Non-coalesced island hole injection structure for ultraviolet light-emitting diodes
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- RGT UNIV OF CALIFORNIA
- Filing Date
- 2026-02-02
- Publication Date
- 2026-08-06
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Figure US2026013459_06082026_PF_FP_ABST
Abstract
Description
[0001] NON-COALESCED ISLAND HOLE INJECTION STRUCTURE FOR ULTRAVIOLET LIGHT-EMITTING DIODES
[0002] CROSS REFERENCE TO RELATED APPLICATION
[0003] This application claims the benefit under 35 U.S.C. Section 119(e) of the following co-pending and commonly-assigned application:
[0004] U.S. Provisional Patent Application Serial No. 63 / 752,109, filed on January 31, 2025. by Michael Wang, Wenting Gong. Shuji Nakamura and James S. Speck, entitled “NON-COALESCED ISLAND HOLE INJECTION STRUCTURE FOR ULTRAVIOLET LIGHT-EMITTING DIODES,” docket number G&C 30794.0866USP1 (UC-2025-371-1);
[0005] which application is incorporated by reference herein.
[0006] BACKGROUND OF THE INVENTION
[0007] 1. Field of the Invention.
[0008] This invention relates to a novel design for ultraviolet (UV) or far-UV lightemitting diodes (LEDs) that are partially or fully transparent. In these devices, the semiconductor layer structures include a novel non-coalesced island hole injection structure which improves the performance and light extraction of the devices.
[0009] Therefore, these devices are superior to the prior art which does not make use of these hole injection structures.
[0010] 2. Description of Related Art
[0011] There is a strong desire for efficient UV LED devices. Wavelengths below 300 nm are universally germicidal so that UV disinfection is considered one of the most promising means to fight pandemic disease outbreaks, improve hygiene of water supplies and medical settings, and improve protocols for disinfection of air and surfaces. Other applications of ultraviolet light include short-range optical communication, 3D printing, epoxy curing, therapeutic uses, and many others.The current state of the art in UV LEDs remains about a factor of five less energy-efficient, and a factor of 10-100 more expensive (in per Watt terms) than Hg-vapor lamp sources. On the other hand, solid-state semiconductor LED based UV light sources are expected to provide many benefits including miniaturization, rapid on / off and dimming for smart functionality, wavelength tunability, durability, and low power consumption. In the future, it is anticipated that UV LEDs will achieve similar efficiency and cost to their blue and white LED counterparts (which vastly outperform all other visible light-emitting technologies), and the market for UV LEDs will grow rapidly. In order to achieve increased market share and improved global health outcomes, novel technologies for efficient UV LEDs are needed.
[0012] Ill-nitride semiconductors are often used for UV LEDs. As used herein, the term “Ill-nitride,” “Group-Ill nitride,” or “nitride,” refers to any alloy composition of the (Al, Ga, In, B, Sc, Y)N semiconductors having the formula ScjYmGanAlxlnyBzN where 0<j<l, 0<m<l, 0<n<l, 0<x<l, 0<y<l, 0<z<l, and j+m+n+x+y+z=l.
[0013] The usefulness of gallium nitride (GaN), aluminum nitride (AIN) and their ternary and quaternary compounds incorporating aluminum and indium (AlGaN, InGaN. AlInGaN), has been well established for the fabrication of visible and ultraviolet optoelectronic devices and high-power electronic devices. These devices are typically grown epitaxially using metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), or other methods.
[0014] The development of AlGaN for short wavelength devices in the ultraviolet spectrum between 190 nm to 380 nm enabled Ill-nitride based light-emitting diodes (LEDs) and laser diodes (LDs) to overtake many other research ventures.
[0015] Consequently, UV LEDs have begun to overtake conventional Hg vapor lamps as the dominant light source for disinfection in some applications such as portable consumer devices and point-of-use w ater disinfection. The expected market for ultraviolet disinfection products is expected to grow significantly in the coming years, but previous UV LED technologies are not yet efficient or inexpensive enough tocompete with Hg-based lamps. Technological advances in UV LED efficiency and output power are needed to address worldwide water insecurity, improve health outcomes in developing and developed nations alike, and to address the rapidly growing consumer, enterprise, and public demand for disinfection products. Other novel applications, such as nanolithography, curing, dermatological therapeutics, and many others are also expected to benefit from improved UV LED performance. Finally, far UV-C light (<225 nm) has been shown to not be carcinogenic or cataractogenic while still being strongly absorbed by DNA and RNA. creating a plethora of novel disinfection applications for AlGaN-based devices.
[0016] LEDs typically include at least one n-type region, p-type region, and active region. The active region further comprises light-emitting regions (quantum wells) and confinement structures (quantum barriers, spacers, carrier blocking layers, and other structures). Each of these semiconductor layers is in pnnciple capable of emitting light, but highly efficient LED operation results when the vast majority of the light is emitted in the quantum wells, so these will be referred to as the light-emitting regions herein. Light emission from the other structures such as doped layers or confinement structures can in some cases be measurable but is usually considered detrimental to LED efficiency as the recombination in these regions is parasitic on the preferred recombination pathway taking place in the quantum wells.
[0017] The external quantum efficiency (EQE) or total efficiency (ty.) of LEDs is defined as the total rate of photon emission from the device divided by the rate of injection of electrical earners into the device, and can be expressed by the following equation:
[0018]
[0019] where the light extraction efficiency, ityv, is defined as the fraction of photons emitted out of the packaged device to those produced within the semiconductor layers, the injection efficiency, rjinj, is defined as the fraction of electron-hole pairsrecombining in the active region as opposed to recombining elsewhere in the device, and the radiative efficiency, rjrad (also known as internal quantum efficiency or IQE), is defined as the fraction of electron-hole pairs recombining in the active region of the device which recombine radiatively, as opposed to non-radiatively.
[0020] UV LEDs can be improved in two major ways: improving the radiative efficiency by improving the light-emitting region and carrier injection or improving the light extraction efficiency by decreasing the optical absorbance of all layers. Due to the difficulties in the growth of highly p-type doped AlGaN material, and the high ionization energy of Mg dopants in p-type AlGaN, prior UV LED technology has always incorporated a layer of p-type GaN on top of the p-type AlGaN layer, to supply holes to the device. However, this p-type GaN layer is optically absorbing to ultraviolet wavelengths, and thus highly detrimental to light extraction from these devices.
[0021] The present invention addresses this issue by the use of a hole injection structure that is an island layer that is not fully coalesced and does not fully cover the rest of the device, allowing for the injection of enough holes for the device to function efficiently while allowing light extraction through regions where the islands of the hole injection structure are not present.
[0022] SUMMARY OF THE INVENTION
[0023] The objective of this invention is to enhance the light output power of III-nitride light-emitting devices, such as LEDs, and especially UV LEDs, by improving the light extraction of the device. Improving the light extraction efficiency leads to an improvement in the energy' efficiency of the Ill-nitride light-emitting semiconductor, enabling the expansion of Ill-nitride semiconductor device applications into various commercial products.
[0024] In the prior art, conventional UV LEDs comprise many semiconductor layers deposited epitaxially on or above a substrate. These layers may include at least: an n-type material, an active region comprising quantum barriers and wells, an electronblocking layer, and a p-type material. These layers are typically grown by MOCVD or some other epitaxial method in an n-down configuration, meaning that the n-lypc layers are deposited first, and the active region and p-type layers are afterwards deposited on or above the n-type layers. This disclosure will assume such an n-down configuration unless otherwise specified, such that terms such as ‘'below” could be understood to mean “to the n-side of’, and “above” can be understood to mean “on the p-side of’, in some contexts.
[0025] The present invention introduces an entirely novel feature into the epitaxial layer structure device: a non-coalesced island hole injection structure. Specifically, a device fabricated according to the present invention includes a Ill-nitride semiconductor structure comprising one or more Ill-nitride semiconductor layers containing at least one high aluminum (Al) composition layer with an Al composition greater than 40%, including: an active region having a single or multiple quantum well structure emitting at ultraviolet (UV) wavelengths between 190 to 380 nm, positioned between an n-type region and a p-type region; and a non-coalesced island hole injection structure comprising non-coalesced islands of III -nitride material adjacent to the p-type region, wherein the Al composition of the non-coalesced island hole injection structure is less than the Al composition of the p-type region, and the non-coalesced island hole injection structure does not fully cover the p-type region. These features drastically improve device output power, efficiency, and uniformity across the growth wafer.
[0026] The Ill-nitride “films,” “layers,”, or “structures,” discussed in this disclosure may individually or commonly comprise multiple layers or islands having varying or graded compositions, a heterostructure comprising layers of dissimilar (Al, Ga, In, B, Sc, Y)N composition, or one or more layers of dissimilar (Al, Ga, In, B, Sc, Y)N composition. It is to be understood that films referred to as AlGaN films are referred to in such a way for simplicity, with the implicit understanding that the real device may include some In, B, Sc, Y, or any other element without departing from the scope of the present embodiment. For example, a variation of the present inventionincluding nitride structures with AlGalnN or AlGaBN is understood to be within the scope of this disclosure.
[0027] The structures disclosed herein may comprise unintentionally doped or intentionally doped structures, with elements such as iron, magnesium, silicon, germanium, oxygen, carbon, and / or zinc, even if not specified directly. The noncoalesced island hole injection structure may be formed by methods including but not limited to MOCVD, HVPE or MBE.
[0028] The structures may further comprise the Ill-nitride layers grown in any crystallographic nitride direction, such as on a conventional c-plane oriented nitride semiconductor crystal, or on a nonpolar plane such as a-plane or m-plane, or on any semipolar plane. In addition, the LED device where the hole injection structure is grown on may be grown in any crystallographic nitride direction, such as on a conventional c-plane oriented nitride semiconductor crystal, or on a nonpolar plane such as a-plane or m-plane, or on any semipolar plane.
[0029] A first nitride semiconductor device of the present invention comprises a UV LED incorporating the non-coalesced island hole injection structure. The noncoalesced island hole injection structure can be located on any part of the device but is preferably adjacent to a p-type layer containing ALGai-xN, where the Al composition of the hole injection structure is less than the Al composition of the region or layer it is adjacent to.
[0030] The non-coalesced island hole injection structure comprises AlxGayIrizN where x+y+z=l and x<l, y<l, z<l. More preferably, the non-coalesced island hole injection structure should comprise ALGai-xN or InxGai-xN where x<l, and more preferably where x<0.2.
[0031] The p-type region adjacent the non-coalesced island hole injection structure should comprise AlxGai-xN where x>0.2. Additionally, the p-type region adjacent to the non-coalesced island hole injection structure may be a p-type doped IIT-nitride AlxGayInzN superlattice where x+y+z=l and x<l, y<l, z<l, and may have p-type doping that is optionally enhanced by polarization doping, for example, an AlxGai-xN / AlyGai-yN superlattice, with a period less than 8 nm, and compositions of 0.1<x< 0.5 and 0.5<y<l, or a polarization doped AlxGai-xN layer where 0<x<l. In the case of a p-type doped superlattice, the dopant is preferably Mg, but can be Be or other elements. In the case of a polarization doped AlxGai-xN layer, the layer can be doped with Mg, Be, or other elements, as well as undoped. The term “undoped” represents the status of not being doped intentionally, including where an impurity diffuses from adjacent nitride semiconductor layers. The impurity concentration due to such a diffused impurity often has a gradient concentration in the layers.
[0032] Further, in the first nitride semiconductor device of the present invention, the non-coalesced island hole injection structure can be formed from the spontaneous formation of island structures during the epitaxial deposition of nitride material on the surface adjacent to it, or from deposition of material onto a lithographically patterned surface where the regions of desired deposition are exposed, and the other regions covered with a different material.
[0033] In the case where the non-coalesced island hole injection structure is formed through MOCVD, preferably at a temperature between 600 °C and 1400 °C and a V / III ratio between 1 and 500, and more preferably at a temperature between 800 °C and 1100 °C, with a V / III ratio between 1 and 100, and the precursor gases should preferably be ammonia, triethylgallium or trimethylgallium, and optionally cyclopentadienyl magnesium, and optionally with a flow of trimethylindium as a surfactant. The non-coalesced island hole injection structure may or may not comprise a small amount of indium.
[0034] Further, in the first nitride semiconductor device of the present invention, the non-coalesced island hole injection structure may be doped with an impurity, such as Mg, Be, or other element, at a concentration between IxlO17cm'3to IxlO21cm'3, and preferably the hole injection structure is doped with magnesium at a concentration between 5xl018cm'3to 5xlO20cm'3.
[0035] Further, in the first nitride semiconductor device of the present invention, the non-coalesced island hole injection structure may comprise islands of any shape,including cylindrical, hexagonal, hillock, circular, or other irregular shape. These islands can have a height between 1 nm and 300 nm, and a width between 1 nm and 10 pm, including a first embodiment having a height between 1 nm and 70 nm and a width between 20 nm and 3000 pm, and a second embodiment having a height between 1 nm and 60 nm and a width between 20 nm and 2000 pm.
[0036] Further, in the first nitride semiconductor device of the present invention, the non-coalesced island hole injection structure may be additionally patterned or shaped after its initial formation to enhance light extraction. The shaping can be achieved through physical and / or chemical processes and may comprise various shapes or sizes.
[0037] For example, the non-coalesced island hole injection structure may be formed from a regrowth of Ill-nitride material after deposition of a masking material that exposes a surface area of an adjacent layer, and the masking material comprises AIN, AI2O3, SiCh, Ga2Os, or AIN.
[0038] Further, in the first nitride semiconductor device of the present invention, the non-coalesced island hole injection structure comprises islands that cover less than 50% of a surface area of an adjacent layer, including embodiments wherein the noncoalesced island hole injection structure comprises islands that cover less than 25% of a surface area of an adjacent layer.
[0039] Further, in the first nitride semiconductor device of the present invention, an in-situ anneal or ex-situ anneal is performed on the Ill-nitride semiconductor structure after grow th of the non-coalesced island hole injection structure at a temperature between 500 °C and 900 °C for a time between 10 seconds and 30 minutes.
[0040] Additionally, a conducting layer may be deposited on or above the Ill-nitride semiconductor structure, wherein the conducting layer comprises indium (In); Ni, In, Al, Au, and / or other metals; indium tin oxide (ITO); indium zinc oxide (IZO); or gallium oxide.
[0041] The present invention also includes devices other than LEDs and having enhanced properties using the above-described structures.BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Referring now lo the drawings in which like reference numbers represent corresponding parts throughout:
[0043] Fig. 1 is a cross-sectional schematic of the first nitride semiconductor device of the present invention, including a non-coalesced island hole injection structure.
[0044] Fig. 2 is an atomic force microscopy (AFM) image of the morphology' of a typical non-coalesced island hole injection structure.
[0045] Fig. 3 is a graph of external quantum efficiency (EQE) (%) vs. Current (mA) of a UVLED with a non-coalesced island hole injection structure, as compared to a conventional UV LED without with a non-coalesced island hole injection structure.
[0046] DETAILED DESCRIPTION OF THE INVENTION
[0047] In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
[0048] Overview
[0049] The present invention describes ultraviolet nitride-based light-emitting device structures incorporating a non-coalesced island hole injection structure deposited or formed on a substrate preferably through MOCVD. The use of nitride-based noncoalesced island hole injection structures incorporated into ultraviolet light-emitting devices offers a means of improving the nitride light-emitting device performance.
[0050] Nitride light-emitting device structures incorporating a non-coalesced island hole injection structure provide a means of enhancing the performance of nitride UV LEDs by greatly increasing the device output power at a constant current, in comparison with nitride UV LEDs without the non-coalesced island hole injectionstructure. The present invention discloses a UV LED device with a non-coalesced island hole injection structure and discloses a method of fabricating such a structure to achieve enhanced device performance.
[0051] Technical Description
[0052] The prior art in UV LEDs typically comprises a p-type region with a simple layer structure, such as one or more layers of uniform doping and composition, or p-type superlattices. Three-dimensional structures such as a non-coalesced island hole injection structure as described herein have not been applied to the p-side of the device in current state-of-the-art, commercially available, UV LEDs. This invention demonstrates the improved light output characteristics of UV LEDs in which a noncoalesced island hole injection structure has been introduced in the p-type side of the device.
[0053] Embodiment 1
[0054] Fig. 1 is a schematic sectional view showing the structure of a Ill-nitride semiconductor structure comprising a light-emitting diode device (an LED device), and illustrating the process steps of a method for fabricating the structure, according to a first embodiment of the present invention. This LED comprises a sapphire (either flat sapphire, or patterned sapphire) substrate 103, and deposited successively in the following order on the substrate 103: a first buffer layer 104 made of AIN (closest to the substrate 103 surface); a second buffer layer 105 made of ALGai-aN; an n-cladding layer 106 made of AlbGai-bN doped with silicon, germanium or other n-type dopant; an active region 102 comprising a multiple quantum well structure made of ALGai-cN quantum wells 102a and barriers AlaGai-dN 102b; a p-side ALGai-eN electron blocking layer 108 doped with magnesium, beryllium, or other p-type dopant; a p-cladding layer 109 comprising a short period superlattice (SPSL) made of alternating layers of AlfGai-rN / AlgGai-gN doped with magnesium, or a bulk layer made of AlhGai-hN impurity doped with magnesium or undoped, or a polarizationdoped layer made of AkGai iN impurity doped with magnesium or undoped; a noncoalesced hole injection structure 101 comprising AljGaklni-j-kN. In all the above described layers, 0<a,b,c,d,e.f,g,h,i,j,k<l, and each of a, b, c, d, e, f g, h, i, j, k can be different from one another.
[0055] A p-contact layer 110 and n-contact layer 107 are then formed after regions of the epitaxial film are etched to expose the n-cladding layer 106. The p-contact layer 110 and n-contact layer 107 may comprise a reflective mirror contact, where the layer is fabricated from various materials that may include metallic V, Al, Ni, Au, Ag, Pt, Pd, In, or other metals, or indium zinc oxide (IZO), indium tin oxide (ITO), MgF2, SiO2, Ga2Os (n-type or intrinsic), or other compounds. The p-contact layer 110 and n-contact layer 107 may comprise different compositions of above-mentioned compounds and may or may not be annealed during the fabrication process.
[0056] The LED device according to the first embodiment has the active layer 102 of the multi quantum well structure sandwiched between an n-type region including the first buffer layer 104, the second buffer layer 105, the n-contact or n-cladding layer 106, and a p-type region including the p-side electron blocking layer 108, the p-type cladding layer 109. and the non-coalesced island hole injection structure 101.
[0057] Additionally, even though the non-coalesced island hole injection structure 101 is formed in direct contact with the p-cladding layer 109 in the illustrated embodiment, another nitride layer may intervene therebetween. Further, all layers other than the non-coalesced island hole-injection layer 101 including the p-cladding layer 109, electron blocking layer 108, multiple quantum well active region 102 including 102a and 102b, n-cladding layer 106, p-contact layer 110, n-contact layer 107, and buffer layers 105 and 104 may vary from the illustrated embodiment significantly, with additional layers in between, on, above, around, or below any of the aforementioned layers.
[0058] In a preferred embodiment, the non-coalesced island hole injection structure 101 comprises AlxGayIni-x-yN doped with magnesium, preferably where x<0.2 and y<0.2, and more preferably where x<0.1 and y<0.05. The precursor gases shouldpreferably be ammonia, triethylgallium or trimethylgallium, and optionally cyclopentadienyl magnesium, with an optional flow of trimethylindium as a surfactant.
[0059] The non-coalesced island hole injection structure 101 preferably is doped to a concentration between 1x1017cm'3to 1x1021cm'3, and more preferably is doped to a concentration between 5x1018cm'3to 5x1020cm'3.
[0060] The non-coalesced island hole injection structure 101 preferably is deposited using MOCVD at a temperature between 600 °C and 1400 °C with a V / III ratio between 1 and 500, and more preferably is deposited using MOCVD at a temperature between 800 °C and 1100 °C with a V / III ratio between 1 and 100.
[0061] The non-coalesced island hole injection structure 101 preferably comprises islands of circular or hillock shape, but may comprise islands of any shape, including cylindrical, hexagonal, and / or irregular shape. The non-coalesced island hole injection structure 101 preferably comprises islands between 1 nm and 300 nm in height and between 1 nm and 10 pm in width, and more preferably islands between 1 nm and 50 nm in height and between 20 nm and 2000 nm in width.
[0062] The non-coalesced island hole injection structure 101 preferably covers less than 50% of a surface of an adjacent layer it is deposited on, and more preferably covers less than 25% of a surface of an adjacent layer it is deposited on.
[0063] The non-coalesced island hole injection structure 101 may be formed from the spontaneous formation of island structures during the epitaxial MOCVD deposition of Ill-nitride material on the surface adjacent to it, or from deposition of material onto a lithographically patterned surface where the regions of desired deposition are exposed, and the other regions covered with a different material that is preferably transparent to UV light.
[0064] The non-coalesced island hole injection structure 101 is preferably annealed in-situ or ex-situ at a temperature between 500 °C and 900 °C for a time between 10 seconds and 30 minutes after the formation of the non-coalesced island hole injection structure.Fig. 2 is an atomic force microscopy (AFM) image of the morphology of a ty pical non-coalesced island hole injection structure fabricated according to a first embodiment of the present invention.
[0065] Advantages and Improvements
[0066] Fig. 3 is a graph of EQE (%) vs. Current (mA) that shows the external quantum efficiency of UV LEDs with a non-coalesced island hole injection structure, as compared to a conventional UV LED without a non-coalesced island hole injection structure. The output power of the LEDs was evaluated by measuring the light output using an integrating sphere. It is clear from Fig. 3 that the use of an optimized noncoalesced island hole injection structure leads to a significant increase in the output power of about 200% at lower currents, and 30-50% at higher currents, as compared to conventional UV-C LED devices without a non-coalesced island hole injection structure.
[0067] Conclusion
[0068] This concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.
Claims
WHAT IS CLAIMED IS:
1. A device, comprising:a IILnitride semiconductor structure comprising one or more Ill-nitride semiconductor layers containing at least one high aluminum (Al) composition layer with an Al composition greater than 40%, including:an active region having a single or multiple quantum well structure emitting at ultraviolet (UV) wavelengths between 190 to 380 nm, positioned between an n-type region and a p-type region; anda non-coalesced island hole injection structure comprising non-coalesced islands of Ill-ni tride material adjacent to the p-type region, wherein an Al composition of the non-coalesced island hole injection structure is less than an Al composition of the p-type region, and the non-coalesced island hole injection structure does not fully cover the p-type region.
2. The device of claim 1, wherein the non-coalesced island hole injection structure comprises AlxGayInzN where x+y+z=l and x<l, y<l, z<l.
3. The device of claim 2, wherein the non-coalesced island hole injection structure comprises AlxGai-xN or InxGai-xN where x<l, and more preferably where x<0.2.
4. The device of claim 1, wherein the non-coalesced island hole injection structure is doped with magnesium at a concentration between IxlO17cm’3to IxlO21cm’3, and preferably the non-coalesced island hole injection structure is doped with magnesium at a concentration between 5xl018cm-3to 5xlO20cm'3.
5. The device of claim 1, wherein the non-coalesced island hole injection structure comprises island of circular, hexagonal, and / or irregular shape having a height between 1 nm and 300 nm and a width between 1 nm and 10 pm, including a first embodiment having a height between 1 nm and 70 nm and a width between 20 nm and3000 m, and a second embodiment having a height between 1 nm and 60 nm and a width between 20 nm and 2000 pm.
6. The device of claim 1, wherein the non-coalesced island hole injection structure is adjacent to a p-type Ill-nitride AlxGayInzN superlattice where x+y+z=l and x<l, y<l, z<l, and the p-type Ill-nitride AlxGayInzN superlattice having p-type doping that is optionally enhanced by polarization doping.
7. The device of claim 1, wherein the non-coalesced island hole injection structure comprises islands that cover less than 50% of a surface area of an adjacent layer, including embodiments wherein the non-coalesced island hole injection structure comprises islands that cover less than 25% of a surface area of an adjacent layer.
8. The device of claim 1, wherein the non-coalesced island hole injection structure is grown using metal organic chemical vapor deposition (MOCVD) at a V / III ratio between 1 and 500, and more preferably at a V / III ratio between 1 and 100, with precursor gases of ammonia and triethylgallium or trimethylgallium.
9. The device of claim 1, wherein the non-coalesced island hole injection structure is grown using MOCVD at a temperature between 600 °C and 1400 °C, and more preferably, at a temperature between 800 °C and 1100 °C.
10. The device of claim 1, wherein an in-situ anneal or ex-situ anneal is performed on the Ill-nitride semiconductor structure after growth of the non-coalesced island hole injection structure at a temperature between 500 °C and 900 °C for a time between 10 seconds and 30 minutes.
11. The device of claim 1, further comprising a conducting layer on or above the Ill-nitride semiconductor structure, wherein the conducting layer comprises indium (In); Ni, In, Al, Au, and / or other metals; indium tin oxide (ITO); indium zinc oxide (IZO); or gallium oxide.
12. The device of claim 1, wherein the non-coalesced island hole injection structure is formed from a regrowth of Ill-nitride material after deposition of a masking material that exposes less than 50% of a surface area of an adjacent layer, including embodiments wherein the non-coalesced island hole injection structure is formed from a regrowth of Ill-nitride material after deposition of the masking material that exposes less than 25% of a surface area of an adjacent layer, and the masking material comprises AIN, AI2O3, SiC>2, Ga2O3, or AIN.
13. The device of claim 12, wherein the non-coalesced island hole injection structure is further shaped after an initial growth of the non-coalesced island hole injection structure, through physical and / or chemical processes.
14. A method, comprising:fabricating a Ill-nitride semiconductor structure comprising one or more III-nitride semiconductor layers containing at least one high aluminum (Al) composition layer with an Al composition greater than 40%, including:an active region having a single or multiple quantum well structure emitting at ultraviolet (UV) wavelengths between 190 to 380 nm, positioned between an n-type region and a p-type region; anda non-coalesced island hole injection structure comprising non-coalesced island of Ill-nitride material adjacent to the p-type region, wherein an Al composition of the noncoalesced island hole injection structure is less than an Al composition of the p-type region, and the non-coalesced island hole injection structure does not fully cover the p-type region.