantageous ternary compounds with GaO, GaAlO, and AlO. Again, (RE x Ga 1-x )2O3, (RE x Ga y Al 1-x-y )2O3 and (RE x Al 1-x The incorporation of dilute impurities of only one species selected from RE={Gd or Er} incorporated into the cation sites of )2O3, where 0≦x, y, z≦1, allows for tuning of the Fermi energy to form n-type conductivity materials exhibiting corundum, hexagonal, and monoclinic crystal symmetries. The inner 4f shell orbitals of Gd provide an opportunity for electronic coupling that avoids parasitic optical 4f-4f energy level absorption at wavelengths below 250 nm.

[0381] Surprisingly, according to the present disclosure, both theoretically and experimentally, x Ga 1-x )2O3 and (Er x Al1-x It has been found that the ternary compound of Er2O3 exhibits a cubic crystal symmetry structure with a direct bandgap when x is approximately 0.5. It is known that the binary erbium oxide Er2O3 has bixbyite crystal symmetry and can be epitaxially grown as a single crystal film on a Si(111) substrate. However, the lattice constant achieved by bixbyite Er2O3 is not readily adaptable for seeding epitaxial films of Ga2O3, GaAlO3, and Al2O3. In accordance with the present disclosure, it has been found that the incorporation of a graded composition of Er along the growth direction, increasing from 0 to 0.5, is necessary to produce the required final surface corresponding to the epitaxy of monoclinic Ga2O3. (Er x Ga 1-x )2O 3、 Cubic crystal symmetry with 0≦x≦0.5 may be utilized, such as compositions that exhibit a direct bandgap.

[0382] Of particular interest is the well-defined direct energy bandgap E of approximately 6.5–7 eV with lattice constants (a=5.18 Å, b=5.38 Å, c=7.41). G (k=0) indicates that x is approximately 0.5 (Er x Al 1-x )2O3. Such structures can be deposited on monoclinic Ga2O3 and corundum Al2O3 substrates or epilayers. As mentioned above, the inner Er 3+ The 4f-4f transition does not exist in the Ek band structure and is therefore classified as a non-parasitic absorber for UV LED applications.

[0383] Bismuth (Bi)

[0384] Bismuth is a known species that functions as a surfactant in GaN non-equilibrium epitaxy of thin gallium nitride GaN films. The surfactant lowers the surface energy for epitaxial film formation, but is generally not incorporated into the growing film. Even gallium arsenide exhibits low Bi incorporation. Bismuth is a volatile species with a high vapor pressure at low growth temperatures, and appears to be an insufficient adatom for incorporation into the growing epitaxial film. Surprisingly, however, the incorporation of Bi into Ga2O3, (Ga,Al)O3, and Al2O3 at dilute levels of x<0.1 is highly efficient using the non-equilibrium growth method described in this disclosure. For example, elemental sources of Bi, Ga, and Al can be co-deposited with activated oxygen (i.e., atomic oxygen, ozone, and nitrous oxide) at overpressure ratios. According to this disclosure, monoclinic and corundum crystal symmetry Ga2O3 and (Ga,Al)O3 with x<0.5 are used for the co-deposition of Bi. x , Al 1-x The incorporation of Bi in )2O3 was found to exhibit conduction-type properties that produce an activated hole carrier concentration suitable for the p-type conduction region of UV LED function.

[0385] Even higher Bi atom incorporation x>0.1 (Bi x Ga 1-x )2O3 and (Bi x Al 1-x )2O3 allows tuning of the band structure of ternary compositions, indeed all the way to stoichiometric binary bismuth oxide Bi2O3. Monoclinic Bi2O3 has lattice constants of (a = 12.55 Å, b = 5.28 Å, and c = 5.67 Å), which corresponds to depositing a strained layer directly on monoclinic Ga2O3.

[0386] Additionally, in some embodiments, orthorhombic and trigonal morphologies can be utilized, which exhibit inherent p-type conductivity properties and indirect bandgaps.

[0387] Of particular interest is the case of x=1 / 3 (Bi x Al 1-x )2O3 orthorhombic crystal symmetry composition is directly E G = 4.78-4.8 eV.

[0388] Palladium (Pd)

[0389] The addition of Pd to GaO, (Ga,Al)O, and AlO may be utilized in some embodiments to produce metallic behavior and is applicable to the formation of ohmic contacts. In some embodiments, palladium oxide (PdO) can be used as an in situ deposited semimetallic ohmic contact to n-type wide bandgap metal oxides due to the compound's inherently low work function (see Figure 9).

[0390] Iridium (Ir)

[0391] Iridium is a preferred platinum group metal for incorporation into Ga2O3, (Ga,Al)O3, and Al2O3. In accordance with the present disclosure, it has been discovered that Ir can be bonded in a wide variety of valence states. Generally, the rutile crystal symmetry form of IrO2 composition is known, exhibiting semimetallic properties. Surprisingly, triply charged Ir 3+ The valence state is possible using non-equilibrium growth methods and is the preferred state for application to Ga2O3, specifically incorporating the corundum crystal symmetry. Iridium has one of the highest melting points and the lowest vapor pressure upon heating. The present disclosure utilizes electron beam evaporation to form an elementally pure beam of Ir species that impinges on the growth surface. When activated oxygen is simultaneously supplied and the corundum Ga2O3 surface is presented for epitaxy, the corundum crystal symmetry form of Ir2O3 composition can be achieved. Furthermore, by co-depositing pure elemental beams of Ir and Ga with activated oxygen, the (Ir) x Ga 1-x Furthermore, the compound (Ir )2O3 with 0≦x≦1.0 can be formed by co-depositing pure elemental beams of Ir and Al with activated oxygen. x Al 1-x(Ga,Al)O3 compounds can be formed. The addition of Ir to host metal oxides including at least one of GaO3, (Ga,Al)O3, and AlO3 can reduce the effective band gap. Furthermore, when the Ir fraction x>0.25, the band gap becomes exclusively indirect in nature.

[0392] Lithium (Li)

[0393] Lithium is a unique atomic species, particularly when combined with oxygen. Pure lithium metal readily oxidizes, and lithium oxide (LiO) is readily formed using non-equilibrium growth techniques with a pure elemental Li beam and activated oxygen directed at a growth surface with well-defined surface crystal symmetry. Cubic crystal symmetry LiO exhibits a large indirect bandgap, Eg, of approximately 6.9 eV, and has a lattice constant of (a = b = c = 4.54 Å). When present within a defective crystal structure, lithium is a mobile atom, and it is this property that is exploited in lithium-ion battery technology. In contrast, the present disclosure seeks to robustly incorporate Li atoms within a host crystal matrix comprising at least one of GaO, (Ga,Al)O, and AlO. Again, dilute Li concentrations can be incorporated into substitutional metal sites in GaO, (Ga,Al)O, and AlO. For example, Li +1 For a valence state of , these compositions are available: (LiO) x (Ga2O3) 1-x =Li 2x Ga 2(1-x) O 3-2x , where 0≦x≦1, and (LiO) x (Al2O3) 1-x =Li 2x Al 2(1-x) O 3-2x , where 0≦x≦1.

[0394] Li at x=0.5 2x Ga 2(1-x) O 3-2x The stoichiometric form of LiGaO2 provides LiGaO2, and Li 2x Al 2(1-x) O 3-2xprovides LiAlO2.

[0395] Both LiGaO2 and LiAlO2 have E G (LiGaO2) = 5.2 eV and E of about 8 eV G It crystallizes in the preferred orthorhombic and trigonal forms of (LiALO2), which have direct and indirect band gap energies, respectively.

[0396] Of particular interest is the relatively small curvature of both valence bands, suggesting a smaller hole effective mass compared to Ga2O3.

[0397] The lattice constants of LiGaO2 are (a=5.09A, b=5.47A, c=6.46A) and for LiAlO2 they are (a=b=2.83A, c=14.39A). Bulk Li(Al,Ga)O2 substrates are available, so Li(Al x Ga 1-x Orthorhombic and trigonal quaternary compositions such as )O2 are also available, allowing UV LED operation in the emission region.

[0398] Even cubic NiO, when incorporated with Li impurities, can improve p-type conductivity and act as a possible electron injection region for holes applied in UV LEDs.

[0399] Additionally, in some embodiments, the additional composition comprises lithium nickel oxide, Li x Ni y O z Theoretical calculations suggest that the possible higher valence states of Ni 2+ and Li 2+ It provides insight into Li2 (+4) Ni +2 O3 (-6) Electronic compositions including =LiNiO3 are available to be fabricated by non-equilibrium growth techniques that produce monoclinic crystal symmetry. According to the present disclosure, LiNiO3 has an E of approximately 5 eV. G Yet another composition has trigonal crystal symmetry (R3m) and is found to form an indirect band gap of Li +1 and Ni+1 Valence state is E G We form the composition Li2NiO2 with a direct band gap between the s-like and p-like states of =8 eV, but the strong d-like states from Ni create intermediate band gap energy states that are continuous across all Brillouin zones and independent of crystal momentum.

[0400] Nitrogen and Fluorine Anion Substitution

[0401] Further, in accordance with the present disclosure, it has been discovered that the selected anionic crystal modifier for the disclosed metal oxide compositions can be selected from at least one of nitrogen (N) and fluorine (F) species. Binary Ga2O3 and ternary (GaxAl) compounds can be prepared by substitutional incorporation of Group III metal cation sites with Group II metal species. 1-x Similar to the creation of p-type activated hole concentrations in GaO, it is further possible to substitute oxygen anion sites during epitaxial growth with activated nitrogen atoms (e.g., in some embodiments, neutral atomic nitrogen species). In accordance with the present disclosure, it has surprisingly been found that the incorporation of dilute nitrogen into a GaO host stabilizes a monoclinic GaO composition during epitaxy. Prolonged exposure of growing GaO to a combination of neutral atomic fluxes of oxygen and nitrogen simultaneously with elemental Ga has been found to form competing GaN-like precipitates.

[0402] In accordance with the present disclosure, it has also been discovered that periodically modulating the growth of GaO by periodically interrupting the Ga and O fluxes and preferentially exposing a terminated surface with only activated atomic neutral nitrogen allows for the incorporation of N into otherwise available O sites within the GaO growth at a portion of the surface. Spacing these N layer growth interruptions by a distance of at least five unit cells of GaO along the growth direction allows for the incorporation of high density impurities that aid in achieving p-type conductivity characteristics in GaO.

[0403] This process can be used for both the corundum and trigonal forms of Ga2O3.

[0404] In some embodiments, a combined approach of Group II metal cation substations and nitrogen anion substations can be utilized to control the p-type conductivity concentration of Ga2O3.

[0405] Incorporation of fluorine impurities into Ga2O3 is also possible, but elemental fluorine sources are difficult. This disclosure uniquely utilizes sublimation of lithium fluoride (LiF) bulk crystals in a Knudsen cell to provide both Li and F compositional components that are codeposited into elemental Ga and Al beams in an active oxygen environment supplied to the growth surface. Such a technique allows for the incorporation of Li and F atoms into epitaxially formed Ga2O3 or LiGaO2 hosts.

[0406] Examples of crystalline symmetry structures formed using exemplary compositions are now described and referenced in Figures 44A-44Z. The compositions shown are not intended to be limiting, as described in the previous section using crystalline modifiers.

[0407] (Al x Ga 1-x Examples of possible crystal symmetry groups 5000 for the ternary composition of .)2O3 are shown in Figure 44A. The calculated equilibrium crystal formation probability 5005 is a measure of the probability that a structure will form for a given crystal symmetry type. The space group nomenclature 5010 used in Figure 44A will be understood by those skilled in the art.

[0408] The non-equilibrium growth methods described herein can potentially select for crystal symmetry types that are otherwise inaccessible using equilibrium growth methods (such as CZ). The general crystal classifications of cubic 5015, tetragonal, trigonal (rhombohedral / hexagonal) 5020, monoclinic 5025, and triclinic 5030 are shown in the inset of Figure 44A.

[0409] For example, it has been discovered in accordance with the present disclosure that monoclinic, trigonal, and orthorhombic crystal symmetry types can be energetically favored by providing kinetic growth conditions that favor only certain space groups for epitaxial formation. For example, as shown in Table I, shown in Figure 43A, the surface energy of the substrate can be selected by judicious preselection of the surface orientation offered for epitaxy.

[0410] FIG. 44B shows a high-quality, coherently strained, elastically deformed unit cell (i.e., the epilayer is called pseudomorphic with respect to the underlying substrate) strain ternary (Al x Ga 1-x 5 shows an exemplary high resolution x-ray Bragg diffraction (HRXRD) curve of an epilayer 5080 of Al 2O 3 . The graph shows the intensity 5035 as a function of Ω-2θ 5040. x Ga 1-x )2O3 x = 0.15 (5050) and x = 0.25 (5065). The substrate was first placed in an ultra-high vacuum chamber (5 × 10 -10 It is prepared by desorption of surface impurities at high temperatures (>800°C) under pressures below 1000 Torr.

[0411] The surface is monitored in real time by reflection high-energy electron diffraction (RHEED) to assess atomic surface quality. Once a bright, streaky RHEED pattern is revealed, indicating an atomically flat surface with a predetermined surface reconstruction of discontinuous surface atomic dangling bonds, an activated oxygen source comprising a radio frequency inductively coupled plasma (RF-ICP) is ignited and directed toward the heated surface of the substrate, generating a flow of essentially neutral atomic oxygen (O*) species and excited molecular neutral oxygen (O2*).

[0412] RHEED is monitored to reveal an oxygen-terminated surface. The source of elemental and pure Ga and Al atoms is provided by an effusion cell containing an inert ceramic crucible heated by a filament and controlled by feedback sensing of a thermocouple strategically placed relative to the crucible to monitor the metal melt temperature within the crucible. High purity elemental metals, 6N to 7N or higher, are used.

[0413] Each source beam flux is measured by a dedicated nude ion gauge, which can be spatially positioned near the center of the substrate to sample the beam flux at the substrate surface. Because the beam flux is measured for each elemental species, the relative flux ratios can be predetermined. During the beam flux measurement, a mechanical shutter is positioned between the substrate and the beam flux measurement. The mechanical shutter also intersects with the atomic beams emitted from each crucible containing each elemental species selected to compose the epitaxial film.

[0414] During deposition, the substrate is rotated to accumulate a uniform volume of the atomic beam intersecting the substrate surface for a given amount of deposition time. The substrate is back-heated by an electrically heated filament, and the use of a silicon carbide (SiC) heater is advantageous to favor oxide growth. SiC heaters offer a unique advantage over refractory metal filament heaters in that they provide broad emissivity in the near-to-mid-infrared range.

[0415] Although not widely known to researchers in the field of epitaxial film growth, most metal oxides have relatively large optical absorption attributes in the near-infrared to far-infrared wavelengths. The deposition chamber is preferentially actively and continuously pumped to achieve and maintain a vacuum near 1e-6 to 1e-5 Torr during epitaxial film growth. Operating in this vacuum range, evaporated metal particles from the surface of each spouting crucible attain essentially non-interacting, ballistic velocities.

[0416] The advantageous placement of the ejection cell beam, formed by the Claussing coefficient of the crucible opening and the large mean free path of UHV, ensures collision-free ballistic transport of the ejected species to the substrate surface. The atomic beam flux from an ejection-type heating source is determined by the Arrhenius behavior of the specific elemental species placed in the crucible. In some embodiments, the flux is greater than 1×10 -6 Al and Ga fluxes in the Torr range are measured at the substrate surface. The oxygen plasma is controlled by the RF power coupled to the plasma and the flow rates of the source gases.

[0417] RF plasma discharges typically operate at pressures between 10 mTorr and 1 Torr. These RF plasma pressures are not compatible with the atomic layer deposition process reported here. -7 Torr ~ 1 × 10 -5 To achieve activated oxygen beam fluxes in the Torr range, a sealed fused silica bulb with a laser-drilled aperture on the order of 100 microns in diameter is placed across the circular end face of the sealed cylindrical bulb. The bulb is coupled to a water-cooled RF antenna driven by a spirally wound copper tube and an impedance matching network, and to a high-power 100 W to 1 kW RF oscillator operating, for example, at 2 MHz to 13.6 MHz or even 20 MHz.

[0418] The plasma is monitored using optical emissions from the plasma discharge, providing precise telemetry of the actual species generated within the valve. The size and number of openings in the valve end face, which interfaces the plasma to the UHV chamber, can be predetermined to achieve a suitable beam flux to maintain long mean-free-path ballistic transport conditions over the source-to-substrate distance. Other in-situ diagnostics that enable precise control and repeatability of film composition and uniformity include the use of ultraviolet polarized optical reflectometry and ellipsometry, as well as residual gas analyzers to monitor species desorption from the substrate surface.

[0419] Other forms of activated oxygen include the use of oxidizers such as ozone (O3) and nitrous oxide (N2O). While all forms—RF plasma, O3, and N2O—work relatively well, RF plasma may be used in certain embodiments due to its simplicity of point-of-use activation. However, RF plasma can generate highly energetic charged ionic species that affect the background conductivity type of the material. This is mitigated by directly removing the opening near the center of the plasma end plate coupled to the UHV chamber. The RF-induced oscillating magnetic field at the center of the cylindrical discharge tube solenoid is maximized along the central axis. Therefore, removing the opening that provides a line of sight from the plasma interior toward the growth surface eliminates charged ionic species that would otherwise be ballistically delivered to the epilayer.

[0420] Referring again to Figure 44B, the growth method was briefly described. A monoclinic GaO (010) oriented substrate 5045 is cleaned in situ via high temperature, such as at about 800 °C for 30 minutes in UHV conditions. The cleaned surface is then terminated with active oxygen adatoms, which form surface reconstructions containing oxygen atoms.

[0421] An optional homoepitaxial GaO buffer layer 5075 is deposited and monitored for crystallographic surface improvement by in situ RHEED. Generally, GaO growth conditions using elemental Ga and activated oxygen require a flux ratio of φ(Ga):φ(O*)<1, i.e., atomic oxygen-rich conditions.

[0422] For flux ratios Φ(Ga):Φ(O*)>1, excess Ga atoms at the growth surface are converted to potentially volatile GaO (g)It can attach to surface-bound oxygen, potentially forming suboxide species, which can desorb from the surface, remove material from the surface, and even etch the Ga2O3 surface. In accordance with the present disclosure, it has been found that for high Al content AlGaO3, this etching process is reduced, if not eliminated, for Al%>50%. The etching process can be used to clean unused Ga2O3 substrates, for example, to assist in the removal of chemical mechanical polishing (CMP) damage.

[0423] To initiate the growth of AlGaO, an activated oxygen source is first optionally exposed to the surface, followed by opening the shutters of both the Ga and Al effusion cells. It has been experimentally found in accordance with the present disclosure that the sticking coefficient of Al is approximately unity, but the sticking coefficient on the growth surface is kinetically dependent on the Arrhenius behavior of desorbed Ga adatoms, which is dependent on the growth temperature.

[0424] Epitaxial (Al x Ga 1-x The relative x = Al% of the 2O3 film is related to x = Φ(Al) / [Φ(Ga) + Φ(Al)]. (Al x Ga 1-x During deposition of Al 2O3, well-defined, high-quality RHEED surface reconstruction streaks are evident. Thickness can be monitored in situ by UV laser reflectometry, and the pseudomorphic strain state can be monitored by RHEED. x Ga 1-x The independent in-plane lattice constant of (Al)2O3 is smaller than that of the underlying Ga2O3 lattice. x Ga 1-x )2O3 grows under tensile strain during elastic deformation.

[0425] The thickness 5085 of the epilayer 5080 at which the elastic energy can be matched or reduced by including misfit dislocations in the growth plane is called the critical layer thickness (CLT), and above this point the film can begin to grow as a partially or fully relaxed grown bulk-like film. Curves 5050 and 5065 are plotted for coherently strained (Al) epilayers with thicknesses below the CLT.x Ga 1-x )2O3 films. For x=0.15, the CLT is >400 nm, and for x=0.25, the CLT is approximately 100 nm. Thickness oscillations 5070, also known as Penderosung fringes, indicate highly coherent, atomically flat epitaxial films.

[0426] In experiments conducted in connection with this disclosure, pure monoclinic AlO epitaxial films grown directly on monoclinic GaO(010) surfaces achieved CLTs of <1 nm. Furthermore, experimentally, Al% >50% achieved low growth rates due to a unique monoclinic bonding arrangement of cations, which was split into approximately 50% tetrahedral and 50% octahedral bonding sites. Al adatoms were found to preferentially incorporate into the octahedral bonding sites during crystal growth and to have a bonding affinity for the tetrahedral sites.

[0427] Superlattices (SLs) are created that can be directly applied to UV LED operation by utilizing quantum size effect tuning mechanisms to quantize the allowed energy levels within narrower bandgap materials sandwiched between two potential energy barriers. Furthermore, SLs are an exemplary medium for creating pseudoternary alloys as discussed herein, further enabling strain management in the layers.

[0428] For example, monoclinic (Al x Ga 1-x The ternary alloy GaO is subjected to asymmetric in-plane biaxial tensile strain when epitaxially deposited on monoclinic GaO. This tensile strain can be managed by keeping the ternary thickness below the CLT within each layer comprising the SL. Furthermore, the thickness of both the GaO and ternary layers can be adjusted to balance the strain by managing the built-in strain energy of the bilayer pair.

[0429] Furthermore, a further embodiment of the present disclosure is to produce a ternary alloy as a bulk or SL grown thick enough to form a substantially strain-free and self-supporting material beyond CLT. This substantially strain-free and relaxed ternary layer has an effective in-plane lattice constant a parameterized by the effective Al% composition SL having. Then, when a first relaxed ternary layer is formed and subsequently another second SL is deposited directly on the relaxed layer, the bilayer pairs forming the second SL can be adjusted such that the layers constituting the bilayer are in equal and opposite strain states of tensile and compressive strain with respect to the first in-plane lattice constant.

[0430] FIG. 44C shows an exemplary SL5115 formed directly on a Ga2O3(010) - oriented substrate 5100.

[0431] The bilayer pairs constituting SL5115 are both monoclinic crystal - symmetric Ga2O3 and ternary (Al x Ga 1-x )2O3(x = 0.15), and the SL period Δ[[ID=​​​​​​​​​​​​​​​​The SL containing the bilayer of [GaO / GaO] has an equivalent Al% defined as:

number

[0434] The tensile strain shown in Figures 23A-23C can be used advantageously towards the formation of light emitting regions.

[0435] FIG. 44D further illustrates the formation of a ternary monoclinic 5130 alloy (Al 2 O 3 ) on yet another crystal orientation of the monoclinic Ga 2 O 3 (001) substrate 5120. x Ga 1-x This demonstrates further flexibility for direct deposition of .

[0436] Again, best results are obtained by paying close attention to high-quality CMP surface preparation of the cleaved substrate surface. Growth recipes in some embodiments utilize in-situ activated oxygen polishing at high temperatures (e.g., 700-800°C) using substrates radiatively heated via a high-power, oxygen-resistant radiative-coupled heater. SiC heaters have the unique property of high near- and far-infrared emissivity. The emissivity of SiC heaters closely matches the inherent Ga2O3 absorption characteristics, thus coupling well with the radiative blackbody spectrum exhibited by SiC heaters. Region 5125 represents the O-terminated process and homoepitaxial growth of a high-quality Ga2O3 buffer layer. SL is then deposited, demonstrating two separate growths with different ternary alloy compositions.

[0437] Shown in Fig. 44D is a coherently strained epitaxial layer of (Al x Ga 1-x )2O3 having a CLT thickness and achieving x of about 15% (5135) and x of about 30% (5140) with respect to the (002) substrate peak 5122. Again, the high-quality film is indicated by the presence of interference fringes in thickness.

[0438] It has further been discovered that an SL structure is also possible on a monoclinic Ga2O3 substrate 5155 with (001) orientation, and the results are shown in Fig. 44E.

[0439] Clearly, HRXRD 5145 and GIXR 5158 indicate a high-quality coherently deposited SL. Peak 5156 is the substrate peak. The SL diffraction peaks 5150 and 5160 enable direct measurement of the SL period, and the SL n=0 peak enables determination of the effective Al% of the SL. In this case, a 10-period SL [(Al SL = 8.6 nm having 0.18 Ga 0.92 )2O3 / Ga2O3] is shown.

[0440] Referring to Fig. 44F, it is desired to demonstrate an application example of the versatility of the metal oxide film deposition method disclosed herein. Two different crystal symmetry type structures are epitaxially formed along the growth direction as defined by Fig. 18. A substrate 5170 (peak 5172) including a monoclinic Ga2O3 (001) oriented surface is presented for homoepitaxy of monoclinic Ga2O3 5175. Next, a cubic crystal symmetry NiO epitaxial layer 5180 is deposited. HRXRD 5165 and GIXR 5190 indicate that the top NiO film peak 5185 with a thickness of 50 nm has excellent atomic flatness and thickness fringes 5195.

[0441] In one example, the mixing and matching of crystal symmetry types can be favorable for a given material composition advantageous for a given function including a UVLED (see Fig. 1), thereby enhancing the flexibility for optimizing the UVLED design. Ni xO (indicating that a metal vacancy structure is possible when 0.5 < x ≤ 1), Li x Ni y O n , Mg x Ni 1-x O and Li x Mg y Ni z O n is a composition that can be advantageously utilized for integration with an AlGaO3 material including a UVLED.

[0442] Since NiO and MgO share very similar cubic crystal symmetries and lattice constants, they are advantageous for bandgap adjustment applications of about 3.8 - 7.8 eV. The d states of Ni affect the optical and conductivity types of the MgNiO alloy and can be adjusted for application to UVLED-type devices. A similar behavior is found in the selective incorporation of Ir into a corundum crystal symmetry ternary alloy (Ir x Ga 1-x [[ID=2~6]])2O3, which exhibits favorable energy positions within the E-k dispersion due to the iridium d-state orbitals for creating p-type conductivity.

[0443] Further, a further example of a metal oxide structure is shown in FIG. 44G. The cubic crystal symmetric MgO(100) oriented surface of the substrate 5205 (corresponding to peak 5206) is presented for the direct epitaxy of Ga2O3. In accordance with the present disclosure, it has been found that the surface of MgO can be selectively modified to create the cubic crystal symmetric form of a Ga2O3 epitaxial layer 5210 (peak 5212 of gamma Ga2O3) that functions as an intermediate transition layer for subsequent epitaxy of monoclinic Ga2O3(100)5215 (peaks 5214 and 5217). Such a structure is represented by the growth process shown in FIG. 20A.

[0444] First, a prepared clean MgO(100) surface is presented for MgO homoepitaxy. The magnesium source is a valved ejection source containing 7N purity Mg with a beam flux of about 1×10 -10 Torr in the presence of active oxygen supplied at φ(Mg):φ(O*) < 1 and a substrate surface growth temperature of 500 - 650 °C.

[0445] RHEED monitoring demonstrates improved, high-quality surface reconstruction of the MgO surface of the epitaxial film. After approximately 10–50 nm of MgO homoepitaxy, the Mg source is closed and the substrate is ramped to a growth temperature of approximately 700 °C under a protective O* flux. The Ga source is then exposed to the growth surface, and RHEED observes an instantaneous change in surface reconstruction toward a Ga2O3 epilayer 5210 with cubic crystal symmetry. After approximately 10–30 nm of cubic Ga2O3 (also known as the gamma phase), direct RHEED observation reveals that the characteristic monoclinic Ga2O3(100) surface reconstruction appears and remains the most stable crystal structure. A 100 nm Ga2O3(100)-oriented film is deposited, and HRXRD5200 and GIXR5220 display the beta Ga2O3(200) peak 5214 and the beta Ga2O3(400) peak 5217. Such coincidences of crystal symmetry are rare but highly advantageous for UV LED applications.

[0446] Yet another example of a complex ternary metal oxide structure applied to UV LEDs is disclosed in Figure 44H. HRXRD5225 and GIXR5245 show the experimental realization of a superlattice containing a ternary lanthanide-aluminum-oxide integrated with a corundum Al2O3 epilayer.

[0447] SL is the corundum crystal symmetry (Al x Er 1-x The crystals comprise a ternary composition of AlO, where the lanthanides are selected from corundum AlO and pseudomorphically grown erbium. The erbium is subjected to non-equilibrium growth via a sublimable 5N purity erbium source using an effusion cell. A flux ratio of φ(Er):φ(Al) of approximately 0.15 was used at a growth temperature of approximately 500 °C under oxygen-rich conditions with [φ(Er) + φ(Al)]:φ(O*)]<1.

[0448] Of particular note is the ability of Er to decompose molecular oxygen at the epilayer surface, thus resulting in a total oxygen overpressure greater than the atomic oxygen flux. A-plane sapphire (11-20) substrates 5235 were prepared and approximately 800The substrate is heated to 500°C and exposed to activated oxygen polishing. In this example, activated oxygen polishing of the bare substrate surface is found to dramatically improve the quality of the subsequent epilayer. A homoepitaxial corundum Al2O3 layer is then formed, monitored by RHEED, showing excellent crystalline quality and atomically flat layer-by-layer deposition. Ten periods of SL are then deposited, shown as satellite peaks 5230 and 5240 in the HRXRD5225 and GIXR5245 scans. Clearly evident are pendulous fringes, indicating excellent coherent growth.

[0449] SL's (Er xSL Al 1-xSL The effective alloy composition of )2O3 is the zero-order SL peak SL relative to the (110) substrate peak 5235. n=0 It can be estimated from the position of xSl that it is about 0.15, forming an SL period (Al x Er 1-x )2O3 layers have been found to have corundum crystal symmetry. This finding is particularly important for UV LED applications, and Figure 44I shows that the x Er 1-x )2O3 EK band structure 5250 is actually E G ≥ 6 eV. The electron energy 1066 is plotted as a function of the crystal wave vector 1067. The conduction band minimum 5265 and the valence band 5260 are maximal at the center 5255 of the Brillouin zone (k = 0).

[0450] Next, 44J is a further ternary magnesium-gallium-oxide with cubic crystal symmetry that can be combined with Ga2O3. x Ga 2(1-x) O 3-2x Further demonstrating the material composition, shown is a 10-period SL [Mg x Ga 2(1-x) O 3-2xThe SL ternary alloy composition is chosen from x=0.5 with a thickness of 8 nm and Ga2O3 of 8 nm. The SL period is

number

[0451] The ability of monoclinic Ga2O3 crystal symmetry to integrate with cubic MgAl2O4 crystal symmetry substrates is demonstrated in Figure 44L. A high-quality single-crystal substrate 5320 (peak 5322) containing MgAl2O4 spinel is cleaved and polished to expose a (100)-oriented crystal surface. The substrate is prepared and polished using activated oxygen at elevated temperatures (~700°C) under UHV conditions (<1e-9 Torr). By maintaining the substrate at the growth temperature of 700°C, the MgGa2O4 film 5330 exhibits excellent registration to the substrate. After approximately 10-20 nm, the Mg is cut off, and only Ga2O3 is deposited as the top film 5325. The GIXR film has excellent planarity, with a thickness fringe 5340 indicating a film >150 nm. The HRXRD shows the transition material MgGaO corresponding to peak 5332 and the GaO(100) oriented epilayer at peak 5327, which indicates monoclinic crystal symmetry. In some embodiments, hexagonal GaO can also be epitaxially deposited.

[0452] The monoclinic Ga2O3 (-201) oriented crystal plane features the unique attribute of a hexagonal oxygen surface matrix with in-plane lattice spacing that allows for registering wurtzite hexagonal symmetry materials. For example, as shown in Figure 44M, peak 5345, wurtzite ZnO5360 (peak 5367) is a substrate Zn x Ga 2(1-x) O 3-2x The ZnO is deposited on the oxygen-terminated Ga2O3 (-201) oriented surface of 5350 (peak 5352). Zn is supplied by sublimation of 7N-purity Zn contained in an effusion cell. The growth temperature is selected from 450 to 650 °C for ZnO, which shows very bright, sharp, narrow RHEED streaks, indicating high crystalline quality. Peak 5362 is (Al x Ga 1-x )2O3. Peak 5355 represents the transition layer.

[0453] Next, the ternary zinc gallium oxide epilayer Zn x Ga 2(1-x) O 3-2x 5365 is deposited by codeposition of Ga with Zn and activated oxygen at 500 °C. The flux ratio [φ(Zn) + φ(Ga)]:φ(O*) < 1 and the metal beam flux ratio φ(Zn):φ(Ga) are chosen to achieve x ~ 0.5. Zn desorbs at much lower surface temperatures than Ga, controlled in part by a surface-temperature-dependent absorption-limited process determined by the Arrhenius behavior of the Zn adatoms.

[0454] Zn is a group metal that advantageously substitutes for available Ga sites in the host crystal. In some embodiments, Zn can be used to modify the conductivity type of the host for dilute concentrations of incorporated Zn, x<0.1. Zn x Ga 2(1-x) O 3-2x The peak labeled 5355 indicates the transition layer formed on the substrate, and Zn x Ga2(1-x)O 3-2x This strongly suggests the high miscibility of Ga and Zn in the ternary system, which provides non-equilibrium growth of alloys over the entire range of 0≦x≦1.x Ga 2(1-x) O 3-2x For x=0.5 in, the Ek band structure provides cubic crystal symmetry, as shown in diagram 5370 of Figure 44N.

[0455] The indirect bandgap indicated by the band extrema 5375 and 5380 can be shaped using SL band engineering, as shown in Figure 27. The valence band dispersion 5385, which exhibits a maximum at k≠0, can be used to create SL periods that can advantageously remap the maximum to an equivalent energy at the zone center, thereby creating a pseudo-direct bandgap structure. Such methods are claimed in their entirety for application to the formation of optoelectronic devices such as the UVLEDs referred to in this disclosure.

[0456] As described in this disclosure, there is a large design space available for crystal modifiers to Ga2O3 and Al2O3 host crystals that can be used for UV LED applications.

[0457] Furthermore, yet another example is disclosed herein in which growth conditions can be adjusted to preselect the specific crystal symmetry type of Ga2O3, i.e., monoclinic (beta phase) or hexagonal (epsilon or kappa phase).

[0458] FIG. 44O shows a specific application of the more general method disclosed in FIG.

[0459] A prepared clean surface of a sapphire C-face substrate 5400 of corundum crystal symmetry is presented for epitaxy.

[0460] The substrate surface is polished with active oxygen at elevated temperatures, such as >750°C and about 800-850°C, creating an oxygen-terminated surface 5405. While maintaining the high growth temperature, a Ga and active oxygen flux is directed onto the epi-surface of the bare Al2O3 surface reconstruction, forming a thin template layer 5396 of corundum Ga2O3 or (Al x Ga 1-x)2O3x<0.5 low Al% corundum, which is then modified by additional codeposited Al flux. After a template layer of approximately 10 nm 5396, the Al flux is closed and Ga2O3 is deposited. The high growth temperature and maintaining a low Al% template 0≦x<0.1 favor the exclusive formation of a monoclinic crystal structure epilayer 5397.

[0461] After the formation of the initial template layer 5396, lowering the growth temperature to approximately 650-750°C favors the growth of GaO only in a new type of crystal symmetry structure with hexagonal symmetry. The hexagonal phase of GaO becomes favored in x>0.1 template layers. The unique properties of the hexagonal crystal symmetry GaO composition 5420 are discussed later. Experimental evidence of the disclosed process for growing epitaxial structure 5395 is provided in Figure 44P, which shows HRXRD scans 5421 for two different growth process results: phase-pure monoclinic GaO and hexagonal crystal symmetry GaO. The HRXRD scans show the C-plane AlO(0001) oriented substrate Bragg diffraction peaks for corundum AlO(0006) 5465 and AlO(0012) 5470. For the monoclinic Ga2O3 top epitaxial film, the diffraction peaks shown at 5445, 5450, 5455, and 5460 represent sharp single-crystal monoclinic Ga2O3 (-201), Ga2O3 (-204), Ga2O3 (-306), and Ga2O3 (-408).

[0462] Orthorhombic crystal symmetry can further exhibit the advantageous property of having non-inversion symmetry, which is particularly advantageous for enabling electric dipole transitions between the conduction and valence band edges of the band structure at zone centers. For example, wurtzite ZnO and GaN both exhibit crystal symmetry with non-inversion symmetry. Similarly, orthorhombic crystals (i.e., space group 33Pna21 crystal symmetry) have non-inversion symmetry, enabling electric dipole optical transitions.

[0463] Conversely, in the growth process, hexagonal Ga2O3 peaks 5425, 5430, 5435, and 5440 represent sharp single-crystal hexagonal crystal symmetries Ga2O3(002), Ga2O3(004), Ga2O3(006), and Ga2O3(008).

[0464] Hexagonal crystal symmetry Ga2O3 and hexagonal (Al x Ga 1-x )2O3 also shows the importance of achieving this in Figure 44Q.

[0465] The energy band structure 5475 shows that the extrema of the conduction band 5480 and the valence band 5490 are both located at the Brillouin zone center 5485, thus favoring UV LED applications.

[0466] Single crystal sapphire is one of the most mature crystalline oxide substrates. Yet another form of sapphire is the corundum M-plane surface, which can be advantageously used to form GaO and AlGaO, as well as other metal oxides discussed herein.

[0467] For example, it has been experimentally discovered in accordance with the present disclosure that the surface energy of sapphire, as dictated by the particular crystallographic planes presented for epitaxy, can be used to preselect the crystal symmetry type of Ga2O3 to be epitaxially formed thereon.

[0468] Considering Figure 44R, the utility of an M-plane corundum Al2O3 substrate 5500 is now disclosed. The M-plane is a (1-100) oriented surface that can be prepared as described above and atomically polished in situ at high growth temperatures of 800°C while exposed to an activated oxygen flux. The oxygen-terminated surface is then cooled to 500-700°C, such as 500°C in one embodiment, and a Ga2O3 film is epitaxially deposited. Over 100-150 nm of corundum crystal symmetry Ga2O3 can be deposited on M-plane sapphire, with approximately 400-500 nm of corundum (Al2O3) deposited on M-plane sapphire. x Ga 1-xIt was found that approximately 0.3-0.45% of Al 2 O 3 x could be deposited. Of particular interest is the 03 Ga 0.7 )2O3 exhibits a direct band gap, equivalent to the energy gap of wurtzite AlN.

[0469] The curves for HRXRD5495 and GIXR5540 show two separate growths on M-plane sapphire 5500. High-quality single-crystal corundum Ga2O3 5510 and (Al 03 Ga 0.7 )2O3 5505 is clearly shown relative to the corundum Al2O3 substrate peak 5502. Thus, an M-plane oriented AlGaO3 film on M-plane sapphire is possible. The GIXR thickness oscillation 5535 shows an atomically flat interface 5520 and film 5530. The curve 5155 indicates the absence of other crystalline phases of Ga2O3 besides the corundum phase (rhombohedral crystal symmetry).

[0470] For completeness, it has also been discovered that, in accordance with the present disclosure, various metal oxides can also be used to utilize even the most technologically mature semiconductor substrate, namely silicon. For example, while bulk GaO substrates are desirable for their crystallographic and electronic properties, they remain more expensive to manufacture than single crystal substrates and, furthermore, are not as easily scalable as Si to large wafer diameter substrates, e.g., up to the 450 mm diameter of Si.

[0471] Thus, embodiments include forming functional electronic Ga2O3 films directly on silicon, and for this purpose, a process has been developed specifically for this application.

[0472] Referring now to FIG. 44S, the results of an experimentally developed process for depositing monoclinic Ga2O3 films on large area silicon substrates are shown.

[0473] Single crystal high quality monoclinic Ga2O3 epilayer 5565 is made of ternary (Ga 1-x Er xThe transition layer is deposited using a compositional grading that can be abrupt or continuous. The transition layer is formed on a cubic transition layer 5570 comprising [(Ga 1-x Er x )2O3 / (Ga 1-y Er y )2O3], where x and y are selected from 0≦x, y≦1. The transition layer is optionally deposited on a binary bixbyite crystal-symmetric Er2O3(111)-oriented template layer 5560 deposited on a Si(111)-oriented substrate 5555. The Si(111) is first heated in UHV to above 900°C and below 1300°C to desorb the native SiO2 oxide and remove impurities.

[0474] A clear temperature-dependent change in the surface reconstruction is observed, which can be used to in situ calibrate the surface growth temperature, which occurs at 830 °C and is only observable on pristine Si surfaces without surface SiO. The temperature of the Si substrate is then reduced to 500-700 °C to remove (Ga 1-y Er y )2O3 film(s) is deposited and then slightly raised to promote epitaxial growth of the monoclinic Ga2O3 (-201) oriented active layer film. If Er2O3 binary is used, activated oxygen is not required and pure molecular oxygen can be used to co-deposit with a pure Er beam flux. As soon as Ga is introduced, activated oxygen flux is required. Other transition layers are also possible and can be selected from the many ternary oxides described herein. HRXRD5550 is a cubic (Ga 1-y Er y The bixbyite ErO peak 5572 is shown along with the bixbyite ErO(111) and (222) peaks 5562. The monoclinic GaO(-201), (-201), and (-402) peaks are also observed as peak 5567, and the Si(111) substrate is observed as peak 5557.

[0475] One application of the present disclosure is the use of cubic symmetry metal oxides for the use of transition layers between Si(001) oriented substrate surfaces to form GaO(001) and (Al,Ga)O(001) oriented active layer films, which is particularly advantageous for mass production.

[0476] The focus here is on developing transparent substrates that can accommodate a wide variety of metal oxide compositions and crystal symmetry types. x Ga 1-x )2O3 and Ga2O3 materials are of great interest, leading to total miscibility (Al x Ga 1-x Al%x and (Al)2O3 1-y Ga y It was again reiterated that the range of Ga%y in )2O3 can be accommodated by the corundum crystal symmetry type composition.

[0477] Here, reference is made to the examples of Figures 44T to 44X.

[0478] FIG. 44T discloses high-quality single-crystal epitaxy of corundum GaO (110) oriented films on AlO (11-20) oriented substrates (i.e., A-plane sapphire). The surface energy of the A-plane AlO surface can be used to fabricate very high-quality corundum GaO and corundum (Al x Ga 1-x Ternary films of GaO can be grown over the entire alloy range, where 0≦x≦1. GaO can be grown to CLTs of approximately 45-80 nm, and the CLT increases dramatically with the introduction of Al, resulting in the growth of ternary (Al x Ga 1-x )2O3 is formed.

[0479] Homoepitaxial growth of corundum Al2O3 is possible over a surprisingly wide growth window. Corundum AlGaO3 can be grown from room temperature up to approximately 750°C. However, all growth requires that the activated oxygen (i.e., atomic oxygen) flux significantly exceeds the total metal flux, i.e., oxygen-rich growth conditions are required. Corundum crystal-symmetric Ga2O3 films are shown in HRXRD5575 and GIXR5605 scans of two separate growths of films of different thicknesses on A-plane Al2O3 substrates. The surface of the substrate 5590 (corresponding to peak 5592) is oriented in the (11-20) plane and is O-polished at a high temperature of approximately 800°C.

[0480] The activated oxygen polishing is maintained while the growth temperature is reduced to an optimum range of 450-600 °C, such as 500 °C. An Al2O3 buffer 5595 is then optionally deposited to 10-100 nm, followed by a ternary (Al x Ga 1-x A GaO epilayer 5600 is formed by co-deposition with appropriately placed Al and Ga fluxes to achieve the desired Al %. Oxygen-rich conditions are essential. Curves 5580 and 5585 show exemplary x=0 GaO films 5600 of 20 and 65 nm, respectively.

[0481] The Penderosung interference fringes of both HRXRD and GIXR show excellent coherent growth, and transmission electron microscopy (TEM) shows 10 7 cm -3 It has been confirmed that a defect density of less than 1000 nm is possible.

[0482] Corundum Ga2O3 films on A-plane Al2O3 greater than about 65 nm exhibit relaxation as evidenced by reciprocal lattice mapping (RSM), yet maintain excellent crystalline quality for films >CLT.

[0483] There are also other ways to further improve the CLT of the binary Ga2O3 film on the A-plane Al2O3. For example, during the high-temperature O polishing step of the unused Al2O3 substrate surface, the substrate temperature can be maintained at about 750 - 800 °C. At this growth temperature, the Ga flux can coexist with activated oxygen, and high-temperature phenomena may occur. According to the present disclosure, Ga effectively diffuses to the uppermost surface of the Al2O3 substrate, and it has been found that a very high-quality corundum (Al x Ga 1-x )2O3 template layer is formed. Growth can be interrupted or continued while the substrate temperature is decreasing to about 500 °C. The template layer functions as an in-plane lattice matching layer closer to Ga2O3, and thus it can be seen that the CLT of the epitaxial film becomes thicker.

[0484] Establishing the unique properties of the A-plane and referring to the surface energy trend disclosed in FIG. 20B, it has been shown that a bandgap-modulated superlattice structure is also possible.

[0485] FIG. 44U shows the unique attributes of the binary Ga2O3 and binary Al2O3 epitaxial layers used to form an SL structure on an A-plane Al2O3 substrate 5625 (corresponding to peak 5627). Excellent SLHRXRD5610 and GIXR5630 data show a plurality of high-quality SL Bragg diffraction satellite peaks 5615 and 5620 having a period Δ SL = 9.5 nm. Not only is the full width at half maximum (FWHM) of each satellite peak 5615 very small, but the oscillation between the peaks of the Pendellösung fringes is also clearly observed. For the N = 10 period of the SL, there are N - 2 Pendellösung oscillations as shown in both HRDRD and GIXR. The zero-order SL peak SL n=0 indicates the average alloy Al% of the digital alloy formed by the SL,

Number

[0486] Image 5660 in Figure 44V shows the crystalline quality observed in an exemplary [Al2O3 / Ga2O3]SL 5645 deposited on A-plane sapphire 5625. The contrast between Ga and Al species is clearly evident, indicating the abrupt interface between the nanometer-scale films 5650 and 5655 containing the SL periods.

[0487] Close inspection of image 5660 shows the region labeled 5635, which is the result of the high-temperature Ga intermixing process described above. The Al2O3 buffer layer 5640 imparts small strain to the SL stack. Careful attention has been paid to keeping the Ga2O3 thickness well below the CLT to create a high-quality SL. However, strain accumulation can occur, and other structures are possible in some embodiments, such as growing the SL structure on a relaxed buffer composition intermediate the compositional endpoints of the materials that make up the SL.

[0488] This allows for strain symmetrization to be engineered so that layer pairs forming the superlattice period have equal and opposite in-plane strain. Each layer is deposited under a CLT and is subjected to biaxial elastic strain (thereby suppressing dislocation formation at the interface). Some embodiments therefore involve designing a SL disposed on a relaxed buffer layer that allows the SL to accumulate zero strain, thus allowing it to be grown effectively unstrained to a theoretically infinite thickness.

[0489] Furthermore, further applications of corundum film growth can be demonstrated on yet another advantageous Al2O3 crystal surface, namely the R-plane (1-102).

[0490] Figure 44W shows a thick ternary corundum (Al2O3) on the R-plane corundum Al2O3. x Ga 1-x This demonstrates the ability to epitaxially deposit sapphire (Ga)O films. Figure 44W also shows the angular separation of the sapphire substrate 5675 prepared using high-temperature O polishing and codeposition of Al and Ga, while reducing the growth temperature from 750 to 500 °C, forming region 5680. Region 5680 is an optional surface layer modification to the sapphire substrate surface, such as an oxygen-terminated surface. The excellent, high-quality ternary epilayer 5670 (corresponding to XRD peak 5672) exhibits sharp Penderosung fringes 5680, providing an alloy composition of x = 0.64 relative to the substrate peak 5677. The film thickness in this case is approximately 115 nm. Also shown in Figure 44W is the angular separation of the symmetric Bragg peaks 5685 of the pseudomorphic corundum GaO epilayer.

[0491] Again, great utility is recognized in creating bandgap epilayer films that can be configured or designed to build the functional regions required for UV LEDs. Thus, strain and composition are tools that can be used to manipulate the known functional properties of materials for UV LED applications in accordance with the present disclosure.

[0492] Figure 44X shows an example of a high-quality superlattice structure possible on an R-plane Al2O3 (1-102) oriented substrate.

[0493] HRXRD5690 and GIXR5710 are shown as examples of SLs epitaxially grown on R-plane Al2O3 (1-102) substrate 5705 (corresponding to peak 5707).

[0494] SL is [(Al x Ga 1-x )2O3 / Al2O3], where x = 0.50. SL = 20 nm. Multiple SL Bragg diffraction peaks 5695 and reflectivity peaks 5715 indicate a coherently grown pseudomorphic structure. Zero-order SL diffraction peak SL n=0 5700 is (AlxSL Ga 1-xSL )2O3 containing SL effective digital alloy x SL where x SL =0.2.

[0495] Such highly coherent, widely differing band gap materials used to create epitaxial SLs with abrupt discontinuities at the interfaces can be used in the formation of quantum confined structures, as disclosed herein for applications in optoelectronic devices such as UV LEDs.

[0496] The energy discontinuities of the conduction and valence bands available at the Al2O3 / Ga2O3 heterointerface in corundum crystal symmetry (R3c) are:

number

[0497] Also, the band offset of the monoclinic crystal symmetry (C2m) heterointerface is:

number

[0498] Some embodiments also involve creating a potential energy discontinuity by creating a Ga2O3 layer with an abrupt change in crystal symmetry.

[0499] For example, it is disclosed herein that corundum crystal symmetry GaO can be epitaxially deposited directly onto a monoclinic GaO (110) oriented surface. Such a heterointerface produces a band offset given by:

number

[0500] These band offsets are sufficient to create a quantum confined structure, as explained below.

[0501] As yet another example of a complex metal oxide heterostructure embodiment, see FIG. 44Y, where a cubic MgO epilayer 5730 is formed directly on a spinel MgAlO(100) oriented substrate 5725. HRXRD 5720 shows the cubic MgAlO(h00), h=4,8 substrate Bragg diffraction peak 5727 and the epitaxial cubic MgO peak 5737 corresponding to the MgO epilayer 5730. The lattice constant of MgO is almost exactly twice that of MgAlO, thus creating a unique epitaxial coincidence due to the in-plane lattice registration at the heterointerface.

[0502] Clearly, a high-quality MgO (100) oriented epilayer is formed, as evidenced by the narrow FWHM. Next, a monoclinic layer of GaO is formed on the MgO layer. The GaO (100) oriented film is evidenced by the 5736 Bragg diffraction peak.

[0503] Cubic MgAl2O4 and Mg x Al 2(1-x) O 3-2x Interest in ternary structures stems from the possibility of direct and large bandgaps.

[0504] Graph 5740 in Figure 44Z shows Mg x Al 2(1-x) O 3-2x The energy band structure for (x approximately 0.5) shows a direct band gap 5745 formed between the extrema of the conduction band 5750 and the valence band 5755.

[0505] Some embodiments also include growing Ga2O3 directly on a lanthanum aluminum oxide LaAlO3 (001) substrate.

[0506] The exemplary structures disclosed in Figures 44A-44Z are intended to demonstrate some possible configurations applicable for use in at least a portion of a UV LED structure. A wide variety of compatible mixed symmetry heterostructures is a further attribute of the present disclosure. As will be appreciated, other configurations and structures are possible and consistent with the present disclosure.

[0507] The unique properties of the AlGaO3 material system described above can be applied to the formation of UV LEDs. Figure 45 shows an exemplary light emitting device structure 1200 according to the present disclosure. The light emitting device 1200 is designed to operate such that optically generated light can be outcoupled vertically through the device. The device 1200 comprises a substrate 1205, a first conductivity type n-doped AlGaO3 region 1210, followed by an unintentionally doped (NID) intrinsic AlGaO3 spacer region 1215, followed by an (Al x Ga 1-x )2O3 / (Al y Ga 1-y 12. The present invention includes a multiple quantum well (MQW) or superlattice 1240 formed using a periodic repeat of .Osb; .Osb; .Osb; where the barrier layers include a larger bandgap composition 1220 and the well layers include a narrower bandgap composition 1225.

[0508] The overall thickness of the MQW or SL 1240 is selected to achieve a desired emission intensity. The thicknesses of the layers comprising the MQW or SL 1240 unit cell are configured to produce a predetermined operating wavelength based on quantum confinement effects. An optional AlGaO3 spacer layer 1230 then separates the MQW / SL from the p-type AlGaO3 layer 1235.

[0509] The spatial energy band profiles using the k=0 representation are disclosed in Figures 46, 47, 49, 51 and 53, which are graphs of spatial band energy 1252 as a function of growth direction 1251. The n-type and p-type conductivity regions 1210 and 1235 are (Al x Ga 1-x)2O3, where x=0.3, followed by NID1215 of the same composition with x=0.3. The MQW or SL1240 is adjusted by keeping the thickness of both the well and barrier layers the same in each design 1250 (Figures 46, 47), 1350 (Figure 49), 1390 (Figure 51), and 1450 (Figure 53).

[0510] The well composition was varied at x = 0.0, 0.05, 0.10, and 0.20, and the barrier consisted of two layers (Al x Ga 1-x )2O3 / (Al y Ga 1-y )2O3, y is fixed at y = 0.4. These MQW regions are at 1275, 1360, 1400, and 1460. The well layer thickness is determined by the unit cell (a w lattice constant) of at least 0.5xa w ~10×a w In this case, one unit cell is selected. Because the corundum and monoclinic unit cells are relatively large, the thickness of the periodic unit cell can be relatively large. However, in some embodiments, sub-unit cell assemblies can be utilized. The MQW region 1275 in FIG. 47 is a Ga2O3 / (Al 0.4 Ga 0.6 The MQW region 1360 of FIG. 49 is configured for a combination of intrinsically or unintentionally doped layers including (Al 0.05 Ga 0.95 )2O3 / (Al 0.4 Ga 0.6 The MQW region 1400 of FIG. 51 is configured for a combination of intrinsically or unintentionally doped layers including (Al 0.1 Ga 0.9 )2O3 / (Al 0.4 Ga 0.6 The MQW region 1460 of FIG. 53 is configured for a combination of intrinsically or unintentionally doped layers including (Al 0.2 Ga 0.8 )2O3 / (Al 0.4 Ga 0.6 )2O3, intrinsically or unintentionally doped layers.

[0511] Ohmic contact metals 1260 and 1280 are also shown. The conduction band edge E C (z)1265 and valence band edge E V (z) 1270 and MQW region 1400 show modulation of bandgap energy with spatially modulated composition, which is yet another particular advantage of the atomic layer epitaxy deposition technique that makes such structures possible.

[0512] 47 shows a schematic representation of the wave functions of electrons 1285 and holes 1290 confined within the MQW region 1275. Electric dipole transitions due to spatial recombination of electrons 1285 and holes 1290 generate photons 1295.

[0513] The emission spectrum can be calculated and plotted in graph 1300 as the emission wavelength 1310 and oscillator absorption intensity 1305 via the wave function overlap integral for spatially dependent quantized electron and hole states (emission intensity is also shown), as shown in Figure 48. Multiple peaks 1320, 1325, and 1330 arise from the recombination of quantized energy states with the MQW. Specifically, the lowest-energy electron-hole recombination peak 1320 is most likely and occurs at approximately 245 nm. Region 1315 indicates that there is no absorption or emission below the energy gap of the MQW. Moving toward shorter wavelengths, the first onset of optical activity is the n=1 exciton peak 1320, which is determined by the MQW configuration.

[0514] The MQW configurations 1275, 1360, 1400, and 1460 result in emission energy peaks 1320 ( FIG. 48 ), 1370 ( FIG. 50 ), 1420 ( FIG. 52 ), and 1470 ( FIG. 54 ), with peak operating wavelengths of 245 nm, 237 nm, 230 nm, and 215 nm, respectively. Graph 1365 of FIG. 50 also shows peaks 1375 and 1380 along with region 1385. Graph 1410 of FIG. 52 also shows peaks 1425 and 1430 along with region 1435. Graph 1465 of FIG. 54 also shows peak 1475 along with region 1480. Regions 1385, 1435, and 1480 indicate no optical absorption or emission of photon energies / wavelengths below the energy gap of the MQWs.

[0515] Furthermore, a further feature of very wide bandgap metal oxide semiconductors is the formation of ohmic contacts to the n-type and p-type regions. Exemplary diode structure 1255 includes a high work function metal 1280 and a low work function metal 1260 (ohmic contact metal). This is due to the relative electron affinity of metal oxides compared to vacuum (see FIG. 9).

[0516] Figures 48, 50, 52, and 54 show optical absorption spectra of the MQW region contained within diode structure 1255. The MQW contains two layers of narrower and wider bandgap material. The thickness of the layers, specifically the narrow bandgap layer, is selected to be small enough to exhibit quantization effects along the growth direction in the conduction and valence potential wells that are formed. The absorption spectra represent the creation of electrons and holes in the quantized states of the MQW upon resonant absorption of incident photons.

[0517] In the reversible process of photon generation, electrons and holes spatially localize to their respective quantum energy levels in the MQW and recombine through the direct band gap. The recombination generates photons with energies approximately equal to the energy of the band gap of the layer, which acts as a potential well with a direct energy gap in addition to the energy separation of the quantized levels within the potential well relative to the conduction and valence band edges. Therefore, the emission / absorption spectrum exhibits a lowest-energy resonant peak representing the UV LED's primary emission wavelength, which is designed to be the desired operating wavelength of the device.

[0518] Figure 55 shows a plot 1500 of known pure metal work function energies 1510, categorizing metal species (elemental metal contacts 1505) from high work function 1525 to low work function 1515 for p-type and n-type ohmic contact applications, providing criteria for selecting metal contacts for each of the conductivity type ranges required by UV LEDs. Line 1520 represents the midpoint work function energy for the upper bound 1525 and lower bound 1515 shown in Figure 55.

[0519] In some embodiments, Ni, Os, Se, Pt, Pd, Ir, Au, W, and their alloys are used for the p-type region, and low work function metals selected from Ba, Na, Cs, Nd, and their alloys can be used. Other choices are possible. For example, in some cases, the common metals Al, Ti, Ti-Al alloys, and titanium nitride (TiN) can also be used as contacts to the n-type epitaxial oxide layer.

[0520] Intermediate contact materials such as semimetallic palladium oxide (PdO), degenerately doped Si or Ge, and rare-earth nitrides can be used. In some embodiments, ohmic contacts are formed in situ for at least part of the deposition process of the contact material to preserve the quality of the metal contact / metal oxide interface. Indeed, some metal oxide configurations allow for single-crystal metal deposition.

[0521] X-ray diffraction (XRD) is one of the most powerful tools available in crystal growth analysis for directly confirming crystalline quality and crystal symmetry type. Figures 56 and 57 show 2D XRD data for example materials: ternary AlGaO3 and binary Al2O3 / Ga2O3 superlattices. Both structures are pseudomorphically deposited on corundum crystal symmetry substrates with A-plane oriented surfaces.

[0522] Referring now to FIG. 56, a 201 nm thick epitaxial ternary (AlO) layer was grown on an A-plane AlO substrate. 0.5 Ga 0.5 A reciprocal lattice map dual-axis X-ray diffraction pattern 1600 of Al 2O3 is shown. Clearly, the in-plane and vertical mismatch of the ternary film is in good agreement with the underlying substrate. The in-plane mismatch parallel to the growth plane is about 4088 ppm, and the vertical lattice mismatch of the film is about 23440 ppm. The ternary layer peak (Al 2O3) relative to the substrate (SUB) is x Ga 1-x The relative vertical displacement of )2O3 indicates excellent film growth compatibility, which is directly advantageous for UV LED applications.

[0523] Referring now to Figure 57, there is shown a dual-axis X-ray diffraction pattern 1700 of a 10-period SL [Al2O3 / Ga2O3] on an A-plane Al2O3 substrate showing an excellent strained Ga2O3 layer (no 2-theta angle broadening) => elastically strained SL. SL period = 18.5 nm and effective SL digital Al% ternary alloy, x_Al ~ 18%.

[0524] In further exemplary embodiments, an optoelectronic semiconductor device according to the present disclosure may be implemented as a metal oxide semiconductor material-based ultraviolet laser device (UVLAS).

[0525] Metal oxide compositions with bandgap energies corresponding to operation in the UVC (150-280 nm) and far / vacuum UV wavelengths (120-200 nm) share the common distinguishing feature of having an intrinsically small optical refractive index far from the fundamental band edge absorption. When operating in optoelectronic devices with energy states very close to the conduction and valence band edges, the effective refractive index is governed by the Kramers-Kronig relation.

[0526] 58A and 58B show a cross section of a metal oxide semiconductor material 1820 having an optical length 1850 along a one-dimensional optical axis, according to an exemplary embodiment of the present disclosure. An incident light vector 1805 is incident on a metal oxide semiconductor material 1820 having an optical length 1850 along a one-dimensional optical axis, the optical length 1850 being a refractive index n MOx Light enters material 1820 from air having a refractive index of 1810. Light within material 1820 is transmitted and reflected at the refractive index discontinuities at each surface along with transmitted light beam 1815 (beam 1810).

[0527] A slab of material of length 1850 can support a number of optical longitudinal modes 1825, as shown in Figure 58A. The transmittance 1815 as a function of optical wavelength incident on the slab exhibits a Fabry-Perot mode structure with modes 1825. For photons trapped within an optical cavity defined by a one-dimensional slab, it is possible, in accordance with the present disclosure, to determine the round-trip losses through the slab and the minimum requisite optical gain required to overcome these losses and enable net gain.

[0528] The threshold gain is calculated in Figure 58B, which shows the transmission coefficient β as a function of optical gain in the slab for forward 1830 and backward 1835 propagating optical beam 1810. For this simple Fabry-Perot case, the slab length L cav Low refractive index n = 1 micrometer MOx = 2.5 requires a threshold gain 1845 calculated by the maximum full width half maximum of the peak gain at 1840.

[0529] Some embodiments implement semiconductor cavities contained in vertical structures 110 (see, e.g., FIG. 2A) with submicron length scales. This is due to the desire to localize electron-hole recombination to a small region. Limiting the physical thickness of the slab where carrier recombination and light emission occur helps reduce the threshold current density required to achieve lasing. Therefore, it is beneficial to understand the required threshold gain by reducing the length of the gain slab.

[0530] 59A-59B show the same optical material as in FIGS. 58A-58B, but with L cav = 500 nm. The smaller cavity length 1860 compared to length 1850 results in fewer allowed optical modes 1870. The required threshold gain needed to overcome the cavity losses increases to 1865 compared to gain 1845 in FIG. 58A, see peaks 1877 calculated for forward and backward propagating modes 1880 and 1885, respectively, shown in FIG. 59B.

[0531] The increase in threshold gain required for a slab of metal oxide material can be dramatically reduced by increasing the length of the slab of optical gain medium, in this case the metal oxide semiconductor region responsible for the light emission process.

[0532] 2A and 2B, instead of using a vertical 110 light-emitting device (i.e., FIG. 2A), some embodiments utilize a planar waveguide structure in which the optical mode overlaps the optical gain layer along a plane-parallel length, i.e., the optical propagation vector is substantially parallel to the plane of the gain slab, even though the gain material is still a thin slab.

[0533] This is shown schematically for structure 140 in FIG. 2B and structure 2360 in FIG. 74. Waveguide structures with optical gain region layer thicknesses well below 500 nm are possible, even as thin as 1 nanometer, supporting quantum wells (see FIGS. 64-68). The longitudinal length of the waveguide can then be on the order of a few microns to several millimeters, or even centimeters. This is an advantage of waveguide structures. An additional requirement is the ability to confine and guide the optical mode along the longitudinal length of the waveguide, which can be achieved by using appropriate refractive index discontinuities. The optical mode is preferably guided in a medium with a higher refractive index compared to the surrounding non-absorbing cladding region. This can be achieved using the metal oxide compositions described in this disclosure, which can be preselected to exhibit advantageous Ek band structures.

[0534] In its most basic configuration, a UVLAS requires at least one optical gain medium and an optical cavity to recycle the generated photons. The optical cavity must also contain a low-loss high reflector (HR) and an out-coupling reflector (OC) that can transmit a portion of the optical energy generated in the gain medium. The HR and OC reflectors are typically plane-parallel or can focus the energy within the cavity into the gain medium.

[0535] FIG. 60 schematically illustrates an embodiment of an optical cavity having an HR 1900, a gain medium 1905 that substantially fills the cavity with length 1935, and an OC 1915 with physical thickness 1910. Standing waves 1925 and 1930 represent two distinct optical wavelength optical fields that match the cavity length. The outcoupled light 1920 results from the OC leaking some of the energy trapped within the cavity gain medium 1905. In one example, thin aluminum metal <15 nm is used in the deep ultraviolet or vacuum UV wavelength region, and the transmittance can be precisely tuned by the Al film thickness 1910. The lowest energy standing wave 1925 has a node (peak intensity of the optical field) at the center node 1945 of the cavity. 1The harmonic (standing wave 1930) appears at nodes 1940 and 1950 as shown.

[0536] FIG. 61 shows output wavelengths 1960 and 1965 from a cavity with energy flow 1970. The cavity length 1935 is the same as in FIG. 60. FIG. 61 shows that the cavity length 1935 can support two optical modes forming standing waves 1930 and 1925 of two different wavelengths. FIG. 61 shows the emission or outcoupling of both wavelength modes (standing waves 1930 and 1925) at wavelengths 1965 and 1960, respectively. That is, both modes propagate. The optical gain medium 1905 substantially fills the optical cavity length 1935. Only peak optical field intensity nodes 1940, 1945, and 1950 couple into the spatial portion of the gain medium 1905. Thus, in accordance with the present disclosure, it is possible to configure a gain medium within an optical cavity as shown in FIG. 62.

[0537] Figure 62 shows a spatially selective gain medium 1980, which has a contracted length compared to the optical gain medium 1905 of Figures 60-61, and is advantageously positioned within the cavity length 1935 to amplify only mode 1925. That is, optical gain medium 1980 supports outcoupling of wavelength 1960 as the optical mode. Thus, the cavity preferentially provides gain to fundamental mode 1925 at the output energy selected as wavelength 1960.

[0538] Similarly, Figure 63 shows two spatially selective gain media 1990 and 1995 advantageously positioned to amplify only the mode of standing wave 1930. The cavity preferentially provides gain to the mode of standing wave 1930 having the output energy selected as 1965.

[0539] This method, which includes spatially positioning gain regions within an optical cavity, is one exemplary embodiment of the present disclosure. This can be achieved by predetermining functional regions as a function of growth direction during the film formation process described herein. Spacer layers between the gain sections can include a substantially non-absorbing metal oxide composition, or can otherwise provide electron carrier transport functionality and aid in optical cavity tuning design.

[0540] Attention now turns to optical gain medium designs for UV LAS applications using the metal oxide compositions described in this disclosure.

[0541] 64A-64B and 65A-65B disclose a single quantum well (QW) bandgap engineered quantum confinement structure. It should be understood that multiple QWs are possible, such as in a superlattice. The wide bandgap electron barrier cladding layer is made of a metal oxide material composition A. x B y O z The potential well material is selected from C p D q O r The metal cations A, B, C, and D are selected from the compositions described herein, where 0≦x, y, z, p, q, r≦1.

[0542] With certain selection of materials, it is possible to achieve the conduction band offset and valence band offset shown in Figures 64A and 64B. (Al 0.95 B 0.05 )2O3=Al 1.9 Ga 0.1 When A=Al and B=Ga, forming O3, and (Al 0.05 B 0.95 )2O3=Al 0.1 Ga 1.9 The case of C=Al and D=Ga forming O3 is shown. The spatial profiles of the conduction band 2005 and valence band 2010 along the growth direction z are shown using the k=0 representation of the respective Ek curves for each material.

[0543] Figure 64A shows the LQW It shows that a QW with a thickness 2015 = 5 nm generates quantized energy states 2025 and 2035 for allowed electron and hole states in the conduction and valence bands, respectively. The lowest quantized electron state 2020 and the highest quantized valence state 2030 participate in spatial recombination processes to generate photons with energy equal to 2040.

[0544] Similarly, Figure 64B shows L QW It shows that a QW with a thickness of 2050 = 2 nm generates quantized energy states within the potential well of allowed states for electrons and holes in the conduction and valence bands, respectively. The lowest quantized electron state 2055 and the highest quantized valence state 2060 participate in spatial recombination processes to generate photons with energy equal to 2065.

[0545] Further reduction in the QW thickness leads to the spatial band structures of Figures 65A and 65B. QW It shows that a QW with a thickness 2070 = 1.5 nm generates quantized energy states within the potential well of allowed states for electrons and holes in the conduction band 2005 and valence band 2010, respectively. The lowest quantized electronic state 2075 and the highest quantized valence state 2080 participate in a spatial recombination process to generate a photon with energy equal to 2085.

[0546] Figure 65B shows the L QW This shows that a QW with a thickness 2090 = 1.0 nm generates quantized energy states within the potential well of allowed states for electrons and holes in the conduction and valence bands, respectively. The QW can support only a single quantized electronic state 2095, which participates in the highest quantized valence state 2100 in a spatial recombination process that generates a photon of energy equal to 2105.

[0547] Spontaneous light emission due to spatial recombination of quantized electron and hole states in the QW structures of Figures 64A, 64B, 65A and 65B is shown in Figure 66. The annihilation of electron-hole pairs is called L QW For = 5.0, 2.5, 2.0, 1.5, and 1 nm, the energy photons are generated with wavelengths peaking at 2115, 2120, 2125, 2130, and 2135, respectively. It is clear from the emission spectrum at 2110 that the same barrier and well compositions are used but the L QW The excellent tunability of the operating wavelength possible in the gain medium by controlling

[0548] Having fully explained the utility of constructing metal oxide compositions for direct application to UVLAS gain media, reference is now made to Figures 67A and 67B, which describe the electronic construction of the gain media in more detail. Figure 67A again shows QWs constructed using metal oxide layers to form the example QW structure described above.

[0549] The QW thickness 2160 is adjusted to achieve recombination energy 2145. The k=0 representation of the QW in Figure 67A shows the non-zero crystal wave vector dispersions of the quantized energy states 2165 and 2180 of the electron (conduction band 2190) and hole (valence band 2205) states. For completeness, the bulk Ek dispersion of the substrate is also shown as 2170 and 2175 at k=0, and 2185 and 2200 for non-zero k. The schematic Ek diagram is important for explaining the population inversion mechanism that creates excess electrons and holes in the conduction and valence bands necessary to provide optical gain.

[0550] The band structure shown in Figure 68A describes the electronic energy configuration states when the conduction band quasi-Fermi energy level 2230 is positioned above the electron quantized energy state 2235. Similarly, the valence band quasi-Fermi energy is selected to create excess hole density 2225 through valence band level 2245. The Ek curve for the conduction band 2195 shows that electronic state 2220 is filled with electrons, where non-zero crystal momentum states |k|>0 are possible. Valence band level 2240 is the valence band edge of the bulk material used in the narrow bandgap region of the MQW. When narrow bandgap materials are confined in an MQW, energy states are quantized, resulting in a dispersion of the band structures of the conduction band 2195 and the valence band 2205. Valence band level 2240 is the valence band maximum of the MQW region. Valence band level 2245 represents the Fermi energy level of the valence band when configured as a p-type material. This fills the region of excess hole density 2225 with holes that can participate in optical gain.

[0551] The optical recombination process can occur at a "vertical transition" where the change in crystal momentum between the electron and hole states is also zero. The allowed vertical transitions are shown as 2215 for k=0 and 2210 for k≠0. The calculation of the integrated gain spectrum for the representative band structure of Figure 68A is shown in Figure 68. The specific input parameters for the gain spectrum are L QW = 2 nm, electron-to-hole concentration ratio 1.0, carrier relaxation time τ = 1 ns, and operating temperature T = 300 K. Curves 2275 to 2280 are Ne ≦5×10 24 m -3 is the electron concentration N e indicates an increase in

[0552] The net positive gain 2250 is the threshold N e Approximately 4x10 24 m -3These parameters are on the order of those achievable by other technologically mature semiconductors such as GaAs and GaN. In some embodiments, metal oxide semiconductors also have an inherently high bandgap, making them less susceptible to gain degradation with operating temperature. This is evidenced by conventional optically pumped high-power solid-state Ti-doped Al2O3 laser crystals.

[0553] Figure 68B shows N e 22 shows the net gain 2265 and net absorption 2270 as a function of . The range of crystal wave vectors that can contribute to the vertical transition determines the width of the net gain region 2250, which is essentially determined by the excess electron 2220 and hole 2225 states that are achievable by manipulating the quasi-Fermi energy.

[0554] Region 2255 is below the fundamental bandgap of the host QW and is therefore non-absorbing. Optical modulators using metal-oxide-semiconductor QWs are therefore possible. Of note is the point of induced transparency 2260, where the QW achieves zero loss.

[0555] Manipulating the quasi-Fermi energy is not the only method available for creating excess electron-hole pairs near the zone center band structure that enables light emission. Consider Figures 69A and 69B, which show the E band structures for a direct band gap material (Figure 69A) and a pseudo-direct band gap material, e.g., a metal oxide SL with a periodicity selected to create a valence maximum as shown in curve 2241 with hole states 2246 in Figure 69B.

[0556] Assuming similar conduction band dispersion 2195, a configuration can be achieved in which the same vertical transition is possible for both valence band types 2205 and 2241. Gain spectra substantially similar to those disclosed in Figure 68B are possible for both types shown in Figures 69A and 69B.

[0557] Ad...

Claims

1. 1. A semiconductor device comprising a semiconductor structure comprising an epitaxial oxide heterostructure, A substrate; (Ni ｘ１ Mg ｙ１ Zn １－ｘ１－ｙ１ ) (Al ｑ１ Ga １－ｑ１ ) ２ O ４ a first epitaxial oxide layer comprising: (Ni ｘ２ Mg ｙ２ Zn １－ｘ２－ｙ２ ) (Al ｑ２ Ga １－ｑ２ ) ２ O ４ and a second epitaxial oxide layer comprising: At least one condition selected from x1≠x2, y1≠y2, and q1≠q2 is satisfied; The semiconductor device comprises: Light emitting diodes (LEDs) that emit light at wavelengths between 150 nm and 280 nm; a laser emitting light at a wavelength between 150 nm and 280 nm; a radio frequency (RF) switch; or A semiconductor device that is a high electron mobility transistor (HEMT).

2. The substrate is made of MgO, LiF, or MgAl ２ O ４ The semiconductor device of claim 1 , comprising:

3. The first epitaxial oxide layer is MgAl ２ O ４ The semiconductor device of claim 1 , comprising:

4. The second epitaxial oxide layer is NiAl ２ O ４ The semiconductor device of claim 1 , comprising:

5. The first epitaxial oxide layer is ｙ１ Zn １－ｙ１ ) Al ２ O ４ and the second epitaxial oxide layer comprises (Ni ｘ１ Zn １－ｘ１ ) Al ２ O ４ The semiconductor device of claim 1 , comprising:

6. The semiconductor device of claim 1 , wherein at least one of the first and second epitaxial oxide layers has cubic symmetry.

7. The semiconductor device of claim 1 , wherein at least one of the first and second epitaxial oxide layers is strained.

8. 10. The semiconductor device of claim 1, wherein at least one of the first and second epitaxial oxide layers is doped n-type or p-type.

9. 10. The semiconductor device of claim 1, wherein the first and second epitaxial oxide layers are layers of a unit cell of a superlattice.

10. 2. The semiconductor device of claim 1, wherein the first and second epitaxial oxide layers are layers of the chirp layer that include alternating layers whose layer thickness varies across the chirp layer.

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