Showing papers on "Gallium nitride published in 1995"

Superbright Green InGaN Single-Quantum-Well-Structure Light-Emitting Diodes

Abstract: Superbright green InGaN single quantum well (SQW) structure light-emitting diodes (LEDs) with a luminous intensity of 12 cd were fabricated The luminous intensity of these green InGaN SQW LEDs (12 cd) was about 100 times higher than that of conventional green GaP LEDs (01 cd) The output power, the external quantum efficiency, the peak wavelength and the full width at half-maximum of green SQW LEDs were 3 mW, 63%, 520 nm and 30 nm, respectively, at a forward current of 20 mA The p-AlGaN/InGaN/n-GaN structure of green InGaN SQW LEDs were grown by metalorganic chemical vapor deposition on sapphire subsutrates

Emerging gallium nitride based devices

Abstract: Wide bandgap GaN has long been sought for its applications to blue and UV emitters and high temperature/high power electronic devices. Recent introduction of commercial blue and blue-green LED's have led to a plethora of activity in all three continents into the heterostructures based on GaN and its alloys with AlN and InN. In this review, the status and future prospects of emerging wide bandgap gallium nitride semiconductor devices are discussed. Recent successes in p-doping of GaN and its alloys with InN and AlN, and in n-doping with much reduced background concentrations have paved the way for the design, fabrication, and characterization of devices such as MESFET's, MISFET's, HBT's, LED's, and optically pumped lasers. We discuss the electrical properties of these devices and their drawbacks followed by future prospects. After a short elucidation of materials characteristics of the nitrides, we explore their electrical transport properties in detail. Recent progress in processing such as formation of low-resistance ohmic contacts and etching is also presented. The promising features of quarternaries and double heterostructures in relation to possible current injection lasers, LED's, and photodetectors are also elaborated on. >

Vertical geometry light emitting diode with group iii nitride active layer and extended lifetime

Abstract: A light emitting diode (20) emits in the blue portion of the visible spectrum and is characterized by an extended lifetime. The light emitting diode comprises a conductive silicon carbide substrate (21); an ohmic contact (22) to the silicon carbide substrate; a conductive buffer layer (23) on the substrate and selected from the group consisting of gallium nitride, aluminum nitride, indium nitride, ternary Group III nitrides having the formula AxB1-xN, where A and B are Group III elements and where x is zero, one, or a fraction between zero and one, and alloys of silicon carbide with such ternary Group III nitrides; and a double heterostructure (24) including a p-n junction on the buffer layer in which the active (25) and heterostructure layers (26, 27) are selected from the group consisting of binary Group III nitrides and ternary Group III nitrides.

Native defects in gallium nitride

Abstract: The results of an extensive theoretical study of native defects in hexagonal GaN are presented. We have considered cation and anion vacancies, antisites, and interstitials. The computations were carried out using ab initio molecular dynamics in supercells containing 72 atoms. N vacancy introduces a shallow donor level, and may be responsible for the n-type character of as-grown GaN. Due to the wide gap of nitrides, self-compensation effects strongly reduce both n-type and p-type doping efficiencies due to the formation of gallium vacancy and interstitial Ga, respectively.

Integrated heterostructures of Group III-V nitride semiconductor materials including epitaxial ohmic contact, non-nitride buffer layer and methods of fabricating same

Abstract: An integrated heterostructure of Group III-V nitride compound semiconductors is formed on a multicomponent platform which includes a substrate of monocrystalline silicon carbide and a non-nitride buffer layer of monocrystalline zinc oxide. The zinc oxide may be formed by molecular beam epitaxy (MBE) using an MBE effusion cell containing zinc, and a source of atomic oxygen, such as an MBE-compatible oxygen plasma source which converts molecular oxygen into atomic oxygen. An ohmic contact for a semiconductor device formed of Group III-V nitride compound semiconductor materials including a layer of aluminum nitride or aluminum gallium nitride, includes a continuously graded layer of aluminum gallium nitride and a layer of gallium nitride or an alloy thereof on the continuously graded layer. The continuously graded layer eliminates conduction or valence band offsets. A multiple quantum well may also be used instead of the continuously graded layer where the thickness of the layers of gallium nitride increase across the multiple quantum well. The ohmic contacts may be used for Group III-V nitride laser diodes, light emitting diodes, electron emitters, bipolar transistors and field effect transistors.

High-luminosity blue and blue-green gallium nitride light-emitting diodes.

Abstract: Compact and efficient sources of blue light for full color display applications and lighting eluded and tantalized researchers for many years. Semiconductor light sources are attractive owing to their reliability and amenability to mass manufacture. However, large band gaps are required to achieve blue color. A class of compound semiconductors formed by metal nitrides, GaN and its allied compounds AIGaN and InGaN, exhibits properties well suited for not only blue and blue-green emitters, but also for ultraviolet emitters and detectors. What thwarted engineers and scientists from fabricating useful devices from these materials in the past was the poor quality of material and lack of p-type doping. Both of these obstacles have recently been overcome to the point where highluminosity blue and blue-green light-emitting diodes are now available in the marketplace.

High brightness electroluminescent device emitting in the green to ultraviolet spectrum and method of making the same

Abstract: A green-blue to ultraviolet light-emitting optical device, e.g. a green-blue to ultraviolet emitting laser or a green-blue to ultraviolet emitting diode, comprising a green-blue to ultraviolet light emitting gallium nitride material on a base structure including a silicon carbide substrate, which preferably consists of 2H-SiC, 4H-SiC, or a-axis oriented 6H-SiC. The carrier mobility and the transparency of the silicon carbide substrate are optimized by the selection of orientation and polytype, thus enhancing device performance. The light-emitting diodes may incorporate a structural modification to increase the light output comprising a dielectric Bragg mirror beneath the LED structure, made of alternating layers of AlN, GaN, InN or their alloys. Methods for making such light-emitting diodes are provided, including a technique for defining individual devices by mesa etching which avoids possible damage to the active area during dicing.

Electronic transport studies of bulk zincblende and wurtzite phases of GaN based on an ensemble Monte Carlo calculation including a full zone band structure

Abstract: The ensemble Monte Carlo technique including the details of the first four conduction bands within the full Brillouin zone is used to calculate the basic electronic transport properties for both zincblende and wurtzite crystal phases of bulk gallium nitride. The band structure throughout the Brillouin zone is determined using the empirical pseudopotential method. Calculations of the electron steady‐state drift velocity, average energy, valley occupancy and band occupancy in the range of electric fields up to 500 kV/cm are presented. It is found that the threshold electric field for intervalley transfer is greater and that the second conduction band is more readily occupied in wurtzite than in zincblende GaN over the range of electric fields examined here.

Gallium nitride group compound semiconductor laser diode

Abstract: A gallium nitride group compound semiconductor laser diode includes at least one pn junction layer disposed between an n-type layer and a p-type layer. The n-type layer is formed from a gallium nitride group compound semiconductor material defined by the composition equation (Alx Ga1-x)y In1-y N (where 0≦x≦1 and 0≦y≦1). The p-type layer, doped with an acceptor impurity, is obtained by electron beam irradiating a gallium nitride group compound semiconductor material defined by the composition equation (Alx' Ga1-x')y' In1-y' N (where 0≦x'≦1, 0≦y'≦1, x=x' or x≠x', and, y=y' or y≠y'). The improved gallium nitride group semiconductor laser diode of the present invention is found to emit light in the visible short wavelength spectrum of light which includes the blue, violet and ultraviolet regions.

Selective growth of zinc‐blende, wurtzite, or a mixed phase of gallium nitride by molecular beam epitaxy

Abstract: We report on the growth of GaN with a zinc‐blende, wurtzite, or a mixed phase structure on (001)GaP and (001)GaAs substrates by a low‐temperature modified molecular beam epitaxy technique. By systematically varying the incident arsenic overpressure, films grown at a moderate substrate temperature of ≊620 °C show predominately wurtzite α‐GaN, zinc‐blende β‐GaN, or a mixed phase of the two. Films containing only the metastable phase β‐GaN were achieved by using a relatively high growth temperature of ≊700 °C and with an arsenic overpressure of ≊2.4×10−5 Torr. X‐ray diffraction measurements indicate an improved crystalline quality for the layers grown at ≊700 °C compared to those grown at ≊620 °C as evident by a narrower full width at half‐maximum of 35 min for β‐GaN, which is among the narrowest reported to date.

Blue‐violet light emitting gallium nitride p‐n junctions grown by electron cyclotron resonance‐assisted molecular beam epitaxy

Abstract: Blue‐violet gallium nitride (GaN) light emitting p‐n junctions were grown by the method of electron cyclotron resonance‐assisted molecular beam epitaxy. This method has been modified to minimize plasma induced defects. Contrary to similar devices grown by metalorganic chemical vapor deposition, these devices do not require any postgrowth annealing to activate the Mg acceptors in the p layer. These devices turn‐on at approximately 3 V and have a spectral emission peaking at 430 nm.

Study of defect states in GaN films by photoconductivity measurement

Abstract: Optical absorption by defect states in gallium nitride (GaN) films was studied by photoconductivity (PC) spectroscopy at room temperature. A number of undoped n‐type and Mg‐doped p‐type samples were employed in the present study. The PC response per absorbed photon decreased by more than four orders of magnitude as GaN became p‐type conducting. Furthermore, all the samples exhibit PC response at photon energies far below the band gap energy of GaN. The optical absorption increases with photon energy hν from 1.5 to 3.0 eV approximately as exp(hν/E0). The parameter E0 ranges from 180 to 280 meV, and is considerably smaller for the insulating p‐type sample. For a p‐type conducting sample, the PC response is flat between 0.7 and 1.4 eV. A model for the density of states distribution in the forbidden gap of GaN and the effect of Mg doping is proposed.

Electrochemical Investigation of the Gallium Nitride‐Aqueous Electrolyte Interface

Abstract: GaN (E{sub g} = {approximately}3.4 eV) was photoelectrochemically characterized and the energetic position of its bandedges determined with respect to SHE. Electrochemical impedance spectroscopy was employed to analyze the interface, determine the space charge layer capacitance, and, subsequently obtain the flatband potential of GaN in different aqueous electrolytes. The flatband potential of GaN varied at an approximately Nernstian rate in aqueous buffer electrolytes of different pHs indicating acid-base equilibria at the interface.

Theoretical study of electron transport in gallium nitride

Abstract: This paper describes characteristic electron transport properties for GaN in bulk and quantum well structures. First, ensemble Monte Carlo calculations of steady‐state electron drift velocity in bulk GaN are presented as a function of applied electric field for different lattice temperatures. At 300 K, the calculated peak steady‐state drift velocity is 2.8×107 cm/s and the threshold field is 160 kV/cm. It is found that the peak steady‐state electron drift velocity decreases only slightly by about 20% as the temperature increases from 300 to 600 K while the threshold field increases slightly by about 20%. Therefore, in addition to its high temperature stability, GaN has a low temperature coefficient making it ideal for high temperature applications. For electron transport in heterostructures, quantum mechanical calculations of the electron capture rate in GaN‐based quantum wells as a function of well thickness are also presented. An oscillatory behavior of the electron capture rate as a function of quantum...

Highly insulating monocrystalline gallium nitride thin films

Abstract: This invention relates to a method of preparing highly insulating GaN single crystal films in a molecular beam epitaxial growth chamber. A single crystal substrate is provided with the appropriate lattice match for the desired crystal structure of GaN. A molecular beam source of Ga and source of activated atomic and ionic nitrogen are provided within the growth chamber. The desired film is deposited by exposing the substrate to Ga and nitrogen sources in a two step growth process using a low temperature nucleation step and a high temperature growth step. The low temperature process is carried out at 100-400° C. and the high temperature process is carried out at 600-900° C. The preferred source of activated nitrogen is an electron cyclotron resonance microwave plasma.

Analysis of two‐step‐growth conditions for GaN on an AlN buffer layer

Abstract: Gallium nitride is grown by metalorganic vapor phase epitaxy with and without a low‐temperature‐grown AlN buffer layer. Variations in the surface morphology and the layer properties are compared between two‐step growth and direct growth to study the effects of various growth conditions. It is found that (i) conditions that stabilize the GaN(0001) surface serve as guidelines for obtaining mirrored surfaces, and (ii) raising GaN growth temperature improves crystallographic, electrical, and luminescence properties of GaN. The observed improvement in the layer properties with increase in GaN growth temperature suggests that increasing N2 dissociation pressure does not affect GaN properties. GaN growth conditions are analyzed thermodynamically to show that NH3 in the growth ambients has the potential to suppress thermal dissociation of GaN.

GaN-type light emitting device formed on a silicon substrate

Abstract: A light emitting device employing gallium nitride type compound semiconductor which generates no crystal defect, dislocation and can be separated easily to chips by cleavage and a method for producing the same are provided As a substrate on which gallium nitride type compound semiconductor layers are stacked, a gallium nitride type compound semiconductor substrate, a single-crystal silicon, a group II-VI compound semiconductor substrate, or a group III-V compound semiconductor substrate is employed.

Cathodoluminescence study of erbium and oxygen coimplanted gallium nitride thin films on sapphire substrates

Abstract: The cathodoluminescence(CL) of erbium and oxygen coimplanted GaN(GaN:Er:O) and sapphire (sapphire:Er:O) was studied as a function of temperature. Following annealing, the 1.54 μm intra‐4f‐shell emission line was observed in the temperature range of 6–380 K. As the temperature increased from 6 K to room temperature, the integrated intensity of the infrared peak decreased by less than 5% for GaN:Er:O, while it decreased by 18% for sapphire:Er:O. The observation of minimal thermal quenching by CL suggests that Er and O dopedGaN is a promising material for electrically pumped room‐temperature optical devices emitting at 1.54 μm.

Synthesis and characterization of high purity, single phase GaN powder

Abstract: Synthesis of high-purity, single-phase gallium nitride (GaN) powder has been achieved by reacting molten Ga with flowing ammonia (NH3) in a hot wall tube furnace. The optimum temperature, NH3 flow rate, and position of the boat in the hot wall tube furnace relative to the NH3 inlet for the complete reaction to pure GaN for our system were 975 °C, 400 standard cubic centimeters per minute (seem) and 50 cm, respectively. The X-ray diffraction (XRD) data revealed the GaN to be single phase with a = 3.1891 A, c = 5.1855 A, in space group P63mc, Z=2 and Dx =6.089 g cm−3. Scanning electron microscopy revealed a particle size distribution in the crushed material between 1 and 5 μm with most of the particles being ≍1 μm.

The Role of Impurities in Hydride Vapor Phase Epitaxially Grown Gallium Nitride

Abstract: Gallium nitride (GaN) films grown by hydride vapor phase epitaxy on a variety of substrates have been investigated to study what role silicon and oxygen impurities play in determining the residual donor levels found in these films. Secondary ion mass spectroscopy analysis has been performed on these films and impurity levels have been normalized to ion implanted calibration standards. While oxygen appears to be a predominate impurity in all of the films, in many of them the sum of silicon and oxygen levels is insufficient to account for the donor concentration determined by Hall measurements. This suggests that either another impurity or a native defect is at least partly responsible for the autodoping of GaN. Additionally, the variation of impurity and carrier concentration with surface orientation and/or nucleation density suggests either a crystallographic or defect-related incorporation mechanism.

Lattice constants, thermal expansion and compressibility of gallium nitride

Abstract: High-resolution X-ray diffraction measurements can be performed at variable temperatures and pressures. The usefulness of such experiments is shown when taking gallium nitride, which is a wide-band semiconductor, as an example. The GaN samples were grown at high pressures (bulk crystals) and as epitaxial layers on silicon carbide and sapphire. The X-ray examinations were done at temperatures of 293-750 K and at pressures of up to 8 kbar. The results served for an evaluation of the basic physical properties of gallium nitride; namely lattice constants, thermal expansion and compressibility. The comparison of monocrystals with epitaxial layers grown on highly mismatched substrates provided important information about the influence of the substrate on the crystallographic perfection of the layers.

Method for growing gallium nitride compound semiconductor crystal, and gallium nitride compound semiconductor device

Abstract: In a method for growing a gallium nitride semiconductor crystal on a single-crystal substrate, the (011) or (101) face of perovskite containing group 13 (3B) rare-earth elements is used as the single-crystal substrate, so that a gallium nitride semiconductor crystal having an excellent crystallinity is formed on the surface of the substrate by epitaxial growth.

Basic studies of gallium nitride growth on sapphire by metalorganic chemical vapor deposition and optical properties of deposited layers

Abstract: We have studied the growth of gallium nitride on c-plane sapphire substrates. The layers were grown in a horizontal metalorganic chemical vapor deposition reactor at atmospheric pressure using trimethylgallium (TMG) and ammonia (NH3). Variation of the V/III ratio (150–2500) shows a distinct effect on the growth rate. With decreasing V/III ratio, we find an increasing growth rate. Variation of the growth temperature (700–1000°C) shows a weak increase in growth rate with temperature. Furthermore, we performed secondary ion mass spectroscopy measurements and find an increasing carbon incorporation in the GaN films with decreasing ammonia partial pressure and a growing accumulation of carbon at the substrate interface. Photoluminescence measurements show that samples with high carbon content show a strong yellow luminescence peaking at 2.2 eV and a near band gap emission at 3.31 eV. With increasing carbon content, the intensity of the 3.31 eV line increases suggesting that a carbon related center is involved.

Threshold Estimation of GaN-Based Surface Emitting Lasers Operating in Ultraviolet Spectral Region

Abstract: The GaN-based vertical cavity surface emitting laser operating in the ultraviolet spectral region is proposed and its threshold current density is estimated. The calculated result indicates that low-threshold surface emitting lasers using a GaN layer as an active region can be realized by employing reasonably highly reflective mirrors such as AlN/AlGaN multilayer mirrors.

Semiconductor light emitting element and manufacturing method therefor

Abstract: A manufacturing method of semiconductor light emitting element including the steps of: (a) laminating a gallium nitride compound semiconductor layer for forming a luminous part on a substrate including at least an n-type layer and a p-type layer, by organic metal compound vapor phase growth method, (b) forming the gallium nitride compound semiconductor layer in a nitrogen gas atmosphere after laminating, and lowering the ambient temperature to the temperature for growing a GaAs compound in vapor phase and annealing the p-type layer of the gallium nitride compound semiconductor, (c) forming a film of at least one type selected from the group consisting of GaAs, GaP, InAs, InP, all doped with Mg, and part of these group III elements replaces by Al. on the surface of the gallium nitride compound semiconductor layer, as a protective layer in the nitrogen atmosphere, and (d) annealing the p-type layer of gallium nitride compound semiconductor layer simultaneously with forming the protective film, and lowering to room temperature after annealing, and removing the protective film by etching.

Doping of gallium nitride using disilane

Abstract: The silicon doping of n-type GaN using disilane has been demonstrated for films grown on sapphire substrates by low pressure organometallic vapor phase epitaxy. The binding energy of an exciton bound to a neutral Si donor has been determined from low temperature (6K) photoluminescence spectra to be 8.6 meV. Nearly complete activation of the Si impurity atom in the GaN lattice has been observed.

Group III nitride compound semiconductor laser diode and method for producing same

Abstract: An improved laser diode is made of a gallium nitride compound semiconductor ((Al x Ga 1-x ) y In 1-y N; 0≦x≦1; 0≦x≦1) with a double heterojunction structure having the active layer held between layers having a greater band gap. The laser diode comprises mirror surfaces formed by cleaving the multi-layered coating and the sapphire substrate in directions parallel to (c axis) of the sapphire substrate. The intermediate zinc oxide (ZnO) layer is selectively removed by wet etching with a ZnO-selective liquid etchant so as to form gaps between the sapphire substrate and the bottom-most sub-layer of the semiconductor laser element layer. The semiconductor laser element layer is cleaved with the aid of the gaps, and the resulting planes of cleavage are used as the mirror surfaces of the laser cavity.

Development of chemical beam epitaxy for the deposition of gallium nitride

Abstract: Modern approaches to the growth of high quality gallium nitride thin films have focused on the use of metal-organic vapour phase epitaxy or plasma-assisted gas source molecular beam epitaxy. However, both of these techniques possess limitations. The present study therefore examined a new approach to GaN deposition using chemical beam epitaxy and the new nitrogen precursor, hydrogen azide. Thin films of gallium nitride (GaN) were successfully prepared. X-ray photoelectron spectroscopy reveals that stoichiometric materials is formed with little or no contamination when HN3 and a range of Ga precursors react on the substrate at temperatures down to 450°C. The results indicate that the incorporation efficiency of N in the GaN film from HN3 is high, suggesting the precursor may provide a more attractive route to the deposition of GaN films under low pressure molecular beam conditions than is currently offered using ammonia or plasma-excited nitrogen beam sources. Electrical measurements on the grown films are also reported.