Showing papers on "Gallium nitride published in 2002"

AlGaN/GaN HEMTs-an overview of device operation and applications

Abstract: Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

Single gallium nitride nanowire lasers

Abstract: There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources.

Gallium Nitride Nanowire Nanodevices

Abstract: Field effect transistors (FETs) based on individual GaN nanowires (NWs) have been fabricated. Gate-dependent electrical transport measurements show that the GaN NWs are n-type and that the conductance of NW−FETs can be modulated by more than 3 orders of magnitude. Electron mobilities determined for the GaN NW FETs, which were estimated from the transconductance, were as high as 650 cm2/V·s. These mobilities are comparable to or larger than thin film materials with similar carrier concentration and thus demonstrate the high quality of these NW building blocks and their potential for nanoscale electronics. In addition, p−n junctions have been assembled in high yield from p-type Si, and these n-type GaN NWs and their potential applications are discussed.

Substrates for gallium nitride epitaxy

Abstract: In this review, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed. Among semiconductors, GaN is unique; most of its applications uses thin GaN films deposited on foreign substrates (materials other than GaN); that is, heteroepitaxial thin films. As a consequence of heteroepitaxy, the quality of the GaN films is very dependent on the properties of the substrate—both the inherent properties such as lattice constants and thermal expansion coefficients, and process induced properties such as surface roughness, step height and terrace width, and wetting behavior. The consequences of heteroepitaxy are discussed, including the crystallographic orientation and polarity, surface morphology, and inherent and thermally induced stress in the GaN films. Defects such as threading dislocations, inversion domains, and the unintentional incorporation of impurities into the epitaxial GaN layer resulting from heteroepitaxy are presented along with their effect on device processing and performance. A summary of the structure and lattice constants for many semiconductors, metals, metal nitrides, and oxides used or considered for GaN epitaxy is presented. The properties, synthesis, advantages and disadvantages of the six most commonly employed substrates (sapphire, 6H-SiC, Si, GaAs, LiGaO 2 , and AlN) are presented. Useful substrate properties such as lattice constants, defect densities, elastic moduli, thermal expansion coefficients, thermal conductivities, etching characteristics, and reactivities under deposition conditions are presented. Efforts to reduce the defect densities and to optimize the electrical and optical properties of the GaN epitaxial film by substrate etching, nitridation, and slight misorientation from the (0 0 0 1) crystal plane are reviewed. The requirements, the obstacles, and the results to date to produce zincblende GaN on 3C-SiC/Si(0 0 1) and GaAs are discussed. Tables summarizing measures of the GaN quality such as XRD rocking curve FWHM, photoluminescence peak position and FWHM, and electron mobilities for GaN epitaxial layers produced by MOCVD, MBE, and HVPE for each substrate are given. The initial results using GaN substrates, prepared as bulk crystals and as free-standing epitaxial films, are reviewed. Finally, the promise and the directions of research on new potential substrates, such as compliant and porous substrates are described.

Estimation of the isotope effect on the lattice thermal conductivity of group IV and group III-V semiconductors

Abstract: The isotope effect on the lattice thermal conductivity for group IV and group III-V semiconductors is calculated using the Debye-Callaway model modified to include both transverse and longitudinal phonon modes explicitly. The frequency and temperature dependences of the normal and umklapp phonon-scattering rates are kept the same for all compounds. The model requires as adjustable parameters only the longitudinal and transverse phonon Gr\"uneisen constants and the effective sample diameter. The model can quantitatively account for the observed isotope effect in diamond and germanium but not in silicon. The magnitude of the isotope effect is predicted for silicon carbide, boron nitride, and gallium nitride. In the case of boron nitride the predicted increase in the room-temperature thermal conductivity with isotopic enrichment is in excess of 100%. Finally, a more general method of estimating normal phonon-scattering rate coefficients for other types of solids is presented.

Trapping effects in GaN and SiC microwave FETs

Abstract: It is well known that trapping effects can limit the output power performance of microwave field-effect transistors (FETs). This is particularly true for the wide bandgap devices. In this paper we review the various trapping phenomena observed in SiC- and GaN-based FETs that contribute to compromised power performance. For both of these material systems, trapping effects associated with both the surface and with the layers underlying the active channel have been identified. The measurement techniques utilized to identify these traps and some of the steps taken to minimize their effects, such as modified buffer layer designs and surface passivation, are described. Since similar defect-related phenomena were addressed during the development of the GaAs technology, relevant GaAs work is briefly summarized.

Silicon carbide benefits and advantages for power electronics circuits and systems

Abstract: Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), provide larger bandgaps, higher breakdown electric field, and higher thermal conductivity. Power semiconductor devices made with SiC and GaN are capable of higher blocking voltages, higher switching frequencies, and higher junction temperatures than silicon devices. SiC is by far the most advanced material and, hence, is the subject of attention from power electronics and systems designers. This paper looks at the benefits of using SiC in power electronics applications, reviews the current state of the art, and shows how SiC can be a strong and viable candidate for future power electronics and systems applications.

Group III nitride based light emitting diode structures with a quantum well and superlattice, group III nitride based quantum well structures and group III nitride based superlattice structures

Abstract: A Group III nitride based semiconductor device is disclosed, comprising: a doped Group III nitride layer; and a gallium nitride based superlattice directly on the doped Group III nitride layer, the gallium nitride superlattice being doped with an n-type impurity and having at least two periods of alternating layers of InXGa1-XN and InYGa1-YN, where 0 ≤ X < 1 and X is not equal to Y and wherein a thickness of a first of the alternating layers is less than a thickness of a second of the alternating layers.

GaN-based optoelectronics on silicon substrates

Abstract: Cracking of GaN on Si usually occurs due to the large thermal mismatch of GaN and Si when layer thicknesses exceed approximately 1 μm in metalorganic chemical vapor deposition (MOCVD) preventing the realization of device-quality material. The thermal stress can be reduced significantly by a combination of different concepts such as the insertion of low-temperature AlN interlayers, introducing multiple AlGaN/GaN interlayers, and growing on prepatterned substrates. The growth of crack-free GaN-based light emitting diodes (LEDs) on silicon on patterned Si(111) with areas of 100 μm×100 μm is reported

Radiation hardness of gallium nitride

Abstract: Gallium nitride (GaN) light emitting diodes (LEDs) were irradiated at room temperature with electrons in the range 300-1400 keV A threshold energy of 440 keV was observed, corresponding to a gallium atom displacement energy of 19/spl plusmn/2 eV This value of the displacement energy compares with that of silicon carbide but is smaller than that of diamond and larger than that of gallium arsenide (GaAs) No threshold energy for the nitrogen atom was observed It is concluded that the nitrogen sublattice repairs itself through annealing The measured displacement energy is used to determine the Rutherford cross section, which permits a theoretical comparison of electron and proton irradiation damage in GaN The effects of 25 MeV electrons on gallium nitride films have been studied by photoluminescence (PL), and according to the literature, they introduce transitions in the near infrared part of the spectrum Experiments on gallium nitride films using 2 MeV protons are reported in this work The same transitions in the near infrared part of the spectrum are observed by PL It is deduced that 2 MeV protons are about 1000 times more damaging than 25 MeV electrons The Rutherford cross section predicts a value of 214 The difference is attributed to the defect recombination rate which depends on the particle type The nature of the transitions in the near infrared part of the spectrum is reviewed The GaN films were annealed at 400/spl deg/C for 30 min As a result of annealing, another transition appears in the green part of the spectrum Transitions involving the gallium vacancy in irradiated GaN are discussed

Nitride semiconductor element and production method for nitride semiconductor element

Abstract: A nitride semiconductor element excellent in characteristics even its element structure is three-dimensionally formed by a selective growth or the like, and a production method therefor. A nitride semiconductor element having an electrode layer (21) formed via a high-resistance region such as an undoped gallium nitride layer (17) on the upper layer of a crystal layer having a side surface (16s) and the upper layer (16t) and being grown three-dimensionally. A high resistance region provided to the upper layer (16t) allows current to flow so as to bypass the high resistance region of the upper layer (16t) to form a current route mainly consisting of the side surface (16s) with the upper layer (16t) bypassed. As a result, current is prevented from flowing to the upper layer (16t) having a poor crystallinity.

Gallium nitride materials and methods

Abstract: The invention provides semiconductor materials including a gallium nitride material layer formed on a silicon substrate and methods to form the semiconductor materials. The semiconductor materials include a transition layer formed between the silicon substrate and the gallium nitride material layer. The transition layer is compositionally-graded to lower stresses in the gallium nitride material layer which can result from differences in thermal expansion rates between the gallium nitride material and the substrate. The lowering of stresses in the gallium nitride material layer reduces the tendency of cracks to form. Thus, the invention enables the production of semiconductor materials including gallium nitride material layers having few or no cracks. The semiconductor materials may be used in a number of microelectronic and optical applications.

Semiconductor light-emitting device

Abstract: PROBLEM TO BE SOLVED: To obtain a semiconductor light emitting device using a gallium nitride series semiconductor, wherein the semiconductor light emitting device such as a light emitting diode or the like having a high luminous efficiency even by using a silicon substrate is obtained. SOLUTION: The semiconductor light emitting device has such a structure that the surface of an active layer 6 composed of the gallium nitride series semiconductor has the uneven structure of a pyramid shape, and the recess of this uneven structure is filled with a first clad layer 7 composed of a p-type gallium nitride series semiconductor. Preferably, the dislocation defect density of a second clad layer 5 composed of an n-type gallium nitride series semiconductor forming a part of an underlaying layer of the active layer 6 is 10 9 to 10 11 /cm 2 , and preferably, the gap of a dislocation defect in the second clad layer 5 is 120 to 170 nm. Further, preferably, the entire thickness of the underlaying layer is 3 μm or less. The active layer 6 is formed by an organic metal vapor deposition, and its film forming pressure conditions are set to atmospheric pressure or rather lower pressure than the atmospheric pressure. COPYRIGHT: (C)2005,JPO&NCIPI

SiC and GaN transistors - is there one winner for microwave power applications?

Abstract: Wide bandgap semiconductors show promise for high-power microwave electronic devices. Primarily due to low breakdown voltage, it has not been possible to design and fabricate solid-state transistors that can yield radio-frequency (RF) output power on the order of hundreds to thousands of watts. This has severely limited their use in power applications. Recent improvements in the growth of wide bandgap semiconductor materials, such as SiC and the GaN-based alloys, provide the opportunity to now design and fabricate microwave transistors that demonstrate performance previously available only from microwave tubes. The most promising electronic devices for fabrication in wide bandgap semiconductors for these applications are metal-semiconductor field-effect transistors (MESFETs) fabricated from the 4H-SiC polytype and heterojunction field-effect transistors (HFETs) fabricated using the AlGaN/GaN heterojunction. These devices can provide RF output power on the order of 5-6 W/mm and 10-12 W/mm of gate periphery, respectively. 4H-SiC MESFETs should produce useful performance at least through X band and AlGaN/GaN HFETs should produce useful performance well into the millimeter-wave region, and potentially as high as 100 GHz.

Pendeoepitaxial gallium nitride semiconductor layers on silicon carbide substrates

Abstract: An underlying gallium nitride layer on a silicon carbide substrate is masked with a mask that includes an array of openings therein, and the underlying gallium nitride layer is etched through the array of openings to define posts in the underlying gallium nitride layer and trenches therebetween. The posts each include a sidewall and a top having the mask thereon. The sidewalls of the posts are laterally grown into the trenches to thereby form a gallium nitride semiconductor layer. During this lateral growth, the mask prevents nucleation and vertical growth from the tops of the posts. Accordingly, growth proceeds laterally into the trenches, suspended from the sidewalls of the posts. The sidewalls of the posts may be laterally grown into the trenches until the laterally grown sidewalls coalesce in the trenches to thereby form a gallium nitride semiconductor layer. The lateral growth from the sidewalls of the posts may be continued so that the gallium nitride layer grows vertically through the openings in the mask and laterally overgrows onto the mask on the tops of the posts, to thereby form a gallium nitride semiconductor layer. The lateral overgrowth can be continued until the grown sidewalls coalesce on the mask to thereby form a continuous gallium nitride semiconductor layer. Microelectronic devices may be formed in the continuous gallium nitride semiconductor layer.

AlGaN/GaN HEMTs on SiC with f/sub T/ of over 120 GHz

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) grown on semi-insulating SiC substrates with a 0.12 /spl mu/m gate length have been fabricated. These 0.12-/spl mu/m gate-length devices exhibited maximum drain current density as high as 1.23 A/mm and peak extrinsic transconductance of 314 mS/mm. The threshold voltage was -5.2 V. A unity current gain cutoff frequency (f/sub T/) of 121 GHz and maximum frequency of oscillation (f/sub max/) of 162 GHz were measured on these devices. These f/sub T/ and f/sub max/ values are the highest ever reported values for GaN-based HEMTs.

GaN-Based Devices on Si

Abstract: Nowadays, GaN-based devices are usually grown on sapphire or silicon-carbide substrates. These are either insulating or very expensive and not available in large diameter. A well-conducting low-cost alternative is silicon also enabling the integration of optoelectronics or high-power electronics with Si-based electronics. The main problem limiting a fast progress of GaN growth on silicon is the thermal mismatch of GaN and Si leading to cracks even below device-relevant layer thicknesses. In the last few years, since the first demonstration of a molecular beam epitaxy grown GaN-based light emitting diode on Si in 1998 the activities in research of GaN on Si increased dramatically. Meanwhile, several concepts to lower stress, avoid cracks, and improve the material quality exist. Meanwhile the material quality has improved significantly and is about as good as on sapphire so that it is only a question of time until GaN-based devices on Si come into market. This article gives a review on the latest developments in group-III nitride growth on Si by metal organic vapor phase epitaxy.

Dislocation effect on light emission efficiency in gallium nitride

Abstract: We modify the model of nonradiative carrier recombination on threading dislocation cores [Z. Z. Bandic, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electron. 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and nonequilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ∼107 cm−2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement.

Strained gallium nitride nanowires

Abstract: Gallium nitride nanowires were synthesized on silicon substrates by chemical vapor deposition using the reaction of gallium and gallium nitride mixture with ammonia. Iron nanoparticles were used as catalysts. The diameter of nanowires is uniform as 25 nm and the lengths are 20–40 μm. The nanowires have single crystalline wurtzite structure with a few stacking faults. A careful examination into x-ray diffraction and Raman scattering data revealed that the separations of the neighboring lattice planes along the growth direction are shorter than those of bulk gallium nitride. The nanowires would experience biaxial compressive stresses in the inward radial direction and the induced tensile uniaxial stresses in the growth direction. The shifts of the band gap due to the stresses have been estimated using the experimental data, showing that the reduction of the band gap due to the tensile stresses can occur more significantly than the increase due to the compressive stresses. The temperature-dependent photoluminescence (PL) of the nanowires exhibit a strong broad band in the energy range of 2.9–3.6 eV. The PL could originate from the recombination of bound excitons. The strong room-temperature PL would be in line with the existence of strains inside the nanowires. The peak appears at the lower energy than that of the epilayer, which is consistent with the decrease of the band gap predicted from the x-ray diffraction and Raman data. The various strengths of stress may result in the widely distributed PL energy position.

Influence of Si-doping on the characteristics of InGaN-GaN multiple quantum-well blue light emitting diodes

Abstract: A detailed study on the effects of Si-doping in the GaN barrier layers of InGaN-GaN multiquantum well (MQW) light-emitting diodes (LEDs) has been performed. Compared with unintentionally doped samples, X-ray diffraction results indicate that Si-doping in barrier layers can improve the crystal and interfacial qualities of the InGaN-GaN MQW LEDs. It was also found that the forward voltage is 3.5 and 4.52 V, the 20-mA luminous intensity is 36.1 and 25.1 mcd for LEDs with a Si-doped barrier and an unintentionally doped barrier, respectively. These results suggests that one can significantly improve the performance of InGaN-GaN MQW LEDs by introducing Si doping in the GaN barrier layers.

Electrical transport properties of individual gallium nitride nanowires synthesized by chemical-vapor-deposition

Abstract: We have synthesized high-quality gallium nitride (GaN) nanowires by a chemical-vapor-deposition method and studied the electrical transport properties. The electrical measurements on individual GaN nanowires show a pronounced n-type field effect due to nitrogen vacancies in the whole measured temperature ranges. The n-type gate response and the temperature dependence of the current–voltage characteristics could be understood by the band bending at the interface of the metal electrode and GaN wire. The estimated electron mobility from the gate modulation characteristics is about 2.15 cm2/V s at room temperature, suggesting the diffusive nature of electron transport in the nanowires.

InAlN/(In)GaN high electron mobility transistors: some aspects of the quantum well heterostructure proposal

Abstract: The replacement of the AlGaN barrier layer of the AlGaN/GaN high electron mobility transistors (HEMTs) with InAlN of various In molar fractions is suggested. Internal polarization fields in the InAlN/(In)GaN quantum well are described using analytical formulae. InAlN/(In)GaN HEMTs quantum well free electron densities, transistor open channel drain currents and threshold voltages are calculated for different In molar fractions considering the maximal acceptable strain. It is suggested that 0.08 ≤ x ≤ 0.27 for a 15 nm thick InxAl1−xN barrier or 0 ≤ y ≤ 0.18 for a 5–10 nm thick InyGa1−yN channel can be applied for strain without layer relaxation while the quantum well free electron densities up to 4.6 × 1017 m−2 and the transistor open channel drain currents up to 4.5 A mm−1 can be expected.

Homoepitaxial gallium-nitride-based electronic devices and method for producing same

Abstract: There is provided an electronic device. The electronic device includes at least one epitaxial semiconductor layer disposed on a single crystal substrate comprised of gallium nitride having a dislocation density less than about 10 5 per cm 2 . A method of forming an electronic device is also provided. The method includes providing a single crystal substrate comprised of gallium nitride having a dislocation density less than about 10 5 per cm 2 , and homoepitaxially forming at least one semiconductor layer on the substrate.

Nitride-based semiconductor light-emitting device

Abstract: A nitride-based semiconductor light-emitting device capable of attaining homogeneous emission with a low driving voltage is obtained. This nitride-based semiconductor light-emitting device comprises a first conductivity type first nitride-based semiconductor layer formed on a substrate, an emission layer, consisting of a nitride-based semiconductor, formed on the first nitride-based semiconductor layer, a second conductivity type second nitride-based semiconductor layer formed on the emission layer, a second conductivity type intermediate layer, consisting of a nitride-based semiconductor, formed on the second nitride-based semiconductor layer, a second conductivity type contact layer, including a nitride-based semiconductor layer having a smaller band gap than gallium nitride, formed on the intermediate layer, and a light-transmitting electrode formed on the contact layer. Thus, a carrier concentration and electric conductivity higher than those of a contact layer (nitride-based semiconductor layer) consisting of gallium nitride is obtained.

Single-crystalline gallium nitride nanobelts

Abstract: Single-crystalline wurtzite gallium nitride nanobelts were synthesized by thermal reaction of gallium, gallium nitride, and ammonia using iron and boron oxide as catalysts. The structure of nanobelts was investigated by high-resolution transmission electron microscopy with electron energy-loss spectroscopy. They have a distinctive triangle tip and thick side edges. The widths are 200–300 nm, the thickness of belt plane is about 1/10 of the width, and the lengths are up to a few tens μm. The growth direction is uniformly perpendicular to the [010] direction.

Gallium nitride based diodes with low forward voltage and low reverse current operation

Abstract: New Group III based diodes are disclosed having a low on state voltage (Vf) and structures to keep reverse current (Irev) relatively low. One embodiment of the invention is Schottky barrier diode (10) made from the GaN material system in which the Fermi level (or surface potential) of is not pinned. The barrier potential (33) at the metal-to-semiconductor junction varies depending on the type of metal (16) used and using particular metals lowers the diode's Schottky barrier potential (33) and results in a Vf in the range of 0.1-0.3V. In another embodiment (40) a trench structure (45) is formed on the Schottky diodes semiconductor material (44) to reduce reverse leakage current and comprises a number of parallel, equally spaced trenches (46) with mesa regions (49) between adjacent trenches (46). A third embodiment of the invention provides a GaN tunnel diode with a low Vf resulting from the tunneling of electrons through the barrier potential (81), instead of over it. An embodiment of the tunnel diode (120) can also have a trench structure (121) to reduce reverse leakage current.

SiO/sub 2//AlGaN/InGaN/GaN MOSDHFETs

Abstract: The characteristics of a novel nitride based field-effect transistor combining SiO/sub 2/ gate isolation and an AlGaN/InGaN/GaN double heterostructure design (MOSDHFET) are reported. The double heterostructure design with InGaN channel layer significantly improves confinement of the two-dimensional (2-D) electron gas and compensates strain modulation in AlGaN barrier resulting from the gate voltage modulations. These decrease the total trapped charge and hence the current collapse. The combination of the SiO/sub 2/ gate isolation and improved carrier confinement/strain management results in current collapse free MOSDHFET devices with gate leakage currents about four orders of magnitude lower than those of conventional Schottky gate HFETs.

Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts

Abstract: A substrate includes non-gallium nitride posts that define trenches therebetween, wherein the non-gallium nitride posts include non-gallium nitride sidewalls and non-gallium nitride tops and the trenches include non-gallium floors. Gallium nitride is grown on the non-gallium nitride posts, including on the non-gallium nitride tops. Preferably, gallium nitride pyramids are grown on the non-gallium nitride tops and gallium nitride then is grown on the gallium nitride pyramids. The gallium nitride pyramids preferably are grown at a first temperature and the gallium nitride preferably is grown on the pyramids at a second temperature that is higher than the first temperature. The first temperature preferably is about 1000° C. or less and the second temperature preferably is about 1100° C. or more. However, other than temperature, the same processing conditions preferably are used for both growth steps. The grown gallium nitride on the pyramids preferably coalesces to form a continuous gallium nitride layer. Accordingly, gallium nitride may be grown without the need to form masks during the gallium nitride growth process. Moreover, the gallium nitride growth may be performed using the same processing conditions other than temperatures changes. Accordingly, uninterrupted gallium nitride growth may be performed.