【作者】 王言虹；

【导师】 郝跃；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 宽禁带半导体材料氮化镓(GaN)以其良好的物理化学和电学性能成为继第一代元素半导体硅(Si)和第二代化合物半导体砷化镓(GaAs)、磷化镓(GaP)、磷化铟(InP)等之后迅速发展起来的第三代半导体材料。与目前绝大多数的半导体材料相比,GaN具有的独特半导体特性(大的直接带隙能、高的饱和漂移速度、大的导带不连续性、良好的热稳定性以及强的自发和压电极化效应)预示了它在高温、高频、大功率等电子领域具有极大的应用潜力。其中,AlGaN／GaN HEMT器件在微波大功率和高温应用方面均具有明显的优势。目前所研究成果主要在耗尽型器件方面,由于高压开关和高速电路的驱动,GaN基增强型器件现已成为关注的研究热点之一。在数字电路、高压开关等领域应用时需要增强型器件,可以确保在只加正的栅压下才会出现工作电流,因而针对GaN基增强型器件的研究和设计具有十分重要的理论意义和应用价值。本课题目的是研究GaN增强型器件的频率和功率性能,对槽栅增强型HEMT器件进行了深入的研究。分析了漂移扩散传输模型、载流子迁移率模型、SRH产生复合模型、Selberherr碰撞电离模型等基本物理模型以及基本工作原理；结合器件模型和材料模型,利用器件仿真软件ATLAS对耗尽型HEMT器件进行了仿真,通过二维仿真,分析了不同结构参数对器件的影响,仿真得出AlGaN层掺杂、势垒层Al组分以及肖特基势垒高度对器件特性的影响。从仿真结果可以知道增大AlGaN层掺杂掺杂浓度、提高势垒层Al组分的比例和降低肖特基势垒高度可以增大沟道电子浓度,使得输出的饱和电流Ids增大,同时阈值电压Vth绝对值也随之增大。在以上仿真结果基础上对相同结构、不同刻蚀深度的槽栅增强型HEMT器件进行仿真,分析了槽栅深度对HEMT器件特性的影响,并对不同栅槽深度(以槽栅深度为Onm,5nm,10nm,15nm为例进行分析)的器件特性进行了模拟,得出了器件饱和电流、最大跨导、阈值电压和频率特性随着栅槽深度的变化规律：当栅槽深度增大时,器件饱和电流逐渐下降,最大跨导逐渐增大,阈值电压向正方向移动,ft、fmax稍微有所减小。同时在栅和AlGaN势垒层间加入了5nm厚的SiO2绝缘层形成MOS HEMT器件,并对MOS结构增强型HEMT器件进行了仿真,与常规槽栅增强型HEMT器件相同,器件饱和电流随着刻蚀深度的增大而有所下降,但最大跨导会随着刻蚀槽栅的加深而增大,阈值电压会随着正方向移动,器件的截止频率ft和最高振荡频率fmax会逐渐减小。随后对槽栅MOS HEMT器件和常规槽栅HEMT器件进行了对比,由于所加的SiO2使栅的耗尽作用变弱造成前者的阈值电压绝对值要比后者大很多,同时在栅压一定的情况下,前者的最大饱和电流也会相应的增大很多。最终,仿真得出槽栅MOS HEMT增强型器件对比常规槽栅HEMT增强型器件,前者在刻蚀深度为13nm之前阈值电压会小于后者,但在刻蚀深度为13nm以后,阈值电压会大于后者的阈值电压,但饱和漏电流会有所降低,同时截止频率ft和最高振荡fmax比前者略有提高。更多还原

【Abstract】 GaN, wide bandgap semiconductor, has excellent performance in physical chemistry and electric properties. Just because of this reason, it is considered the third generation semiconductor materials, likes the first generation element semiconductor materials Si and the second generation compound semiconductor materials such as GaAs, GaP and InP. Compare with recently semiconductor materials, GaN has some semiconductor features (large direct bandgap, high saturation drift velocity, large conduction band discontinuities, high thermal stability and strong piezoelectric and spontaneous polarization) which indicates it can be applied in high-temperature, high-frequency and high-power field. Especially, AlGaN/GaN devices have far outweigh any semiconductor materials in microwave high power and high-temperature occasion.However, all of research focuses on depletion-mode GaN devices for the usage in high-voltage switching and driving of high speed circuit. It ensures that only if we take positive gate voltage that get the operating current in above mentioned occasion. So the research and design has an important issue and worth for depletion-mode GaN devices.This paper analyzes the basic operation principle and physical model such as the drift diffusion transport model, carrier mobility model, SRH generation-recombination model and selberherr’s impact ionization model. Considering device model and material properties, we simulate the depletion-mode devices using device simulation tools ATLAS. By means of numerous 2D device simulation, juxtaposes the different effect which caused by different structure parameters. Meanwhile, find out that AlGaN layer doping, Al barrier layer constituent and Schottky barrier height can influence devices performance. From simulation, it thinks that we can increase the channel electron concentration, improve the output saturation current Ids and threshold voltage Vth via increasing doping level of AlGaN layer, improving the ratio of Al barrier layer constituent, decreasing Schottky barrier height.Based on above mentioned simulation result, we take the simulation for recessed-gate enhancement-mode HEMT devices with same structure, different etching depth and analyze the effect on HEMT devices properties with different recessed-gate depth. For example in the occasion of different recessed gate depth (0nm,5nm, 10nm). Then originate the relationships of saturation current, maximum transconductance, threshold voltage and frequency characteristic with the recessed-gate depth changing. Higher recessed-gate depth, then we can get lower saturation current; lower maximum transconductance and the threshold voltage move positive direction, but ft and fmax reduce a little. When generate 5nm SiO2 isolation layer between gate and AlGaN barrier layer, simulate for this MOS enhancement mode HEMT devices and find that the saturation current will lower, the maximum transconductance higher and threshold voltage move positive direction with increasing etching depth comparing with traditional enhancement mode HEMT devices. Because of SiO2 isolation layer existing, the threshold voltage modulus of MOS HEMT devices is higher than traditional. At the same time, MOS HEMT devices’ saturation current is higher than latter under certain gate voltage condition.Finally, the threshold voltage of MOS HEMT devices is lower than latter when the etching depth is less than 13nm. Nevertheless threshold voltage and saturation current of MOS HEMT are higher than latter but maximum oscillation frequency and cutoff frequency lower when the etching depth is higher than 13nm.更多还原