Showing papers on "Gallium nitride published in 1998"

Group III nitride photonic devices on silicon carbide substrates with conductive buffer interlayer structure

Abstract: An optoelectronic device with a Group III Nitride active layer is disclosed that comprises a silicon carbide substrate; an optoelectronic diode with a Group III nitride active layer; a buffer structure selected from the group consisting of gallium nitride and indium gallium nitride between the silicon carbide substrate and the optoelectronic diode; and a stress-absorbing structure comprising a plurality of predetermined stress-relieving areas within the crystal structure of the buffer structure, so that stress-induced cracking that occurs in the buffer structure occurs at predetermined areas rather than elsewhere in the buffer structure.

Damage-free separation of GaN thin films from sapphire substrates

Abstract: Gallium nitride thin films grown on sapphire substrates were successfully separated and transferred onto Si substrates using single 38 ns KrF excimer laser pulses directed through the transparent substrate at fluences in the range of 400–600 mJ/cm2. The absorption of the 248 nm radiation by the GaN at the interface induces rapid thermal decomposition of the interfacial layer, yielding metallic Ga and N2 gas. The substrate is easily removed by heating above the Ga melting point of 30 °C. Scanning electron microscopy and x-ray diffraction of the GaN films before and after lift-off demonstrate that the structural quality of the GaN films is not altered by the separation and transfer process.

Electron transport in wurtzite indium nitride

Abstract: We present the velocity-field characteristics of wurtzite indium nitride, determined using an ensemble Monte Carlo approach. It is found that indium nitride exhibits an extremely high peak drift velocity at room temperature, 4.3×107 cm/s, at a doping concentration of 1.0×1017 cm−3. We also demonstrate that the saturation drift velocity of indium nitride, 2.5×107 cm/s, is comparable to that of gallium nitride, and much larger than that of gallium arsenide. Our results suggest that the transport characteristics of indium nitride are superior to those of gallium nitride and gallium arsenide, over a wide range of temperatures, from 150 to 500 K, and doping concentrations, up to 1.0×1019 cm−3. Hence, indium nitride has considerable potential for device applications.

Gallium nitride whiskers formed by selective photoenhanced wet etching of dislocations

Abstract: Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure of n-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 μm. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN.

Gallium nitride semiconductor structures including a lateral gallium nitride layer that extends from an underlying gallium nitride layer

Abstract: A gallium nitride semiconductor layer is fabricated by masking an underlying gallium nitride layer with a mask that includes an array of openings therein, and growing the underlying gallium nitride layer through the array of openings and onto the mask, to thereby form an overgrown gallium nitride semiconductor layer. Although dislocation defects may propagate vertically from the underlying gallium nitride layer to the grown gallium nitride layer through the mask openings, the overgrown gallium nitride layer is relatively defect free. The overgrown gallium nitride semiconductor layer may be overgrown until the overgrown gallium nitride layer coalesces on the mask, to form a continuous overgrown monocrystalline gallium nitride semiconductor layer. The gallium nitride semiconductor layer may be grown using metalorganic vapor phase epitaxy. Microelectronic devices may be formed in the overgrown gallium nitride semiconductor layer.

Efficiency of NH3 as nitrogen source for GaN molecular beam epitaxy

Abstract: We show that optical reflectivity measurements can be used to evaluate the part of a NH3 flux which reacts with a Ga-terminated GaN surface or with a Ga-flux simultaneously impinging on the surface, as in standard molecular beam epitaxy situation. At least for temperatures not exceeding 700 °C, the ratio of the reacted part of the NH3 flux to the incident flux can be assimilated to the NH3 cracking efficiency. Being nearly zero below a threshold temperature of 450 °C, it increases with temperature but remains low (∼4%) explaining why an exceptionally high V/III flux ratio is necessary to grow GaN using NH3.

Gallium nitride semiconductor structure including laterally offset patterned layers

Abstract: A gallium nitride semiconductor layer is fabricated by masking an underlying gallium nitride layer with a first mask that includes a first array of openings therein and growing the underlying gallium nitride layer through the first array of openings and onto the first mask, to thereby form a first overgrown gallium nitride semiconductor layer. The first overgrown layer is then masked with the second mask that includes a second array of openings therein. The second array of openings is laterally offset from the first array of openings. The first overgrown gallium nitride layer is then grown through the second array of openings and onto the second mask, to thereby form a second overgrown gallium nitride semiconductor layer. Microelectronic devices may then be formed in the second overgrown gallium nitride semiconductor layer.

Gallium nitride (GaN)

Abstract: List of Contributors. R.J. Molnar, Hydride Vaper Phase Epitaxial Growth of III-V Nitrides. T.D. Moustakas, Growth of III-V Nitrides by MBE. Z. Lilental-Weber, Defects in Bulk GaN and Homeopitaxial Layers. C.G. Van de Walle and N.M. Johnson, Hydrogen in III-V Nitrides. W. Gotz and N.M. Johnson, Characterization of Dopants and Deep Level Defects in Gallium Nitride. B. Gil, Stress Effects on Optical Properties. C. Kisielowski, Strain in GaN Thin Films and Heterostructures. J.A. Miragliotta and D.K. Wickenden, Nonlinear Optical Properties of Gallium Nitride. B.K. Meyer, Magnetic Resonance Investigations on Group III-Nitrides. M.S. Shur and M.A. Khan, GaN and AIGaN Ultraviolet Detectors. C.H. Qui and J.I. Pankove, III-V Nitride Based X-Ray Detectors. Subject Index. Contents of Volumes in This Series.

Deep ultraviolet enhanced wet chemical etching of gallium nitride

Abstract: We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally doped n-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid (H3PO4) and potassium hydroxide (KOH) solutions of pH values ranging from −1 to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in dilute H3PO4 and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN.

Method for producing a gallium nitride epitaxial layer

Abstract: The invention concerns a method for producing a gallium nitride (GaN) epitaxial layer characterised in that it consists in depositing on a substrate a dielectric layer acting as a mask and depositing on the masked gallium nitride, by epitaxial deposit, so as to induce the deposit of gallium nitride patterns and the anisotropic lateral growth of said patterns, the lateral growth being pursued until the different patterns coalesce. The deposit of the gallium nitride patterns can be carried out ex-situ by dielectric etching or in-situ by treating the substrate for coating it with a dielectric film whereof the thickness is of the order of one angstrom. The invention also concerns the gallium nitride layers obtained by said method.

Electrical characteristics of magnesium-doped gallium nitride junction diodes

Abstract: Electrical characteristics of lateral p+n diodes made from gallium nitride epitaxial layers on sapphire substrates are reported. The current–voltage characteristics are observed to have several distinct regions in which a tunneling current has been identified at low forward bias in addition to the conventional temperature-dependent diffusion current observed at moderate forward bias. A tunneling behavior indicates the presence of deep-level traps at the junction, which alter the electrical behavior of these junctions compared to the conventional behavior. In addition, space-charge-limited currents are found to influence these junctions at large forward and reverse bias.

Method of forming gallium nitride crystal

Abstract: The method of forming gallium nitride crystal comprises the following three steps: the first step of heating a silicon substrate 1 in gas atmosphere including gallium, the second step of forming the first gallium nitride 3 on the silicon substrate 1, the third step of forming the second gallium nitride 4 on the first gallium nitride 3 at the higher temperature than when the first gallium nitride 3 has been formed. The method including these three steps can produce a thick film crystal of gallium nitride having excellent flatness and crystallinity.

Study of avalanche breakdown and impact ionization in 4H silicon carbide

Abstract: Epitaxial p-n diodes in 4H SiC are fabricated with uniform avalanche multiplication and breakdown. Photomultiplication measurements were performed to determine electron and hole ionization rates. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained. We discuss ionization mechanisms in 4H SiC and make a comparison between silicon carbide and gallium nitride.

Phonon density of states of bulk gallium nitride

Abstract: We report the measured phonon density of states of a bulk GaN powder by time-of-flight neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45–65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model.

Molecular-beam epitaxy of gallium nitride on (0001) sapphire substrates using ammonia

Abstract: Ammonia is used for growing undoped GaN layers by gas source molecular-beam epitaxy on c-plane sapphire substrates. The growth mode is layer by layer as shown by the observation of reflection high-energy electron diffraction intensity oscillations. The structural quality is studied by x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Low-temperature photoluminescence (PL) and reflectivity demonstrate intrinsic excitonic emission. Room-temperature PL exhibits a strong band-edge intensity and a weak deep-level emission, the so-called yellow band. Finally, secondary ion mass spectroscopy is carried out to check the residual impurity levels of Si, C, and O.

Atomic force microscopy observation of threading dislocation density reduction in lateral epitaxial overgrowth of gallium nitride by MOCVD

Abstract: Extended defect reduction at the surface of GaN grown by lateral epitaxial overgrowth (LEO) on large-area GaN/Al2O3 wafers by low pressure MOCVD is demonstrated by atomic force microscopy. The overgrown GaN has a rectangular cross section with smooth (0001) and facets. The density of mixed character threading dislocations at the surface of the LEO GaN is reduced by at least 3–4 orders of magnitude from that of bulk GaN. Dislocation-free GaN surfaces exhibit an anisotropic step structure that is attributed to the orientation dependence of the dangling bond density at the step edges.

H2GaN3 and Derivatives: A Facile Method to Gallium Nitride

Abstract: We describe the formation and properties of H2GaN3 (1), which is a very simple and stable molecular source for chemical vapor deposition (CVD) of GaN heterostructures. Compound 1 and the perdeutera...

GaN semiconductor light emitting device having a group II-VI 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-IV compound semiconductur substrate is employed.

Gallium nitride type compound semiconductor light-emitting device having buffer layer with non-flat surface

Abstract: A gallium nitride type compound semiconductor light-emitting device of the present invention includes: a substrate; a buffer layer, formed on the substrate, having a thick region and a thin region in terms of a thickness taking a surface of the substrate as a reference level; and a semiconductor layered structure, formed on the buffer layer, at least including an undoped gallium nitride type compound semiconductor layer, a gallium nitride type compound semiconductor active layer, and a P-type gallium nitride type compound semiconductor cladding layer.

Optical activation of Be implanted into GaN

Abstract: Single crystalline (0001) gallium nitride layers were implanted with beryllium. Photoluminescence (PL) measurements were subsequently performed as a function of implantation dose and annealing temperature. One new line in the PL spectra at 3.35 eV provided strong evidence for the presence of optically active Be acceptors and has been assigned to band–acceptor (eA) recombinations. The determined ionization energy of 150±10 meV confirmed that isolated Be has the most shallow acceptor level in GaN. Co-implantation of nitrogen did not enhance the activation of the Be acceptors.

Gallium nitride/conjugated polymer hybrid light emitting diodes: Performance and lifetime

Abstract: We report on pure white light emission from GaN/conjugated polymer hybrid light emitting diodes (LEDs) using a single layer of conjugated polymer. When the conjugated polymer is properly encapsulated, the hybrid LEDs can operate at least 5000 h, with decay in output luminosity comparable to that of commercial blue GaN lamps. By using different conjugated polymers, emission with a full range of colors is demonstrated with the hybrid LED.

Epitaxial growth of GaN thin film on sapphire with a thin ZnO buffer layer by liquid target pulsed laser deposition

Abstract: Epitaxially grown gallium nitride thin films were deposited on sapphire(0001) substrates with a thin zinc oxide buffer layer by a liquid target pulsed laser deposition technique. The GaN thin film optimized at a substrate temperature of 600 °C has an epitaxial relationship with ZnO buffered sapphire(0001) of (0001)GaN//(0001)ZnO//(0001)sapphire, and (1010)GaN//(1010)ZnO//(1120)sapphire. The surface morphology was also improved by applying a ZnO buffer layer shown by scanning electron microscopy. Although the as-grown GaN thin film showed no band edge or yellow band photoluminescence at room temperature, a weak band edge luminescence of 3.42 eV could be seen at 20 K.

Light-emitting diode

Abstract: PROBLEM TO BE SOLVED: To enhance the visibility of a light-emitting diode having a light-emitting element made of a gallium nitride based compound semiconductor material and to improve the luminance of the light-emitting diode. SOLUTION: The light-emitting diode comprises a metal stem, a metal post, a light-emitting element arranged on the metal stem and a resin mold that surrounds the entirety of the light-emitting element, wherein the resin mold is doped with a fluorescent dye or fluorescent pigment that, when excited by light emitted from the light-emitting element, emits the fluorescence of a wavelength different from an excitation wavelength. The fluorescent dye or the fluorescent pigment emits visible light of a wavelength longer than the excitation wavelength when excited by visible light coming from the light-emitting element. The light-emitting element is provided with a gallium nitride based compound semiconductor made of stacked n- and p-type layers that emit visible light. The light-emitting element composed of the gallium nitride based compound semiconductor has an electrode connected to the metal post through a gold line by means of wire bonding. COPYRIGHT: (C)2005,JPO&NCIPI

Compound semiconductor device based on gallium nitride

Abstract: A compound semiconductor device based on gallium nitride which can have a thick gallium nitride semiconductor layer serving to prevent cracks or defects attributable to a strain caused by a difference in lattice constant or coefficient of thermal expansion. Between a contact layer (4) consisting of a film of n-type GaN and a clad layer (5) consisting of a film of a n-type AlyGa1-yN is interposed a crack-preventive buffer layer (5) having both of the compositions of the two films.

The piezoelectric coefficient of gallium nitride thin films

Abstract: A laser interferometer was used to measure the d33 piezoelectric coefficient of wurtzite GaN. The GaN was in the form of 1 μm thick films, grown by chemical vapor deposition and the measurement of the piezoelectric coefficient was made with a spatial resolution of 100 μm. Sample mounting was found to play an important part in the observed response. For rigidly mounted samples, the measured d33 was 2.0±0.1 pm V−1.

High quality, semi-insulating gallium nitride and method and system for forming same

Abstract: A method for growing high-quality gallium nitride over a substrate is disclosed. The method comprises growing first layer with a high dislocation density over the substrate, a second layer having a high number of point defects and a reduced dislocation density as compared to the dislocation density of the first layer over the first layer, and a third layer having a reduced number of point defects as compared to the second layer over the second layer. The resulting gallium nitride is semi-insulating, which inhibits parasitic current flow and parasitic capacitive effects, yet it not so insulating that electron flow in adjacent transistor channels is inhibited.

Low defect density gallium nitride epilayer and method of preparing the same

Abstract: A GaN epilayaer grown on a lattice mismatched saphire substrate is subjected to rapid thermal processing in order the reduce the defect density especially in the proximate the top (device) surface of the GaN epilayer.