Low-defect optoelectronic device grown by MBE and other techniques

Abstract

To provide a technique for improving the conversion efficiency of an optoelectronic device grown by MBE, including a long wavelength optoelectronic device, and a method for manufacturing an efficient optoelectronic device.SOLUTION: A method for growing an optoelectronic device by molecular beam epitaxy (MBE) includes providing a substrate in an MBE growth chamber, growing an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer on the substrate, and controlling the growth such that the light emitting layer includes a plurality of In-containing quantum well layers having an In content greater than 20% and a plurality of In-containing barrier layers having an In content greater than 1%, and is free of GaN barriers, and the growing the light emitting layer includes alternating growth of the quantum well layers and the barrier layers, and the quantum well layer has a defect density less than 5×1015 / cm3.SELECTED DRAWING: None

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application 62 / 705,186 filed June 15, 2020, U.S. Provisional Patent Application 62 / 706,961 filed September 21, 2020, U.S. Provisional Patent Application 63 / 198,345 filed October 12, 2020, and U.S. Provisional Patent Application 63 / 200,687 filed March 22, 2021, the disclosures of which are incorporated herein by reference in their entireties.

[0002] Technical Field This document relates generally to optoelectronic devices and techniques for manufacturing optoelectronic devices with low defect counts. [Background technology]

[0003] background Semiconductor optoelectronic devices, such as lasers and light-emitting diodes (LEDs), that convert electrical energy into light energy, are widespread in the modern world and are known for their efficiency in converting electrical energy into light energy. However, some III-nitride optoelectronic devices suffer from poor conversion efficiency. For example, red optoelectronic devices are generally not as efficient as blue or green LEDs. Furthermore, optoelectronic devices grown using some techniques, such as molecular beam epitaxy (MBE), can be relatively inefficient. Summary of the Invention [Problem to be solved by the invention]

[0004] overview The present disclosure describes techniques for improving the conversion efficiency (i.e., efficiency of converting electrical energy into light energy) of optoelectronic devices, including techniques for improving the conversion efficiency of optoelectronic devices grown by MBE, including long wavelength optoelectronic devices. Implementations include optoelectronic devices and / or methods of making optoelectronic devices. Optoelectronic devices are characterized by their structure that results in high efficiency. Implementations include epitaxy reactors and methods of making efficient optoelectronic devices using epitaxy reactors. [Means for solving the problem]

[0005] Reference may be made herein to MBE epitaxy, however the techniques described herein may be applied to other growth techniques including metalorganic chemical vapor deposition (MOCVD), plasma enhanced epitaxy, sputtering, hydride vapor phase epitaxy (HVPE), pulsed layer deposition, and combinations of these various techniques.

[0006] In a general aspect, a method for growing an optoelectronic device by molecular beam epitaxy (MBE) includes providing a substrate in an MBE growth chamber; growing on the substrate an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer; and controlling the growth such that the light emitting layer includes a plurality of In-containing quantum well layers having an In content greater than 20% and a plurality of In-containing barrier layers having an In content greater than 1%, and no GaN barriers; growing the light emitting layer includes growing alternating quantum well layers and barrier layers, and the quantum well layers are at least 5×10 15 / cm 3 The method is performed so as to have a defect density of less than 100 nm.

[0007] Implementations may include one or more of the following features, alone or in any combination with each other.

[0008] For example, the quantum well layer has an optical band gap (E o ), the defect may have E o / 2 with an energy within + / - 300meV.

[0009] In another example, defects can cause Shockley-Read-Hall recombination in the quantum well layer.

[0010] In another example, the defects may include nitrogen vacancies. In another example, the defects may include gallium-nitrogen divacancies.

[0011] In another example, growing the light emitting region can include growing the quantum well layers and the barrier layers at a growth temperature of less than 550°C.

[0012] In another example, growing the light emitting region can include growing quantum well layers and barrier layers at a growth temperature of less than 500°C.

[0013] In another example, growing the light emitting region comprises growing the quantum well layers and the barrier layers at a growth temperature above 550° C. and a nitrogen flux of 1×10 15 atoms / cm 2 10 / second or more.

[0014] In another example, growing the light emitting region can include providing a flux of nitrogen and a flux of a group-III species to the substrate, with a ratio of the nitrogen flux to the flux of the group-III species being at least five.

[0015] In another example, the optoelectronic device may be one of an LED or a laser diode. In another example, growing the light emitting region may include providing nitrogen plasma to the wafer from a plurality of different nitrogen cells with a distance between each nitrogen cell and the wafer of less than 50 cm, and the provided nitrogen plasma may provide at least 1×10 -5 with a beam equivalent pressure of N adatoms exceeding 10 Torr.

[0016] In another example, growing the light emitting region may include providing a nitrogen plasma to the wafer from a plurality of different nitrogen cells, with a distance between each nitrogen cell and the wafer being less than 50 cm, and a flux of nitrogen species on the wafer provided by the nitrogen plasma is greater than or equal to 2×10 15 atoms / cm 2 / sec.

[0017] In another example, the contrast ratio of the nitrogen species flux on the wafer may be less than 0.1. In another example, providing a nitrogen plasma may include providing an N2 flux to provide the plasma and maintaining the plasma at a power that is less than three times the minimum power required to ignite the plasma.

[0018] In another example, the method may further include growing at least one first barrier layer under In-rich conditions, the barrier layer having an In content in the range of 0.1% to 10%, and the method may further include growing at least one quantum well layer directly on the first barrier layer under In-rich conditions, the quantum well layer having an In content in the range of 10% to 50%, and during a transition between the growth of the at least one first barrier layer and the growth of the at least one quantum well layer, In is provided to the wafer and the nitrogen plasma is active.

[0019] In another example, the optoelectronic device may have an internal quantum efficiency of at least 10%. In another example, 5 × 10 -11 A vacuum having a hydrogen partial pressure of less than 1×10 Torr can be created in the reaction chamber and the growth controlled to provide one or more of the quantum well layers with a hydrogen partial pressure of less than 1×10 18 The method includes controlling the growth to have a hydrogen concentration of less than 1 / cubic centimeter.

[0020] In another general aspect, an MBE apparatus for growing an optoelectronic device including an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer is disclosed, the MBE apparatus comprising a reaction chamber, a wafer holder within the reaction chamber configured to hold a wafer in place during growth of the optoelectronic device, and a plurality of group III cells configured to provide group III species to a wafer held by the wafer holder, each group III cell providing group III species to the wafer from a different direction, the MBE apparatus further comprising a plurality of nitrogen plasma cells configured to provide nitrogen plasma to the wafer held by the wafer holder, each nitrogen plasma cell providing nitrogen plasma to the wafer from a different direction and with a distance between an exit of the cell and the wafer less than 50 cm, the plurality of nitrogen plasma cells providing a nitrogen plasma having a density of 2×10 15 atoms / cm 2 3. The method of claim 2, further comprising: generating a nitrogen flux of greater than 1000 rpm over the wafer;

[0021] Implementations may include one or more of the following features, alone or in any combination with each other.

[0022] For example, multiple nitrogen plasma cells can generate 1×10 -5 It may be configured to generate nitrogen adatom pressures in excess of Torr.

[0023] In another example, multiple nitrogen plasma cells can be configured to produce a nitrogen flux contrast ratio on the wafer of less than 0.1.

[0024] In another example, a plurality of nitrogen plasma cells may be configured to provide an N2 flux to provide a nitrogen plasma and sustain the plasma at a power less than three times the minimum power required to ignite the plasma.

[0025] In another example, the multiple group III cells and multiple nitrogen plasma cells may be configured to provide a nitrogen flux and a group III species flux to the wafer with a ratio of nitrogen flux to group III species flux of at least 5.

[0026] In another example, a reaction chamber can have a characteristic height and a characteristic length that is greater than the characteristic height.

[0027] In another embodiment, the apparatus is also operably connected to a reaction chamber and configured to generate 5×10 -11 The reaction chamber may include one or more vacuum pumps configured to create a vacuum in the reaction chamber having a hydrogen partial pressure of less than Torr.

[0028] In another general aspect, an MOCVD apparatus is disclosed for growing an optoelectronic device including an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer, the MOCVD apparatus including a reaction chamber, a wafer holder in the reaction chamber configured to hold a wafer in place during growth of the optoelectronic device, a plurality of group III cells configured to provide an indium-containing organometallic precursor and a gallium-containing organometallic precursor to the wafer held by the wafer holder, and an ammonia cell configured to provide ammonia to the wafer held by the wafer holder, the group III cells and the ammonia cell configured to provide the indium-containing organometallic precursor, the gallium-containing organometallic precursor, and ammonia into the reaction chamber at a rate sufficient to generate a total pressure in the reaction chamber of greater than 2 atmospheres when growing the optoelectronic device.

[0029] Implementations may include one or more of the following features, alone or in any combination with each other.

[0030] For example, the apparatus may also include an exhaust chamber coupled to the reaction chamber and configured to maintain a total pressure within the reaction chamber above a predetermined value.

[0031] In another example, the ammonia cell can be configured to provide ammonia in a liquid phase to the reaction chamber.

[0032] In another general aspect, a method is provided for growing an InGaN optoelectronic device in an MOCVD reaction chamber, the method including an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer, the light emitting layer including an InGaN quantum well layer having an In% of greater than 35%, the method includes controlling a surface temperature of a wafer on which the InGaN optoelectronic device is grown, the surface temperature being at least 750° C. during the growth of the light emitting layer of the optoelectronic device, the method further includes providing an indium-containing organometallic precursor and a gallium-containing organometallic precursor into the reaction chamber and to the wafer when the surface temperature of the wafer is greater than 750° C. during the growth of the light emitting layer of the optoelectronic device, and providing an N-containing species to the wafer when the surface temperature of the wafer is greater than 750° C. during the growth of the light emitting layer of the optoelectronic device at a rate such that a partial pressure of the N-containing species at the surface of the wafer is greater than 1.5 atmospheres, the indium-containing organometallic precursor, the gallium-containing organometallic precursor, and the N-containing species being provided into the reaction chamber at a rate sufficient to generate a total pressure in the reaction chamber greater than 2 atmospheres during the growth of the light emitting layer of the optoelectronic device.

[0033] Implementations may include one or more of the following features, alone or in any combination with each other.

[0034] For example, exhaust of gases through an exhaust chamber coupled to the reaction chamber may be metered to maintain the total pressure within the reaction chamber above a predetermined value greater than 2 atmospheres.

[0035] In another example, providing the N-containing species to the reaction chamber can include providing ammonia to the reaction chamber at a temperature less than 600°C.

[0036] In another example, providing the N-containing species to the reaction chamber can include providing ammonia in a liquid phase to the reaction chamber.

[0037] In another example, providing the N-containing species to the reaction chamber can include providing liquid phase ammonia to the reaction chamber at a temperature less than 200°C.

[0038] In another example, the light-emitting layer can be configured to emit light at wavelengths greater than 600 nm with an internal quantum efficiency greater than 20%.

[0039] In another example, the light emitting layer has a current of 1 A / cm 2 When driven at higher current densities, they can be configured to emit light at wavelengths longer than 600 nm with internal quantum efficiency greater than 20%.

[0040] In another example, the N-containing species may be provided such that the N-containing species forms a boundary layer on the wafer, and the partial pressure of the N-containing species may exceed 1.5 atmospheres at the boundary layer.

[0041] In another example, at least two of the indium-containing precursor, the gallium-containing precursor, and the N-containing species may be provided at separate times during the growth of a light-emitting layer of an optoelectronic device.

[0042] In another example, at least two of an indium-containing precursor, a gallium-containing precursor, and an N-containing species may be provided at separate locations within the chamber.

[0043] In another example, an optoelectronic device may be grown by any of the methods described in claims 28-37.

[0044] The above illustrative summary, as well as other illustrative objects and / or advantages of the present disclosure, and the manner in which they are accomplished, are further described in the following detailed description and its accompanying drawings. [Brief description of the drawings]

[0045] [Figure 1] 1 is a schematic diagram of the semiconductor layer structure (or stack) of a III-nitride LED. The LED includes several semiconductor layers that are epitaxially grown (e.g., by MOCVD, MBE, etc.) on a substrate in the z-direction from the substrate. [Diagram 2] FIG. 1 is a schematic diagram of a system for epitaxially growing LEDs. [Diagram 3]1 is a graph of an exemplary experimental relationship between defect density on the horizontal axis and conversion efficiency on the vertical axis for InGaN LEDs grown by MOCVD. [Figure 4] 1 is a graph showing the relationship between the lower limit of IQE of an LED and the defect density of the LED. [Diagram 5] 1 is a graph showing the relationship between the lower limit of IQE of an LED and the defect density of the LED on a linear scale of IQE. [Figure 6A] 1 is a graph of an exemplary spectrum of light emitted from an LED showing the relationship between brightness from the LED on the vertical axis and the energy of that brightness on the horizontal axis. [Figure 6B] 1 is a graph of an exemplary defect density in an LED on the vertical axis as a function of the energy of photons emitted from the LED on the horizontal axis, as obtained by measurements such as DLOS. [Figure 7] 1 is a graph of experimental data showing the relationship between Ed and Ep. [Figure 8] 1 is a graph of experimental data showing the relationship between growth temperature and InN decomposition rate obtained from experiments. [Figure 9] 1 is a graph of an emission spectrum from a plasma in an MBE growth chamber where the incoming N 2 flow was 7.5 standard cubic centimeters per minute ("sccm") and a plasma power of 350 W was used to generate the plasma. [Figure 10A] 13 is a graph of the emission spectrum from the plasma in the growth chamber for different plasma powers ranging from 175 W to 404 W (for a constant incoming N2 flow of 7.5 sccm). [Figure 10B] 13 is a graph showing values ​​of R for various different combinations of incoming N2 flow rate and plasma power. [Figure 11] 13 is a plot of dots representing LED samples grown at different combinations of incoming N2 flow rate and plasma power. [Figure 12]FIG. 1 is a plot of dots representing LEDs grown with different molecular N2 to atomic N ratios, showing the photoluminescence (PL) intensity emitted from the LEDs when operated at a temperature of 300 K and excited by 8 mW of 325 nm laser excitation. [Figure 13] 1 is a graph showing the measured IQE for five different LED samples as a function of the photocurrent density J generated by the laser in the active region. [Figure 14] 1 is a graph of the PL spectra of these samples having barriers with indium contents of 0.2%, 5%, and 6%, the PL spectrum of each sample being measured at similar excitation powers. [Figure 15] FIG. 1 is a graph of In % in the QW layer of an MBE grown LED as a function of Ga flux onto the wafer in the growth chamber when In flux and plasma conditions are constant; the measured partial pressure of Ga in the growth chamber on the horizontal axis of the graph serves as a proxy for Ga flux onto the wafer surface. [Figure 16] FIG. 1 is a timing diagram of exemplary fluxes of three different species (N, Ga, In) into a growth chamber and onto a wafer as a function of time to enable pulsed growth of a semiconductor epitaxial stack on the wafer. [Figure 17A] 1 is an exemplary epitaxial stack of an LED structure having a light emitting region with 50 nm thick GaN barriers and 2.7 nm thick InGaN QWs grown under standard plasma conditions. [Figure 17B] FIG. 1 is an exemplary epitaxial stack of an LED structure having a light emitting region with 10 nm thick InGaN barriers and 2.7 nm thick InGaN QWs with In%=7% grown in molecular N-rich plasma conditions, with no break between adjacent barrier and QW growth. [Figure 18] 1 is a spectral graph showing the PL spectrum emitted from an LED when operated at a temperature of 300 K and excited by 8 mW of 325 nm laser excitation. [Figure 19A]1 is a graph of carbon content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in an LED device as a function of depth from the surface of the LED device (x-axis). [Figure 19B] 1 is a graph of oxygen content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in an LED device as a function of depth from the surface of the LED device (x-axis). [Figure 19C] 1 is a graph of calcium content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in an LED device as a function of depth from the surface of the LED device (x-axis). [Figure 19D] 1 is a graph of magnesium content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in an LED device as a function of depth from the surface of the LED device (x-axis). [Figure 19E] 1 is a graph of hydrogen content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in an LED device as a function of depth from the surface of the LED device (x-axis). [Figure 20A] 1 is a schematic diagram of an exemplary growth chamber having a generally cylindrical shape with a characteristic lateral dimension L (eg, diameter) and a characteristic height H. [Figure 20B] FIG. 2 is a schematic diagram of an end view of an array of multiple cells providing the same first species and multiple cells providing the same second species. [Figure 21A] 1 is a graph of the contrast function C as a function of D / d using a linear scale. [Figure 21B] 1 is a graph of the contrast function C as a function of D / d using a logarithmic scale. [Figure 22]1 is a spectrograph showing the PL spectra emitted from LEDs grown in an NH3 and H2 rich environment and an environment with little NH3 and H2 background when operated at a temperature of 300 K and excited by 8 mW of 325 nm laser excitation. [Figure 23] FIG. 1 is a schematic diagram of a system for epitaxially growing LEDs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Components in the drawings are not necessarily drawn to scale and may not be in scale relative to each other. Like reference numerals indicate corresponding parts throughout the several views.

[0047] Detailed Description This disclosure describes techniques for fabricating efficient III-nitride optoelectronic devices, such as optoelectronic devices grown by MBE. For convenience, reference will be made herein to LEDs and techniques for fabricating LEDs, but the techniques also apply generally to laser diodes, L The present invention is applicable to optoelectronic devices, including EDs.

[0048] 1 is a schematic diagram of the semiconductor layer structure (or stack) of a III-nitride LED 100. The LED includes several semiconductor layers that are epitaxially grown (e.g., by MOCVD, MBE, etc.) on a substrate 102 in the z-direction from the substrate. For example, the layers may include a light emitting region 103 (also known as an active region) that includes multiple quantum well layers 104 and barrier layers 106. An n-doped waveguide layer 108 and a p-doped waveguide layer 110 may be disposed on either side of the light emitting region. An electron blocking layer 112 may be disposed between the light emitting region 103 and the p-doped waveguide layer 110. An underlayer 114 may be included in the stack between the light emitting region 103 and the n-doped waveguide layer 108.

[0049] Electrons may be supplied to the light emitting region 103 through the n-doped waveguide layer 108, and holes may be supplied to the light emitting region 103 through the p-doped waveguide layer 110. Recombination of electrons and holes in the quantum well layer 104 may result in the generation of light by radiative recombination. The light generated in the light emitting region may be confined by the waveguide layers 108, 110, which have a lower refractive index than the light emitting region, and thus the light is emitted in the y-direction from the light emitting region 103 at the edge of the LED 100.

[0050] The quantum wells 104 and barriers 106 of the light emitting region 103 may contain indium and nitrogen (e.g., InGaN or AlInN or AlInGaN), with different percentages of constituent materials in the wells and barriers. In one implementation, the InGaN barriers may contain about 2% indium (i.e., In%=2%) and the InGaN wells may contain about 30% indium (i.e., In%=30%). More complex epitaxial structures are also possible. For example, the barrier layers may include more complex multi-layer barriers, whose composition varies within the barrier layers. In one implementation, the barrier layers may include AlInN layers or other layers configured to modify the strain of the crystal structure of the stack. In some cases, the barrier layers may compensate for the compressive strain caused by the In-containing light emitting layer, because the strain affects the incorporation of defects into the stack, and therefore the composition of the barrier layers may be selected to reduce the defect density.

[0051] Various light emitting region 103 structures may, for example, include quantum wells of various thicknesses (e.g., in the range of 1-10 nm) and numbers (e.g., in the range of 1-20), have double heterostructures (e.g., having thicknesses in the range of 10-100 nm), and have layers with various compositions (e.g., having step or graded profiles). Additionally, the barrier layers and / or light emitting layers may have different In contents than those specifically provided as examples herein.

[0052] For clarity, In% values ​​used herein to describe the composition of a layer are average percentages for the composition across the entire layer. For example, InGaN underlayer 114 may be formed as an InGaN / InGaN superlattice, and values ​​of In>2% refer to the composition averaged across the superlattice layer. The percentages relate to the relative composition of group III elements (e.g., Al, Ga, In) in a layer. For example, InGaN with In%=10% is In 0.1 Ga 0.9 Equivalent to N.

[0053] 2 is a schematic diagram of a system 200 for epitaxially growing LEDs. The system 200 includes a vacuum chamber 202 (also known as a growth chamber) and one or more wafers w1, w2, w3 that provide substrates on which semiconductor layers are grown. The system 200 may include one or more wafer holders 201 configured to hold the wafers in place during epitaxial growth. Cells c1, c2, c3, c4, c5 are deposited, e.g., via MBE, on the wafers w1, w2, w3 and / or on layers previously grown on the wafers to produce the materials (e.g., gallium, indium, aluminum, gallium arsenide ... Cells c1, c2, c3, c4, c5 may include valves to control the flow of materials from the cells to the vacuum chamber 202 and may include shutters to block the flow of all materials from the cells to the vacuum chamber 202.

[0054] The system 200 may include one or more vacuum pumps 222 operably connected to the vacuum chamber 202 and configured to maintain a low pressure vacuum within the chamber 202. The vacuum pumps 222 may include, for example, turbo pumps, cryogenic pumps, ion getter pumps, titanium sublimation pumps, etc. The system 200 may include one or more pressure sensors 220 configured to measure a pressure within the vacuum chamber 202, which may be used to determine a flux of material from one or more cells c1, c2, c3, c4, c5 to be deposited on the wafers w1, w2, w3. The system 200 may include one or more heaters 223 configured to heat the wafers w1, w2, w3 to a predetermined temperature and one or more temperature sensors 224 for determining a temperature of the wafers w1, w2, w3 on which the semiconductor stack is grown. The system 200 may include one or more AC (e.g., radio frequency) or DC high voltage sources 226 electrically connected to one or more electrodes 228a, 228b configured to generate plasma of material emitted from one or more of the cells c1, c2, c3, c4, c5 in the vacuum chamber 202. The electrodes 228a, 228b for generating the plasma may be located within the cells c1, c2, c3, c4, c5 in the chamber 202 and / or external to the cells c1, c2, c3, c4, c5. The system may include a controller 230 including a memory that stores machine-executable instructions and a processor configured to execute the stored instructions, the execution of the instructions causing the controller 230 to control the operation of one or more other elements of the system 200. For example, the controller 230 may control the flow rate of material from the cells c1, c2, c3, c4, c5 to the wafers w1, w2, w3, control the temperature of 224, control the power applied to the electrodes to generate plasma of the material, etc.

[0055] As described herein, by using appropriate control of the parameters when epitaxially growing LEDs by MBE (e.g., control of the flux of a particular material from the cell onto the wafer, control of the relative amounts of different materials provided to the wafer, control of the parameters of the plasma in the vacuum chamber, control of the temperature of the epitaxial growth, control of the geometry of the MBE system, control of the timing of the flux of the different materials used to create the different layers), LEDs with excellent efficiency can be grown.

[0056] Conventionally, MBE growth of LEDs has been known to result in LEDs with relatively low efficiency, e.g., having a wall plug efficiency (WPE) of up to a few percent (WPE is a measure of the efficiency with which an LED converts electrical power into light output). WPE can be expressed as the ratio of the radiant flux from the LED (i.e., the total radiometric light output of the LED measured in watts) to the power input to the LED to drive the light output (also measured in watts). In contrast, the techniques described herein can provide MBE-grown LEDs with significantly higher WPEs (e.g., greater than 30%, 40%, 50%, 60%, 70%).

[0057] Inefficiencies in LEDs can be attributed to certain classes of defects in the semiconductor structure of the LED, and techniques are described herein for fabricating LED structures with lower defect densities and therefore higher efficiencies. Defects can suppress efficiency by a variety of mechanisms, such as by causing non-radiative Shockley-Read-Hall recombination, causing trap-assisted tunneling, and inducing defect-assisted droop (including defect-assisted Auger recombination).

[0058] The defect may be characterized by its energy, measured, for example, by deep level optical spectroscopy (DLOS). The defect may have an energy that is approximately in the middle of the gap of the light emitting layer of an LED, for example a blue light emitting LED containing about 13% indium ([In]=13%). For photonic indium gallium nitride (InGaN) quantum wells (QWs), the DLOS energy may be about 1.6 eV.

[0059] The defects may further be characterized by a defect concentration that varies across the light emitting InGaN layer, which may occur because defects are efficiently incorporated during InGaN growth, thus reducing the available defect density as growth progresses. In some implementations, the InGaN layer may have a defect density that follows an exponential profile that decreases along the growth direction. The exponential profile may be characterized by a decay length between 1 nm and 100 nm.

[0060] The defects may also be characterized by their chemical structure. For example, the defects may be associated with intrinsic defects including nitrogen vacancies (VN) and / or gallium vacancies (VGa) in the stack. In particular, the defects may be associated with nitrogen and group III elements (V III -N ) is an example of a divacancy containing gallium-nitrogen divacancy (V Ga-N ) and indium-nitrogen divacancy (V In-N ). The defects may include the divacancy itself, or a defect based on a divacancy (such as an interstitial atom in a divacancy). The interstitial species may include a metal atom. The defects may be complexes that combine a vacancy and an impurity (such as carbon, oxygen, hydrogen, metal, etc.).

[0061] In an LED, multiple defects, which may include, for example, one or more of the above characteristics, may collectively contribute to reduced conversion efficiency in the LED. As described herein, implementations provide improved conversion efficiency in the LED by producing LEDs with reduced defect density.

[0062] In some implementations of the techniques described herein, the defect density may be below a predetermined threshold.

[0063] FIG. 3 is a graph of an exemplary experimental relationship between defect density on the horizontal axis and conversion efficiency on the vertical axis for InGaN LEDs grown by MOCVD. Conversion efficiency is expressed in terms of internal quantum efficiency (IQE), which is the sum of the total number of recombinations, i.e., radiative and non-radiative (R nr ) recombination in the LED relative to the total number of recombinations (R nr ), defined as:

[0064]

number

[0065] The lowest density points in the graph of Figure 3 are obtained by cathodoluminescence, and the remaining points are obtained by DLOS. As can be seen from Figure 3, defects can limit the efficiency of an LED, and similarly, MBE-grown LEDs with similar defect densities can be expected to achieve similar efficiencies.

[0066] In some implementations, the LED has at least one light emitting layer that includes indium and nitrogen (e.g., the light emitting layer can include InGaN or AlInN or AlInGaN). The light emitting layer can be characterized by a total density of defects located around the midgap, which is greater than or equal to 10 per cubic centimeter. 15 Fewer than 5 x 10 defects per cubic centimeter 15 Defects less than 5 x 10 per cubic centimeter 14 Fewer than 10 defects per cubic centimeter 14 The LED may be characterized by a defect density D and an IQE, which may be approximately related by:

[0067]

number

[0068] where D is in cm -3where k parameterizes the defect activity (higher values ​​of k correspond to more active defects). In some implementations, k is between 3×10 -14 cm 3 or 1×10 -14 cm 3 or 3×10 -15 cm 3 or 1×10 -15 cm 3 or 1×10 -16 cm 3 This model represents, for example, the IQE of an LED operating at low to moderate current densities, where the IQE results from a trade-off between radiative and defect-driven recombination.

[0069] FIG. 4 is a graph of the relationship between the lower limit of the IQE of an LED and the defect density of the LED according to equation (2) above for three different values ​​of k, which may characterize the actual defects in the LED. In some implementations, k is at least 1×10 -14 cm 3 and D is 5 × 10 14 cm -3 Figure 5 is a graph of the relationship between the lower limit of LED IQE and the defect density of an LED, showing the same data as Figure 4, but with a linear scale for IQE, showing the defect density required to obtain a desired IQE. Several implementations of epitaxially grown LEDs are characterized by a maximum defect density and a minimum IQE. Table 1 describes such implementations.

[0070] [Table 1]

[0071] For clarity, "near midgap" refers to the band gap E g The defect energy E is essentially equal to half d Thus, in some implementations,

[0072]

number

[0073] where ΔE represents the tolerance in energy. In some implementations, ΔE is 300 The band gap E g can be difficult to evaluate directly, and therefore, in the above formula (3), the optical band gap E o or the peak energy of emission E p The relevant quantities, such as E g may be used as a substitute for

[0074] FIG. 6A is a graph of an exemplary spectrum of light emitted from an LED showing the relationship between the brightness from the LED on the vertical axis and the energy of the brightness on the horizontal axis. The peak energy E p is shown in Figure 6(A). The optical band gap E o can be estimated from the low-energy tail of the LED luminescence spectrum, E o is the horizontal intercept of the tangent to the low-energy tail of the spectrum, as shown in FIG. 6A.

[0075] FIG. 6B is a graph of an exemplary defect density in an LED on the vertical axis as a function of the energy of photons exciting the LED on the horizontal axis, as obtained by measurements such as DLOS. d may be estimated from the onset of the defect energy rise in the relationship shown in FIG. 6B. d can be slightly below the half-band gap point (due to the nature of III-N bonds). Thus, in some implementations, the defect energy is given by the peak energy E p (units are meV),

[0076]

number

[0077] where 370 meV is the approximate expected shift between the midgap and some of the defect levels, and ΔE is the tolerance in energy with the values ​​mentioned above.

[0078] Figure 7 shows the E d and E p 7 is a graph of experimental data showing the relationship between σ and σ, and the slope and intercept of the line in FIG. 7 support the validity of equation (4). The data points plotted in FIG. 7 are obtained by DLOS measurements.

[0079] In addition to DLOS, other techniques may be used to measure defects, including secondary ion mass spectrometry (SIMS), deep level transient spectroscopy (DLTS), positron annihilation, imaging spectroscopy (e.g., cathodoluminescence, scanning near-field optical microscopy (SNOM)). Some of these techniques may be better suited to detecting certain types of defects.

[0080] Some implementations provide low defect density in long wavelength LEDs, for example, with a peak emission wavelength of at least 560 nm (or 580 nm, 590 nm, 600 nm, 610 nm, 620 nm, 630 nm). Currently, conventional long wavelength devices have poor IQE (e.g., only a few percent for red InGaN emitters), which is due to excessive defects in the LED structure. In contrast, implementations fabricated using the techniques described herein have low defect density and a peak IQE of at least 10% (or 20%, 30%, 40%, 50%, 60%, 70%, 80%). Some implementations are characterized by their growth conditions. The growth conditions may be selected to promote a reduction in defect density.

[0081] In some implementations, the growth temperature can affect defect density in MBE grown LEDs. For clarity, as described herein, the growth temperature refers to the surface temperature of the wafer, which may differ from the hardware setpoint temperature by a known offset.

[0082] FIG. 8 is a graph of experimental data showing the relationship between growth temperature and InN decomposition rate (measured in monolayer ("ML") / s) from experiments, where an increase in InN decomposition rate is associated with LEDs. The nitrogen pressure in the growth chamber was 5.5×10 -5 Torr. The nitrogen flux at the growing semiconductor surface is 2.3×10 15 atoms / cm 2 / sec. Thus, growth at low temperatures may limit or inhibit the decomposition of InN and reduce the formation of N-vacancy related defects when growing In-containing layers.

[0083] Thus, in some implementations, LEDs are grown at very low growth temperatures. For example, the light emitting layer may be grown at temperatures below 500° C. (or below 550° C., below 525° C., below 475° C., or below 450° C.). The growth temperature may be low enough that the In-N bonds are stable on a timescale of a few seconds. In some cases, this corresponds to a growth temperature below 500° C. or lower.

[0084] In some implementations, the temperature and N pressure are jointly configured to stabilize In-N bonds. In some implementations, the N adatom pressure is at least 1×10 -5 Torr (or 2×10 -5 Torr, 5×10 -5 Torr, 1×10 -4 Torr, 5×10 -4 Torr) and the temperature is less than 500°C (or 550°C, 525°C, 475°C, 450°C).

[0085] In some implementations, the stacked structure may be annealed after growth. The annealing may lead to crystalline reorganization. The annealing may be performed in vacuum or in an ambient gas (including an ambient gas containing one or more of N2, H2, O2). The annealing temperature may be substantially higher than the growth temperature of the active layer. In some implementations, the annealing temperature may be at least 700°C (or 800°C, 900°C, 1000°C, 1100°C). In some implementations, the annealing temperature is at least 100°C (or 200°C, 300°C) higher than the growth temperature of the active layer.

[0086] In some implementations, the active layer is grown at a higher growth temperature, e.g., at least 550°C (or 575°C, 600°C, 625°C, 650°C, 675°C, 700°C). At such temperatures, In-N bonds may become unstable, which may lead to the formation of N vacancies. To avoid this, implementations may utilize a relatively high nitrogen flux or pressure. For example, the nitrogen flux at the growing semiconductor surface may be greater than 1×10 15 atoms / cm 2 / sec~1×10 16 atoms / cm 2 / sec. In some implementations, the flux can be in the range of 10 15 (or 2×10 15 , 5×10 15 , 1×10 16 , 2×10 16 , 5×10 16 ) atoms / cm 2 / sec.

[0087] A high nitrogen adatom flux may be achieved by various means. In a plasma-assisted MBE reactor, the flux may increase with the flow of N2 precursor gas and / or the power of the plasma. Thus, some implementations use high N2 flow and / or high plasma power. However, since very high plasma power may promote defects in the crystal, in some implementations the plasma power is kept below a certain threshold and a high N2 flow is selected to achieve a desired flux of nitrogen reactive species at the wafer surface. Some implementations use growth parameters that result in a high N flow (to reduce the density of N-related vacancies) without using excessive plasma power (which may promote other defects).

[0088] In a series of experiments, we investigated the effect of nitrogen plasma conditions on the composition of the plasma and the resulting IQE of the LED structure. Two plasma parameters were varied: the flow rate of the incoming N2 gas and the power of the plasma. We then measured the composition of species in the plasma as a function of the variable parameters using optical spectroscopy, i.e., by measuring the optical spectrum emitted by the plasma. The plasma produced two types of species: atomic N (with sharp features in the optical spectrum) and N2 (causing a smooth feature in the optical spectrum) and molecular N3 (causing a smooth feature in the optical spectrum).

[0089] 9 is a graph of an emission spectrum from a plasma in an MBE growth chamber where the incoming N2 flow was 7.5 standard cubic centimeters per minute ("sccm") and 350 W of plasma power was used to generate the plasma (it should be understood that these values ​​may vary substantially depending on the size and dimensions of the MBE growth chamber, the design of the electrical system generating the plasma, etc.). Several sets of relatively sharp and relatively smooth features can be seen in the graph of FIG. 9, with the relative magnitudes of these features indicating the relative presence of N and N2 species in the plasma.

[0090] FIG. 10A is a graph of the emission spectra from the plasma in the growth chamber for different plasma powers ranging from 175 W to 404 W (for a constant incoming N2 flow of 7.5 sccm). Comparison of the different spectra shows that the relative amount of atomic N increases for higher plasma powers. We derived an index R to quantify the relative ratio of molecular to atomic N species in the plasma, namely R=I(661) / (I(821)-I(814)), where I(xxx) denotes the light intensity at a wavelength of xxx nm. In the spectrum shown in FIG. 10(A), the emission peak at 661 nm is characteristic of molecular N2, the emission peak at 821 nm is characteristic of atomic N, and I(814) is used for background subtraction since 814 nm is a wavelength of low emission.

[0091] FIG. 10B is a graph showing values ​​of R for various different combinations of incoming N2 flow rate and plasma power, showing that R increases with increasing N2 flow rate and decreasing plasma power. The spectra in FIG. 10A represent spectra captured with an uncalibrated spectrometer and are therefore expressed in arbitrary units. Nevertheless, the wavelength sensitivity of the silicon detector of the spectrometer is smooth in the wavelength range of interest, and therefore R can be used as a semi-quantitative indicator of the composition of the plasma (e.g., R~10 is the relative abundance of N2 in the plasma). (R~1 indicates a relatively small amount of N2 molecules).

[0092] FIG. 10B shows the value of R for various different combinations of incoming N2 flow and plasma power. For a given N2 flow value, the minimum power P required to ignite the plasma is m where R tends to be highest near the plasma ignition threshold. For example, for a given N2 flow, R is a function of P m and αP m where α is a multiplicative coefficient, for example, equal to 1.1, 1.3, or 1.5, and / or R is a function of P m and P m +Δ, where Δ is equal to, for example, 20W, 50W, or 100W.

[0093] Thus, we have shown that the species composition of the plasma can be controlled, and quantified by R, through control of the incoming N2 flow and plasma power. We also investigated how this species composition of the plasma, quantified by R, affects the IQE of the LEDs by growing a series of LEDs under various conditions.

[0094] Figure 11 is a plot of points representing LED samples grown with different combinations of incoming N2 flow rate and plasma power. Numbers above the points on the plot indicate sample identifiers, with a rectangle around the sample identifier indicating that the sample contained a single quantum well, and sample identifiers without a surrounding rectangle corresponding to samples with multiple quantum wells. As can be seen from Figure 11, if the plasma power is too low, the plasma will not ignite, and high growth rates correspond to high plasma power and high N2 flow.

[0095] FIG. 12 is a plot of dots representing LEDs grown with different molecular N2 to atomic N ratios, operating at a temperature of 300 K and excited by 8 mW of 325 nm laser excitation, and L The photoluminescence (PL) intensity emitted from the ED is plotted as a function of R in FIG. 12. As can be seen from FIG. 12, samples with low R values ​​suffer from low intensity, while samples with intermediate or high R values ​​are brighter and have higher intensity.

[0096] Thus, we show that plasma conditions corresponding to relatively high R values ​​are beneficial for material quality, which may be due to a reduction in the density of defects that are detrimental to IQE. Beneficial plasma conditions may be achieved by utilizing moderate plasma power (i.e., plasma power that is not too high compared to the minimum power required for plasma ignition) for a given N2 flow. Such conditions may be achieved for relatively low or relatively high growth rates by selecting appropriate N2 flows and plasma powers, as shown in FIG. 11. For example, a desired N2 flow may be selected to promote a desired epitaxial growth rate, and then an appropriate value of plasma power that is not too high compared to the ignition power may be selected for that N2 flow rate.

[0097] Such plasma conditions (e.g., P for N flow rate used to grow the light-emitting region) m By growing the light emitting region of the LED by MBE with a plasma power of less than 30% above the value of 100 nm, we grew a sample with InGaN QW layers and InGaN barriers. For this sample, we measured an IQE of about 10% for an emission wavelength of about 430 nm. This sample did not have a GaN layer in direct contact with the QW layer of the LED, and the barrier layers on both sides of the QW layer contained indium. The QWs and barriers were grown without growth interruption at the interface between different adjacent layers. Two Ga cells were placed in the MBE reactor (i.e., growth chamber), and the two cells had different flow rates of Ga into the reactor. One Ga cell was used for the growth of the QWs and another Ga cell was used for the growth of the barriers. This configuration allowed modulation of the In content in the QWs and barrier layers without a gradient in the temperature of the substrate on which the layers were grown, eliminating the need for growth interruptions. For clarity, the growth interruption may be described as a period during which substantial growth of the epitaxial stack does not occur between periods during which substantial growth of the epitaxial stack occurs. The growth interruption may also be described as a step during which conditions are selected to dry the surface from a selected metal species (e.g., Ga).

[0098] FIG. 13 is a graph showing the IQE measured for three different LED samples as a function of the photocurrent density J generated by 405 nm laser radiation provided to the active area of ​​the LED. A / cm on the horizontal axis. 2 The photocurrent density J, expressed in units of equivalent current density, was determined by measuring the laser power density impinging on the LED sample and multiplying it by the absorption coefficient of the LED's emitting area, and the IQE is given by: One sample grown with suitable plasma conditions and an InGaN barrier layer without temporarily interrupting the growth had a peak IQE of about 10%.

[0099] Optoelectronic devices can be grown under suitable plasma conditions to achieve high material quality, e.g., conditions where the plasma power is not too high compared to the minimum ignition power of the selected N2 flow. For example, the plasma power can be less than 1.1 times, or less than 1.3 times, or less than 1.5 times the minimum ignition power. Implementations further include methods for operating an MBE reactor under such conditions, methods for selecting such plasma conditions, and methods for measuring the optical spectrum of the plasma to achieve such conditions, including conditions with a relatively high molecular to atomic ratio.

[0100] To further study the effect of the barriers on LED efficiency, a series of LED structures with 2.7 nm thick InGaN quantum wells sandwiched between 50 nm thick InGaN barriers were fabricated with different structures having barriers with different In% (i.e., 0.2%, 5% and 6%). The layers were grown by MBE, and in each case the transition between the QWs and the barrier did not require a growth interruption because both layers were grown under In-rich conditions.

[0101] Figure 14 is a graph of the PL spectra of these samples with barriers having indium contents of 0.2%, 5%, and 6%, where the PL spectrum of each sample is measured at similar pump power. The PL intensities of all of these samples are substantially similar, regardless of the In concentration in the barrier layer. Thus, improved efficiency of the LED may be achieved by growing the barrier of the LED under appropriate MBE conditions and the barrier / QW transition, regardless of the composition of the resulting barrier.

[0102] Such LED structures including InGaN barrier layers (e.g., with In% of 0.2% or more) differ from conventional LED structures in that conventional structures have GaN barriers (typically grown under Ga-rich conditions) and InGaN QWs (typically grown under In-rich conditions). After the GaN barrier is grown in a conventional structure, Ga atoms may remain on the wafer surface and may need to be flushed away from the surface to allow InGaN growth, a process that may require a growth interruption. Growth interruption may occur, for example, by (1) thermal desorption; or (2) consumption of Ga by exposure to N plasma. Thermal desorption may be appropriate when the substrate temperature exceeds a threshold temperature (e.g., about 700° C. if the metal species is Ga, or 790° C. if the metal species is Al). During thermal desorption, the cell providing the metal atoms to the growth chamber may be closed to prevent additional metal atoms from reaching the chamber, and the N-plasma source may be turned off. The duration of the thermal desorption interruption may depend on the substrate temperature and the amount of accumulated Ga on the surface. For example, for growth at 720°C, the thermal desorption interruption may take several minutes (e.g., 1-3 minutes) if thermal desorption alone is used to sufficiently flush the surface Ga atoms to proceed with the next step in the growth process. In some implementations, the duration of the effective growth interruption may be shortened by flushing the surface Ga atoms through both thermal desorption and exposure of the surface Ga atoms to N plasma. At lower substrate temperatures (e.g., 650°C, which may be appropriate for growing InGaN), thermal desorption may not occur effectively to flush the Ga atoms. At such lower growth temperatures, the surface Ga atoms may be exposed to N plasma to flush the surface Ga atoms and grow GaN in the process. This means keeping the N flux from the cell to the growth chamber open during the duration of the interruption and closing (closing) all metal fluxes from the cell to the growth chamber. In this case, the duration of the interruption may depend on the N plasma growth rate and the amount of excess Ga at the surface. The amount of Ga at the surface may be minimized by setting the Ga flux only slightly above the Ga / N stoichiometry.In some implementations, reflection high-energy electron diffraction (RHEED) measurements may be used to determine the required interruption length, since the metal surface will have a faint diffraction pattern, but upon drying of the surface, high intensity is restored.

[0103] In contrast to these conventional structures, growth interruptions between the QWs and the barriers may be avoided by setting the Ga flux lower than the Ga / N stoichiometry. By itself, setting the Ga flux lower than the Ga / N stoichiometry may result in a degradation of the material quality, and therefore a surfactant, e.g., indium, may be used to maintain a metal-rich surface without the need for interruptions. Thus, for such structures with InGaN barriers, both the barrier and the QWs are grown in In-rich conditions, and therefore there is no need to flush out the Ga atoms before growing the QWs. Such growth conditions may result in a wide range of InGaN compositions in the barriers (e.g., between 0.2% and 6%, as in the aforementioned experiments) (although in some implementations higher or lower In concentrations are acceptable). Some implementations include barriers grown in In-rich conditions, but the resulting In concentration in the grown LEDs is very low (perhaps too low to be detected). Nevertheless, such growth conditions may avoid growth interruptions.

[0104] As mentioned above, the growth interruption may include periods during which no substantial growth occurs between periods during which substantial growth occurs, or may include steps in which conditions are selected to dry the surface from the selected metal species (e.g., Ga). The growth interruption may last at least 60 seconds (or 30 seconds, 10 seconds, 1 second). Depending on the growth conditions, a short growth interruption may be tolerable or detrimental. In some implementations, even an interruption of a few seconds or more may be problematic if it leads to substantial defect generation.

[0105] The light emitting region with QWs and barriers (or more generally, the active region with multiple layers including at least one In-containing QW) can be grown using MBE, where the transition between growing several adjacent layers of the light emitting region is done without growth interruption or with an interlayer pause of less than 0.1 s (or 1 s, 5 s, 10 s, 30 s). In some implementations, the growth conditions are selected such that the Ga flux into the growth chamber and onto the wafer is below Ga / N stoichiometry at the transition between layers. In some implementations, metal species (including In) are always injected into the growth chamber during the transition.

[0106] Some implementations may use a growth interruption, but employ conditions that prevent the formation of defects during the interruption. For example, species may still be implanted in the growth chamber and on the wafer surface during the interruption, but no substantial growth on the wafer occurs. In may be implanted but Ga and N are not, or a different metal species may be deposited. A different gas (such as H, or N2 that does not come from a plasma) may be injected.

[0107] Some implementations utilize several cells to facilitate avoidance of growth interruptions. With multiple Ga cells providing different Ga atom fluxes, the Ga flow may be rapidly modulated without pause, for example, by opening and closing a shutter between the cell and the growth chamber, as demonstrated herein. For example, for higher In concentration in MBE grown LEDs, a lower Ga flow may be used while a constant In flow is used.

[0108] FIG. 15 is a graph of In % in the QW layer of an MBE grown LED as a function of Ga flux onto the wafer in the growth chamber when the In flux and plasma conditions are constant, with the measured partial pressure of Ga in the growth chamber on the horizontal axis of the graph serving as a proxy for Ga flux onto the wafer surface.

[0109] As can be seen from FIG. 15, for constant In flux and plasma conditions, the In composition of the QWs can be controlled by controlling the Ga flux (F_Ga). Each point on the graph of FIG. 15 corresponds to an MBE grown LED. In a first region, or range of F_Ga values ​​below a first threshold, the In% decreases with decreasing F_Ga. In a second region, or range of F_Ga values ​​between the first and second thresholds, there is a plateau of relatively constant In composition for intermediate values ​​of F_Ga. In a third region, for high F_Ga values ​​above the second threshold, the In% decreases with increasing F_Ga. The QWs may be grown in the second region (where the In% is most stable) or the third region (where precise control of the In% may be enabled by controlling the F_Ga). The barriers may be grown in the third region where precise control of the In% is enabled by controlling the F_Ga. In the third region, very low In% may be achieved at higher values ​​of F_Ga, above the second threshold. All these growths remain in the In-rich regime (i.e., when the growth chamber contains an In-rich atmosphere), and therefore no flushing of Ga atoms between layers is required. Some implementations use two In cells to control the In concentration in the various different layers (e.g., QWs and barriers).

[0110] In some implementations, the MBE grown light emitting region may include only a single QW (or other light emitting layer such as a double heterostructure), in which case the techniques described herein may be applied to the transition between the single QW and its adjacent barrier layer.

[0111] Some implementations combine the aforementioned techniques for growing adjacent layers of different material composition (e.g., uninterrupted QWs and barriers) with the aforementioned techniques for controlling plasma conditions to control the proportion of molecular nitrogen in the plasma. For example, in some implementations, the incoming N2 flow and plasma power are selected to provide a high ratio of molecular to atomic N species in the plasma, and the active region is grown without interruption between the growth of different layers in the active region.

[0112] In some implementations, the MBE grown active region includes various layers (e.g., barriers) grown in M-rich conditions, where M is a metal element other than Ga. M may be In (as in the sample above), but other metals may be used, including Al, Sn, Sb, and other suitable metals. M may be a metal that does not significantly incorporate into the crystal structure of the stack, in which case M may serve the purpose of maintaining metal-rich conditions at the surface while avoiding Ga accumulation at the surface. M may be a metal that evaporates at a relatively low temperature, such as Sn. When M is different from In, In may or may not be present during the growth of the barrier layers. In some implementations, the QWs may be grown in In-rich conditions, and at least one barrier adjacent to the QWs (above and / or below) may be grown in M-rich conditions.

[0113] For clarity, as used herein, the terms In-rich / M-rich / Ga-rich correspond to the relative stoichiometry of the metal species. Alternatively, the light emitting region of the LED may be grown under N-rich conditions. In some cases, the flux of N species is highest, followed by the flux of M and / or In, and the flux of Ga is lowest.

[0114] In some implementations, the ratio of nitrogen to group III elements (V / III) is high, corresponding to N-rich conditions. This ratio may be greater than 10 (or 2, 5, 20, 50, 100). When growing In-containing layers, the ratio of indium flux to Ga flux may be high, which may be greater than 2 (or 5, 10, 20, 50, 100).

[0115] At growth temperatures on wafers below 600° C., the flux conditions may be as follows: N_flux>In_flux>Ga_flux. In some implementations, the In-containing layer is grown under conditions satisfying N_flux>In_flux*m and In_flux>Ga_flux*m, where m is a number greater than 2 (or 5, 10).

[0116] At growth temperatures on wafers above 600° C., the flux conditions may be as follows: In_flux>N_flux>Ga_flux. In some implementations, the In-containing layer is grown under conditions satisfying In_flux>N_flux*m and N_flux>Ga_flux*m, where m is a number greater than 2 (or 5, 10).

[0117] Some layers may be grown with a metal M (e.g., Sn, Al, Sb, or other suitable metal) different from Ga and In. The conditions may satisfy N_flux>M_flux*m and M_flux>Ga_flux*m, or the conditions may satisfy M_flux>N_flux*m and N_flux>Ga_flux*m, where m is a number greater than 2 (or 5, 10).

[0118] In some implementations, the light emitting region includes a quantum well and a barrier, and the barrier may be grown at the same growth temperature as the quantum well. In some implementations, the barrier may include a two-stage barrier, where a first portion of the barrier is grown at a first temperature substantially equal to the temperature at which the QW is grown, and a second portion of the barrier is grown at least 50° C. (or 25° C., 75° C., 100° C.) higher than the first temperature. The barrier may comprise InGaN with an In composition of at least 1% (or 2%, 3%, 5%) or with a composition in the range of 0.1%-1% (or 0.1%-5%, or 0.1%-10%, or 0.5%-10%). The barrier may comprise InGaN with an In composition of at least 1% (or 2%, 3%, 5%) or with an In composition in the range of 0.1%-1% (or 0.1%-5%, or 0.1%-10%, or 0.5%-10%). Additional steps may be envisaged (for example the temperature may be varied more than twice during the growth of the layer). Other variations are possible, including temperature gradients.

[0119] In some cases, growth of an In-free GaN layer beneath or within the active region can be detrimental to the efficiency of MBE-grown LEDs due to defects, including vacancies, that can ride on the GaN surface and tend to become incorporated into the overlying In-containing layer.

[0120] Thus, in some implementations, the active region of an MBE-grown LED includes multiple In-containing layers but does not include any GaN layers. This is in contrast to conventional LEDs, where GaN layers are often present as barriers between QW layers or between an InGaN underlayer and the active region. Referring again to FIG. 1, some implementations of MBE-grown LEDs include an In-containing underlayer 114 (e.g., In%>2% and at least 20 nm thick) and an alternating series of InGaN barriers (e.g., In%>1%) and QW layers (e.g., In%>20%). In some implementations, no layers with In%<1% (or 2%) are present between the QW layers. Some implementations include one or more In-containing QW layers, with In%>1% (or 2%, 5%) throughout the QW layers. For multiple quantum well structures, the light-emitting layer may be at least 20 nm thick.

[0121] Some implementations emit light at longer wavelengths. Thus, the light emitting QW layers may be characterized by an In concentration of at least 35% (or 25%, 30%, 40%, 45%, 50%). Once the active region is grown, non-In-containing layers may be present above the active region (e.g., in the EBL and p-doped GaN waveguide layers). In-containing layers may include InGaN, AlInN, and AlInGaN.

[0122] In some implementations, a pulsed / modulated growth scheme may be used in the growth chamber, where the flux of different materials from the cells into the growth chamber and onto the wafer surface is modulated. In some cases, In and Ga are injected into the growth chamber from the cells at different times. In some cases, the N flux is varied over time. In some implementations, a series of alternating steps may be performed, where the first step has a low N flux and a high Ga flux, and the second step has a high N flux and a high In flux. These first and second steps may be repeatedly alternated (e.g., for a period of about a few seconds or tens of seconds). In each step, a partial layer may be formed on the semiconductor stack grown on the wafer, leading to the formation of an InGaN layer after sufficient steps have been performed. In some implementations, a very low N flux onto the wafer in the growth chamber may be achieved by closing a shutter between the N cell and the growth chamber.

[0123] The above N flux differences may also be applied to a process for growing a light emitting region including a GaN layer. In some implementations, the GaN layer is grown with a relatively low N flux and the In-containing layer is grown with a relatively high N flux. The relatively high N flux may be at least 2x (or 3x, 5x, 10x, 15x, 20x, 50x) the relatively low N flux. The N flux may be varied while other growth parameters (such as temperature) are maintained. The N flux may be rapidly varied by activating different N sources (e.g., different N cells) that provide different N fluxes. In some implementations, a first cell may provide a low N flux and a second cell may provide a high N flux. The second cell may be grown with a high N flux for some layers (e.g., The cell may be closed (e.g., by a shutter) during the growth of a layer (e.g., a GaN layer) and opened (e.g., by opening a shutter) during the growth of another layer (e.g., an In-containing layer). This approach may be generalized to more than two cells to provide more than two different N fluxes. In some implementations, this approach of using multiple different cells to provide different N fluxes allows for a significant increase in the N flux on the wafer (e.g., 2x or more, as described above) in a short time (e.g., less than 0.1 s or 1 s or 10 s).

[0124] In some implementations, a first portion of the epitaxial stack may be grown under first plasma conditions, and a second portion of the epitaxial stack, including the active region, may be grown under second plasma conditions. The second plasma conditions may be selected to improve the efficiency of the active region. As disclosed herein, this may correspond to a relatively high molecular-to-atomic N species ratio in the plasma, or a relatively low plasma power and high N flow (i.e., closer to the upper boundary of the plasma ignition diagram shown in FIG. 11). The first plasma conditions may be used to optimize the growth of other portions of the epitaxial stack (e.g., if the plasma conditions used for the active region growth are not optimal for other portions of the epitaxial stack). Properties that may be optimized by the first growth conditions may include growth rate; morphology (such as smooth or step-flow morphology); preferential growth in a particular direction (e.g., preferential growth vertically or along c-planes, along m-planes, along a-planes, along semi-polar planes); and efficient incorporation of dopants (including Si and / or Mg).

[0125] 16 is a timing diagram 1600 of exemplary fluxes of three different species (N, Ga, In) into a growth chamber and onto a wafer as a function of time to enable pulsed growth of a semiconductor epitaxial stack on the wafer. The timing diagram includes three graphs of each of the three exemplary fluxes over time, with the amount of flux for the species shown on the vertical axis of the graph for the species and the time of the flux shown on the horizontal axis. The units of the vertical axis of each graph are arbitrary, and the units of the horizontal axis are arbitrary but the same for each graph.

[0126] As shown in the timing diagram 1600, the N flux varies between high and low values. When the N flux is low, Ga flows, and when the N flux is high, In flows. The duration of each flow step may be short enough to correspond to about one or a few atomic monolayers, or a fraction of a monolayer (e.g., less than 1 ML, less than 0.75 ML, less than 0.5 ML, less than 0.25 ML) deposited on the epitaxial stack. In some implementations, the amount of In flux may vary over the In implantation step rather than occurring at a constant amount, allowing growth of a layer with a composition that varies over the growth step. In the exemplary timing diagram 1600 shown in FIG. 16, the first three In flow steps have a relatively high In flux (e.g., to grow a QW layer) and the last two steps have a relatively low In flux (e.g., to grow a barrier layer). The number of steps to form a layer may be at least 10 (or 2, 5, 20, 50, 100, 500, 1000).

[0127] Impurity incorporation in epitaxial layers grown by MBE can affect the brightness and efficiency of MBE-grown LEDs. To understand these effects, we observed impurities in conventional LED structures with GaN barriers and InGaN QWs grown under standard plasma conditions, and in LED structures with InGaN barriers and QWs grown under molecular N-rich plasma conditions with no interruption between the growth of adjacent barriers and QWs, and compared the optical performance of the different structures.

[0128] FIG. 17A shows a LE with a light emitting region having a 50 nm thick GaN barrier and a 2.7 nm thick InGaN QW (with In % of about 12%) grown under standard plasma conditions. 17 is an exemplary epitaxial stack 1710 of the .D structure. The light emitting region was grown using MBE with an approximately 10 second break between barrier growth and QW growth, and a 100 nm thick layer GaN was grown below the light emitting region at high temperature. An underlying structure with a 2 micrometer thick GaN layer and a free-standing GaN step electron injection (SEI) layer was grown using metalorganic vapor phase epitaxy (MOVPE) followed by the MBE grown layers.

[0129] FIG. 17B is an exemplary epitaxial stack 1750 of an LED structure having a light emitting region with a 10 nm thick InGaN barrier with In%=7% and 2.7 nm thick InGaN QWs with In%=12% grown in molecular N rich plasma conditions, with no break between adjacent barrier and QW growth. MBE was used to grow the light emitting region with no break between barrier growth and QW growth, and also used to grow a 100 nm thick layer GaN below the light emitting region at high temperature. The InGaN barriers at the top and bottom extremes of the light emitting region are 50 nm and 100 nm thick to provide good morphology between the InGaN light emitting region and the surrounding GaN layers, and ensure that the process break between the InGaN and GaN layers occurs relatively far from the QW layers. An underlying structure with a 2 micrometer thick GaN layer and a free-standing GaN step electron injection (SEI) layer was grown using metalorganic vapor phase epitaxy (MOVPE), followed by the MBE grown layers. The light emitting region was grown using MBE, and a 100 nm thick GaN layer was grown below the light emitting region at high temperature. An underlying structure with a 2 micrometer thick GaN layer and a free-standing GaN step electron injection (SEI) layer was grown using MOVPE, followed by the MBE grown layers.

[0130] Figure 18 is a spectrograph showing the PL spectra emitted from these LEDs when operated at a temperature of 300 K and excited by 8 mW of 325 nm laser excitation. The spectra in Figure 18 are labeled by the device (1710 or 1750) associated with the spectrum. From the spectra in Figure 18, it is clear that LEDs with InGaN barriers grown under molecular N-rich plasma conditions and with no break between adjacent barrier and QW growth have much brighter photoluminescence, and therefore a higher IQE, than LEDs with GaN barriers grown under standard plasma conditions with a break between QW and barrier growth.

[0131] The indium content and impurity content of devices 1710, 1750 at different depths from the surface were measured with a mass spectrometer (e.g., a time-of-flight secondary ion mass spectrometer) to determine the amount of various different impurities in the device, for different layers of the device, and to identify how the impurities may affect the optical performance of the device.

[0132] 19A is a graph showing the carbon content (lower trace and left y-axis) and indium content (upper trace and right y-axis) as a function of depth from the surface of the device (x-axis) in LED devices 1710 and 1750. As can be seen in FIG. 19A, the standard LED structure 1710 has a 1×10 16 cm -3 Less than 1×10 15 cm -3 17. The LED device 1750 has a higher baseline level of carbon impurities compared to the LED device 1750, which has a carbon concentration below the detection limit.

[0133] 19B is a graph of oxygen content (lower trace and left y-axis) and indium content (upper trace and right y-axis) as a function of depth from the surface of the device (x-axis) in LED devices 1710 and 1750. As can be seen from FIG. 19B, standard LED structure 1710 has a higher baseline level of oxygen impurity compared to LED device 1750. In addition, an oxygen concentration peak is present in conventional device 1710 at a depth corresponding to the QWs (as can be seen by comparing the In concentration peak with the oxygen concentration peak), which may be caused by a growth interruption between the barrier and the QWs. The improved structure 1750 is 1×10 18 cm -3 Since the carbon concentration is less than 100 nm and no growth interruptions occur between adjacent QWs and the barrier, there are no peaks and the oxygen concentration is relatively constant throughout the light-emitting region.

[0134] FIG. 19C is a graph of calcium content (lower trace and left y-axis) and indium content (upper trace and right y-axis) in LED devices 1710 and 1750 as a function of depth from the surface of the device (x-axis). As can be seen from FIG. 19C, the standard LED structure 1710 appears to have a higher baseline level of calcium, with a Ca peak present at the growth interruption depth. The improved structure has a 3×10 15 cm -3 The calcium concentration is below the detection limit everywhere except near the surface (which is believed to be an artifact).

[0135] 19D is a graph of magnesium content (lower trace and left y-axis) and indium content (upper trace and right y-axis) as a function of depth from the surface of the device (x-axis) in LED devices 1710 and 1750. As can be seen in FIG 19D, the standard LED structure 1710 has a magnesium peak at the depth of the QWs closest to the surface of the device, while the improved structure 1750 shows no such peak and has a magnesium content of approximately 1x10 throughout the entire active region. 17cm -3 has a relatively constant Mg concentration.

[0136] 19E is a graph of hydrogen content (lower trace and left y-axis) and indium content (upper trace and right y-axis) as a function of depth from the surface of the device (x-axis) in LED devices 1710 and 1750. As can be seen from FIG 19E, the standard LED structure 1710 has a higher baseline level of hydrogen than the improved device 1750.

[0137] SIMS measurements presented in Figures 19A, 19B, 19C, 19D, 19E show that plasma conditions affect the incorporation of some impurities into the epitaxial stack of LED devices. It is possible that the plasma generates defects (including N, Ga, In vacancies) in the epitaxial structure and that the plasma conditions may affect this mechanism. Thus, to reduce defect formation, plasmas with lower power and / or lower atomic to molecular N ratios may be selected. Defects generated in the stack may react with impurities present in the reactor to form complexes (e.g., forming vacancy complexes such as VGa-O, VN-O, VGa-C, VN-C, etc.). Thus, examples of realizations of techniques for operating a reactor or growing epitaxial stacks according to the parameters described herein include polymeric N2 plasma conditions, no growth interruptions between the barriers and the QWs, 1x10 18 cm -3 (or 1×10 17 cm -3 , or 1 × 10 16 cm -3 and the presence of low impurities in the reactor chamber to achieve a density of one or a few selected impurities (including C, O, Ca, Mg) in the active region below a predetermined value such as 0.1%.

[0138] In some implementations, epitaxial reactors (including MBE reactors) are provided that implement the techniques described herein and that produce devices produced by such reactors.

[0139] Conventional MBE reactors may suffer from a trade-off between the seed flux and the uniformity of the flux over the wafer on which the LEDs are grown. If the material source (e.g., the MBE cell) is close to the wafer, the flux from the cell to the wafer may be high, but the uniformity of the flux over the surface of the wafer may be poor, because the flux is approximately 1 / r 2 where r is the source-to-wafer distance and r is not constant across the surface of the wafer. Uniformity can be improved by increasing r (e.g., to make the flux nearly constant across the wafer), but r With an increase in the rf, the flux of material onto the wafer simultaneously decreases.

[0140] Implementations may include a reactor configured to provide a relatively high flux of a species (e.g., nitrogen species), the flux being relatively constant across a surface of a wafer having a diameter (or characteristic lateral dimension perpendicular to the source-to-wafer direction) of at least 10 cm (or 5 cm, or 15 cm, or 20 cm), and the species flux may vary by less than + / - 20% (or + / - 10%, or + / - 5%, or + / - 2%, or + / - 1%) from an average value across the wafer surface. In some implementations, uniformity may be obtained across multiple wafers rather than across a single wafer. The average flux at the wafer surface may be at least 1×10 -5 (or at least 1×10 -6 , or at least 5 × 10 -7 , or at least 1 × 10 -7 ) Torr of beam equivalent pressure (BEP).

[0141] To provide a substantially uniform flux of species across the surface of the wafer, the MBE reactor may include multiple cells providing the same species, which may be contained at different locations in the growth chamber and / or may emit the species toward the wafer from different locations within the growth chamber. Figure 20A is a schematic diagram of an exemplary growth chamber 2000 having a generally cylindrical shape with a characteristic lateral dimension L (e.g., diameter) and a characteristic height H. In some implementations, the chamber has a "flat" geometry with L>H (or L>2*H, or L>3*H, or L>5*H), and at least two (or at least three, or at least five, or at least seven, or at least ten, or at least fifteen) cells c1, c2, c3, c4, c5 of the same species may be distributed across the first wall 2002 of the chamber opposite the second wall 2004 of the chamber where at least one wafer w1, w2, w3 is located (i.e., the cells c1, c2, c3, c4, c5 on the first wall 2002 face the wafer).

[0142] Some implementations of the reactor geometry may include a sufficiently small characteristic distance, such as less than 50 cm (or less than 40 cm, or less than 30 cm, or less than 20 cm, or less than 10 cm) between the cell and the wafer to provide a flux of molecular N. This may facilitate a high N flux.

[0143] In the exemplary geometry of FIG. 20A, L=1.6*H, there are five cells c1, c2, c3, c4, c5 providing the same species on the first wall 2002 of the chamber 2000. On the second wall 2004 of the chamber 2000, there are three wafers w1, w2, w3. The individual fluxes of species from the different cells c1, c2, c3, c4, c5 (dashed circles) combine to provide a relatively constant overall flux profile at the surface of the wafer. FIG. 20A shows a two-dimensional cross section of the chamber 2000, where the different cells c1, c2, c3, c4, c5 are arranged in a one-dimensional line, but the different cells c1, c2, c3, c4, c5 may be arranged in a two-dimensional or three-dimensional array within the chamber.

[0144] FIG. 20B is a schematic diagram of an end view of an array of multiple cells 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H providing the same first species and multiple cells 2M, 2N, 2O, 2P, 2Q, 2R providing the same second species, the cells being arranged on the wall 2010 of the chamber. The cells may be used to provide multiple types of materials, including Ga, N, In, Al, and other species. The cells may be distributed and interspersed with one another on the wall 2010, with cells 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H providing the first species and cells 2M, 2N, 2O, 2P, 2Q, 2R providing the second species. Although cells for providing two species are shown, cells for providing more than two species are possible. A sufficient number of cells providing the same species may be arranged on the wall 2010 in a distributed and interspersed arrangement to provide the species to the wafer in the chamber with a high degree of uniformity that exceeds a threshold value.

[0145] The degree of flux uniformity can be quantified using a simplified model. Referring again to FIG. 20A, a chamber with infinite lateral extent L is assumed, and a first wall 2002 is assumed to contain an infinite square periodic array of point source cells, with each cell separated by its nearest neighbor by a distance d. Emission from an infinite number of cells produces an interference pattern containing flux minima and maxima at the second wall 2004. For a constant flux of species from each cell, the flux maximum (F(D / d) at the target on the second wall is max ) and the minimum flux (F(D / d) min ) depends on the distance D between the source (i.e., the exit aperture of the cell) and the target on the second wall, and on the distance d between the nearest neighboring cells. The flux nonuniformity is expressed by the contrast function C(D / d)=(F(D / d) max -F(D / d) min ) / (F(D / d) max C=1 corresponds to very high heterogeneity and the minimum flux drops to zero, which can occur when D is small compared to the distance d between the cells. C=0 corresponds to a perfectly uniform distribution.

[0146] FIG. 21A is a graph of the contrast function C as a function of D / d using a linear scale. FIG. 21B is a graph of the contrast function C as a function of D / d using a logarithmic scale. The contrast decreases as the value of D / d increases. For D / d>0.5, C is less than 0.1. For D / d>1, C is less than 0.01. Thus, in some implementations including an array of cells providing the same species to a wafer to provide a high degree of species flux uniformity to the wafer, D / d may be at least 0.5 (or at least 0.7, or at least 1, or at least 1.5, or at least 2, or at least 3, or at least 5), where d is the average distance between the nearest neighbor cells and D is the minimum value from the cell to the wafer. In some implementations, the experimental flux contrast value may be less than 0.1 (or less than 0.05, or less than 0.01).

[0147] In some implementations, a homogeneous wafer has a diameter of 200 mm (or 300 mm) and the fluxes of various species (including, e.g., N, Ga, In, Al) provided to the wafer are uniform across the surface of the wafer within + / - 10% (or within + / - 20%, or within + / - 5%, or within + / - 1%, or within + / - 0.1%).

[0148] The total pressure during growth may be selected to maintain a percolation regime where the mean free path of the species in the chamber is longer than the distance between the cell and the wafer. The pressure may be selected to maintain a percolation regime where the mean free path of the species in the chamber is longer than the distance between the cell and the wafer. -5 Torr (or 5×10 -5 Less than 5×10 Torr -6 Less than Torr or 1×10 -6 The pressure may be selected in the range of 1×10 -5 From 1×10 -4 Torr (or 5×10 -5 , or other).

[0149] To investigate the effect of impurities in the MBE reactor growth chamber on the efficiency of the LEDs fabricated in the reactor, NH3 was intentionally introduced into the reactor before growing the samples, and NH3 was adsorbed onto the interior surfaces of the growth chamber. Residual NH3 adsorbed in the reactor evaporates during the growth of the LEDs (as confirmed by mass spectrometry measurements of the background vacuum in the chamber), causing the incorporation of H into the crystalline LED structure, which was grown in an NH3- and H2-rich environment.

[0150] The inner surface of the growth chamber was then baked at high temperature to remove the adsorbed NH3 from the growth chamber surfaces. Bake temperatures above 120°C, above 150°C, above 200°C, or above 250°C may be used. A second LED was then grown in the reactor in an environment with much less NH3 and H2 present. Mass spectrometry measurements of the background vacuum in the chamber showed that the NH3 and H2 concentrations were significantly lower than the H2 concentrations in the growth chamber. Measurements confirmed that the partial pressures of NH3 and H2 during LED growth were approximately one order of magnitude lower than those before the bake-out process.

[0151] FIG. 22 is a spectrograph showing the emitted PL spectra from an LED grown in an NH3 and H2 rich environment (Sample 1) and an LED grown in an environment with little NH3 and H2 background (Sample 2) when operated at a temperature of 300K and excited by 8mW of 325nm laser excitation. From the spectra in FIG. 22, it is clear that the PL intensity of Sample 1 is strongly suppressed compared to that of Sample 2, indicating that the presence of background hydrogen may be detrimental to the IQE of the LED by itself or by forming complex defects. Sample 2 was grown at 1×10 -10 Background pressure of approximately 5 x 10 Torr on the sample -4 A collisional hydrogen flux of about monolayer / sec and about 1 × 10 18 ~1×10 19 cm -3 corresponds to the H concentration.

[0152] Some implementations have been done with 1×10 -10 Torr (or 5×10 -11 Torr, or 1×10 -11 Torr, or 5 × 10 -12 Some implementations include growing at low background pressures of less than 1×10 Torr. Some implementations include reactors where the vacuum in the growth chamber is maintained by one or more cryogenic pumps and / or turbo pumps and / or ion getter pumps. Cryogenic pumps may be particularly effective at pumping water vapor and may also reduce the hydrogen partial pressure. Ion getter pumps may be effective at pumping hydrogen gas when operating at high vacuum. The type, number and pump power of the vacuum pumps may be selected to achieve a predetermined vacuum level for a given reactor geometry / volume. Some implementations include growing at low background pressures of less than 1×10 at the active area of ​​the LED. 18 cm -3 Less than (or 1×10 17 cm -3 The present invention includes an MBE reactor capable of growing LEDs having a hydrogen concentration of less than 20% (or less than 20% by weight). In some implementations, the hydrogen concentration in the epitaxial stack may be reduced by a post-growth annealing step (e.g., thermal annealing). Such provision may reduce the incorporation of impurities other than hydrogen, including carbon, oxygen, and metals. Some implementations thus exhibit an IQE of at least 20% (or 30%, 40%, 50%), as disclosed in more detail in this disclosure.

[0153] Some implementations combine various improvements disclosed herein, which may include lower background pressure, plasma with optimized atomic / molecule ratios, low concentrations of species / impurities, and sufficient flux of species, including N and / or group III species.

[0154] In some implementations, the formation of nitrogen vacancy-related defects can be mitigated by growing the LED structure at high pressure, for example in an MOCVD reactor. Conventional MOCVD reactors often operate at pressures in the range of 0.1 to 1 atm, and in some implementations, the pressure can be at least 5 atm (or at least 1.5 atm, 2 atm, or at least 3 atm, or at least 10 atm, or at least 20 atm, or at least 50 atm). The pressure can be a total gas pressure or a partial pressure of the N-containing species (e.g., ammonia). The pressure can be throughout the growth chamber or can be a local pressure measured in close proximity to the wafer. In some implementations, the N-containing species is injected near the surface of the growth wafer to obtain high local pressure. The N-containing species can include ammonia, N-radicals, and reactive N-species. Reactions in the N-containing species (e.g., ammonia cracking) can occur near the wafer surface or at least 10 cm (or at least 100 cm) away from the wafer.

[0155] 23 is a schematic diagram of an MOCVD reactor system 2300 for epitaxially growing LEDs. The reactor system 2300 includes a chamber 2302 (also known as a growth chamber) and one or more wafers w1, w2, w3, w4, w5, w6, w7, w8, w9, w10, w11, w12, w13, w14, w15, w16, w17, w18, w19, w20, w21, w22, w23, w24, w25, w26, w37, w38, w39, w40, w41, w42, w43, w44, w45, w46, w47, w48, w50, w51, w52, w53, w54, w55, w56, w57, w58, w69, w60, w61, w62, w6 and w3. The system 2300 may include one or more wafer holders 2301 configured to hold the wafers in place during epitaxial growth. Sources s1, s2, s3, s4, s5 provide materials (e.g., gallium, indium, aluminum, nitrogen, hydrogen, etc.) to be deposited, for example by MOCVD, on the wafers w1, w2, w3 and / or on layers previously grown on the wafers to form the semiconductor layers of the LEDs. The sources s1, s2, s3, s4, s5 may include valves to control the flow of materials from the sources to the chamber 2302 and may include shutters to block the flow of all materials from the cells to the chamber 2302. Materials from sources s1, s2, s3, s4, s5 may be provided to the wafers w1, w2, w3 to grow devices on the wafers at different times and / or from different locations during the growth of the device's light-emitting layers.

[0156] The reactor system 2300 may include one or more exhaust chambers 2322 operably connected to the chamber 2302 and configured to maintain a predetermined pressure in the chamber 2302. The system 2300 may include one or more pressure sensors 2320 configured to measure the pressure in the chamber 2302, which may be used to determine the flux of material from one or more sources s1, s2, s3, s4, s5 to be deposited on the wafers w1, w2, w3. The reactor system 2300 may include one or more heaters 2323 configured to heat the surfaces of the wafers w1, w2, w3 on which the optoelectronic devices are grown to a predetermined surface temperature, and one or more temperature sensors 2324 for determining the surface temperature of the wafers w1, w2, w3 on which the semiconductor stack is grown. The reactor system 2300 may include a controller 2330 including a memory that stores machine-executable instructions and a processor configured to execute the stored instructions, execution of which causes the controller 2330 to control the operation of one or more other elements of the system 2300. For example, the controller 2330 may control the flow rate of materials from sources s1, s2, s3, s4, s5 to the wafers w1, w2, w3, control the temperature of 2324, control the power applied to the electrodes to generate a plasma of the materials, etc.

[0157] The reactor 2300 may be configured to hold a high pressure in the chamber 2302. In some implementations, the reactor may include a growth chamber that may be sealed to reach high pressure and may also be open to a second chamber (e.g., to load wafers and access hardware). In some implementations, a load lock mechanism may be used to separate the growth chamber from the second chamber, so the two chambers may operate at different pressures.

[0158] In some implementations, the reactor may be operated with only NH3, i.e., without N2 or H2 carrier gas. The percentage of N2 and H2 may be less than 1% of the total input gas. In some implementations, liquid NH3 (also known as LNH3) may be used to both carry the precursors and deliver nitrogen species to the wafer. The use of LNH3 may facilitate high pressures (on the order of about 10 bar). LNH3 may pass through a bubbler of organometallic species (including, for example, trimethylaluminum (TMA), trimethylgallium (TMG), triethylgallium (TEG), and trimethylindium (TMI)) and flow in a line carrying the species entrapped in the bubbler. Such a line may terminate in a gas injector in the growth chamber. The LNH3 may then be vaporized in the injector in close proximity to the wafer.

[0159] In some implementations, NH3 may be heated to a high temperature in the injector to achieve or promote its vaporization. In some implementations, this temperature may remain below 600° C. (or below 550° C.) to prevent decomposition of NH3 into a gas. In some implementations, the injector may have a temperature between 300° C. and 600° C., or below 550° C.

[0160] In another implementation, the LNH3 is heated at a relatively low temperature in the injector, e.g., below 200° C. (or may remain below 100°C, or below 0°C, or below -50°C, or below -80°C). In such an implementation, NH3 may be injected in liquid form and only heated to vaporization upon reaching the heated wafer. This promotes NH3 decomposition very close to the surface of the wafer. The corresponding boundary layer of the gas phase may have a thickness of less than 1 cm (or 5 mm, 2 mm, 1 mm). The wafer may be held at a temperature that allows cracking of NH3, for example at least 550°C or higher.

[0161] In some implementations, the reactor chamber is equipped to operate at high pressure. The pressure may be at least 1 atm (or at least 1.5 atm, 2 atm, or in the range of 1-5 atm or 1-10 atm). The exhaust may be designed to maintain such high pressure. The reactor may be used in dual modes, with one mode using high pressure (such as 2 atm, or above 1 atm) and another mode using low pressure (such as below 1 atm). For example, high pressure may be used for In-containing alloys and low pressure for Al-containing alloys. The two modes may be performed in separate chambers (possibly using a load lock to separate the pressure regions) or in the same chamber with varying pressure.

[0162] The pressure in the reaction chamber may be adjusted at the exhaust level by a device that controls the high pressure. For example, the reactor 2300 may include an exhaust chamber where gas from the reaction chamber is exhausted, and the exhaust chamber may meter the exhaust of gas to maintain the total pressure in the reaction chamber above a predetermined value above 2 atmospheres. The pressure may be controlled by using a valve to prevent or limit the exhaust, and a pump to regulate the pressure. To allow safe operation of the high pressure line, the high pressure line may be embedded in other lines. The reactor chamber may feature multiple (at least two) exhausts, for example, one exhaust for the high pressure regime and one exhaust for the low pressure regime. The two different exhausts may have two types of pumping systems.

[0163] The growth chamber and lines may be recessed in the apparatus to protect the environment from leakage. The susceptor may contain holes surrounding the wafer through which decomposition products may pass.

[0164] The injector may consist of several vaporization nozzles that allow for a pressure gradient of NH3 by precisely controlling the local pressure. The hole diameter may control the flow of each injector, varying the hole size to achieve a predetermined pressure profile.

[0165] In some implementations, InGaN layers are grown at high pressures, such as above 1.5 atm (or 2, 3, 5, 10, 20, 50, 100 atm), which may promote low defect densities as taught herein, especially for high In content layers that would otherwise be prone to defect formation, including defects associated with N vacancies.

[0166] In some implementations, In-containing layers with high In% (e.g., greater than 35%) may be grown at high pressure and high growth temperature. High pressure may promote incorporation of In into the grown crystal, thereby allowing for a desired In content in the crystal despite a relatively high growth temperature. This is in contrast to conventional MOCVD processes (e.g., MOCVD at operating pressures below 1 atm), where low temperatures may be necessary to achieve high In content. Some implementations use growth temperatures at least 100°C (or 200°C, 300°C, 500°C) higher than the stability temperature of In-N bonds at atmospheric pressure (e.g., about 550°C). The operating gas pressures used at such high temperatures may be sufficient to eliminate or limit dissociation of In-N bonds and make the In-N bonds stable.

[0167] In some implementations, InGaN layers grown at high pressure have a densification rate of at least 35% (or 40%, 45%, 50%, 60%) and may be grown at high temperatures of at least 750°C (or 780°C, 800°C, 820°C, 840°C, 860°C). Growth at high temperatures may be desirable to facilitate high material quality and high efficiency of the grown devices, comparable to the efficiency of standard (blue or green) InGaN QWs, where the IQE may exceed 20%, 50%, or 80%. In some implementations, InGaN layers grown at high pressure with an In concentration of at least 35% (or 40%, 45%, 50%, 60%) may have a peak IQE of at least 20% (or 30%, 40%, 50%, 60%, 70%, 80%). The high pressure may be a total pressure higher than atmospheric pressure or a partial pressure of N-containing species (e.g., ammonia) that may limit the formation of defects, including N-vacancy related defects.

[0168] In addition, the high pressure reactor may be configured to promote laminar or quasi-laminar gas flow to avoid turbulence in the chamber. The reactor geometry may be vertical or horizontal, and a thin boundary layer may be facilitated, for example, by providing a showerhead or gas nozzle near the wafer, a ceiling close to the wafer, and / or additional gas flows to push the precursor gas toward the wafer surface. The temperature of the reactor chamber may be lower than the wafer temperature to limit growth on the reactor chamber surface. The chamber surface may be at least 100° C. (or 200° C., 300° C., 500° C.) cooler than the wafer surface. The flows of precursor gases (e.g., Ga-bearing gas, In-bearing gas, N-bearing gas, e.g., TMG, TMI, and NH3) may be separated in time (pulsed growth) or spatially separated (separate implantation regions).

[0169] MOCVD growth at high temperatures can lead to reactor operation under thermodynamic limitations. In contrast, in some configurations, the combination of high temperature and high pressure can keep the reactor operation under mass transport limitations.

[0170] The high pressure grown epitaxial structure may have the following features: It may include an In(x)Ga(1-x)N based quantum well layer. It may include an In(y)Ga(1-y)N containing barrier layer for defect reduction, where x and y are percentage values ​​and y is less than x (e.g., at least 5%, 10%, 15%, 20%). The active region may have x>35% (or 40%, 45%, 50%, 55%, 60%) and it may have a thickness less than 3.5 nm (or 3 nm, 2.5 nm, 2 nm). The quantum well layer may be pseudomorphic with the underlayer and may undergo partial or complete strain relaxation with a lattice constant that is within 10% (or 20%, 50%) of its bulk / relaxed lattice constant.

[0171] Implementations may include methods for improving the IQE of LEDs grown at high pressure. For example, multiple samples may be grown at various pressures, each pressure being superatmospheric (e.g., greater than 1.5, 2, 3, 5, 10, 20, 50, or 100 atm). In each sample growth, the pressure and other growth parameters (including temperature, gas flow, III / V ratio) may be configured such that the defect density is progressively improved and the IQE improves by at least 5% (or 10%, 20%) from the first sample to the last sample. This technique may be used to grow LEDs with high In% active area and / or a given current density (e.g., greater than 1 A / cm). 2 , 10A / cm 2 , 100A / cm 2 ) and long wavelength (e.g., at least 580 nm, 600 nm, 620 nm, 650 nm) LEDs. For example, the grown light-emitting layer may be applied to LEDs emitting at a current of 1 A / cm 2 It can be configured to emit light at wavelengths longer than 600 nm (when driven at higher current densities) with an internal quantum efficiency greater than 20%.

[0172] The techniques described herein may be applied to growth techniques that may include MBE, MOCVD, plasma-assisted deposition (including remote plasma CVD or radical-enhanced MOCVD), pulsed laser deposition, or other techniques known in the art. An implementation includes ensuring an unusually high nitrogen flow during layer growth, particularly for InGaN-containing layers.

[0173] In some implementations, a plasma may be generated within the growth chamber. The plasma may include a nitrogen (N2) plasma source to provide the N species for growth (instead of using ammonia as the N source). This allows growth at lower temperatures than conventional MOCVD.

[0174] In some implementations, this low growth temperature may be used when growing the barrier and / or active layers. Some implementations of the grown LED may include an In-containing underlayer that may reduce the defect density in the active layer. This may be followed by growth of a GaN layer at a growth temperature lower than 800°C (or 700°C, 750°C, 850°C, 900°C, 950°C, 1000°C). The temperature may be such that a low density of defects (including defects associated with N vacancies) is generated. This is followed by growth of an In-containing active layer at a growth temperature lower than 700°C (or 600°C, 650°C, 750°C, 800°C). The density of defects in the In-containing layer may be low as taught herein. The defect may be a defect that causes SRH. It may be a defect associated with N vacancies, Ga vacancies, Ga-N divacancies.

[0175] In some implementations, the use of plasma-assisted epitaxial growth may allow for a larger N species flow when growing the active layer compared to conventional MOCVD. MOCVD N pressure may be limited by the low cracking of ammonia at low temperatures. In contrast, implementations utilize N plasma sources and may therefore maintain high N fluxes even at moderate or low growth temperatures.

[0176] Some implementations combine conventional MOCVD growth with plasma-assisted growth of an In-containing underlayer. For example, some InGaN-containing layers may be grown by MOCVD and some layers may be grown by plasma-assisted growth to maintain low temperatures. In some implementations, the In-containing underlayer may be grown by MOCVD; the GaN barrier may be grown at low temperatures by plasma-assisted growth to avoid defect formation; the In-containing active layer may be grown by either MOCVD or plasma-assisted PA growth; and additional layers may be further grown.

[0177] The techniques described herein may be applied to a variety of semiconductor optoelectronic devices, including not only LEDs, but also laser diodes, superluminescent diodes, and other light emitters, as well as electronic devices (including transistors, RF devices, and power electronic devices).

[0178] The techniques described herein can be used to obtain semiconductor materials, for example grown by MBE, for use in electronic devices. MBE may be useful because of its very low pressure, which can allow for very low defect densities. For example, the concentration of undesired species in a layer (e.g., oxygen, carbon, dopants, or impurities that generally affect electron transport or conductivity) can be as low as 1×10 14 / cm 3 Less than (or 1×10 13 / cm 3 Less than 1×10 12 / cm 3 Less than 1×10 11 / cm 3 Less than or equal to 1 × 10 10 / cm 3The doping density may be less than 100 nm. This may be useful, for example, when an undoped layer is desired in an electronic device. Conversely, MBE may be more prone to forming vacancy-related defects or near-midgap defects, as disclosed herein. These may also be problematic for electronic devices, for example, because they facilitate defect-assisted tunneling. Implementations utilize the present teachings to combine a low density of undesired impurities with a low density of vacancy-related and / or near-midgap defects.

[0179] More generally, implementations include electronic devices (and methods of making same) that have low concentrations of undesirable impurities and further have low concentrations of vacancy-related defects and / or near-midgap defects, such as by MBE or other methods disclosed herein. This may be achieved by growth techniques.

[0180] In the specification and / or drawings, several embodiments have been disclosed. The present disclosure is not limited to such exemplary embodiments. The use of the term "and / or" includes any and all combinations of one or more of the associated listed items. Unless otherwise specified, certain terms are used in an inclusive and descriptive sense and are not intended to be limiting. As used herein, spatially relative terms (e.g., in front of, behind, above, below, etc.) are intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the figures. For example, the "front" of a mobile computing device may be the surface facing the user, in which case the phrase "in front of" means closer to the user.

[0181] Although certain features of the described implementations have been shown as described herein, many modifications, substitutions, changes, and equivalents will occur to those skilled in the art. It should therefore be understood that the claims are intended to cover all such modifications and changes that are within the scope of the implementations. It should be understood that these are presented only as examples and not as limitations, and that various changes in form and details may be made. Any part of the apparatus and / or method described herein may be combined in any combination except mutually exclusive combinations.

[0182] The implementations described herein may include various combinations and / or subcombinations of the functions, components and / or features of the different implementations described.

[0183] In the above description, numerous details are set forth. However, it will be apparent to one skilled in the art having the benefit of this disclosure that implementations of the present disclosure may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the description.

[0184] Some portions of the detailed description are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

[0185] It should be noted, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as is apparent from the above discussion, throughout the description, discussions using terms such as "identify," "determine," "calculate," "detect," "send," "receive," "produce," "store," "rank," "extract," "obtain," "allocate," "divide," "operate," "filter," "modify," and the like refer to operations and processes of a computer system or similar electronic computing device that manipulates and converts data represented as physical (e.g., electronic) quantities in the computer system's registers and memory into other data similarly represented as physical quantities in the computer system's memory or registers or other such information storage, transmission, or display devices.

[0186] Implementations of the present disclosure also relate to apparatus for performing the operations herein. may be specially constructed for the required purposes, or may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored on a non-transitory computer-readable storage medium, such as any type of disk, including, but not limited to, a floppy disk, an optical disk, a CD-ROM and a magneto-optical disk, a read-only memory (ROM), a random-access memory (RAM), an EPROM, an EEPROM, a magnetic or optical card, a flash memory, or any type of medium suitable for storing electronic instructions.

[0187] The term "example" or "exemplary" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "example" or "exemplary" should not necessarily be construed as preferred or advantageous over other aspects or designs. Rather, use of the term "example" or "exemplary" is intended to present a concept in a specific manner. The term "or" as used in this application is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified or clear from the context, "X includes A or B" is intended to mean any of the natural inclusive permutations. That is, if X includes A, or X includes B, or X includes both A and B, then "X includes A or B" is satisfied under any of the foregoing examples. Additionally, the articles "a" and "an" as used in this application and claims are intended to mean any of the following unless otherwise specified: "one or more" should generally be construed to mean "one or more" unless otherwise specified or unless it is clear from the context that a singular form is intended. Additionally, use of the phrases "implementation" or "one embodiment" or "an implementation" or "an implementation" throughout is not intended to refer to the same embodiment or implementation unless explained to do so. Additionally, the phrases "first," "second," "third," "fourth," etc., as used herein are meant as labels to distinguish different elements and do not necessarily have an ordinal meaning in accordance with their numerical designations.

[0188] The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description that follows. In addition, the present disclosure is not described with reference to any particular programming language. It will be understood that a variety of programming languages ​​may be used to implement the teachings of the present disclosure as described herein.

[0189] The above description describes numerous specific details, such as examples of specific systems, components, methods, etc., to provide a good understanding of some implementations of the present disclosure. However, it will be apparent to those skilled in the art that at least some implementations of the present disclosure may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram form to avoid unnecessarily obscuring the present disclosure. Thus, the above specific details are merely examples. It is contemplated that a particular implementation may vary from these illustrative details and still be within the scope of the present disclosure.

[0190] It should be understood that the above description is illustrative, and not restrictive. Many other implementations will be apparent to those skilled in the art upon reading and understanding the above description. The scope of the present disclosure should therefore be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. 1. A method for growing an optoelectronic device by molecular beam epitaxy (MBE), comprising the steps of: Providing a substrate in an MBE growth chamber; growing an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer on the substrate; and controlling the growth such that the light emitting layer comprises a plurality of In-containing quantum well layers having an In content greater than 20% and a plurality of In-containing barrier layers having an In content greater than 1%, and no GaN barriers; growing the light emitting layer includes alternately growing the quantum well layers and the barrier layers; and the quantum well layers are 5×10 １５ / cm ３ The method is performed so as to have a defect density of less than

2. The quantum well layer has an optical band gap (E ｏ ), and the defect is E ｏ 2. The method of claim 1, wherein the electron has an energy within + / - 300 meV of .

3. 2. The method of any one of the preceding claims, wherein defects cause Shockley-Read-Hall recombination in the quantum well layer.

4. 2. The method of any one of the preceding claims, wherein the defects comprise nitrogen vacancies.

5. The method of claim 4 , wherein the defects comprise gallium-nitrogen divacancies.

6. 2. The method of any one of the preceding claims, wherein growing the light emitting region comprises growing the quantum well layers and the barrier layers at a growth temperature of less than 550°C.

7. 2. The method of any one of the preceding claims, wherein growing the light emitting region comprises growing the quantum well layers and the barrier layers at a growth temperature of less than 500°C.

8. Growing the light emitting region comprises growing the quantum well layers and the barrier layers at a growth temperature greater than 550° C. with a nitrogen flux of 1×10 １５ atoms / cm ２ 6. The method of claim 1, further comprising growing the nanoparticles at a temperature of greater than 1000 nm / s.

9. 13. The method of any one of the preceding claims, wherein growing the light emitting region comprises providing to the substrate a flux of nitrogen and a flux of a group III species, with a ratio of the nitrogen flux to the flux of the group III species being at least 5.

10. 10. The method of any one of the preceding claims, wherein the optoelectronic device is either an LED or a laser diode.

11. Growing the light emitting region includes providing nitrogen plasma to the substrate from a plurality of different nitrogen cells with a distance between each nitrogen cell and the substrate being less than 50 cm, the provided nitrogen plasma having a concentration of at least 1×10 －５ 2. The method of any one of the preceding claims, having a beam equivalent pressure of N adatoms exceeding 1000 psig (2.0 Torr).

12. Growing the light emitting region includes providing nitrogen plasma to the substrate from a plurality of different nitrogen cells, with a distance between each nitrogen cell and the substrate being less than 50 cm, and a flux of nitrogen species on the substrate provided by the nitrogen plasma is greater than or equal to 2×10 １５ atoms / cm ２ 13. The method of any one of the preceding claims, wherein the .lambda. / second is greater than

13. 13. The method of claim 12, wherein the contrast ratio of the flux of the nitrogen species on the substrate is less than 0.

1. Method of posting.

14. Providing the nitrogen plasma comprises: To provide the plasma, N ２ Providing a flux; and maintaining the plasma at a power less than three times the minimum power required to ignite the plasma.

15. further comprising growing at least one first barrier layer under In-rich conditions, said barrier layer having an In content in the range of 0.1% to 10%, and growing at least one quantum well layer directly on the first barrier layer under In-rich conditions, the quantum well layer having an In content in the range of 10% to 50%; 10. The method of claim 1, wherein during a transition between growth of the at least one first barrier layer and growth of the at least one quantum well layer, In is provided to the substrate and the nitrogen plasma is active.

16. 10. The method of any one of the preceding claims, wherein the optoelectronic device has an internal quantum efficiency of at least 10%.

17. During the growth of the n-doped layer, the p-doped layer, and the light-emitting layer in the reaction chamber, －１１ and generating a vacuum having a hydrogen partial pressure of less than 1×10 Torr in one or more of the quantum well layers. １８ 2. The method of any one of the preceding claims, wherein the hydrogen concentration is less than 1 / cubic centimeter.

18. 1. An MBE apparatus for growing an optoelectronic device comprising an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer, comprising: A reaction chamber; a wafer holder within the reaction chamber configured to hold a wafer in place during growth of the optoelectronic devices; a plurality of group III cells configured to provide a group III species to a wafer held by the wafer holder, each group III cell providing the group III species to the wafer from a different direction, the MBE apparatus further comprising: a plurality of nitrogen plasma cells configured to provide nitrogen plasma to the wafer held by the wafer holder, each nitrogen plasma cell providing the nitrogen plasma to the wafer from a different direction and with a distance between an outlet of the cell and the wafer being less than 50 cm, the plurality of nitrogen plasma cells comprising: １５ atoms / cm ２ 4. An MBE apparatus configured to generate a nitrogen flux on the wafer of greater than 1000 nm / sec.

19. The nitrogen plasma cells were placed in a 1×10 －５ 20. The apparatus of claim 18 configured to generate a nitrogen adatom pressure of greater than Torr.

20. The apparatus of any one of claims 18 to 19, wherein the plurality of nitrogen plasma cells are configured to produce a contrast ratio of the nitrogen flux on the wafer of less than 0.

1.

21. The plurality of nitrogen plasma cells include To provide the nitrogen plasma, N ２ Provides flux, 21. Apparatus according to any one of claims 18 to 20, configured to maintain the plasma at a power less than three times the minimum power required to ignite the plasma.

22. The plurality of group III cells and the plurality of nitrogen plasma cells provide a nitrogen flux and a group III species flux to the wafer, the ratio of the nitrogen flux to the group III species flux being at least 5.

22. Apparatus according to any one of claims 18 to 21, configured to provide:

23. The apparatus of any one of claims 18 to 22, wherein the reaction chamber has a characteristic height and a characteristic length that is greater than the characteristic height.

24. operatively connected to the reaction chamber and configured to receive 5×10 －１１ The apparatus of any one of claims 18 to 23, further comprising one or more vacuum pumps configured to generate a vacuum having a hydrogen partial pressure of less than Torr.

25. 1. An apparatus for growing InGaN optoelectronic devices, comprising an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer, the light emitting layer comprising a quantum well layer having an In % greater than 35%, the apparatus comprising: A reaction chamber; a wafer holder within the reaction chamber configured to hold a wafer in place at a temperature of at least 750° C. during growth of the light emitting layer of the optoelectronic device; a plurality of group III sources configured to provide indium-containing organometallic precursors and gallium-containing organometallic precursors to the wafer held by the wafer holder during growth of the light emitting layer of the optoelectronic device; a source of N-containing species configured to provide the N-containing species to the wafer held by the wafer holder during growth of the light emitting layer of the optoelectronic device, at a partial pressure of the N-containing species at the wafer greater than 1.5 atmospheres; the Group III source and the source of the N-containing species are configured to provide the indium-containing organometallic precursor, the gallium-containing organometallic precursor, and the N-containing species into the reaction chamber at a rate sufficient to produce a total pressure in the reaction chamber of greater than 2 atmospheres during growth of the light-emitting layer of the optoelectronic device.

26. 26. The apparatus of claim 25, further comprising an exhaust chamber coupled to the reaction chamber and configured to maintain a total pressure within the reaction chamber above a predetermined value.

27. The apparatus of any one of claims 25 to 26, wherein the source of N-containing species is configured to provide ammonia in the liquid phase to the reaction chamber.

28. 1. A method of growing an InGaN optoelectronic device comprising an n-doped layer, a p-doped layer, and a light emitting layer between the n-doped layer and the p-doped layer by MOCVD in a reaction chamber, the light emitting layer comprising an InGaN quantum well layer having an In% greater than 35%, the method comprising: controlling a surface temperature of a wafer on which the InGaN optoelectronic device is grown to at least 750° C. during growth of the light emitting layer of the optoelectronic device; providing an indium-containing organometallic precursor and a gallium-containing organometallic precursor into the reaction chamber and to the wafer during growth of the light emitting layer of the optoelectronic device, when the surface temperature of the wafer is greater than 750° C.; providing a N-containing species to the wafer during growth of the light emitting layer of the optoelectronic device at a rate such that a partial pressure of the N-containing species at a surface of the wafer is greater than 1.5 atmospheres when the surface temperature of the wafer is greater than 750° C.; wherein the indium-containing organometallic precursor, the gallium-containing organometallic precursor, and the N-containing species are provided into the reaction chamber at rates sufficient to produce a total pressure in the reaction chamber of greater than 2 atmospheres during growth of the light-emitting layer of the optoelectronic device.

29. 30. The method of claim 28, further comprising metering exhaust of gas through an exhaust chamber coupled to the reaction chamber to maintain a total pressure within the reaction chamber above a predetermined value greater than 2 atmospheres.

30. The method of any one of claims 28 to 29, wherein providing the N-containing species to the reaction chamber comprises providing ammonia to the reaction chamber at a temperature of less than 600°C.

31. The method of any one of claims 28 to 30, wherein providing the N-containing species to the reaction chamber comprises providing ammonia to the reaction chamber in a liquid phase.

32. 32. The method of claim 31 , wherein providing the N-containing species to the reaction chamber comprises providing the liquid phase ammonia to the reaction chamber at a temperature less than 200° C.

33. The method of any one of claims 28 to 32, wherein the grown light emitting layer is configured to emit light at wavelengths longer than 600 nm with an internal quantum efficiency greater than 20%.

34. The grown light emitting layer has a current density of 1 A / cm ２ 34. The method of claim 33, configured to emit light at wavelengths longer than 600 nm with an internal quantum efficiency greater than 20% when driven at higher current densities.

35. 34. The method of any one of claims 28 to 33, wherein providing the N-containing species comprises providing the N-containing species such that the N-containing species forms a boundary layer on the wafer, and a partial pressure of the provided N-containing species exceeds 1.5 atmospheres at the boundary layer.

36. 36. The method of any one of claims 28 to 35, further comprising providing at least two of the indium-containing precursor, the gallium-containing precursor, and the N-containing species at different times during growth of the light emitting layer of the optoelectronic device.

37. The method of any one of claims 28 to 35, further comprising providing at least two of the indium-containing precursor, the gallium-containing precursor and the N-containing species at separate locations within the chamber.

38. An optoelectronic device grown by any one of the methods of claims 28 to 37.

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