The effects of reactive ion etching-induced damage on the characteristics of ohmic contacts to n-Type GaN

The effects of reactive ion etching n-GaN surfaces with both SiCl₄ and Ar plasmas have been investigated using transmission line measurements. The measurements were made from ohmic contacts consisting of Al (as-deposited) and Ti/Al (as-deposited and rapid thermal annealed). The contact resistance, specific contact resistance, and sheet resistance were investigated as functions of the dc plasma self-bias voltage and etch time. The contact resistance extracted from contacts fabricated on surfaces etched with SiCl₄ was found to be improved over the unetched samples for all conditions investigated. Dry etching the surface with Ar severely degraded the contact resistance over the unetched sample except at the lower self-bias voltages. Rapid thermal annealing of etched samples prior to Al deposition was found to be effective in removing some of the reactive ion etching/SiCl₄-induced damage.     

Final polishing of Ga-polar GaN substrates using reactive ion etching

Reactive ion etching of {0001} oriented plate-like GaN single crystals has been investigated using SiCl₄:Ar:SF₆ chemistry. The reactive ion etching process is highly chemical. Large anisotropy of the etching rate and of the morphology has been established on (000 ) N-polar and (0001) Ga-polar sides of the GaN crystals, with remarkably higher rate on the N-polar side. Atomic force microscopy measurements have shown smooth surface and good polishing effect obtained on Ga-polar side, while N-polar surface exhibits an increased roughness of a factor of 10 after RIE.     

Improved sidewall morphology on dry-etched SiO2 masked GaN features

A number of different methods have been investigated for minimizing sidewall roughness on dry etched GaN features formed using high density plasmas. In many instances, striations on dry etched mesas are a result of roughness in the initial photoresist mask employed, and this roughness is transferred sequentially to the dielectric mask and then to the GaN. Flood exposure of the photoresist, optimization of the bake temperature, choice of plasma chemistry, and ion flux/energy for patterning the dielectric mask all influence the final GaN sidewall morphology.     

GaN功率MMIC背面通孔工艺优化及可靠性分析

介绍了改进GaN功率MMIC背面通孔工艺的相关方法,并对通孔进行了可靠性方面的测试与分析。通过优化机械研磨的方法,减薄圆片至75μm左右,保持片内不均匀性在4%以内;利用ICP对基于SiC衬底的GaN功率MMIC进行了背面通孔工艺的优化,减少了孔底的柱状生成物。随后的可靠性测试测得圆片通孔的平均电阻值为6.3 mΩ,平均电感值为17.2 nH;对通孔样品在0.4 A工作电流175°C节温下进行了工作寿命试验,200 h后通孔特性无明显退化。     

ICP刻蚀GaN侧壁倾角以及刻蚀速率的控制

深入研究了Cl2基气体电感耦合等离子体(ICP)刻蚀系统对于GaN材料侧壁倾角的控制以及刻蚀速率的影响。通过调整ICP离子源功率、射频功率、气体流量、腔室压力等参数,经实验验证,实现了从23°～83°侧壁倾角的大范围工艺控制,为GaN基器件工艺提供了有益指导。     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

High-temperature characteristics of AixGa1-xN/GaN Schottky diodes

High-temperature characteristics of the metal/AlxGa1_xN/GaN M/S/S (M/S/S) diodes have been studied with current-voltage (I-V) and capacitance-voltage (C-V) measurements at high temperatures. Due to the presence of the piezoelectric polarization field and a quantum well at the AIxGa1_xN/GaN interface, the AIxGa1_xN/GaNdiodes show properties distinctly different from those of the AIxGa1_xN diodes. For the AIxGa1_xN/GaN diodes, an increase in temperature accompanies an increase in barrier height and a decrease in ideality factor, while the AIxGa1_xN diodes are opposite. Furthermore, at room temperature, both reverse leakage current and reverse break-down voltage are superior for the AIxGa1_xN/GaN diodes to those for the AIxGa1_xN diodes.     

磁场对反应离子刻蚀速率影响的研究

本文简要报道了P型衬底1.5μm隐埋新月型激光器的制备和特性,激光器在室温下连续工作的典型阈值电流为20mA低的为15mA,发射波长为1.53μm,最高连续工作温度105℃.     

Photoluminescence characteristics of GaN/lnGaN/GaN quantum wells

Photoluminescence (PL) characteristics of GaN/lnGaN/GaN single quantum wells (QWs) and an InGaN/GaN single heterojunction were studied using continuous wave (CW) and pulsed photoluminescence in both edge and surface emitting configurations. Samples were grown on c-plane sapphire substrates by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Room temperature and 77K PL measurements were performed using a CW Ar-ion laser (305 nm) and a frequency tripled (280 nm), pulsed, mode-locked Ti: sapphire laser. CW PL emission spectra from the quantum wells (24, 30, 80Å) were all blue shifted with respect to the reference sample. The difference (i. e., the blue shift) between the measured value of peak emission energy from the QW and the band-edge emission from the reference sample was attributed to quantum size effects, and to strain arising due to a significant lattice mismatch between InGaN and GaN. In addition, stimulated emission was observed from an InGaN/GaN single heterojunction in the edge and surface emitting configu-ration at 77K. The narrowing of emission spectra, the nonlinear dependence of output emission intensity on input power density, and the observation of a strongly polarized output are presented.     

Growth of GaN on porous SiC and GaN substrates

We have studied the growth of GaN on porous SiC and GaN substrates, employing both plasma-assisted molecular-beam epitaxy (PAMBE) and metal-organic chemical-vapor deposition (MOCVD). For growth on porous SiC, transmission electron microscopy (TEM) observations indicate that the epitaxial-GaN growth initiates primarily from surface areas between pores, and the exposed surface pores tend to extend into GaN as open tubes and trap Ga droplets. The dislocation density in the GaN layers is similar to, or slightly less than, that observed in layers grown on nonporous substrates. For the case of GaN growth on porous GaN, the overgrown layer replicates the underlying dislocation structure (although considerable dislocation reduction can occur as this overgrowth proceeds, independent of the presence of the porous layer). The GaN layers grown on a porous SiC substrate were found to be mechanically more relaxed than those grown on nonporous substrates; electron-diffraction patterns indicate that the former are free of misfit strain or are even in tension after cooling to room temperature.     

Temperature Dependent Raman Scattering of Phonon Modes and Defect Modes in GaN and p-Type GaN Films

Raman spectra of undoped GaN and Mg-doped GaN films grown by metal-organic chemical-vapor deposition on sapphire are investigated between 78 and 573K.A peak at 247cm－1 is observed in both Raman spectra of GaN and Mg-doped GaN.It is suggested that the defect-induced scattering is origin of the mode.The electronic Raman scattering mechanism and Mgrelated local vibrational mode are excluded.Furthermore,the differences of E2 and A1(LO) modes in two samples are also discussed.The stress relaxation is observed in Mg-doped GaN.     

GaN技术发展新趋势

氮化镓(GaN)是第三代半导体的典型代表,受到学术界和产业界的广泛关注,正在成为未来超越摩尔定律所依靠的重要技术之一。对于射频(RF)GaN技术,在电信和国防两大主要应用增长行业,尤其是军用领域对先进雷达和通信系统不断增加的需求,推动了RF GaN器件向更高频率、更大功率和更高可靠性发展。文章梳理了在该领域中GaN RF/微波HEMT、毫米波晶体管和单片微波集成电路(MMIC)、GaN器件空间应用可靠性和抗辐射加固等技术发展的脉络。在功率电子方面,对高效、绿色和智能化能源的需求拉动GaN功率电子、电源变换器向快速充电、高效和小型化方向发展。简述了应用于纯电动与混合动力电动汽车(EV/HEV)、工业制造、电信基础设施等场合的GaN功率器件的研发进展和商用情况。在数字计算特别是量子计算前沿,GaN是具有应用前景的技术之一。介绍了GaN计算和低温电子技术研究的几个亮点。总而言之,对GaN技术发展几大领域发展的最新趋势作了概括性描述,勾画出技术发展的粗略线条。     

GaN和p型GaN薄膜中声子模和缺陷模的变温喇曼散射

研究了MOCVD生长的GaN及掺Mg GaN薄膜从78到578K下的喇曼散射谱.在GaN和掺Mg GaN的谱中都观察到一个位于247cm-1的峰,此峰被认为是缺陷诱导的散射峰,而非电子散射和Mg的局域模.同时讨论了两个谱中E2和A1(LO)声子峰的频率和线形.在掺Mg GaN样品中观察到应力松弛现象.     

AlGaN/GaN界面特性研究进展

GaN是一种宽禁带半导体材料,由于具有优越的热稳定性和化学稳定性,使这种材料和与其相关的器件可以工作在高温和恶劣的环境中,并可用于大功率微波器件。本文主要介绍AlGaN/GaN有关界面特性,该特性反映了纵向纳米尺度下的能带特性;从AlGaN/GaNHEMT设计出发,给出了材料性质和结构参数对AlGaN/GaN异质结二维电子气特性影响的研究结果;讨论了AlGaN/GaN界面2DEG载流子的输运性质;分析了材料缺陷对AlGaN/GaN界面2DEG性质的影响;指出了有待研究的问题和方向。     

AlxGa1-xN/GaN肖特基二极管的高温特性

High-temperature characteristics of the metal/AlxGa1-xN/GaN M/S/S （M/S/S） diodes have been studied with current-voltage （I-V） and capacitance-voltage （C-V） measurements at high temperatures. Due to the presence of the piezoelectric polarization field and a quantum well at the AlxGa1-xN/GaN interface, the AlxGal-xN/GaN diodes show properties distinctly different from those of the AlxGa1-xN diodes. For the AlxGa1-xN/GaN diodes, an increase in temperature accompanies an increase in barrier height and a decrease in ideality factor, while the AlxGa1-xN diodes are opposite. Furthermore, at room temperature, both reverse leakage current and reverse breakdown voltage are superior for the AlxGa1-xN/GaN diodes to those for the AlxGa1-xN diodes.     

采用氨化技术制备成簇生长的光滑线状氮化镓

通过在1 000℃时氨化Ga2O3/MgO/Si(111)薄膜15 min,制备出成簇生长的光滑的长直线状GaN。用X射线衍射(XRD)、扫描电子显微镜(SEM)和高分辨率电子显微镜(HRTEM)对样品进行测试分析。结果表明,线状GaN为六方纤锌矿结构单晶相,表面光滑,且成簇生长,直径在200 nm~400 nm左右,其长度可达5μm~20μm。     

n型GaN欧姆接触的研究进展

Ⅲ-Ⅴ族GaN基材料以其在紫外光子探测器、发光二极管、高温及大功率电子器件等方面的应用潜能而被广为研究.其中,低阻欧姆接触是提高GaN基器件光电性能的关键.金属/GaN界面上较大的欧姆接触电阻一直是影响器件性能及可靠性的一个问题.对于各种应用来说, GaN的欧姆接触需要得到改进.通过对相关文献的归纳分析,本文主要介绍了近年来在改进n-GaN工艺,提高欧姆接触性能等方面的研究进展.     

激光等离子体的辐射与自吸收现象研究

脉冲强激光辐照固体靶材时,会讯速地在靶材表面形成一个高高压的等离子体区哉。该等离子体区域在吸收入射激光的同时,会发出很强的紫外以至ｘ光辐射,它们与靶材有着更强的耦合。本文给出了等离子体中辐射传输的微分方程,并通过对等离子体中辐射和自吸收现象进行讨论,给出了在考虑再辐射效应时,等离子体辐射能流与等离子体参数及激光参数的关系。     

立方相GaN的持续光电导

研究了金属有机物化学气相外延 (MOVPE)方法生长的非故意掺杂的立方相 Ga N的持续光电导效应 .在六方相 Ga N中普遍认为持续光电导效应与黄光发射有关 ,而实验则显示在立方 Ga N中 ,持续光电导效应与其中的六方相 Ga N夹杂有关系 ,而与黄光发射没有关系 .文中提出 ,立方相 Ga N与其中的六方相 Ga N夹杂之间的势垒引起的空间载流子分离是导致持续光电导现象的物理原因 .通过建立势垒限制复合模型 ,解释了立方相 Ga N的持续光电导现象的物理过程 ,并对光电导衰减过程的动力学作了分析 .对实验数据拟合的结果证明以上的模型和推导是与实验相符的 .