(In)GaN/AlGaN/GaN异质结构中的二维电子和空穴气研究

	(In)GaN/AlGaN/GaN异质结构中的二维电子和空穴气研究
其他题名	Study of the Two-Dimensional Carrier Gases in (In)GaN/AlGaN/GaN heterostructures
	闫俊达
学位类型	博士
导师	王晓亮
	2017-06-01
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	微电子学与固体电子学
关键词	氮化镓异质结构二维空穴气二维电子气高电子迁移率晶体管
其他摘要	氮化镓（GaN）基高电子迁移率晶体管（HEMTs）具备诸多优良的性质，如临界击穿电场大、二维电子气（2DEG）浓度和电子迁移率高、耐高温、抗辐射等，非常适合高性能功率器件的研制。本论文从GaN基功率器件的研究进展和面临的技术挑战出发，基于能带工程，首先研究了增强型器件用Ga面极性InGaN/AlGaN/GaN异质结构材料的设计原则，之后探究了N面极性GaN/AlGaN/GaN HEMT材料结构中二维空穴气（2DHG）和2DEG的浓度调控机制。最后进行了相关材料的生长与器件验证。所取得的主要研究成果如下：1. Ga面极性增强型InGaN/AlGaN/GaN异质结构的理论研究首次从理论上系统研究了InGaN帽层的组分和厚度、AlGaN势垒层组分和厚度、以及InGaN中的p型掺杂对InGaN/AlGaN/GaN异质结构中AlGaN/GaN界面处的2DEG的调控作用。在一定条件下，该结构中可出现2DHG和2DEG共存。此时，InGaN/AlGaN上界面的2DHG成为一屏蔽层，阻止下界面的2DEG被InGaN耗尽。在一定的势垒层Al组分下，AlGaN势垒层存在一个临界厚度，在该临界厚度之下时，InGaN/AlGaN/GaN HEMT材料结构中2DHG和2DEG不能共存。此时，2DEG可以被一定组分、厚度的InGaN帽层耗尽。因此，要想制备增强型InGaN/AlGaN/GaN HEMTs器件，AlGaN势垒层的厚度应选取在该临界厚度以下。2. N面极性GaN/AlGaN/GaN异质结构的理论研究首次系统分析了N面极性GaN/AlGaN/GaN异质结构。在一定组分厚度的AlGaN势垒层下，AlGaN/GaN单异质结结构中存在2DHG；AlGaN层的Al组分和厚度越大，2DHG的面密度也越大。对于非故意掺杂的GaN/AlGaN/GaN异质结构而言，从理论上首次指出AlGaN/GaN下界面处的价带顶电子是GaN/AlGaN上界面处2DEG的本质来源之一，2DEG的出现依赖于AlGaN背势垒层和GaN顶层材料参数的选取。而对于AlGaN背势垒或GaN缓冲层故意掺杂（n型）的GaN/AlGaN/GaN异质结构而言，施主的电离也是2DEG的来源之一。相比Ga面极性HEMT结构，N面极性HEMT结构中沟道电子的限域能力更好，也更有利于形成极低的器件欧姆接触电阻，因而将来有望用来制备高性能功率器件。3. Ga面极性InGaN/AlGaN/AlN/GaN异质结构的实验研究设计生长了10 nm In_0.1Ga_0.9N/22 nm Al_0.23Ga_0.77N/1 nm AlN/3.5 μm GaN 异质结构材料。(-1015)晶面的倒易空间Mapping显示，InGaN、AlGaN共格生长在GaN缓冲层上。器件的转移特性曲线存在一电流平台（32.0 mA/mm），是由InGaN/AlGaN上界面的2DHG对沟道中2DEG产生屏蔽引起的。相对于无InGaN帽层的器件，该器件的阈值电压发生正向偏移（从-4.0 V增大到-2.1 V）。; GaN-based high electron mobility transistors (HEMTs) have great potential in applying as power devices, due to the outstanding properties of GaN, such as the high critical electric field, high two-dimensional electron gas (2DEG) sheet density and electron mobility, high temperature and irradiation resistance. To begin with, this thesis introduces the current development and technical challenges of GaN-based power devices. Based on energy band engineering, the design of Ga-polar InGaN/AlGaN/GaN heterostructures for enhancement mode operation is studied. The regulation mechanisms of the two-dimensional hole gas (2DHG) and 2DEG in N-polar GaN/AlGaN/GaN HEMT structures are also disscussed. Finally, experimental work is conducted to identify our theoretical work. The main achievements in this thesis are as follows: 1. Simulation work on enhancement mode Ga-polar InGaN/AlGaN/GaN heterostructuresFor the first time, Ga-polar InGaN/AlGaN/GaN heterostructures are systematically studied. The influences of InGaN cap layer thickness and In content, AlGaN barrier thickness and Al content，p-type doping concentrations in InGaN cap layer on 2DEG sheet density are presented. It shows that under certain conditions, the 2DHG and 2DEG can be coexisting. Then 2DHG shows to be a screen layer, preventing 2DEG from being further depleted by InGaN cap layer. For certain Al content, there exists a critical thickness of AlGaN barrier When AlGaN barrier thickness is chosen under the critical thickness, 2DEG and 2DHG will not coexist, no matter how thick is the InGaN cap layer. In order to fabricate E-mode InGaN/AlGaN/GaN HEMT devices, AlGaN barrier parameter should be chosen under the critical thickness curve.2. Theoretical Investigations on the N-polar GaN/AlGaN/GaN heterostructuresFor the first time, a systematical study of N-polar GaN/AlGaN/GaN heterostructures is conducted. 2DHG exists in AlGaN/GaN single-heterojunction structures when certain AlGaN barrier parameters are adopted. 2DHG sheet density increases with the increase of Al content and AlGaN layer thickness. For the unintentionally doped GaN/AlGaN/GaN heterostructures, electrons from the valence band edge at the bottom AlGaN/GaN interface provides to be the source of 2DEG at the GaN/AlGaN upper interface essentially. The appearance of 2DEG relies on the adoption of AlGaN barrier and GaN top layer parameters. As for GaN/AlGaN/GaN heterostructures with AlGaN back barrier and GaN buffer n-type doped, the ionization of the donors provides to be another electron source. Compared with Ga-polar HEMTs, N-polar HEMTs can better channel electron confinement and ultra-low ohmic contact resistance. Therefore, N-polar HEMT structures are promising in fabricating high performance power devices in the future.3. Experimental research of Ga-polar InGaN/AlGaNAlN/GaN heterostructures10 nm In_0.1Ga_0.9N/22 nm Al_0.23Ga_0.77N/1 nm AlN/3.5 μm GaN heterostructures are designed and grown by MOCVD. (-1015) planes’ RSMs show that InGaN and AlGaN layers are both coherently grown on GaN buffers. A drain current plateau (𝐼_ds=32.0 mA/mm) is present in the device’s transfer characteristics, which is due to the the screening effect of 2DHG to 2DEG in the conduction channel. Compared to device without InGaN cap, this device shows a positive shift of threshold voltage (from -4.0 V to -2.1 V).
学科领域	半导体器件
语种	中文
公开日期	2017-06-05
文献类型	学位论文
条目标识符	http://ir.semi.ac.cn/handle/172111/28218
专题	中科院半导体材料科学重点实验室
推荐引用方式 GB/T 7714	闫俊达. (In)GaN/AlGaN/GaN异质结构中的二维电子和空穴气研究[D]. 北京. 中国科学院研究生院,2017.

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