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.     

A simple method of extracting the polarization charge density in the A1GaN/GaN heterostructure from current-voltage and capacitance-voltage characteristics

An Ni Schottky contact on the AlGaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN/GaN heterostructure is obtained from the forward current-voltage characteristics. With the measured capacitance-voltage curve and the flat-band voltage, the polarization charge density in the AlGaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodinger’s and Poisson’s equations.     

Sodium beta-alumina thin films as gate dielectrics for A1GaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

<正>Sodium beta-alumina（SBA） is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al₂O₃ as the precursors.The X-ray diffraction（XRD） spectrum reveals that the deposited thin film is amorphous.The binding energy and composition of the deposited thin film,obtained from the X-ray photoelectron spectroscopy（XPS） measurement,are consistent with those of SBA.The dielectric constant of the SBA thin film is about 50.Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor（MISHEMT） is measured to be（3.5～9.5）×10¹⁰ cm^-2·eV^-1 by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7×10¹² cm^-2.Compared with the AlGaN/GaN metal-semiconductor heterostructure high-electronmobility transistor（MESHEMT）,the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However,the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from—5.5 V to—3.5 V.From XPS results,the surface valence-band maximum（VBM-E_F） of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition.The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum （VBM-E_F）,the reduction of interface traps and the effects of sodium ions,and/or the fixed charges in SBA on the two-dimensional electron gas（2DEG）.     

Neutron irradiation effects on A1GaN//GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors(HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10 15 cm 2.The dc characteristics of the devices,such as the drain saturation current and the maximum transconductance,decreased after neutron irradiation.The gate leakage currents increased obviously after neutron irradiation.However,the rf characteristics,such as the cut-off frequency and the maximum frequency,were hardly affected by neutron irradiation.The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism.It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas(2DEG) decreased after neutron irradiation.There was no evidence of the full-width at half-maximum of X-ray diffraction(XRD) rocking curve changing after irradiation,so the dislocation was not influenced by neutron irradiation.It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.     

高击穿电压的AIGaN/GaN FP-HEMT研究与分析

就蓝宝石衬底上制备的AlGaN／GaN场（field plate）HEMT器件、常规HEMT器件性能进行了分析对比．结果证明两种结构的器件直流参数变化不大，但是采用场板后器件的击穿电压从52V提高到了142V．在此基础上利用Sivaco软件对两种器件进行模拟仿真，深入分析了FP对器件击穿电压的影响．     

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.     

GaN1-xPx薄膜的结构特性研究

用金属有机物化学气相沉积技术在蓝宝石衬底上外延了高P组分的GaN1-xPx 薄膜.利用x射线衍射仪和拉曼光谱仪研究了P对GaN1-xPx晶体结构的影响.研究结果表明:随着P组分比的增加,GaN1-xPx(0002)衍射峰逐渐向小角度移动,即晶格常数变大;与非掺杂GaN相比,GaN1-xPx薄膜的拉曼光谱中出现了4个新的振动模式,将它们分别归因于P族团引起的准局部振动模式、Ga-P键振动引起的间隙模,以及来自缺陷引起的无序激活散射.同时,随着P组分比的增加,A1(LO)模式的频率向低频方向移动,这种红移现象起因于合金化和应变的影响.     

Influence of double A1N buffer layers on the qualities of GaN films prepared by metal-organic chemical vapour deposition

<正>In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire (0001) substrate with double AlN buffer layers.The buffer layer consists of a low-temperature(LT) AlN layer and a high-temperature(HT) AlN layer that are grown at 600℃and 1000℃,respectively.It is observed that the thickness of the LT-AlN layer drastically influences the quality of GaN thin film,and that the optimized 4.25-min-LT-AlN layer minimizes the dislocation density of GaN thin film.The reason for the improved properties is discussed in this paper.     

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.     

纤锌矿AlGaMAlN／GaN异质结构中光学声子散射影响的电子迁移率

对含有A1N插入层纤锌矿A1xGal-xN／A1N／GaN异质结构,考虑有限厚势垒和导带弯曲的实际异质结势,同时计入自发极化和压电极化效应产生的内建电场作用,采用数值自洽求解薛定谔方程和泊松方程,获得二维电子气（2DEG）中电子的本征态和本征能级．依据介电连续模型和Loudon单轴晶体模型,用转移矩阵法分析该体系中可能存在的光学声子模及三元混晶效应．进一步,在室温下计及各种可能存在的光学声子散射,推广雷．丁平衡方程方法,讨论2DEG分布及二维电子迁移率的尺寸效应和三元混晶效应．结果显示：A1N插入层厚度和A1xGal-xN势垒层中A1组分的增加均会增强GaN层中的内建电场强度,致使2DEG的分布更靠近异质结界面,使界面光学声子强于其他类型的光学声子对电子的散射作用而成为影响电子迁移率的主导因素．适当调整A1N插入层的厚度和A1组分,可获得较高的电子迁移率．     

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

In this paper, a new current expression based on both the direct currect （DC） characteristics of the A1GaN/GaN high election mobility transistor （HEMT） and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the A1GaN/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 A1GaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-p-m wide （Such an A1GaN/GaN HEMT is denoted as A1GaN/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.     

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 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.     

Channel temperature determination of a multifinger AlGaN/GaN high electron mobility transistor using a micro-Raman technique

Self-heating in a multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of the AlGaN/GaN HEMT is estimated from the calibration curve of a passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1°C is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.     

辐射感生应力弛豫对Alm Ga1-m N/GaN HEMT电学特性的影响

基于电荷控制原理建立了辐射感生AlmGa1-mN势垒层应力弛豫对AlmGa1-mN/GaN HEMTs器件电学特性影响的解析模型,并进行了仿真分析.结果表明,对于高Al组分HEMTs器件,AlmGa1-mN势垒层中辐射感生的应力弛豫影响更为显著.辐射感生应力弛豫不但导致2DEG下降和阈值电压正向漂移,而且能够引起漏极输出电流的明显下降.辐射感生应力弛豫是赝配AlmGa1-mN/GaN HEMTs辐射损伤的重要机理之一.     

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.     

MMIC LNA based novel composite-channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMTs

A microwave monolithic integrated circuit （MMIC） C-band low noise amplifier （LNA） using 1 μm-gate composite-channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN high electron mobility transistors （CC-HEMTs） has been designed, fabricated and characterized. The material structure and special channel of CC-HEMT were given and analysed. The MMIC LNA with CC-HEMT showed a noise figure of 2.4 dB, an associated gain of 12.3 dB, an input return loss of -6 dB and an output return loss of -16 dB at 6GHz. The IIP3 of the LNA is 13 dBm at 6 GHz. The LNA with 1 μm ×100 μm device showed very high-dynamic range with decent gain and noise figure.[第一段]