温度对一维压电半导体梁弯曲特性的影响

采用微分算子法,理论研究了一维热压电半导体梁在横向力作用下的静态弯曲问题,得到了位移、电势、载流子、温度以及剪力、弯矩、电位移和电流密度等物理场的解析解,并分析了温度对n型ZnO压电半导体悬臂梁力电热耦合性能的调控作用.研究结果表明:温度能显著影响压电半导体梁的力电场分布,造成电势、载流子、电场和电位移在高温区域发生显著变化,而对于位移、剪力和弯矩影响较小.该温度调控效果主要是由热释电效应产生的极化电荷引起的.     

GaN／AIN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发，采用有限元方法计算了GaN／AIN量子点结构中的应变分布，研究了其自发极化、压电极化以及极化电荷密度．结果表明，应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化，使电子聚集在量子点顶部，空穴聚集在量子点下面的湿润层中，在量子点结构中产生显著的极化电场，并讨论了电场的存在对能带带边的形状以及能级分布的影响．     

GaN/AlN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发,采用有限元方法计算了GaN/AlN量子点结构中的应变分布,研究了其自发极化、压电极化以及极化电荷密度.结果表明,应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化,使电子聚集在量子点顶部,空穴聚集在量子点下面的湿润层中,在量子点结构中产生显著的极化电场,并讨论了电场的存在对能带带边的形状以及能级分布的影响.     

GaN/AlN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发,采用有限元方法计算了GaN/AlN量子点结构中的应变分布,研究了其自发极化、压电极化以及极化电荷密度.结果表明,应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化,使电子聚集在量子点顶部,空穴聚集在量子点下面的湿润层中,在量子点结构中产生显著的极化电场,并讨论了电场的存在对能带带边的形状以及能级分布的影响.     

半导体技术

O4712007060630GaN/AlN量子点结构中的应变分布和压电效应/梁双,吕燕伍(北京交通大学物理系)//半导体学报.―2007,28(1).―42～46.从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发,采用有限元方法计算了GaN/AlN量子点结构中的应变分布,研究了其自发极化、压电极化以及极化电荷密度。结果表明,应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化,使电子聚集在量子点顶部,空穴聚集在量子点下面的湿润层中,在量子点结构中产生显著的极化电场,并讨论了电场的存在对能带带边的形状以及能级分布的影响。图4表1…     

一种压电半导体纳米线的热电耦合性能研究

采用有限元分析方法,研究了一种n型压电半导体纳米线(氧化锌)的电热耦合性能,分析了外部温度对氧化锌纳米线内部机械场、电场及电流场分布的影响,并讨论了本构方程线性化对电学参数的影响。研究结果表明,温度对氧化锌纳米线的电场、载流子浓度和电流密度影响很大,采用线性本构和非线性本构求得的电场、电子浓度和电流密度最大相差分别为24%,32%和68%,基于非线性本构分析压电半导体的电学性能会引起很大误差。该研究结果可为压电半导体器件利用温度调控电场、电流提供理论依据。     

温度梯度对GaN热压电pn结电学性能的影响

热感应产生的极化电势可以改变压电半导体结构内的力电物理量,这在人工智能、微机电系统(MEMS)中极具应用价值.文章针对温度梯度作用下的氮化镓(GaN)压电pn结,采用二维压电半导体多场耦合方程和精确的热电物理边界条件,数值分析了温度梯度改变对GaN热压电pn结内极化强度、电势、电场、载流子分布及电流等物理场的影响.结果表明:由于温度梯度场和极化电荷之间存在耦合,热压电pn结电学性能对温度梯度高度敏感,由温度改变产生的热感应极化电荷可以有效调节该结构的开启电压和载流子传输特性,这为操控与温度相关的智能异质结器件电流传输提供了新的方法和理论指导.     

具有栅介质电场屏蔽作用的新型GaN纵向槽栅MOSFET器件设计

基于氮化镓(GaN)等宽禁带(WBG)半导体的金氧半场效应晶体管(MOSFET)器件在关态耐压下,栅介质中存在与宽禁带半导体临界击穿电场相当的大电场,致使栅介质在长期可靠性方面受到挑战。为了避免在GaN器件中使用尚不成熟的p型离子注入技术,提出了一种基于选择区域外延技术制备的新型GaN纵向槽栅MOSFET,可通过降低关态栅介质电场来提高栅介质可靠性。提出了关态下的耗尽区结电容空间电荷竞争模型,定性解释了栅介质电场p型屏蔽结构的结构参数对栅介质电场的影响规律及机理,并通过权衡器件性能与可靠性的关系,得到击穿电压为1 200 V、栅介质电场仅0.8 MV/cm的具有栅介质长期可靠性的新型GaN纵向槽栅MOSFET。     

压电式微位移机构动态特性研究

压电陶瓷驱动器在较高电场的作用下将产生严重的非线性,从而影响其定位精度。压电陶瓷驱动器的非线性不仅与材料的非线性、蠕变、滞后等因素有关,还与器件的动态响应特性有关。动态响应的迟滞非线性是影响压电式微位移驱动器控制性能的一个关键因素,直接关系到控制精度的提高。该文采用前馈控制同数字比例、积分和微分环节(PID)控制相结合的复合控制算法对一维压电式微位移机构的控制过程进行校正补偿,建立了动态特性的闭环校正控制系统。实测结果表明,机构的动态响应时间显著缩短,实现了机构的快速响应。     

高温AlN模板上p型GaN的生长研究

利用低压金属有机物化学气相沉积技术,采用均匀掺杂和渐变Mg-δ掺杂方法,分别在氮化镓(GaN)和高温氮化铝(HT-AlN)模板上,生长了p型GaN外延材料.生长后,双晶X射线衍射和霍尔测试结果表明:HT-AlN模板上采用渐变Mg-δ掺杂方法生长的p型GaN材料,具有最好的晶体质量和电学性能.该p型GaN样品的(0002)面半峰宽值小至178",其空穴氧浓度为5.78×1017 cm-3.在对Cp2Mg/TMGa进行了优化试验后,p型GaN的空穴氧浓度被提高到8.03×1017 cm-3.     

压电半导体的极化处理及性能研究

极化处理是压电半导体材料制备及构件设计中的关键工艺,直接影响着其压电性能。根据夹层极化的方法,研制出一种多样性极化实验装置,解决了压电半导体的极化问题,并对极化后的GaN材料性能进行了系统研究。实验结果表明:(1)极化使GaN材料具备了压电性能,改变了其力电性能参数；(2)极化显著提高了压电半导体的导电能力,改变了其弯曲强度。     

Nonlinear interaction of acoustic surface waves in epitaxial gallium arsenide

A technique is described for obtaining the nonlinear interaction between two surface waves propagating in a piezoelectric semiconductor. The coupling between the waves is associated with the transverse electric fields of the surface wave and the carriers in the semiconductor. The effective carrier concentration for the interaction has been altered by forming a surface-depletion region beneath a metal?semiconductor contact. This scheme has been used to produce the convolution of two oppositely travelling acoustic waves in epitaxial gallium arsenide, and it has been found that a strong nonlinearity can be obtained at small acoustic-power levels.     

Mechanism investigation of NiO<Subscript>x</Subscript> in Au/Ni/p-type GaN ohmic contacts annealed in air

Recently, Au/Ni/p-type GaN ohmic contacts annealed in an air ambient have been widely investigated. However, to obtain a low specific-contact resistance, the annealing window is limited. In this study, to understand the oxidation function of metallic Ni, the Au/Ni/p-type GaN structure was annealed in an air ambient for 10 min at various temperatures. Using x-ray photoelectron spectroscopy (XPS) analysis, the metallic Ni was oxidized into NiO and NiO_1.3 compositions at annealing temperatures of 500°C and 600°C, respectively. However, metallic Ni still existed on the interface of the Ni/p-type GaN annealed at 400°C. The associated barrier heights of 0.42 eV, 0.21 eV, and 0.31 eV were obtained with p-type GaN for the Ni, NiO, and NiO_1.3 contacts, respectively. The hole concentrations of p-type NiO and p-type NiO_1.3 were 2.6×10¹⁶ cm⁻³ and 2.0×10¹⁸ cm⁻³, respectively. The lower hole concentration of the p-type NiO would lead to reducing the valence-band bending of the p-type GaN, as well as the barrier height for holes crossing from the p-type NiO to the p-type GaN. The formation of NiO was thus an important issue for lowering the specific-contact resistance of the Au/Ni/p-type GaN ohmic contacts annealed in an air ambient.     

脉冲激光双光束沉积掺Mg的GaN薄膜的研究

采用脉冲激光双光束沉积系统在Si(111)衬底上生长了掺Mg的GaN薄膜和未掺杂GaN薄膜。利用X射线衍射(XRD)、原子力显微镜(AFM)、室温范德堡霍尔测量及光致发光(PL)光谱对两类薄膜进行对比分析，结果显示，所生长的GaN薄膜均为六方纤锌矿晶体结构，掺Mg可细化所生长的GaN薄膜晶粒。随着掺Mg量的增加，GaN薄膜无需后处理即可由”型导电转化为p型导电，GaN薄膜的光学性能随p型载流子浓度增大而提高；然而掺Mg却导致GaN薄膜结晶质量下降，掺镁量过大的GaN薄膜中p型载流子浓度反而减少，光致发光中黄发射峰增强较大。研究表明通过优化脉冲激光双光束沉积参数无需任何后处理可直接获得高空穴载流子浓度的p型GaN薄膜。     

p-GaN与Ni/Pt欧姆接触的研究

本文对p-GaN与Ni/Pt形成欧姆接触及其电流传输机制进行了研究。I-V变温测试曲线是线形的,表明Ni/Pt与p-GaN之所以能形成欧姆接触,是因为Ni/Pt与p-GaN接触在空气中退火时界面处的p-GaN空穴浓度增加了,从而降低了有效势垒高度。在148K～323K范围内,单位接触电阻R_c随测试温度T的升高趋于呈指数下降,表明Ni/Pt与p-GaN欧姆接触的电流传输机制遵循热电子发射。     

Low-operation voltage of InGaN/GaN light-emitting diodes by using aMg-doped Al0.15Ga0.85N/GaN superlattice

Low-resistivity Mg-doped Al_0.15Ga_0.85N/GaN strained-layer superlattices were grown. In these superlattices, the maximum hole concentration is 3×10¹⁸/cm³ at room temperature. Hall-effect measurements indicate high conductivity of this structure in which the high activation efficiency is attributed to the strain-induced piezoelectric fields. This work also fabricated InGaN/GaN blue LEDs that consist of a Mg-doped Al_0.15Ga_0.85N/GaN SLs. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 3 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V     

The effect of built-in electric field in GaN/AlGaN quantum wells with high AIN mole fraction

Spontaneous and piezoelectric polarization in hexagonal GaN/AlGaN heterostructures give rise to large built-in electric fields. The effect of the builtin electric field in GaN/Al_xGa_1−xN quantum wells was investigated for x=0.2 to 0.8 by photoluminescence studies. The quantum well structures were grown by molecular beam epitaxy on (0001) sapphire substrates. Cross-sectional transmission electron microscopy performed on the samples revealed abrupt interfaces and uniform layer thicknesses. The low temperature (4 K) photoluminescence peaks were progressively red-shifted due to the quantum confined Stark effect depending on the AlN mole fraction in the barriers and the thickness of the GaN quantum well. Our results verify the existence of very large built-in electric fields of up to 5 MV/cm in GaN/Al_0.8Ga_0.2N quantum wells.