Impact of strain relaxation of AlGaN barrier layer on the performance of high Al-content AlGaN/GaN HEMT

Owing to large direct bandgap energy, high saturation drift velocity, large conduction band discontinuities, high thermal stability and strong piezoelectric and spontaneous po- larization[1-4], AlGaN/GaN HEMTs have advantages over electronic devices based on Si, GaAs and their alloys in high-frequency, -temperature and -power applications. Many researches show[5,6] that the characteristics of AlGaN/GaN HEMTs depend on two-dimensional gas (2DEG) in heterostructures which has intimate r…     

AlGaN/GaN HEMT热形貌分布特性仿真

该文从泊松方程、连续性方程和晶格热方程出发,采用商用TCAD软件建立A1GaN/GaNHEMT器件二维模型.针对自加热效应,在不同的直流偏置电压下,对AlGaN/GaN HEMT器件进行了二维数值分析,获得相应的热形貌分布.     

Ni/AlGaN/GaN结构中肖特基势垒温度特性

通过I-V测量研究了AlGaN/GaN异质结构上的肖特基接触与温度的关系.在室温下肖特基势垒高度为0.75 eV,理想因子为2.06.温度升高,肖特基势垒高度增加,理想因子下降,主要原因是受异质结和二维电子气的影响.在正向电流为1 mA时,室温下的正向电压为1.65 V,从室温到300℃范围内正向电压的温度系数为-1.6 mV/℃.     

双AlN插入层法在Si图形衬底上进行AlGaN/GaN HEMT的MOCVD生长

双AlN插入层方法被用来在Si（111）图形衬底上进行AlGaN/GaN高迁移率晶体管（HEMT）的金属有机物化学气相沉积（MOCVD）外延生长。Si图形衬底采用SiO2掩膜和湿法腐蚀（无掩膜）两种方法进行制备。高温生长双AlN插入层用来释放GaN外延层和Si衬底之间由于晶格失配和热失配而产生的张应力。AlGaN/GaN HEMT的生长特性被讨论和分析。在使用优化的双AlN插入层之前,可以在图形[1-100]方向观察到比[11-20]方向更多的由于应力而引起的裂纹。这是由于GaN在（1-100）面比（11-20）更稳定。建议在图形设计中,长边应沿着[11-20]方向进行制备。拉曼测试显示在图形凹角处比凸角处有更大的拉曼频移,证明在图形凹角处有更大的张应力。     

AlGaN/GaN HEMT在N2中高温退火研究

通过N2气氛中对蓝宝石衬底AlGaN／GaN HEMT在200～600℃退火1min和5min的多批实验,研究了在不同温度和时间退火冷却后器件直流参数的变化．对器件欧姆接触和肖特基接触在高温退火前后的特性进行了对比分析．确定出了最有利于高电子迁移率晶体管特性提高的退火温度为500℃．退火时间为5min．该条件退火后高电子迁移率晶体管最大跨导提高8．9%．肖特基栅反向漏电流减小2个数量级．阈值电压绝对值减小．退火后肖特基势垒高度提高．在减小栅泄漏电流的同时对沟道电子也有耗尽作用．这是饱和电流和阈值电压变化的主要原因．采用扫描电子显微镜观察肖特基退火后的形貌,500℃未发现明显变化．600℃有起泡现象．     

Nonselective etching of GaN/AlGaN heterostructures by Cl2/Ar/BCl3 inductively coupled plasmas

A systematic study of the nonselective and smooth etching of GaN/AlGaN heterostructures was performed using Cl2/Ar/BCl3 inductively coupled plasmas (ICP).Nonselective etching can be realized by adjusting the BCl3 ratio in the Cl2/Ar/BCl3 mixture (20%-60%), increasing the ICP power and dc bias, and decreasing the chamber pressure. Surface morphology of the etched heterostructures strongly depends on the gas chemistry and the chamber pressure. Specifically, with the addition of 20% BCl3 to Cl2/Ar (4:1) gas mixture, nonselective etching of GaN/Al0.28Ga0.72N heterostructures at high etch rate is maintained and the surface root-mean-square (rms) roughness is reduced from 10.622 to 0.495 nm, which is smoother than the as-grown sample. Auger electron spectroscopy (AES) analysis shows that the effective removal of residual oxygen from the surface of AlGaN during the etching process is crucial to the nonselective and smooth etching of GaN/AlGaN herterostructures at high etch rate.     

Nonselective etching of GaN/AlGaN heterostructures by Cl_2/Ar/BCl_3 inuctively coupled plasmas

~~Nonselective etching of GaN/AlGaN heterostructures by Cl_2/Ar/BCl_3 inuctively coupled plasmas~~     

Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al₂O₃ as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design, better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis were obtained, and the superiority of this MOS-HEMT device structure with ALD Al₂O₃ gate dielectric was exhibited. Supported by the National Natural Science Foundation of China (Grant No. 60736033) and the National Basic Research Program of China (“973“) (Grant No. 51327020301)     

不同厚度氮镓铟/氮化镓量子阱的光学特性研究

针对半导体薄膜厚度对器件光学特性的影响,利用金属有机物气相外延法研究了蓝宝石衬底上生长的InGaN/GaN单量子阱结构,其在室温下的的光学特性.大量实验结果表明,随着样品InGaN势阱层宽度的增加,光致发光谱的发光峰值波长出现了明显的红移现象,而且发光强度下降,谱线半高全宽展宽.通过对不同样品的透射、反射光谱研究发现,量子阱层窄的样品在波长接近红外区时出现无吸收的现象,而在阱层较宽的样品中没有发现这一现象.     

电压传感器结构设计及误差特性研究

电力系统对电压的测量主要采用电磁式电压互感器,需进行二次变压,才能将电网上的信号变为电子测量装置可用的信号。本文中的电压传感器采用电阻分压,可将初级电压直接转化为10V以内的微信号,以供测量保护用,装置具有体积小、传输频带宽、不存在饱和问题、无谐振点等优点。从路的角度分析了该分压器的误差特性,从场的角度比较了几种传感器结构方案,分析了各方案的幅值误差、相角误差及最大场强,从而得到一种最佳方案,并分析了该方案的幅值误差的频率特性。     

Wafer bonding technique used for the integration of cubic GaN/GaAs (001) with Si substrate

We successfully used the metal mediated-wafer bonding technique in transferring the as-grown cubic GaN LED structure of Si substrate. The absorbing GaAs substrate was removed by using the chemical solutions of NH4OH : H2O2=1 : 10. SEM and PL resuls show that wafer bonding technique could transfer the cubic GaN epilayers uniformly to Si without affecting the physical and optical properties of epilayers. XRD result shows that there appeared new peaks related to AgGa2 and Ni4N diffraction, indicating that the metals used as adhesive and protective layers interacted with the p-GaN layer during the long annealing process. It is just the reaction that ensures the reliability of the integration of GaN with metal and minor contact resistance on the interface.     

新式电压传感器结构设计及误差特性研究

电力系统使用的电压互感器大多采用电磁式结构,需进行二次变压,才能将电网上的信号变为电子测量装置可用的信号,所研究的电压传感器采用电阻分压,可将初级电压直接转化为10V的微信号电子测量装置使用,与传统的电压互感器相比,具有体积小,传输频带宽,不存在饱和问题,无谐振点等优点,并从路的角度分析了该分压器的误差特性,从场的角度对几种传感器结构的设计方案进行了比较。     

Nonselective etching of GaN/AlGaN heterostructures by Cl<Subscript>2</Subscript>/Ar/BCl<Subscript>3</Subscript> inductively coupled plasmas

A systematic study of the nonselective and smooth etching of GaN/AlGaN heterostructures was performed using Cl₂/Ar/BCl₃ inductively coupled plasmas (ICP). Nonselective etching can be realized by adjusting the BCl₃ ratio in the Cl₂/Ar/BCl₃ mixture (20%–60%), increasing the ICP power and dc bias, and decreasing the chamber pressure. Surface morphology of the etched heterostructures strongly depends on the gas chemistry and the chamber pressure. Specifically, with the addition of 20% BCl₃ to Cl₂/Ar (4∶1) gas mixture, nonselective etching of GaN/Al_0.28Ga_0.72N heterostructures at high etch rate is maintained and the surface root-mean-square (rms) roughness is reduced from 10.622 to 0.495 nm, which is smoother than the as-grown sample. Auger electron spectroscopy (AES) analysis shows that the effective removal of residual oxygen from the surface of AlGaN during the etching process is crucial to the nonselective and smooth etching of GaN/AlGaN herterostructures at high etch rate.     

超/特高压输电线路工频参数文件的制作方法

超/特高压线路导线间距、位置差别较大,造成导线的自阻抗、自导纳互阻抗和互导纳等参数相差较大.文章探讨带修正系数k1至k6的线路参数计算公式,根据导线（避雷线）不同换位段的物理结构计算导线参数使其与实测工频参数一致,制作出不同换位段精确的导线参数文件.对不同换位段的线路采用特征模量分解方法计算转移矩阵;将各换位段的矩阵顺序相乘得到整条线路转移矩阵;从而计算出导线的正序阻抗、正序导纳、零序阻抗和零序导纳.改变修正系数k1至k6使计算的导线参数为精确值,由此计算的导线正序和零序参数与实测值相等.该方法获得的导线参数文件可以为更精确的工程计算提供技术支持.     

低阈值电压高束流Ga离子源的研制

本文提出了改进型液态镓离子源发射体的制作方法,使制成的发射体尖端曲率半径小于0.4μm,成功率超过90％。通过时发射体特殊络合处理,增大离子源的发射电流和稳定性。降低发射阈值电压。在总引出电压为5.5 kV时,总发射束流可达250μA,阈值电压降至1 kV左右。适当选择加热温度改进和提高镓离子源的发射状态,提高离子源的性能。     

Fabrication of GaN epitaxial films on Al_2O_3/Si (001) substrates

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54/5位直流数字电压表的设计

介绍了高精度、高分辨率数字电压表的一种设计方法,可作数字万用表或精密测量仪器的表头,供设计者参考。     

高频高压电子束焊机电源的研制

传统的工频整流式电子束焊机高压电源体积和重量均很大,输出电压电力的控制动态误差大、效率低、谐波严重.基于高频斩波的电子束技术,我们研制了我国第一台60kV/6kW的全数字逆变式电子束焊机高频高压电源样机.该电源采用20kHz高频斩波调压技术,以IPM模块为全桥逆变元件,实现了高压电源的高频小型化.控制系统采用数字信号处理器（DSP）、复杂可编程逻辑器件（CPLD）等芯片组成电路,实现了电源的自动调节、过压过流保护及高压自放电快速恢复功能.用该电源系统取代电子束焊机原有的高压电源进行焊接试验,测试表明,该电源的各项性能指标均已达到设计目标,并满足焊接工艺的实际要求.     

SF_6/N_2混合气体绝缘特性的试验研究及理论分析

应用自制的试验模型对SF6/N2混合气体的绝缘能力进行了试验研究,并和纯净的SF6、N2的绝缘能力进行了比较,获得了SF6/N2混合气体在不同比例下的击穿电压与气体间隙距离之间的曲线.经综合比较、分析确定50%SF6 50%N2的混合气体的经济技术指标比较高,可以在电气设备中作为绝缘介质广泛应用.