InAlN在不同模板上的MOCVD外延

在相同的生长条件下,分别在高质量的GaN 和 AlN 模板上生长InAlN外延层。 测试结果显示：本实验的两个样品的In组分均为～16%,但在AlN模板上生长的InAlN外延层的晶体质量和表面形貌都要优于在GaN模板上生长的样品。其中,在GaN模板上生长的InAlN样品的（002）和（102）峰摇摆曲线的半峰宽分别为309.3″和339.1″,样品表面的粗糙度为0.593 nm,v坑密度约为4.2108cm-2;而在AlN模板上生长的InAlN样品的（002）和（102）峰摇摆曲线的半峰宽分别为282.3″和313.5″,样品表面的粗糙度为0.39 nm,v坑密度约为2.8108cm-2 。综合以上结果可初步得知,在AlN模板上生长的InAlN外延层的晶体质量和表面形貌都要优于在GaN模板上生长的InAlN外延层,因此,相对于GaN模板来说,AlN模板更适宜高质量的InAlN 外延层的生长。     

GaN缓冲层上低温生长AIN单晶薄膜

采用电子回旋共振等离子体增强金属有机物化学气相沉积（ECR－PEMOCVD）技术，在α－Al2O3（0001）（蓝宝石）衬底上，分别以高纯氮气（N2）和三甲基铝（TMAl）为氮源和铝源低温生长氮化铝（AlN）薄膜。利用反射高能电子衍射（RHEED）、原子力显微镜（AFM）和X射线衍射（XRD）等测量样品，研究了AlN缓冲层和氮化镓（GaN）对六方AlN外延层质量的影响，实验表明在GaN缓冲层上能够低温生长出C轴取向的AlN单晶薄膜。     

AIN、GaN立方晶体的静态性质和AIN/GaN异质结的价带偏移

采用LMTO能带从头计算方法,计算了闪锌矿（立方）结构AIN和GaN的静态性质;用平均键能方法,预言了AlN与GaN自由应变生长、以AlN为衬底和以GaN为衬底等三种不同应变状态下AlN／GaN应变层异质结的△Ev值;最后,采用超原胞（AIN）n（GaN）n（001）,（n=1,3,5）界面自洽计算方法,考察了超晶格中平均键能Em的“对齐”程度和验证了价带偏移△Ev计算结果的准确性。     

AlN外延薄膜的生长和特征

文章研究了AlN薄膜的晶体质量、表面形貌、应力等性质与AlN生长工艺的依赖关系。通过对低温成核厚度、成核温度和高温生长AlN所用Ⅴ／Ⅲ比的研究，制备出了具有较好晶体质量的AlN薄膜。高分辨三晶X射线衍射给出AlN薄膜的（002）和（105）的半高宽分别为16．9arcsec和615arcsec，接近国际上报道的较好结果。原子力显微镜对表面形貌的分析表明AlN薄膜的粗糙度为5．7nm。拉曼光谱表明E2（high）模向高能方向移动，说明蓝宝石上外延的AlN薄膜处于压应变状态。光学吸收谱在204nm处具有陡峭的带边吸收，也表明了AlN外乏正薄膜具有辅好妯晶体盾量。     

射频磁控溅射生长C轴择优取向AIN压电薄膜

采用射频磁控反应溅射工艺，在Si（400）衬底上制备了高c轴取向的AlN薄膜。用X射线衍射仪（XRD）分析了薄膜特征。研究了不同的Ar／N2比、衬底偏压、工作压强对AlN薄膜c轴择优取向的影响。研究了AlN薄膜在以氮终止的硅衬底和纯净硅衬底两种表面状态的生长机制，发现在以氮终止的硅衬底表面生长的AlN薄膜非常容易得到c轴择优取向的AlN薄膜。     

通过双中温AlN插入层提高半极性(1122)面AlN薄膜的表面形貌和晶体质量

利用金属有机化学气相沉积方法在蓝宝石衬底上生长了一系列具有双中温AlN插入层(MTG-AlN)的半极性AlN薄膜样品。中温生长的AlN插入层具有较大的表面粗糙度,形成了类似纳米级图形化衬底结构,能够有效阻断高温生长的半极性AlN样品中堆垛层错的传播,从而提高半极性AlN样品的表面形貌和晶体质量。通过原子力显微镜和X射线衍射仪的表征,研究了MTG-AlN插入层厚度在20～100 nm之间的变化对半极性AlN样品的表面形貌和晶体质量的影响。结果表明,所有半极性AlN样品都具有■取向。当插入的MTG-AlN中间层厚度约为80 nm时,半极性AlN样品表面粗糙度显著降低,晶体质量明显改善。     

6H-SiC衬底上采用不同厚度AlN缓冲层对GaN外延层的影响

采用不同厚度AlN作为缓冲层在6H-SiC衬底上生长了GaN外延层,并利用X射线衍射,拉曼散射和透射电子显微镜等对GaN性质进行了研究。AlN缓冲层的应变状态对GaN的晶体质量和表面形貌有很大影响。较厚的AlN缓冲层会导致GaN表面出现裂纹,而太薄的AlN缓冲层会导致GaN层较高的位错密度,从而恶化器件性能。分析了GaN产生裂纹和高位错密度的机制,并采用较优厚度（100nm）的AlN缓冲层生长出高质量的GaN外延层。     

直接氮化法制备单晶AlN纳米线

采用直流电弧放电装置,通过金属铝和氮气直接反应,在钼阴极上沉积出大量的AlN纳米线。利用XRD、SEM、TEM和拉曼(Raman)光谱对所制样品的结构、形貌和光学特性进行了表征。结果表明:大部分AlN纳米线沿着[001]方向生长,平均直径为45nm,长度5μm左右;Raman光谱的峰值与单晶体材料AlN的结果一致,说明AlN纳米线结晶质量较好。     

AlN阻挡层对AlGaN/GaNHEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

AlN阻挡层对AlGaN/GaN HEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

声速对硅基氮化铝复合声子晶体带隙影响

该文基于布喇格散射机理,采用有限元仿真技术重点研究材料声速对二维AlN/B/Si复合声子结构体带隙特性的影响。首先以Mo作为B层,逐次分析AlN、AlN/Mo、AlN/Mo/Si出现最大带隙宽度时,AlN、Mo、Si各层厚度的最优值;然后分别选取具有声速梯度的材料作为B层,研究B材料声速对复合声子晶体带隙宽度变化率的影响。结果表明,当B层与Si、AlN的声速差值小于3 000 m/s时,B层厚度的变化引起复合声子晶体带隙宽度变化率低于25%,而B层与Si、AlN的声速差值越大,改变B层厚度会造成带隙宽度变化率越大,最高可达100%。     

AlN薄膜制备技术研究

采用磁控溅射法制备了AlN薄膜并研究了射频(RF)等离子清洗对AlN薄膜结晶取向度的影响,实验表明,RF等离子清洗基片3min后AlN薄膜c轴取向摇摆曲线半峰宽达到1.3°;通过Mo薄膜衬底对AlN薄膜结晶取向度的影响发现,取向度好的Mo薄膜衬底有利于c轴取向AlN薄膜的生长;Ar气体流量对AlN薄膜应力的影响使AlN薄膜应力从-390(压应力)~73 MPa(张应力)可调。     

Growth of AlN Films as a Function of Temperature on Mo Films Deposited by Different Techniques

The authors investigated the combined influences of substrate temperature and methods for preparing underlying Mo electrodes on the crystallinity, morphology, and electrical properties of AlN films using x-ray diffraction, scanning electron microscopy, and a network analyzer, respectively. The substrate temperature of the AlN films was varied from 20°C to 600°C. The underlying Mo electrodes were deposited by direct-current (DC) and radiofrequency (RF) sputtering techniques. A change in the AlN crystallites varied with the substrate temperature and differed for DC- and RF-sputtered Mo bottom electrodes. With increasing substrate temperature, the preferred orientation of AlN films on DC-sputtered Mo bottom electrodes varied from the $ \left( {10\overline{1} 0} \right) $ orientation to the (0002) orientation. The $ \left( {10\overline{1} 0} \right) $ orientation did not appear in the AlN films on RF-sputtered Mo bottom electrodes at low substrate temperature (20°C). The optimum substrate temperature for depositing (0002)-oriented AlN on Mo films was 400°C. At this substrate temperature, AlN films deposited on RF-sputtered Mo bottom electrodes exhibited better crystalline quality and greater frequency response with only one resonance peak compared with DC-sputtered Mo bottom electrodes. The cause of these phenomena is also discussed.     

Electrical characterization of AlN MIS and MIM structures

Aluminum nitride (AlN) thin films have been deposited on p-Si[100] and Mo-Si[100] substrates. The sputter deposited Mo was polycrystalline, predominantly showing a [110] orientation. Thin AlN films were grown under different process conditions in a physical vapor deposition (PVD) system to attain highly textured polycrystalline films as well as close to amorphous films. MIS and MIM structures were fabricated and electrical properties such as the dielectric constant, leakage current, and high-frequency behavior were investigated. It is found that the dielectric constant is 10 and does not change with the crystallinity of the films. High-frequency measurements up to 10 GHz show no frequency dispersion of the capacitance. The leakage current stays relatively constant between films and is believed to be Poole-Frenkel controlled. Capacitance-voltage (C-V) measurements for MIS structures revealed the presence of charges in the interface layer between the substrate and the dielectric film. The temperature dependence of the capacitance has also been studied.     

The fabrication and dry etching of poly-Si/TaN/Mo gate stack in the metal inserted poly-Si stack structure

The Mo-based metal inserted poly-Si stack (MIPS) structure is an appropriate choice for metal gate and high-k integration in sub-45 nm gate-first CMOS device. A novel metal nitride layer of TaN or AlN with high thermal stability has been introduced between Mo and poly-Si as a barrier material to avoid any reaction of Mo during poly-Si deposition. After Mo-based MIPS structure is successfully prepared, dry etching of poly-Si/TaN/Mo gate stack is studied in detail. The three-step plasma etching using the Cl₂/HBr chemistry without soft landing step has been developed to attain a vertical poly-Si profile and a reliable etch-stop on the TaN/Mo metal gate. For the etching of TaN/Mo gate stack, two methods using BCl₃/Cl₂/O₂/Ar plasma are presented to get both vertical profile and smooth etched surface, and they are critical to get high selectivity to high-k dielectric and Si substrate. In addition, adding a little SF₆ to the BCl₃/O₂/Ar plasma under the optimized conditions is also found to be effective to smoothly etch the TaN/Mo gate stack with vertical profile.     

薄膜声体波谐振器(FBAR)的研究进展

综述了国内外FBAR技术的研究现状和进展。分析了基于空气腔和布拉格反射层两种主流FBAR的结构、工作原理和建模方法。阐述了适用于FBAR的压电薄膜材料、电极材料以及布拉格反射层材料的选择。并介绍了作为FBAR主要应用的射频滤波器和双工器的拓扑结构和设计方法,以及制备FBAR器件时需克服的关键技术等问题。     

InAlN/AlN/GaN HEMT电学特性仿真与分析

研究了一种新型GaN基HEMT结构,即InAlN/AlN/GaN异质结层结构,并对其直流特性以及频率特性进行了仿真。通过理论分析,结合TCAD软件,与常规AlGaN/AlN/GaNHEMT进行对比。对栅长为1μm的器件进行仿真,结果表明,器件的最大跨导为450mS/mm,最大电流密度为2A/mm,电流增益截止频率fT=15GHz,最高振荡频率fmax=35GHz。     

Epitaxial growth of zinc-blende AIN on Si(100) substrates by plasma source molecular beam epitaxy

Epitaxial zinc-blende AlN films were deposited on Si(100) substrates by plasma source molecular beam epitaxy (PSMBE). The lattice parameter of the zinc-blende AlN was determined to be 4.373Å. The epitaxial relationship between film and substrate was (100)AlN‖(100)Si and [011]AlN‖[011]Si. The zinc-blende AlN films were formed using a hollow cathode source with a pulse d.c. power supply in the PSMBE system. The high energy and large density of the Al⁺ and N⁺ species emerging from the hollow cathode and the presence of a substrate surface with cubic symmetry are probably the main factors for the formation of the metastable zinc-blende phase of AlN.