蓝宝石衬底上AIGaN／GaN HEMT自热效应研究

建立了包含“自热效应”的AIGaN／GaN HEMT（高电子迁移率晶体管）直流I-V特性解析模型。从理论的角度分析了自热效应对AlGaN／GaN HEMT器件的影响，并同已有的实验结果进行了对比，符合较好。证明基于这种模型的理论分析适于AIGaN／GaN HEMT器件测试及应用的实际情况。     

一种紧凑的GaN高电子迁移率晶体管大信号模型拓扑

GaN高电子迁移率晶体管（HEMT）以其复杂的器件特性使其大信号建模变得十分困难,尽管EEHEMT、Angelov等模型结构曾经成功应用于GaAs HEMT/MESFET的大信号模型,但当它们被用于GaN HEMT建模时却不再准确和完备.面向GaN HEMT器件的大信号模型,本文提出了一种紧凑的模型拓扑,此模型拓扑综合了GaN HEMT器件的直流电压-电流（I-V）特性、非线性电容、寄生参数、栅延迟漏延迟与电流崩塌、自热效应以及噪声等特性.经验证此模型拓扑在仿真中具有很好的收敛性,适用于GaN HEMT器件的大信号模型的建立,满足GaN基微波电路设计对器件模型的需求.     

一种新的AlGaN/GaN HEMT半经验直流特性模型

在EEHEMT1模型的基础上给出一种新的A1GaN/GaN HEMT半经验直流特性模型,考虑了栅源电压对膝点电压的影响,得到描述AlGaN/GaN HEMT器件I-Ⅴ特性的方程.此模型可以应用于蓝宝石和SiC两种不同衬底AlGaN/GaN HEMT器件的I-Ⅴ特性模拟.仿真结果和实验测量结果拟合误差小于3%.     

一种新的AlGaN/GaN HEMT半经验直流特性模型

在EEHEMT1模型的基础上给出一种新的A1GaN/GaN HEMT半经验直流特性模型,考虑了栅源电压对膝点电压的影响,得到描述AlGaN/GaN HEMT器件I-Ⅴ特性的方程.此模型可以应用于蓝宝石和SiC两种不同衬底AlGaN/GaN HEMT器件的I-Ⅴ特性模拟.仿真结果和实验测量结果拟合误差小于3%.     

一种改进的AlGaN/GaN HEMT全局直流模型

对Angelov直流FET模型进行改进,并应用同一遗传算法对改进前后的模型进行全局直流模型参数提取,平均相对误差分别为4.58%和1.8%。将模型计算值与实验数据进行对比,结果表明,改进后的模型能更加准确地描述AlGaN/GaN HEMT源漏电流随栅、漏电压变化的全局直流输出特性,从而为AlGaN/GaN HEMT提供一种准确的全局直流模型和精确的参数提取方法。     

AlN阻挡层对AlGaN/GaN HEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

AlN阻挡层对AlGaN/GaNHEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

AlGaN/GaN HEMT小信号模型参数提取算法

本文采用了新型的22元件AlGaN/GaN HEMT小信号等效电路模型,较传统的模型,增加了栅漏电导Ggdf和栅源电导Ggsf来表征GaN HEMT的栅极泄漏电流。同时针对新型的栅场板、源场板结构器件,提出了一种改进的寄生电容参数提取方法,使之适用于提取非对称器件的小信号模型参数。为验证此模型,获得了S参数的测试结果和模型仿真结果,此二者的吻合度较高,表明新型的22元件小信号模型精确、稳定而且物理意义明确。     

AlGaN/GaN HEMT器件的光电特性研究

本文采用Silvaco TCAD软件在海威华芯0.25μm AlGaN/GaN HEMT工艺和设计规则下建立了AlGaN/GaN HEMT的二维仿真模型,对AlGaN/GaN HEMT器件在有/无光照条件下进行了击穿特性的仿真和研究,结果表明器件的光电流可以达到暗电流的4000倍以上;采用脉冲响应法对AlGaN/GaN HEMT器件进行了光电响应速度的仿真,结果表明该器件可实现580Hz光脉冲到电脉冲的转换。因此,本文研究的常规非光电工艺AlGaN/GaN HEMT器件可以用来制作具有内部增益的雪崩型紫外光电探测器。     

AlGaN/GaN材料HEMT器件优化分析与I-V特性

在考虑AlGaN/GaN异质结中的压电极化和自发极化效应的基础上,自洽求解了垂直于沟道方向的薛定谔方程和泊松方程.通过模拟计算,研究了AlGaN/GaN HEMT器件掺杂层Al的组分、厚度、施主掺杂浓度以及栅偏压对二维电子气特性的影响.用准二维物理模型计算了AlGaN/GaN HEMT器件的输出特性,给出了相应的饱和电压和阈值电压,并对计算结果和AlGaN/GaN HEMT器件的结构优化进行了分析.     

蓝宝石衬底上AlGaN/GaN HEMT自热效应研究

建立了包含“自热效应”的A lG aN/G aN HEM T(高电子迁移率晶体管)直流I-V特性解析模型。从理论的角度分析了自热效应对A lG aN/G aN HEM T器件的影响,并同已有的实验结果进行了对比,符合较好。证明基于这种模型的理论分析适于A lG aN/G aN HEM T器件测试及应用的实际情况。     

Large-Signal Model for AlGaN/GaN HEMTs Accurately Predicts Trapping- and Self-Heating-Induced Dispersion and Intermodulation Distortion

In this paper, an accurate table-based large-signal model for AlGaN/GaN HEMTs accounting for trapping- and self-heating-induced current dispersion is presented. The B-spline-approximation technique is used for the model-element construction, which improves the intermodulation-distortion (IMD) simulation. The dynamic behavior of the trapping and self-heating processes is taken into account in the implementation of the model. The model validity is verified by comparing the simulated and measured outputs of the device tested under pulsed and continuous large-signal excitations for devices of 1-mm gate width. Single- and two-tone simulation results show that the model can efficiently predict the output power and its harmonics and the associated IMD under different input-power and bias conditions.     

Thermal effects in AlGaN/GaN/Si high electron mobility transistors

Group III-nitride compounds are of increasing interest for designing high power and high temperature transistors. A considerable progress in the growth and process technology of these devices has been achieved. However, there are still limitations concerning particularly the lack of native substrates. Comparison of the AlGaN/GaN high electron mobility transistors investigated favours the SiC substrate. Recently, encouraging results have been reported for AlGaN/GaN/Si. The crucial problem found in AlGaN/GaN transistors operating at high biases is the self-heating induced by high power dissipation in the active zone. The present work reports on a study of the self-heating in AlGaN/GaN HEMTs grown on Si(1 1 1). The electron-band parameters of the heterostructures have been calculated self-consistently by taking into account the piezoelectric and spontaneous polarizations. As an experiment support, direct-current characteristics of AlGaN/GaN/Si HEMTs have been used to derive the drain voltage-dependent temperature rise in the conductive channel. As has been found, the self-heating is relatively weak. An improvement in the electron transport is achieved by optimizing the epilayers and adjusting the electrode sizes at output of the transistors investigated.     

Power performance and scalability of AlGaN/GaN power MODFETs

The scalability of power performance of AlGaN/GaN MODFETs with large gate periphery, as necessary for microwave power devices, is addressed in this paper. High-frequency large-signal characteristics of AlGaN/GaN MODFETs measured at 8 GHz are reported for devices with gatewidths from 200 μm to 1 mm. 1-dB gain compression occurred at input power levels varying from -1 to +10 dBm as the gatewidth increased, while gain remained almost constant at -17 dB. Output power density was ~1 W/mm for all devices and maximum output power (29.9 dBm) occurred in devices with 1-mm gates, while power-added efficiency remained almost constant at ~30%. The large-signal characteristics were compared with those obtained by dc and small-signal S-parameters measurements. The results illustrate a notable scalability of AlGaN/GaN MODFET power characteristics and demonstrate their excellent potential for power applications     

Thermal analysis of AlGaN-GaN power HFETs

In this paper, we present a thermal analysis of AlGaN-GaN power heterojunction field-effect transistors (HFETs). We report the dc, small-signal, large-signal, and noise performances of AlGaN-GaN HFETs at high temperatures. The temperature coefficients measured for GaN HFETs are lower than that of GaAs pseudomorphic high electron-mobility transistors, confirming the potential of GaN for high-temperature applications. In addition, the impact of thermal effects on the device dc, small-signal, and large-signal characteristics is quantified using a set of pulsed and continuous wave measurement setups. Finally, a thermal model of a GaN field-effect transistor is implemented to determine design rules to optimize the heat flow and overcome self-heating. Arguments from a device, circuit, and packaging perspective are presented.     

AlGaN/GaN heterostructure field-effect transistor model includingthermal effects

A new AlGaN/GaN heterostructure field-effect transistor (HFET) model, in the framework of the gradual channel approximation and based on Monte Carlo simulations of the electron transport properties, is presented. The effects on the dc HFET output characteristics arising from contact resistances, from the ungated access channels between the gate and the source and between the gate and the drain, and from self-heating are analyzed. By examining the channel potential, the ungated regions are shown to have nonlinear characteristics. The solution method uses implicit analytical relationships for the current in the gated and ungated segments of the channel that are connected by matching boundary conditions. Thermal effects on the transport parameters associated with self-heating are included self-consistently. The model results are in very good agreement with experimental data from AlGaN/GaN HFETs fabricated on sapphire substrates. The model also identifies several device design parameters that need to be adjusted to obtain optimized performance in terms of output current and transconductance     

Theoretical Study of Electron Confinement in Submicrometer GaN HFETs Using a Thermally Self-Consistent Monte Carlo Method

This paper studies various existing advanced GaN heterostructures, which are introduced to provide better confinement of the 2-D electron gas in the channel using a Monte Carlo simulation method coupled with a 3-D solution of the heat diffusion equation. It is shown that the introduction of acceptors in the buffer layer and the introduction of an InGaN back-barrier layer at the bottom of the channel, in a single heterojunction AlGaN/GaN heterostructure field-effect transistor (HFET), improve charge confinement in the channel. It is also shown how the inclusion of an AlGaN carrier exclusion layer at the AlGaN/GaN interface significantly improves the current-handling capability of the HFET. This paper is also a study of the effect of carrier confinement on the thermal performance of each structure; the results show that better confinement of carriers in the HFET channel is accompanied by an enhancement of the influence of self-heating effects.     

Device reliability study of AlGaN/GaN high electron mobility transistors under high gate and channel electric fields via low frequency noise spectroscopy

A set of different short term stress conditions are applied to AlGaN/GaN high electron mobility transistors and changes in the electronic behaviour of the gate stack and channel region are investigated by simultaneous gate and drain current low frequency noise measurements. Permanent degradation of gate current noise is observed during high gate reverse bias stress which is linked to defect creation in the gate edges. In the channel region a permanent degradation of drain noise is observed after a relatively high drain voltage stress in the ON-state. This is attributed to an increase in the trap density at the AlGaN/GaN interface under the gated part of the channel. It was found that self-heating alone does not cause any permanent degradation to the channel or gate stack. OFF-state stress also does not affect the gate stack or the channel.     

Identifying the spatial position and properties of traps in GaN HEMTs using current transient spectroscopy

Time constant spectra are extracted from current transients based on the Bayesian deconvolution and used to characterize traps in GaN high-electron mobility transistors. Two kinds of traps with different time constants in an actual device were identified in the AlGaN barrier layer and the GaN layer, respectively. In particular, the trapping process in the AlGaN barrier layer was identified at the region near the drain side under gate contact. Trapping mechanisms of both two traps are discussed. Additionally, we observe that the trap in the AlGaN barrier layer requires sufficient electric field to activate the trapping process and a high drain voltage (V_ds) accelerates the trapping processes both in the AlGaN barrier layer and the GaN layer. In addition, detrapping experiments with different filling conditions were performed to confirm their spatial positions. The influence of self-heating is excluded during the experiment by keeping the power density at a very low level, and the trapping effect is the sole factor accounting for the current transients.     

Investigation on thermo-mechanical responses in high power multi-finger AlGaN/GaN HEMTs

Both transient temperature and thermal stress responses in high power multi-finger AlGaN/GaN high electron mobility transistors (HEMTs), caused by their self-heating effects, are characterized in the present study. Instead of using commercial software, self-developed algorithm based on hybrid time-domain finite element method (TD-FEM) is applied for thermo-mechanical co-simulation of such 3-D structure. The temperature-dependent properties of most constitutive parameters of all materials involved, in particular for electrical conductivities, thermal conductivities, thermal expansion coefficients, and Young’s modulus, are described by several sets of nonlinear polynomial expressions. The algorithm accuracy is validated in detail, with good agreement achieved in comparison with the commercial software COMSOL. It is believed that this study will be useful for effectively evaluating the reliability and lifetime of AlGaN/GaN HEMTs and their monolithic microwave integrated circuits (MMIC) used in high power communication systems and radars.