Ⅲ族氮化物极化掺杂场效应晶体管基础研究

发布时间：2018-05-17 20:34

本文选题：氮化物 + 极化　；参考：《北京科技大学》2016年博士论文

【摘要】：极化效应是Ⅲ族氮化物材料最鲜明的特点之一,在Ⅲ族氮化物微电子和光电子器件中扮演着十分重要的角色。GaN HFET (Heterojunction Field Effect Transistor,HFET)的工作基础正是AlGaN/GaN突变结界面由于极化效应产生的二维电子气。当AlGaN/GaN异质结界面材料组份呈渐变状态,极化效应产生的极化强度就会随之渐变,进而在组份渐变的AlGaN中就会出现由极化产生的呈三维分布的自由电子。这种由极化效应导致材料中存在大量三维分布的自由载流子的现象被称作极化掺杂。这种新颖的掺杂形式和载流子分布方式给GaN基电子器件设计带来更多的选择,如极化掺杂场效应晶体管(Polarization Doped Field Effect Transistor,PolFET)。相较于传统的氮化物电子器件,基于极化掺杂的PolFET表现出迥然不同的器件特性,具有高线性度、高可靠性等诸多特点。本论文以MOCVD (Metal Organic Chemical Vapor Deposition, MOCVD)制备氮化物材料为基础,系统研究了氮化物材料生长、AlGaN/GaN PolFET器件的设计、制备和器件性能。研究了GaN外延材料生长中的工艺优化,包括缓冲层的优化、生长工艺参数的调整、GaN外延层应力控制等。经过优化, SiC衬底上GaN外延层(002)和(102)面的X射线摇摆曲线半高宽分别达到185 arcsec和261arcsec,并提出SiC衬底上GaN外延应力变化模型。使用MOCVD方法制备了组份渐变的AlGaN/GaN材料,体掺杂浓度1.2E+18 cm-3,迁移率达到732 cm2/V·s。使用二次离子质谱进行了组份分析,发现自表面起A1组份由35%到0%单调变化,正是组份的线性变化引起的极化梯度导致了缓变AlGaN层中自由电子准体三维分布。使用变频电导-电压测试表征了该组份渐变的AlGaN/GaN材料的陷阱行为。与传统的突变AlGaN/GaN异质结构中存在大量的陷阱堆积相比,在缓变AlGaN/GaN异质结中没有发现明显的陷阱堆积,这是因为缓变结材料消除了脆弱的突变异质界面。另外,在缓变AlGaN/GaN结构中观察到陷阱时间常数与偏置电压呈线性指数关系,这是界面陷阱的典型特征,说明缓变AlGaN/GaN异质结构具有多界面特性。基于缓变AlGaN/GaN异质结材料制备了高线性AlGaN/GaN PolFET器件。在5V栅压工作范围内,AlGaN/GaN PolFET器件的直流和射频特性均对偏置点不敏感,非常适合WiMAX和LTE-Advanced等无线通信系统的线性放大器等应用。采用动态Ⅰ-Ⅴ测试表征了AlGaN/GaN PolFET器件的陷阱行为,相较于传统的基于突变结材料的AlGaN/GaN HFET中较大的电流崩塌,基于缓变结材料的AlGaN/GaN PolFET器件呈现出极小的电流崩塌行为。通过模拟仿真进行了该现象的机理分析,缓变组份AlGaN材料拓宽了电子沟道,而AlGaN缓变材料中含有大量可移动电子,屏蔽了沟道中下半部分载流子与表面陷阱的作用,从而抑制了PolFET器件的电流崩塌。进行了AlGaN/GaN PolFET器件直流高温特性研究。发现随着温度的升高,器件的漏极电流和跨导都单调下降。相较于传统AlGaN/GaN基HFET, PolFET的漏极电流下降幅度更小。AlGaN/GaN PolFET器件不同栅偏置下的跨导下降行为表现出不同的温度依赖关系,当栅压为-2V时,跨导下降的温度系数为-0.5,而栅压为-5 V时,跨导下降温度系数为-1.5。研究了AlGaN/GaN缓变异质结材料中不同空间位置载流子的输运规律,从AlGaN/GaN PolFET独特的载流子行为出发,提出准多沟道模型对PolFET的高温特性进行了分析
[Abstract]:Polarization effect is one of the most distinct characteristics of nitride materials, which plays a very important role in.GaN HFET (Heterojunction Field Effect Transistor, HFET) in the third group of nitride microelectrons and optoelectronic devices. The basis of the working basis is the two-dimensional electron gas produced by the polarization effect of the AlGaN/GaN junction interface when the AlGaN/GaN is different. The material components of the mass interface are gradually changing, and the polarization intensity of the polarization effect will gradually change, and then there will be a three-dimensional free electron produced by polarization in the AlGaN of the component gradually. This phenomenon is called polarization doping in the phenomenon of a large number of three dimensional distribution in the material. New types of doping and carrier distribution bring more options for the design of GaN based electronic devices, such as polarization doped field effect transistors (Polarization Doped Field Effect Transistor, PolFET). Compared with traditional nitride electronic devices, polarization based PolFET shows very different device characteristics and high lines. On the basis of MOCVD (Metal Organic Chemical Vapor Deposition, MOCVD) preparation of nitride materials, this paper systematically studies the growth of nitride materials, the design, preparation and performance of AlGaN/GaN PolFET devices, and studies the process optimization in the growth of GaN epitaxial materials, including the optimization of the buffer layer. The adjustment of the growth process parameters, the stress control of the GaN epitaxial layer, and so on. After optimization, the X ray rocking curve of the GaN epitaxial layer (002) and (102) surface on the SiC substrate is 185 arcsec and 261arcsec respectively, and the GaN epitaxial stress change model on the SiC substrate is put forward. The AlGaN/GaN material of the component gradual change is prepared by the MOCVD square method, and the volume doping concentration is 1.. 2E+18 cm-3, the mobility of 732 cm2/V. S. was analyzed by two ion mass spectrometry. It was found that the A1 component from the surface was monotonically changed from 35% to 0%. It was the polarization gradient caused by the linear variation of the components that resulted in the three-dimensional distribution of the free electron quasi body in the slowly changing AlGaN layer. The trap behavior of lGaN/GaN material. Compared with a large number of traps in the traditional mutant AlGaN/GaN heterostructure, there is no obvious trap accumulation in the slowly changing AlGaN/GaN heterojunction. This is because the slow transition material eliminates the fragile mutation heterogeneous interface. In addition, the trap time constant is observed in the slowly changing AlGaN/GaN structure and the trap time constant is observed. The bias voltage has a linear exponential relationship, which is a typical feature of the interface trap. It shows that the slow variant AlGaN/GaN heterostructure has multiple interface characteristics. A high linear AlGaN/GaN PolFET device is prepared based on the slowly varying AlGaN/GaN heterojunction material. The DC and RF characteristics of the AlGaN/GaN PolFET devices are not sensitive to the bias point in the 5V gate voltage range. It is very suitable for applications of linear amplifiers such as WiMAX and LTE-Advanced wireless communication systems. The trap behavior of AlGaN/GaN PolFET devices is characterized by dynamic I-V test. Compared to the larger current collapse in the AlGaN/GaN HFET based on the traditional mutant junction material, the AlGaN/GaN PolFET device based on the retarded junction material is very small. The mechanism analysis of the phenomenon is carried out by simulation. The slow variable component AlGaN material widens the electronic channel, while the AlGaN slowly varying material contains a large number of movable electrons, shielding the role of the carrier and surface traps in the middle and lower part of the channel, thus inhibiting the current collapse of the PolFET device. AlGaN/GaN PolFET has been carried out. It is found that the leakage current and transconductance of the device decrease monotonically with the increase of temperature. Compared to the traditional AlGaN/GaN based HFET, the drop of the leakage current of the PolFET is smaller than that of the.AlGaN/GaN PolFET device under different gate bias. When the temperature coefficient is -0.5 and the gate pressure is -5 V, the transconductance drop temperature coefficient is -1.5. to study the transport law of different space carriers in the AlGaN/GaN slowly varying heterojunction material. From the unique carrier behavior of AlGaN/GaN PolFET, the quasi multi channel model is proposed to analyze the high temperature characteristics of PolFET.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ126.2;TN386

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