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Showing papers on "Gallium nitride published in 2011"


Journal ArticleDOI
TL;DR: Electrically pumped Fabry-Perot type waveguide lasing from laser diodes that consist of Sb-doped p-type ZnO nanowires and n-typeZnO thin films are demonstrated, which exhibit highly stable lasing at room temperature, and can be modelled with finite-difference time-domain methods.
Abstract: Ultraviolet semiconductor lasers are widely used for applications in photonics, information storage, biology and medical therapeutics. Although the performance of gallium nitride ultraviolet lasers has improved significantly over the past decade, demand for lower costs, higher powers and shorter wavelengths has motivated interest in zinc oxide (ZnO), which has a wide direct bandgap and a large exciton binding energy. ZnO-based random lasing has been demonstrated with both optical and electrical pumping, but random lasers suffer from reduced output powers, unstable emission spectra and beam divergence. Here, we demonstrate electrically pumped Fabry-Perot type waveguide lasing from laser diodes that consist of Sb-doped p-type ZnO nanowires and n-type ZnO thin films. The diodes exhibit highly stable lasing at room temperature, and can be modelled with finite-difference time-domain methods.

571 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a methodology to study trapping characteristics in GaN HEMTs that is based on current-transient measurements and identify several traps inside the AlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.
Abstract: Trapping is one of the most deleterious effects that limit performance and reliability in GaN HEMTs. In this paper, we present a methodology to study trapping characteristics in GaN HEMTs that is based on current-transient measurements. Its uniqueness is that it is amenable to integration with electrical stress experiments in long-term reliability studies. We present the details of the measurement and analysis procedures. With this method, we have investigated the trapping and detrapping dynamics of GaN HEMTs. In particular, we examined layer location, energy level, and trapping/detrapping time constants of dominant traps. We have identified several traps inside the AlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.

370 citations


Journal ArticleDOI
TL;DR: In this paper, high-voltage GaN field-effect transistors fabricated on Si substrates were reported to have high breakdown voltage of 1200 V and low dynamic on-resistance at highvoltage operation.
Abstract: This letter reports high-voltage GaN field-effect transistors fabricated on Si substrates. A halide-based plasma treatment was performed to enable normally off operation. Atomic layer deposition of Al2O3 gate insulator was adopted to reduce the gate leakage current. Incorporation of multiple field plates, with one field plate connected to the gate electrode and two field plates connected to the source electrode successfully enabled a high breakdown voltage of 1200 V and low dynamic on-resistance at high-voltage operation.

369 citations


Journal ArticleDOI
TL;DR: With the use of p-type modulation doping in the dot-in-a-wire heterostructures, this work has demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2).
Abstract: Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm2. The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

273 citations


Journal ArticleDOI
TL;DR: The study reveals that local changes in polarization and reduction of unit cell volume with respect to bulk values lead to the observed size effect, which has strong implication in the field of energy harvesting, as piezoelectric voltage output scales with the piezOElectric coefficient.
Abstract: Nanowires made of materials with noncentrosymmetric crystal structure are under investigation for their piezoelectric properties and suitability as building blocks for next-generation self-powered nanodevices. In this work, we investigate the size dependence of piezoelectric coefficients in nanowires of two such materials − zinc oxide and gallium nitride. Nanowires, oriented along their polar axis, ranging from 0.6 to 2.4 nm in diameter were modeled quantum mechanically. A giant piezoelectric size effect is identified for both GaN and ZnO nanowires. However, GaN exhibits a larger and more extended size dependence than ZnO. The observed size effect is discussed in the context of charge redistribution near the free surfaces leading to changes in local polarization. The study reveals that local changes in polarization and reduction of unit cell volume with respect to bulk values lead to the observed size effect. These results have strong implication in the field of energy harvesting, as piezoelectric voltage...

267 citations


Journal ArticleDOI
TL;DR: In this paper, lattice-matched In0.17Al0.83N/GaN high-electron-mobility transistors on a SiC substrate with a record current gain cutoff frequency (fT) of 300 GHz were presented.
Abstract: This letter reports lattice-matched In0.17Al0.83N/GaN high-electron-mobility transistors on a SiC substrate with a record current gain cutoff frequency (fT) of 300 GHz. To suppress the short-channel effects (SCEs), an In0.15Ga0.85N back barrier is applied in an InAlN/GaN heterostructure for the first time. The GaN channel thickness is also scaled to 26 nm, which allows a good immunity to SCEs for gate lengths down to 70 nm even with a relatively thick top barrier (9.4-10.4 nm). In a 30-nm-gate-length device with an on-resistance (Ron) of 1.2 Ω · mm and an extrinsic transconductance (gm.ext) of 530 mS/mm, a peak fa of 300 GHz is achieved. An electron velocity of 1.37-1.45 × 107 cm/s is extracted by two different delay analysis methods.

237 citations


Journal ArticleDOI
TL;DR: Small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation.
Abstract: Properties that can now be achieved with advanced, blue indium gallium nitride light emitting diodes (LEDs) lead to their potential as replacements for existing infrastructure in general illumination, with important implications for efficient use of energy. Further advances in this technology will benefit from reexamination of the modes for incorporating this materials technology into lighting modules that manage light conversion, extraction, and distribution, in ways that minimize adverse thermal effects associated with operation, with packages that exploit the unique aspects of these light sources. We present here ideas in anisotropic etching, microscale device assembly/integration, and module configuration that address these challenges in unconventional ways. Various device demonstrations provide examples of the capabilities, including thin, flexible lighting “tapes” based on patterned phosphors and large collections of small light emitters on plastic substrates. Quantitative modeling and experimental evaluation of heat flow in such structures illustrates one particular, important aspect of their operation: small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation.

223 citations


Journal ArticleDOI
TL;DR: GaN has a wideband transparency window covering ultraviolet, visible and infrared wavelengths, and its platform provides a viable route for the on-chip generation of optical wavelengths in both the far infrared and near-UV through a combination of χ2 enabled sum-/difference-frequency processes.
Abstract: We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The χ2 nonlinear susceptibility is measured to be as high as 16 ± 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and infrared wavelengths, our platform provides a viable route for the on-chip generation of optical wavelengths in both the far infrared and near-UV through a combination of χ2 enabled sum-/difference-frequency processes.

200 citations


Proceedings ArticleDOI
23 May 2011
TL;DR: In this paper, the authors present a short review of the current state of the art in active switching device performance for both SiC and GaN, and present the SiC wafer roadmap looks very favorable as volume production takes off.
Abstract: Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now available on the commercial market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper reviews the current state of the art in active switching device performance for both SiC and GaN. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. The SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. Power module demonstrations are beginning to appear in scientific reports and real applications. A short review is therefore given. Other advantages of SiC is the possibility of high temperature operation (> 300 °C) and in radiation hard environments, which could offer considerable system advantages.

190 citations


Patent
Wataru Saito1, Ichiro Omura1
26 Oct 2011
TL;DR: In this article, a p-type gallium nitride (GaN) layer electrically connected to a source electrode and extending and projecting to a drain electrode side with respect to a gate electrode is formed.
Abstract: In a nitride semiconductor device according to one embodiment of the invention, a p-type gallium nitride (GaN) layer electrically connected to a source electrode and extending and projecting to a drain electrode side with respect to a gate electrode is formed on an undoped or n-type aluminum gallium nitride (AlGaN) layer serving as a barrier layer

172 citations


Journal ArticleDOI
TL;DR: The Auger recombination coefficients in defect-free InGaN nanowires (NW) and inGaN/GaN dot-in-nanowire (DNW) samples grown on (001) silicon by plasma-assisted molecular beam epitaxy are measured and are in reasonably good agreement with theoretical predictions for In GaN alloy semiconductors.
Abstract: We have measured the Auger recombination coefficients in defect-free InGaN nanowires (NW) and InGaN/GaN dot-in-nanowire (DNW) samples grown on (001) silicon by plasma-assisted molecular beam epitaxy. The nanowires have a density of ∼1 × 1011 cm−2 and exhibit photoluminescence emission peak at λ ∼ 500 nm. The Auger coefficients as a function of excitation power have been derived from excitation dependent and time-resolved photoluminescence measurements over a wide range of optical excitation power density. The values of C0, defined as the Auger coefficient at low excitation, are 6.1 × 10−32 and 4.1 × 10−33 cm6·s−1 in the NW and DNW samples, respectively, which are in reasonably good agreement with theoretical predictions for InGaN alloy semiconductors. Light-emitting diodes made with the NW and DNW samples exhibit no efficiency droop up to an injection current density of 400 A/cm2.

Journal ArticleDOI
TL;DR: In this article, the conduction band offset and interface charge density of the alumina/GaN interface were determined by analyzing the capacitance-voltage characteristics of atomic layer deposited Al2O3 films on GaN substrates.
Abstract: We report on our investigation of the electrical properties of metal/Al2O3/GaN metal-insulator-semiconductor capacitors. We determined the conduction band offset and interface charge density of the alumina/GaN interface by analyzing the capacitance-voltage characteristics of atomic layer deposited Al2O3 films on GaN substrates. The conduction band offset at the Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band conditions in the GaN was inferred, which we attribute to a fixed net positive charge density of magnitude 4.60 × 1012 cm−2 at the Al2O3/GaN interface. We provide hypotheses to explain the origin of this charge by analyzing the energy band line-up.

Proceedings ArticleDOI
06 Mar 2011
TL;DR: In this paper, a successful operation of Gallium Nitride (GaN)-based three-phase inverter with high efficiency of 99.3% for driving motor at 900W under the carrier frequency of 6kHz was presented.
Abstract: In this paper, we present a successful operation of Gallium Nitride(GaN)-based three-phase inverter with high efficiency of 99.3% for driving motor at 900W under the carrier frequency of 6kHz. This efficiency well exceeds the value by IGBT (Insulated Gate Bipolar Transistor). This demonstrates that GaN has a great potential for power switching application competing with SiC. Fully reduced on-state resistance in a new normally-off GaN transistor called Gate Injection Transistor (GIT) greatly helps to increase the efficiency. In addition, use of the bidirectional operation of the lateral and compact GITs with synchronous gate driving, the inverter is operated free from fly-wheel diodes which have been connected in parallel with IGBTs in a conventional inverter system.

Journal ArticleDOI
TL;DR: In this article, a lattice-matched In0.17Al0.83N/GaN high-electron mobility transistors on a SiC substrate with a record current gain cutoff frequency (fT) was reported.
Abstract: We report lattice-matched In0.17Al0.83N/GaN high-electron mobility transistors on a SiC substrate with a record current gain cutoff frequency (fT). The key to this performance is the use of an oxygen plasma treatment to form a thin oxide layer on the InAlN barrier and to reduce the gate leakage current by more than two orders of magnitude. In addition, the RF transconductance (gm) collapse is reduced in the O2-treated devices, which results in a significant improvement in the fT . In a transistor with a gate length of 30 nm, an fT of 245 GHz is achieved, the highest value ever reported in GaN-based field-effect transistors.

Journal ArticleDOI
TL;DR: In this paper, the effect of AlGaN back barriers in the dc and RF performance of In0.17Al0.83N/GaN high-electron mobility transistors grown on SiC substrates was investigated.
Abstract: This letter studies the effect of AlGaN back barriers in the dc and RF performance of In0.17Al0.83N/GaN high-electron mobility transistors grown on SiC substrates. When compared to conventional structures without a back barrier, the back barrier effectively prevents the degradation of drain-induced barrier lowering and significantly improves the output resistance in sub-100-nm-gate-length devices. The reduction in short-channel effects helps to increase the frequency performance of AlGaN back-barrier devices. For a 65-nm gate length, the current gain cutoff frequency (fT) of a transistor with an AlGaN back barrier is 210 GHz, which is higher than that of the standard device with the same gate length (fT = 195 GHz).

Journal ArticleDOI
TL;DR: In this article, the role of traps in limiting the maximum gate-drain electric field and the equivalent electron temperature in GaN-based high-electron mobility transistors is investigated.
Abstract: This paper presents a fast methodology for the investigation of trapping and hot-electron effects in GaN-based high-electron mobility transistors (HEMTs). The presented method is based on pulsed ID-VG measurements and electroluminescence characterization and provides a rapid and effective evaluation of the following: 1) the presence of traps in the region under the gate; 2) trapping phenomena occurring in the gate-drain access region; 3) the role of traps in limiting the maximum gate-drain electric field and the equivalent electron temperature. The method is validated by means of a split-wafer experiment carried out on GaN-based HEMTs with different gate materials with and without passivation.

Journal ArticleDOI
TL;DR: In this article, a simple edge termination is described which can be used to achieve nearly ideal parallel-plane breakdown voltage for GaN devices, which involves implanting a neutral species on the edges of devices to form a high resistive amorphous layer.
Abstract: In this letter, a simple edge termination is described which can be used to achieve nearly ideal parallel-plane breakdown voltage for GaN devices. This technique involves implanting a neutral species on the edges of devices to form a high-resistive amorphous layer. With this termination, formed by using argon implantation, the breakdown voltage of GaN Schottky barrier diodes was increased from 300 V for unterminated diodes to 1650 V after termination.

Journal ArticleDOI
TL;DR: In this article, gate-recessed AlGaN/AlN/GaN metal-oxide-semiconductor heterostructure high-mobility transistors (MOS-HEMTs) on SiC substrate are fabricated.
Abstract: Gate-recessed AlGaN/AlN/GaN metal-oxide-semiconductor heterostructure high-mobility transistors (MOS-HEMTs) on SiC substrate are fabricated. The device with a gate length of 0.6 μm and a gate periphery of 100 μm exhibits a maximum dc drain current density of 1.59 A/mm at VGS = 3 V with an extrinsic transconductance (gm) of 374 mS/mm. An extrinsic current gain cutoff frequency (fT) of 19 GHz and a maximum oscillation frequency (fmax) of 50 GHz are deduced from S-parameter measurements. The output power density is 13 W/mm, and the associated power-added efficiency is 73% at 4-GHz frequency and 45-V drain bias. The power performance is comparable to state-of-the art AlGaN/GaN HEMTs, which demonstrates the great potential of gate-recessed MOS-HEMTs as a very promising alternative to GaN HEMTs.

Journal ArticleDOI
TL;DR: The unique properties of GaN nanowires grown by molecular beam epitaxy are reviewed in this article, including the absence of residual strain, exclusion of most extended defects, long photoluminescence lifetime, low surface recombination velocity, and high mechanical quality factor.
Abstract: The unique properties of GaN nanowires grown by molecular beam epitaxy are reviewed. These properties include the absence of residual strain, exclusion of most extended defects, long photoluminescence lifetime, low surface recombination velocity, and high mechanical quality factor. The high purity of the nanowires grown by this method allows for controllable n-type doping. P-type doping presents more challenges but has been demonstrated in active light-emitting diode devices. The present understanding of nucleation and growth of these materials is also reviewed.

Journal ArticleDOI
TL;DR: In this paper, undoped AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated with a Si-CMOS-compatible technology based on Ti/Al/W ohmic and Schottky contacts are reported.
Abstract: This letter reports undoped AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated with a Si-CMOS-compatible technology based on Ti/Al/W ohmic and Schottky contacts. The use of ohmic recess is key to reduce the contact resistance of this Au-free metallization below 0.5 Ω·mm. Comparison of HEMTs fabricated on the same wafer with and without ohmic recess shows that the recess provides a tenfold reduction in contact resistance, resulting in a fivefold lower forward voltage drop at IDS = 100 mA/mm. The reported Au-free AlGaN/GaN HEMT fabrication technology provides similar performance (i.e., contact resistance, leakage current, and breakdown voltage) than state-of-the-art Au-based AlGaN/GaN HEMTs and can be used in standard Si fabs without the risk of contamination.

Journal ArticleDOI
TL;DR: In this article, the vertical breakdown of high-electron-mobility transistors (HEMTs) is analyzed with respect to i-GaN thickness (TGaN) and buffer thickness (TBuf).
Abstract: Vertical breakdown studies on AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by metal-organic chemical vapor deposition (MOCVD) on a silicon substrate are studied to analyze the breakdown dependence with regard to i-GaN thickness (TGaN) and buffer thickness (TBuf). A high breakdown field (Ec) of 2.3 MV/cm was observed for MOCVD grown epilayers of total thickness of 5.5 μm on Si. Increasing TBuf is more significant than TGaN toward controlling the vertical leak age and demonstrates a high breakdown. For transistor operation at high voltages, GaN layers grown on thick buffers are highly resistive to the flow of leakage currents. A high figure of merit (BV2/Rd.ON) of 5.4 × 108 V2 · Ω-1· cm-2 was observed for an AlGaN/GaN HEMT grown on Si using a thick buffer.

Journal ArticleDOI
TL;DR: In this paper, the authors present a local substrate removal technology (under the source-to-drain region) reminiscent of through-silicon vias and report on the highest ever achieved breakdown voltage (VBD) of AlGaN/GaNs/AlGaN double heterostructure FETs on a Si (111) substrate with only 2-μm-thick buffer.
Abstract: In this letter, we present a local substrate removal technology (under the source-to-drain region), reminiscent of through-silicon vias and report on the highest ever achieved breakdown voltage (VBD) of AlGaN/GaN/AlGaN double heterostructure FETs on a Si (111) substrate with only 2-μm-thick AlGaN buffer. Before local Si removal, VBD saturates at ~700 V at a gate-drain distance (LGD) ≥ 8 μm. However, after etching away the substrate locally, we measure a record VBD of 2200 V for the devices with LGD = 20 μm. Moreover, from Hall measurements, we conclude that the local substrate removal integration approach has no impact on the 2-D electron gas channel properties.

Journal ArticleDOI
TL;DR: In this paper, a GaN super heterojunction field effect transistors (super HFET) based on the polarization junction concept is demonstrated for the first time and the electrical measurements show breakdown voltages over 1.1 kV with specific on-resistance of 6.1 mΩ· cm^2.
Abstract: GaN super heterojunction field effect transistors (super HFET) based on the polarization junction concept are demonstrated for the first time. The super HFET has charges of 2-D electron gas and hole gas, respectively induced by positive and negative polarization charges at GaN/AlGaN/GaN heterointerfaces. Analogous to the RESURF concept, these unintentionally doped positive and negative polarization charges compensate each other in the off state condition to enhance the breakdown capability of the super HFET. The super HFETs have been fabricated on sapphire substrates and the electrical measurements show breakdown voltages over 1.1 kV with specific on-resistance of 6.1 mΩ· cm^2.

Journal ArticleDOI
TL;DR: In this article, a two-step electrode process on p-GaN and characteristics of GaN p-n junction diodes on free-standing GaN substrates with low specific ON-resistance Rοn and high breakdown voltage VB were described.
Abstract: This letter describes a new two-step electrode process on p-GaN and characteristics of GaN p-n junction diodes on free-standing GaN substrates with low specific ON-resistance Rοn and high breakdown voltage VB. We develop a two-step process for anode electrodes in order to avoid plasma damage to the p+-GaN contact layer during the sputtering process. The specific ON-resistance is further improved due to a new low-damage process. The breakdown voltage of the diodes with the field-plate (FP) structure is over 1100 V, and the leakage current was low, i.e., in the range of 10-9 A. The specific ON-resistance of the diodes of 50 μm in diameter with the FP structure was 0.4 mΩ · cm2. Baliga's figure of merit (VB2/Ron) of 3.0 GW/cm2 is obtained. These are the best values ever reported among those achieved by GaN p-n junction diodes on free-standing GaN substrates.

Proceedings ArticleDOI
23 May 2011
TL;DR: In this article, a combination of an AlGaN back-barrier with the carbon-doped buffer prevents early off-state punch-through of normally-off GaN transistors.
Abstract: Normally-off GaN transistors for power applications in p-type GaN gate technology with a modified carbon-doped GaN buffer are presented. A combination of an AlGaN back-barrier with the carbon-doped buffer prevents early off-state punch-through. Simultaneously, the on-state resistance could be kept low and the threshold voltage with 1.1 V high enough for secure normally-off operation. 1000 V breakdown strength has been obtained for devices with 6 μm gate-drain spacing. The resulting breakdown scaling slope is 170 V/μm gate-drain distance. The on-state resistance is 7.4 Ωmm. The resulting V Br -to-R ON A ratio (1000 V, 0.62 mΩcm2) is beyond so far reported ratios for normally-off GaN transistors. Modifications of the p-type GaN layer have shown to additionally increase the threshold voltage by 0.4 V without paying a price in the on-state resistance of the device.

Journal ArticleDOI
TL;DR: In this article, the authors reported the first experimental observation of electron velocity enhancement by aggressive lateral scaling of GaN HEMTs, which achieved an extremely small on resistance of 0.44 Ω·mm, high maximum drain current density of 2.3 A/mm, and high peak extrinsic transconductance of 905 mS/mm.
Abstract: In this letter, we report the first experimental observation of electron velocity enhancement by aggressive lateral scaling of GaN HEMTs. Through reduction of the source-drain distance down to 170 nm using n+-GaN ohmic regrowth, 45-nm gate AlN/GaN/Al0.08Ga0.92N HEMTs exhibited an extremely small on resistance of 0.44 Ω·mm , a high maximum drain current density of 2.3 A/mm, a high peak extrinsic transconductance of 905 mS/mm, and a record fT/fmax of 260/394 GHz. Delay time analysis showed that the outstanding fT was mainly due to significantly reduced electron transit time at higher drain-source voltages resulting from suppressed drain delay and enhanced electron velocity in the laterally scaled GaN HEMTs.

Journal ArticleDOI
Feng Xie1, Hai Lu1, Xiangqian Xiu1, Dunjun Chen1, Ping Han1, Rong Zhang1, Youdou Zheng1 
TL;DR: In this article, metal-semiconductor-metal ultraviolet photodetectors are fabricated on low-defect-density homoepitaxial GaN layer on bulk GaN substrate.
Abstract: Metal-semiconductor–metal ultraviolet photodetectors are fabricated on low-defect-density homoepitaxial GaN layer on bulk GaN substrate The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is ∼5 × 10 6 cm −2 The photodetector with a high UV-to-visible rejection ratio of up to 1 × 10 5 exhibits a low dark current of

Journal ArticleDOI
TL;DR: In this paper, a surface potential-based model for AlGaN/GaN modulation-doped field effect transistors (MODFETs) is built for the first time.
Abstract: In this paper, a surface-potential-based (SP-based) model for AlGaN/GaN modulation-doped field-effect transistors (MODFETs) is built for the first time. First, a closed-form analytical approximation for the Fermi potential EF relative to the bottom of the conduction band at the AlGaN/GaN interface is presented and verified to be accurate enough under different biases and temperatures. Then, the potential of the bottom of the conduction band at the AlGaN/GaN interface φs is defined as the SP, and the value of φs relative to ground is calculated. The development of SP-based compact dc model is achieved based on this calculation. Velocity saturation, channel length modulation, drain-induced barrier lower effect, and self-heating effect are included in the presented model. Compared with the Vth-based model developed by our group, this SP-based model provides a symmetric and more accurate but simpler description for AlGaN/GaN MODFETs. The calculated dc characteristics and transconductance for devices with different lengths are in excellent agreement with the experimental data over the full range of applied gate and drain biases and under different temperatures.

Journal ArticleDOI
TL;DR: In this paper, Ta-based ohmic contacts to gallium nitride high electron mobility transistor (GaN HEMT) epitaxial structures were investigated and two metallization schemes were considered.
Abstract: Ta-based ohmic contacts to gallium nitride high electron mobility transistor (GaN HEMT) epitaxial structures were investigated. Two metallization schemes were considered: Ta/Al/Ni(Ta)/Au and Ta/Al/Ta. The latter was superior in terms of lower contact resistance (R-c) and wider process window. The metallizations were applied to two different heterostructures (GaN/Al0.14Ga0.86N/GaN and Al0.25Ga0.75N/GaN). The lowest measured R-c was 0.06 and 0.28 Omega mm, respectively. The main advantage of the Ta-based ohmic contacts over conventional Ti-based contacts was the low anneal temperature. The optimum temperature of annealing was found to be 550-575 degrees C. From optical and scanning electron microscopy, it was clear that excellent surface morphology and edge acuity were obtained at these low temperatures. This facilitates lateral scaling of the GaN HEMT. TEM images were taken of the contact cross sections onto which EDX measurements were performed. The aim was to investigate the microstructure and the contact mechanism. Storage tests at 300 degrees C for more than 400 h in air ambient showed no deterioration of R-c.

Patent
31 Mar 2011
TL;DR: In this article, a light emitting device with a relatively simple configuration is provided that emits stable light having a plurality of wavelengths, in which a composite substrate 3 and a gallium-nitride-based semiconductor layer 5 are used.
Abstract: A light emitting device having a relatively simple configuration is provided that emits stable light having a plurality of wavelengths. The light emitting device 1 comprises, in sequence, a composite substrate 3 and a gallium nitride-based semiconductor layer 5 including a light emitting layer 9. The composite substrate 3 includes a base 19 and a gallium nitride layer, the gallium nitride-based semiconductor layer 5 being disposed on a principal surface of the gallium nitride layer, the angle θ defined by the c-axis of the gallium nitride layer and a normal line N1 to the principal surface S1 of the gallium nitride layer ranging from 50 to 130 degrees, the light emitting layer 9 emitting light with an absolute value of the degree of polarization of 0.2 or more, the base 19 containing a fluorescent material that emits a fluorescent light component induced by irradiation of a light component emitted from the light emitting layer 9. Accordingly, the light emitting device 1 can emit white light produced by superposition of blue light directly emitted from the light emitting layer 9 and yellow light induced by blue light incident on the base 19 from the light emitting layer 9.