An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

In this paper, a new current expression based on both the direct currect(DC) characteristics of the AlGaN/GaN high election mobility transistor(HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I–V, S-parameter, and radio frequency(RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide(Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT(10 × 125 μm)). The improved large signal model simulates the I–V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.     

Effect of Si doping in wells of A1GaN/GaN superlattice on the characteristics of epitaxial layer

An A1GaN/GaN superlattice grown on the top of a GaN buffer induces the broadening of the full width at half maximum of （102） and （002） X-ray diffraction rocking curves. With an increase in the Si-doped concentration in the GaN wells, the full width at half maximum of the （102） rocking curves decreases, while that of the （002） rocking curves increases. A significant increase of the full width at the half maximum of the （002） rocking curves when the doping concentration reaches 2.5 × 10^19 cm-3 indicates the substantial increase of the inclined threading dislocation. High level doping in the A1GaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.     

The degradation mechanism of an AIGaN/GaN high electron mobility transistor under step-stress

Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.     

Significant performance enhancement in A1GaN/GaN high electron mobility transistor by high-κ organic dielectric

The electrical properties of A1GaN/GaN high electron mobility transistor （HEMT） with and without high-κ organic dielectrics are investigated. The maximum drain current ID max and the maximum transconductance gm max of the organic dielectric/A1CaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare A1GaN/GaN HEMT, respectively. Both the threshold voltage VT and gm max of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the A1GaN/GaN HEMT by introducing the high-κ organic dielectric.     

The effects of ^60Co γ-ray irradiation on the DC characteristics of enhancement-mode A1GaN/GaN high-electron-mobility transistors

The effects of ^60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electron- mobility transistors （E-mode HEMTs） are investigated. The results show that having been irradiated by^60Co γ-rays at a dose of 3 Mrad （Si）, the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode A1GaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.     

Effects of SiNx on two-dimensional electron gas and current collapse of A1GaN/GaN high electron mobility transistors

SiNx is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiNx films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.     

Effects of interface roughness on photoluminescence full width at half maximum in GaN/AIGaN quantum wells

Low temperature photoluminescence （PL） measurements have been performed for a set of GaN/AlxGal xN quantum wells （QWs）. The experimental results show that the optical full width at half maximum （FWHM） increases relatively rapidly with increasing A1 composition in the AlxGal xN barrier, and increases only slightly with increasing GaN well width. A model considering the interface roughness is used to interpret the experimental results. In the model, the FWHM＇s broadening caused by the interface roughness is calculated based on the triangle potential well approximation. We find that the calculated results accord with the experimental results well.     

Characterization of Al2O3/GaN/AIGaN/GaN metal- insulator-semiconductor high electron mobility transistors with different gate recess depths＊

In this paper, in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor （MIS） high electron mobility transistors （HEMTs）, we demonstrate better performances of recessed-gate A1203 MIS-HEMTs which are fabricated by Fluorine-based Si3N4 etching and chlorine- based A1CaN etching with three etching times （15 s, 17 s and 19 s）. The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of A1GaN/CaN HEMT. Through the recessed-gate etching, the transconductanee increases effectively. When the recessed-gate depth is 1.02 nm, the best interface performance with Tit----（0.20--1.59） p~s and Dit ：（0.55-1.08）x 1012 cm-2.eV- 1 can be obtained. After chlorine-based etching, the interface trap density reduces considerably without generating any new type of trap. The accumulated chlorine ions and the N vacancies in the AIGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices. By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times, it is found that a low power chlorine-based plasma etching for a short time （15 s in this paper） can enhance the performances of MIS-HEMTs effectively.     

Enhancement-mode A1GaN/GaN high electronic mobility transistors with thin barrier＊

An enhancement-mode （E-mode） A1GaN/GaN high electron mobility transistor （HEMTs） was fabricated with 15-nm A1GaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around -1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs （-3.5 V）. Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-tim gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/ram, respectively. Compared with the 22-nm barrier E-mode devices, VT of the thin barrier HEMTs is much more stable under the gate step-stress,     

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AIGaN hole blocking layer

Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency （IQE）. The results indicate that LEDs with an n-AIGaN HBL with gradual AI composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conven tional p-A1GaN EBL or a common n-A1GaN HBL. Meanwhile, the efficiency droop is alleviated when an n-A1GaN HBL with gradual A1 composition is used.     

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor(HEMT) with an artificial neural network(ANN).The AlGaN/GaN HEMT device structure and its fabrication process are described.The circuit-based Neuro-space mapping(neuro-SM) technique is studied in detail.The EEHEMT model is implemented according to the measurement results of the designed device,which serves as a coarse model.An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model.Its optimization is performed.The simulation results from the model are compared with the measurement results.It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model.     

Low-resistance Ohmic contact on polarization-doped AIGaN/GaN heterojunction

High electronic density is achieved by polarization doping without an impurity dopant in graded AIGaN films. Low specific contact resistance is studied on the polarization-doped A1GaN/GaN heterojunctions by using the transmission line method （TLM）. The sheet density of polarization-doped A1GaN/GaN heterojunction is 6 × 10 14 cm-2 at room temperature. The linearly graded material structure is demonstrated by X-ray diffraction. The cartier concentration and mobility are characterized by a temperature-dependent Hall measurement. Multiple-layer metal （Ti/A1/Ti/Au） is deposited and annealed at 650 ℃ to realize the Ohmic contacts on the graded A1GaN/GaN heterojunctions.     

The influence of A1GaN/GaN superlattices as electron blocking layers on the performance of blue InGaN light-emitting diodes

P-A1GaN/P-GaN superlattices are investigated in blue InGaN light-emitting diodes as electron blocking layers. The simulation results show that efficiency droop is markedly improved due to two reasons： （i） enhanced hole concentration and hole carrier transport efficiency in A1GaN/GaN superlattices, and （ii） enhanced blocking of electron overflow between multiple quantum-wells and A1CaN/GaN superlattices.     

Performance improvement of GaN-based light-emitting diode with a p-InAIGaN hole injection layer

The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power, a reduction in current leakage and alleviation of efficiency droop. These improvements can be attributed to the p-InA1GaN serving as hole injection layers, which can alleviate the band bending induced by the polarization field, thereby improving both the hole injection efficiency and the electron blocking efficiency.     

High-efficiency S-band harmonic tuning GaN amplifier

In this paper, we present a high-efficiency S-band gallium nitride （GaN） power amplifier （PA）. This amplifier is fabri- cated based on a self-developed GaN high-electron-mobility transistor （HEMT） with 10 mm gate width on SiC substrate. Harmonic manipulation circuits are presented in the amplifier. The matching networks consist of microstrip lines and discrete components. Open-circuited stub lines in both input and output are used to tune the 2rid harmonic wave and match the GaN HEMT to the highest efficiency condition. The developed amplifier delivers an output power of 48.5 dBm （70 W） with a power-added efficiency （PAE） of 72.2% at 2 GHz in pulse condition. When operating at 1.8-2.2 GHz （20% relative bandwidth）, the amplifier provides an output power higher than 48 dBm （,-~ 65 W）, with a PAE over 70% and a power gain above 15 dB. When operating in continuous-wave （CW） operating conditions, the amplifier gives an output power over 46 dBm （40 W） with PAE beyond 60% over the whole operation frequency range.     

Performance enhancement of an InGaN light-emitting diode with an AIGaN/InGaN superlattice electron-blocking layer

The efficiency enhancement of an InGaN light-emitting diode （LED） with an A1GaN/InGaN superlattice （SL） electron-blocking layer （EBL） is studied numerically, which involves the light-current performance curve, internal quan- tum efficiency electrostatic field band wavefunction, energy band diagram carrier concentration, electron current density, and radiative recombination rate. The simulation results indicate that the LED with an A1GaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular A1GaN EBL or a normal A1GaN/GaN SL EBL because of the appropriately modified energy band diagram, which is favorable ibr the injection of holes and confinement of elec- trons. Additionally, the efficiency droop of the LED with an AIGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.     

Improved crystal quality of GaN film with the in-plane lattice-matched Ino.17Alo.s3N interlayer grown on sapphire substrate using pulsed metal-organic chemical vapor deposition

We report on an improvement in the crystal quality of GaN film with an Ino.17Alo.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations （TDs） in GaN film with the InA1N interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy （TEM） measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InA1N interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InA1N interlayer. Atomic force microscopy measurement shows that the InA1N interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InA1N interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.     

Effect of high temperature band gap of GaN annealing on strain and nanoparticles

<正>Black-coloured GaN nanoparticles with an average grain size of 50 nm have been obtained by annealing GaN nanoparticles under flowing nitrogen at 1200℃for 30 min.XRD measurement result indicates an increase in the lattice parameter of the GaN nanoparticles annealed at 1200℃,and HRTEM image shows that the increase cannot be ascribed to other ions in the interstitial positions.If the as-synthesised GaN nanoparticles at 950℃are regarded as standard,the thermal expansion changes nonlinearly with temperature and is anisotropic;the expansion below 1000℃is smaller than that above 1000℃.This study provides an experimental demonstration for selecting the proper annealing temperature of GaN.In addition,a large blueshift in optical bandgap of the annealed GaN nanoparticles at 1200℃is observed,which can be ascribed to the dominant transitions from the C（Γ₇） with the peak energy at 3.532 eV.     

The etching of a-plane GaN epilayers grown metal-organic chemical vapour deposition

Morphology of nonpolar （1120） a-plane GaN epilayers on r-plane （1102） sapphire substrate grown by low-pressure metal-organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.     

Breakdown characteristics of AIGaN/GaN Schottky barrier diodes fabricated on a silicon substrate

In this work, the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes （SBDs） fabricated on the silicon substrate are investigated. The breakdown voltage （BV） of the SBDs first increases as a function of the anodeto-cathode distance and then tends to saturate at larger inter-electrode spacing. The saturation behavior of the BV is likely caused by the vertical breakdown through the intrinsic GaN buffer layer on silicon, which is supported by the post-breakdown primary leakage path analysis with the emission microscopy. Surface passivation and field plate termination are found effective to suppress the leakage current and enhance the BV of the SBDs. A high BV of 601 V is obtained with a low on-resistance of 3.15 mΩ·cm^2.