基于磁光晶体的光纤电流传感器磁串扰效应研究

对光学电流传感器测量电流时存在的相邻导线磁串扰问题进行了研究,提出了一种利用传感头的摆放位置和角度来消除磁串扰对电流测量影响的方法.通过理论分析给出了磁串扰的大小与两导线间距以及传感头与主导线的距离和夹角之间的定量关系,从而确定测量条件下的传感头的最佳摆放方案,并以此为依据进行了相应的实验测量和分析,结果表明当传感头处于最佳摆放位置时较好的消除了相邻导线磁串扰的影响,提高了光学电流传感器的测量精度.     

GaAs-GaN键合界面热应力的电子背散射衍射研究

采用扫描电镜(SEM)和电子背散射衍射(EBSD)技术,观察和分析了GaAs和GaN晶片热压键合的界面热应力和晶片键合质量.利用EBSD测量了GaAs-GaN键合界面的菊池花样质量、晶格转动、晶格错配和位错密度等应力敏感参数.结果表明,晶片键合质量良好,键合界面中心区域的热应力小于边缘区域的热应力.GaN层和GaAs层中的应力影响范围,在中心区域分别约为100 nm和300 nm,在边缘区域分别约为100 nm和500nm.EBSD显示的应力分布图与模拟应力场相似.模拟和计算表明,最大剥离应力和剪切应力分布在键合界面的边缘.剥离应力是导致晶片解键合的主要原因.     

分层沉积GaAs/SiO2纳米薄膜的结构和吸收光谱

应用射频磁控溅射方法分别在抛光硅片和石英玻璃片上分层沉积了GaAs/SiO2纳米薄膜.通过X射线衍射(XRD)、原子力显微镜(AFM)、扫描电子显微镜(SEM)及吸收光谱的测试,发现衬底温度、退火、氢掺杂等制备工艺对分层沉积的GaAs/SiO2纳米薄膜的微观结构和光学性质有明显的影响.本文对相关机理作了探讨.     

金刚石微铣刀头图形化法的制备研究

微细铣削加工技术是具有较高相对精度的精密三维微小零件的制造技术,微零件尺寸和精度在很大程度上依赖于微切削刀具的切削性能.CVD金刚石膜作为一种具有众多卓越特性的功能材料,是制造新型超硬微铣刀的优越刀具材料.本文开展了硅微模具图形化法沉积金刚石膜微铣刀头的实验研究,成功制作了特征尺寸为25 μm、50 μm和100 μm双层金刚石微铣刀头.SEM,ADE等分析结果表明采用的工艺能够获得表面质量好、形状和尺寸精度很高的金刚石微铣刀头,该工艺能够实现批量制造,是制作金刚石微铣刀的理想方法.     

电化学共沉积法制备GaAs纳米结构薄膜及表征

以含一定比例Ga与As2O3的酸性溶液(pH=2.5)作为前驱溶液,以Pt片为对电极,饱和甘汞电极(SCE)为参比电极,室温下利用三电极电化学站在Ti衬底上恒压沉积GaAs薄膜.然后对GaAs薄膜进行退火处理.利用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM),以及荧光光度计(PL)分别对不同沉积电压下所制备的薄膜的晶体结构,薄膜形貌以及光学性能进行分析表征.结果表明:沉积电压以及退火过程对GaAs薄膜的形貌、晶体结构、薄膜质量有很大影响,所制备的GaAs薄膜退火前晶化程度较低,部分粒子表现出不均匀团聚.光致发光峰为红光发射,且单色性好.退火后的GaAs薄膜为面心立方晶型,呈纳米颗粒状,薄膜的光电性能明显提高.     

GaAs晶体坩埚下降法生长及掺杂效应

作为第二代半导体材料,GaAs晶体自60年前被发现以来已广泛应用于激光、通讯和显示等领域,并发展出液封提拉法、水平布里奇曼法、垂直梯度凝固法等多种生长工艺.本文总结了GaAs晶体的最新研究进展,探讨了各种生长方法的特点及其应用,重点报道了GaAs晶体坩埚下降法生长的研究成果.坩埚下降法具有一炉多产、易操作、低成本等优点,已成为GaAs晶体产业化的重要途径.掺杂不仅能调节GaAs晶体的性能,还会对晶体生长产生重要影响.本文还给出了Bi、Si、Zn等掺杂GaAs晶体生长结果,探讨了它们的性能、缺陷以及在不同领域里的应用.     

Tb掺杂的非晶碳膜/GaAs/Ag异质结的光敏特性研究

采用脉冲激光沉积方法在低阻GaAs上制备了Tb掺杂的非晶碳膜(a-C∶ Tb)/GaAs p-n结.利用Ag与GaAs 之间的肖特基接触特性,构成了a-C∶Tb/GaAs p-n结与Ag/GaAs肖特基结的反向串联结构.该异质结具有红光敏感特性,室温在光强为45 mW/cm2光照下的光灵敏度达到近1000.Tb掺杂大大提高了光灵敏度.     

TiO2/ZnO复合微球的制备及其光催化性能研究

以碳微球为模板,采用溶胶凝胶法、水热法等方法分别制备了TiO2微球、ZnO微球和TiO2/ZnO复合微球,采用扫描电子显微镜、X-射线衍射仪等对样品进行了表征,结果表明:制备的TiO2微球、ZnO微球和TiO2/ZnO复合微球,各微球直径在5 ～ 10 μm之间.在紫外光和可见光下研究了制备的光催化剂对亚甲基蓝溶液和湖水的光催化性能,光催化实验表明:三种微球中TiO2/ZnO复合微球具有良好的光催化性能.     

微／纳米锌粉两步氧化法制备ZnO的机理研究

采用在乙醇溶剂中以H2O2预氧化微/纳米锌粉,再在较高温度下热氧化的方法制备了高质量的ZnO粉末.通过X射线衍射、场发射电子显微镜、热重-差示扫描量热等方法对制备产物进行了相关表征.根据PBR金属氧化理论和相关分析结果研究了微/纳米锌粉不同的氧化生长机制,并建立了微/纳米锌粉的晶体生长模型.     

半导体GaAs—Ga0.65Al0.35As多量子阱的光谱性质及实现激光制冷的可能

我们利用光致发光(PL)和激发光谱(PLE)技术研究了GaAs量子阱的光谱性质,在GaAs量子阱的光致发光中观察到上转换发光,首次提出GaAs量子阱结构可能实现激光制冷,探索了GaAs量子阱结构的发光机理。     

Growth and characterization of GaAs layers on polished Ge/Si by selective aspect ratio trapping

Epitaxial GaAs layers have been deposited on polished Ge film grown on exactly (0 0 1) oriented Si substrate by metal-organic chemical vapor deposition (MOCVD) via aspect ratio trapping (ART) method. Double-crystal X-ray diffraction shows that the full-width at half-maximum (FWHM) of the (4 0 0) reflection obtained from 1 μm GaAs is 140 arcsec. Scanning electron microscopy (SEM) of the GaAs layer surface shows that the amount of antiphase domain defects (APD) raised from GaAs/Ge interface using Ge ART on Si is dramatically reduced compared to GaAs layers grown on exact (0 0 1) Ge substrate. Defect reduction and Ge diffusion at vicinal GaAs/Ge interface were investigated via cross-section transmission electron microscopy (X-TEM) and secondary ion mass spectrometry (SIMS). Film morphology and optical properties were evaluated via SEM and room temperature photoluminescence (PL).     

MOVPE growth of GaAs on Ge substrates by inserting a thin low temperature buffer layer

High quality GaAs layers have been grown by low pressure MOVPE on Ge(001) and Ge(001) 9° off oriented in [110] direction by using a thin low temperature (LT) GaAs layer. Investigations of the initial growth step were performed at different V/III ratios and temperatures. To show the good buffer layer quality solar cell structures were grown on off oriented n‐Ge(001) and n‐GaAs(001) substrates. The surface morphology was studied by atomic force microscopy which showed the step‐flow growth mode on 1.2 µm thick GaAs/Ge structures. The crystalline qualities of this structures and the smooth surface morphology were investigated by double crystal X‐ray diffraction (XRD) and atomic force microscopy (AFM). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relaxation mechanism of GaP/InGaAlP/GaAs heterostructure

Transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM) were carried out to investigate the structural properties of the GaP/In_0.48(Al_0.7Ga_0.3)_0.52P heterostructures grown on GaAs (0 0 1) substrates. The lattice-matched In_0.48(Al_0.7Ga_0.3)_0.52P/GaAs material system could be used as a defect-free substrate because no lattice misfit exists between the In(AlGa)P layer and the GaAs substrate. Both TEM and HREM measurements indicated that there were not only misfit dislocations, but also microtwins at the GaP/In(AlGa)P heterointerface. The mechanism of the microtwins formation is elucidated.     

Precise structure control of GaAs/InGaP hetero-interfaces using metal organic vapor phase epitaxy and its abruptness analyzed by STEM

Fabrication of abrupt InGaP on GaAs (InGaP/GaAs) and GaAs on InGaP (GaAs/InGaP) hetero-interfaces has been difficult using metal organic vapor phase epitaxy (MOVPE) due to the exchange of P and As during the fabrication steps. Indium (In) surface segregation during InGaP growth also degrades the abruptness. Here, the MOVPE gas-switching sequence to fabricate atomically abrupt hetero-interfaces was optimized and the effects of this optimization on the hetero-interface abruptness were quantitatively evaluated using the Z-contrast method with scanning transmission electron microscopy (STEM). Results revealed that (a) in the fabrication of InGaP/GaAs hetero-interface, the GaAs top layer should be stabilized using As-source gas supply, and the excess As layer on GaAs should be terminated using an additional supply of Ga species, and (b) in the fabrication of GaAs/InGaP interface, the InGaP layer should be grown using the flow modulation method to suppress In surface segregation. In conclusion, the abruptness of hetero-interfaces of InGaP/GaAs and GaAs/InGaP was improved by using these optimized gas-switching sequences.     

GaN/GaAs(1 0 0) superlattices grown by metalorganic vapor phase epitaxy using dimethylhydrazine precursor

Superlattices of cubic gallium nitride (GaN) and gallium arsenide (GaAs) were grown on GaAs(1 0 0) substrates using metalorganic vapor phase epitaxy (MOVPE) with dimethylhydrazine (DMHy) as nitrogen source. Structures grown at low temperatures with varying layer thicknesses were characterized using high resolution X-ray diffraction and atomic force microscopy. Several growth modes of GaAs on GaN were observed: step-edge, layer-by-layer 2D, and 3D island growth. A two-temperature growth process was found to yield good crystal quality and atomically flat surfaces. The results suggest that MOVPE-grown thin GaN layers may be applicable to novel GaAs heterostructure devices.     

Surface analysis of different oriented GaAs substrates annealed under bismuth flow

Several orientations of GaAs substrates, including (1 0 0), (4 1 1), (1 1 1) and (5 1 1) have been annealed in a metalorganic vapour phase epitaxy (MOVPE) horizontal reactor at different annealing temperatures and under different trimethyl-bismuth (TMBi) flux. Surface morphology of the annealed GaAs substrates was investigated by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show islands formation on all the studied samples. The density and size of Bi islands vary greatly with annealing temperature and TMBi flow. For different substrate orientations, the activation energies were deduced from Arrhenius plot of island density. Except for (5 1 1) oriented GaAs, all the studied orientations show the same activation energy of 1.8 eV. For low annealing temperature 420 °C, and under different Bi flux, each oriented substrate shows a specific behaviour. For higher temperatures 700 °C and above Bi islands are totally removed and the substrates are smooth. Surface change of (1 0 0) oriented GaAs substrate was in situ monitored by laser reflectometry.     

Growth of embedded ErAs nanorods on (4 1 1)A and (4 1 1)B GaAs by molecular beam epitaxy

The low solubility of Er in GaAs results in the formation of ErAs nanostructures when GaAs is grown with 5–6 at% Er/Ga ratio by molecular beam epitaxy on GaAs surfaces. For growth on the (4 1 1)A GaAs surface, cross-sectional scanning transmission electron microscopy images show the presence of ErAs nanorods embedded in a GaAs matrix extending along the [2 1 1] direction with a spacing of roughly 7 nm and a diameter of roughly 2 nm. Growth on the GaAs (4 1 1)B surface resulted in only nanoparticle formation. Variation of the polarized optical absorption with in-plane polarization angle is consistent with coupling to surface plasmon resonances of the semimetallic nanostructures.     

Influence of initial growth parameters on the structural and optical properties of GaAs on (001) Si

The structural and optical properties of GaAs on (001) Si substrates were investigated by transmission electron microscopy (TEM) and low-temperature photoluminescence (PL). It was found that the success of the two-step growth technique is controlled by the quality (morphology and defect density) of the low-temperature grown AlGaAs nucleation layer. GaAs epilayers grown on low V/III ratio AlGaAs nucleation layers exhibit improved surface morphologies and structural properties. These results were confirmed by optical measurements where it was shown that the best PL response was obtained from GaAs epilayers in which the initial AlGaAs nucleation layers were deposited at a low V/III ratio.     

Effects of surface reconstruction on CdTe/GaAs(001) interface structure

CdTe/GaAs(001) heterostructures were fabricated by molecular beam epitaxy on chemically etched and thermally deoxidized GaAs(001) substrates, as well as GaAs(001) (3×1) buffer layers grown in situ by molecular beam epitaxy. Different growth protocols were also explored, leading to Te-induced (6×1) or (2×1) surface reconstructions during the early growth stage. High-resolution cross-sectional transmission electron microscopy was used to examine the final interface structure resulting from the different substrate preparations, and surface reconstructions. The (2×1) surface reconstruction led to pure (001) growth, while the (6×1) reconstruction led to an interface which included small (111)-oriented inclusions. In addition, deposition on etched and deoxidized GaAs(001) wafers led to preferential CdTe growth within etch pits and resulted in a macroscopically rough interface region.     

Multiatomic step formation on GaAs(001) vicinal surfaces during thermal treatment

We observed the surface morphology of vicinal GaAs(001) after thermal treatment in AsH₃/H₂ atmosphere by atomic force microscopy (AFM). Clear multiatomic steps were formed under the high temperature thermal treatment. Next, we investigated the mechanism of step bunching during thermal treatment by two experiments from the view point of Ga atom evaporation. One is the selective thermal treatment using a partially masked GaAs wafer, and the evaporation amount of Ga atoms was estimated by AFM. The other is the investigation of photoluminescence (PL) peak energy shifts for AlGaAs/GaAs single quantum wells with a thermal treatment process at the top of the GaAs quantum well layer, compared to those without thermal treatment. These results indicate that the evaporation hardly occurs during the thermal treatment process. Therefore, step bunching phenomena on GaAs(001) vicinal surfaces during thermal treatment are probably caused by migration of the atoms detached from upside steps and their re-incorporation to downside steps.