Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors （HEMTs）

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.     

Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements, high resolution x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The results reveal that the formation of surface oxide is the main reason for the degradation, and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.     

Al2O3绝缘层的AlGaN/GaN MOSHEMT器件研究

在研制AlGaN/GaN HEMT器件的基础上,采用ALD法制备了Al₂O₃ AlGaN/GaN MOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al₂O₃薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现：所制备的Al₂O₃薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较 关键词： 2O₃')" href="#">Al₂O₃ ALD GaN MOSHEMT     

AlGaN/GaN高电子迁移率晶体管肖特基高温退火机理研究

在不同应力条件下,研究了AlGaN/GaN高电子迁移率晶体管高温退火前后的电流崩塌、栅泄漏电流以及击穿电压的变化.结果表明,AlGaN/GaN高电子迁移率晶体管通过肖特基高温退火以后,器件的特性得到很大的改善.利用电镜扫描(SEM)和X射线光电子能谱(XPS)对高温退火前、后的肖特基接触界面进行深入分析,发现器件经过高温退火后,Ni和AlGaN层之间介质的去除,并且AlGaN材料表面附近的陷阱减少,使得肖特基有效势垒提高,从而提高器件的电学特性. 关键词： AlGaN/GaN高电子迁移率晶体管 肖特基接触 界面陷阱     

氮化物MOCVD反应室流场的仿真与分析

在立式MOCVD反应室中,通过对生长氮化镓(GaN)薄膜材料的仿真,发现衬底表面反应物三甲基镓物质的量的浓度分布与实际生长的GaN薄膜的厚度分布一致,同时,仿真结果表明,薄膜的厚度分布与反应室内涡旋的分布相关.通过分析涡旋产生的原因,对反应条件和反应室的几何条件作了进一步优化,发现在较低的反应室压强、较低的壁面温度和较大的气体入口半径条件下,能使涡旋明显减小,提高薄膜生长的均匀性.     

立式MOCVD反应室中一种刻槽基座的热分析

在立式感应加热的氮化物MOCVD反应室中, 提出了一种刻槽结构的基座;利用有限元法,给出了使衬底温度分布最均匀的槽的位置和大小.与传统的基座相比,这种刻槽优化后的基座,使衬底温度分布的均匀性显著提高.另外,通过对基座温度随加热时间变化的分析,发现刻槽基座的热传导规律,即刻的槽改变了基座中感应产生热量的热传导方向,衬底中的热量是由槽上下基座部分传递而来的,且随时间的增大,基座的温度趋于恒定,衬底的温度趋于均匀,均匀的衬底温度有利于提高生长薄膜的质量.     

The reliability of AlGaN/GaN high electron mobility transistors under step-electrical stresses

In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors (HEMTs) still lack solid reliability. Devices under accelerated DC stress tests (off-state, V_DS =0 state, and on-state step-stress) are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] (Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415). However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.     

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

Self-heating in 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 AlGaN/GaN HEMT is estimated from the calibration curve of 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 ℃ 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.     

Effects of donor density and temperature on electron systems in AlGaN/AlN/GaN and AlGaN/GaN structures

It was reported by Shen et al that the two-dimensional electron gas (2DEG) in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schr\"{o}dinger--Poisson equations, theoretical investigation is carried out about the effects of donor density (0--1\times 10¹⁹cm^-3 and temperature (50--500K) on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective \Delta E_c is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective \Delta E_c. The Capacitance--Voltage (C-V) carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.     

基于I-V-T和C-V-T的GaN上Ni/Au肖特基接触特性研究

基于对制作在n-GaN上的肖特基二极管的变温I-V测试和C-V测试，采用表面势垒减薄模型对肖特基二极管的电流输运特性进行了研究.试验结果表明，肖特基接触的电流输运机理非常复杂，在不同的温度条件和偏压条件下有着不同的电流输运机理.在此基础上对肖特基接触I-V特性方程进行了修正，得到了很好的拟合曲线.试验表明，高温I-V法提取的势垒高度与常温C-V法提取的势垒高度接近于根据金属功函数得出的理论势垒高度值. 关键词： 氮化镓 肖特基二极管 表面势垒减薄模型 热电子场发射