GaSb衬底上外延InAsxSb1-x材料的LP-MOCVD研究

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备, 在(100)面GaSb单晶衬底上外延生长了InAsSb材料.用X射线双晶衍射、光学显微镜和扫描电镜、电子探针能谱仪等对材料特性进行了表征，分析研究了生长温度、Ⅴ/Ⅲ比、过渡层等对外延层的影响.并且获得了与GaSb衬底晶格失配度较低的表面光亮的晶体质量较好的InAsSb外延层.     

低压MOCVD生长参量对Ⅱ型InAs/GaSb超晶格材料表面形貌的影响

采用自制低压金属有机源化学气相沉积设备,在（100）面GaSb单晶衬底上生长了Ⅱ型InAs/GaSb超晶格材料.利用双晶X射线衍射、光学显微镜、原子力显微镜和光致发光谱等分析手段对材料特性进行了表征,获得了表面光亮的晶体质量较好的Ⅱ型InAs/GaSb超晶格材料,在77 K下得到光致发光谱峰值波长为3.25 μm.研究了生长温度、过渡层、界面层对其表面形貌的影响,得出生长温度在500 ℃~520 ℃,无过渡层,使用InAsSb界面层有利于改善材料的表面形貌.     

Sb-mediated growth of high-density InAs quantum dots and GaAsSb embedding growth by MBE

Self-assembled InAs quantum dots (QDs) with high-density were grown on GaAs(0 0 1) substrates by antimony (Sb)-mediated molecular beam epitaxy technique using GaAsSb/GaAs buffer layer and InAsSb wetting layer (WL). In this Sb-mediated growth, many two-dimensional (2D) small islands were formed on those WL surfaces. These 2D islands provide high step density and suppress surface migration. As the results, high-density InAs QDs were achieved, and photoluminescence (PL) intensity increased. Furthermore, by introducing GaAsSb capping layer (CL), higher PL intensity at room temperature was obtained as compared with that InGaAs CL.     

Structure and properties of GZO thin films grown on ZnO buffer layers

Thin gallium-doped zinc oxide (in GZO the Ga₂O₃ contents are approximately 3 wt%) films having different ZnO buffer layers were deposited using radio frequency (rf) magnetron sputtering. The use of a grey-based Taguchi method to determine the processing parameters of ZnO buffer layer deposition has been studied by considering multiple performance characteristics. A Taguchi method with an L₉ orthogonal array, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) is employed to investigate the performance characteristics in the deposition operations. The effect and optimization of ZnO buffer deposition parameters (rf power, sputtering pressure, thickness, and annealing) on the structure, morphology, electrical resistivity, and optical transmittance of the GZO films are studied. Annealing treatment and reduction in thickness resulted in a decrease in root-mean-square (RMS) surface roughness of the ZnO buffer layer. Using the optimal ZnO buffer layer obtained by the application of the grey-based Taguchi method, the electrical resistivity of GZO films was decreased from 2.94×10⁻³ to 9.44×10⁻⁴ Ω cm and the optical transmittance in the visible region was slightly increased from 84.81% to 85.82%.     

Enhancement of L10 ordered FePt by Pt buffer layer

L₁₀-ordered FePt thin films prepared by molecular-beam epitaxy on MgO (0 0 1) substrate at 320 °C with different thickness of Pt buffer layer have been investigated. The out-of-plane coercivity increases with increasing thickness of Pt buffer. The maximum values of the long-range order parameter and uniaxial magnetic anisotropy energy are 0.72 and 1.78×10⁷ erg/cm³, respectively, for films with 12 nm thick Pt buffer layer, where the c/a ratio (0.976) shows the minimum value. The reason for the enhancement in ordering is due to the proper lattice strains Pt buffer bestows on FePt layer, these strains are equal to the contraction in lattice parameter c and the expansion in a. Studies of angular-dependent coercivity revealed that the magnetization reversal behaviour shifts from a domain-wall motion dominated case towards a near rotational mode with increasing thickness of Pt buffer layer.     

GaSb layers with low defect density deposited on (001) GaAs substrate in two-dimensional growth mode using molecular beam epitaxy

We report on the growth of fully relaxed and smooth GaSb layers with reduced density of threading dislocations, deposited on GaAs substrate. We prove that three parameters have to be controlled in order to obtain applicable GaSb buffers with atomically smooth surface: interfacial misfit (IMF), the etch pit density (EPD) and the growth mode.The GaSb/GaAs interfacial misfit array and reduced EPD ≤1.0 × 10⁷ cm^?2 were easily obtained using As-flux reduction for 3 min and Sb-soaking surface for 10 s before the GaSb growth initiation. The successive growth of GaSb layer proceeded under the technological conditions described by the wide range of the following parameters: r_G ∈ (1.5 ÷ 1.9) Å/s, T_G ∈ (400 ÷ 520)°C, V/III ∈ (2.3 ÷ 3.5). Unfortunately, a spiral or 3D growth modes were observed for this material resulting in the surface roughness of 1.1 ÷ 3.0 nm. Two-dimensional growth mode (layer by layer) can only be achieved under the strictly defined conditions. In our case, the best quality 1-μm-thick GaSb buffer layer with atomically smooth surface was obtained for the following set of parameters: r_G = 1.5 Å/s, T_G = 530 °C, V/III = 2.9. The layer was characterized by the strain relaxation over 99.6%, 90° dislocations array with the average distance of 5.56 nm, EPD ～8.0 × 10⁶ cm^?2 and 2D undulated terraces on the surface with roughness of about 1 ML. No mounds were observed. We belive that only thin and smooth GaSb layer with reduced EPD may be applied as the buffer layer in complex device heterostructures. Otherwise, it may cause the device parameters deterioration.     

GaP layers grown on GaN with and without buffer layers

The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition (MOCVD) has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature (HT) GaP growth. These sites can promote the two-dimensional (2D) growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680°C is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum (FWHM) of the (111) plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the (111) plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional (3D) growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3 , while it turned to be polycrystalline when the substrate is pretreated by TEGa.     

Organic Photovoltaic Cells with Improved Performance Using Bathophenanthroline as a Buffer Layer

采用Bphen作为缓冲层,研究Bphen处在电子受体材料C₆₀和阴极Ag之间对有机薄膜光伏电池(OPV)性能的影响．通过引入2.5nm厚的Bphen,在100 mW/cm²光照下,CuPc/C₆₀结构的器件效率从0.87%提高到2.25%． 对光生电流-电压的分析表明,Bphen缓冲层可以有效的提高电子从C₆₀层向Ag阴极的传输能力和平衡器件中载流子的传输能力．系统研究了Bphen厚度对OPV器件性能的影响,发现随着Bphen厚度的增加,电导率的降低是限制器件性能的主要原因．此外,采用紫外-可见光分光光度计测试了器件的吸收光谱,发现Bphen缓冲层可以增强CuPc/C₆₀的光吸收能力．     

硅衬底GaN基LED N极性n型欧姆接触研究

在Si衬底GaN基垂直结构LED的N极性n型面上,利用电子束蒸发的方法制作了Ti/Al电极,通过了I-V曲线研究了有无AlN缓冲层对这种芯片欧姆接触的影响.结果显示,去除AlN缓冲层后的N极性n型面与Ti/Al电极在500到600 ℃范围内退火才能形成欧姆接触.而保留AlN缓冲层的N极性n型面与Ti/Al电极未退火时就表现为较好的欧姆接触,比接触电阻率为2×10^-5 Ω·cm²,即使退火温度升高至600 ℃,也始终保持着欧姆接触特性.因此,AlN缓冲层的存在是Si衬底GaN基垂直结构LED获得高热稳定性n型欧姆接触的关键. 关键词： 硅衬底 N极性 AlN缓冲层 欧姆接触     

ZnSe-ZnS超晶格的通光蚀孔及列阵研究

用MOCVD方法在GaAs衬底上生长ZnSe-ZnS超晶格.用化学腐蚀方法在GaAs衬底上开一个通光窗口,使该窗口上仅剩有1～1.8μm厚的生长层.室温下测量了蚀孔后由于化学腐蚀造成生长层表面差异的ZnSe-ZnS超晶格的吸收光谱.研究了带有生长过渡层和无过渡层的超晶格质量对其吸收光谱性能的影响.发现过渡层的存在保护了超晶格激子吸收性能.在此基础上首次采用新工艺在3×3mm2面积上把GaAs衬底金部腐蚀掉,剩下均匀、光滑的ZnSe-ZnS超晶格层,在其上做出了300×300μm2的列阵,为在ZnSe-ZnS超晶格上实现光学双稳的集成化提供了必要条件.     

GaSb/AlSb/GaAs应变层结构的分子束外延生长

本文以反射式高能电子衍射(RHEED)和其强度振荡为监测手段,在半绝缘GaAs衬底上成功地生长GaSb/AlSb/GaAs应变层结构,RHEED图样表明,GaSb正常生长时为Sb稳定的C(2×6)结构,AlSb为稳定的(1×3)结构,作者观察并记录GaSb,AlSb生长时的RHEED强度振荡,并利用它成功地生长10个周期的GaSb/AlSb超晶格,透射电子显微镜照片显示界面平整、清晰,采用较厚的AlSb过渡层及适当的生长条件,可在半绝缘GaAs衬底上生长出质量好的GaSb外延层,其X射线双晶衍射半峰宽小于 关键词：     

Thermal stability of SiGe films on an ultra thin Ge buffer layer on Si grown at low temperature

The thermal stability of SiGe films on an ultra thin Ge buffer layer on Si fabricated at low temperature has been studied. The microstructure and morphology of the samples were investigated by high-resolution X-ray diffraction, Raman spectra and atomic force microscopy, and using a diluted Secco etchant to reveal dislocation content. After thermal annealing processing, it is observed that undulated surface, threading dislocations (TDs) and stacking faults (SFs) appeared at the strained SiGe layer, which developed from the propagation of a misfit dislocation (MD) during thermal annealing, and no SFs but only TDs formed in strain-relaxed sample. And it is found that the SiGe films on the Ge layer grown at 300 °C has crosshatch-free surface and is more stable than others, with a root mean square surface roughness of less than 2 nm and the threading dislocation densities as low as ∼10⁵ cm⁻². The results show that the thermal stability of the SiGe films is associated with the Ge buffer layer, the relaxation extent and morphology of the SiGe layer.     

A high mobility C60 field-effect transistor with an ultrathin pentacene passivation layer and bathophenanthroline/metal bilayer electrodes

C₆₀ field-effect transistor (OFET) with a mobility as high as 5.17 cm²/V·s is fabricated. In our experiment, an ultrathin pentacene passivation layer on poly-(methyl methacrylate) (PMMA) insulator and a bathophenanthroline (Bphen)/Ag bilayer electrode are prepared. The OFET shows a significant enhancement of electron mobility compared with the corresponding device with a single PMMA insultor and an Ag electrode. By analysing the C₆₀ film with atomic force microscopy and X-ray diffraction techniques, it is shown that the pentacene passivation layer can contribute to C₆₀ film growth with the large grain size and significantly improve crystallinity. Moreover, the Bphen buffer layer can reduce the electron contact barrier from Ag electrodes to C₆₀ film efficiently.     

Effect of MgO buffer layer thickness on the electrical properties of MgZnO thin film transistors fabricated by plasma assisted molecular beam epitaxy

We report the fabrication and electrical characteristics of thin film transistors based on MgZnO thin films with different thicknesses of MgO buffer layer. The MgZnO thin films with MgO buffer layers were grown on SiO₂/p-Si substrates by plasma assisted molecular beam epitaxy. The effects of the buffer layer thickness on the structural properties of MgZnO films are investigated by X-ray diffraction, and the results show that the crystal quality of the MgZnO film is enhanced with 4 nm MgO buffer layer. The MgZnO TFT with 4 nm MgO buffer layer exhibits an n-type enhancement mode characteristics with a field effect mobility of 1.85 cm²/V s, a threshold voltage of 27.6 V and an on/off ratio of above 10⁶.     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr_0.52Ti_0.48)O₃溶胶，用Sol-gel法在Pt/Ti/SiO₂/Si基片上沉积一层厚度不同的Pb(Zr_0.52Ti_0.48)O₃ (PZT52)过渡层，经400℃烘烤、550℃退火等程序后，再用Sol-gel法在PZT52过渡层上沉积Pb(Zr_0.52Ti_0.48)O _{关键词： PZT铁电薄膜 择优取向 过渡层 剩余极化强度}     

Infrared diode laser spectroscopy

Three types of lasers (double-heterostructure 66 K InAsSb/InAsSbP laser diode, room temperature, multi quantum wells with distributed feedback (MQW with DFB) (GaInAsSb/AlGaAsSb based) diode laser and vertical cavity surface emitting lasers (VCSELs) (GaSb based) have been characterized using Fourier transform emission spectroscopy and compared. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) for the strongest absorption line of the v₃ + v₅ band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm⁻¹ spectral range in case of InAsSb/InAsSbP laser (fundamental bands of v₁, v₅). Laser sensitive detection (laser absorption together with high resolution Fourier transform infrared technique including direct laser linewidth measurement, infrared photoacoustic detection of neutral molecules (methane, form-aldehyde) is discussed.     

The influence of argon ion bombardment on the electrical and optical properties of clean silicon surfaces

The effect of low energy noble gas ion bombardment on the electrical and optical properties of Si(211) surfaces has been investigated by surface conductivity and field effect measurements, ellipsometry and AES. With this combination of techniques, information is obtained concerning the electrical properties, the chemical composition and the damage of the surface layer. Upon ion bombardment in the energy range of 500–2000 eV, ellipsometry shows the formation of a damaged surface layer with optical properties close to those of an evaporated amorphous silicon film. In order to measure the conductivity changes as sensitive as possible, nearly intrinsic silicon crystals were used. For the clean, 5200 Ω cm Si(211) surface, bombarded only with a mass-analyzed argon ion beam, a small increase in conductivity is found to occur after a small ion dose (saturation after 5 × 10¹⁴ ions cm^?2 while after 5 × 10¹³ ions cm^?2 already half of the increase has occurred). The effect was found to be independent of ion energy between 500 and 2000 eV. As the field effect signal did not change after this treatment, it is concluded that the surface state density in the neighbourhood of the Fermi level shows a slight decrease.     

缓冲夹层影响异质结有机光伏器件性能研究

制备了结构为CuPc/缓冲层/C₆₀异质结的有机光伏器件,分别选用三氧化钼和红荧烯为缓冲层,研究了增加缓冲层对器件性能的影响.结果表明,增加三氧化钼和红荧烯缓冲层后器件的开路电压和光电转换效率都得到提高,器件的短路电流密度和填充因子都有所降低.开路电压从没有缓冲层时的0.39 V分别提高到0.58 V、0.55 V,转换效率从0.36%提高到0.44%,短路电流从1.92 mA/cm²分别降低到1.77 mA/cm²、1.81 mA/cm²,填充因子从0.48分别减少到0.43、0.44.进一步研究表明器件的短路电流密度受缓冲层厚度的影响很大,当缓冲层厚度很小时,器件短路电流密度还有所增加,但随着缓冲层厚度的增加,短路电流密度逐渐减小,当缓冲层厚度为10 nm时,器件短路电流密度减少到0.35 mA/cm².开路电压随着厚度的增加逐渐增加,从1 nm时的0.43 V增加10 nm时0.63 V.根据整数电荷转移模型和界面能级理论解释有机光伏器件开路电压提高以及短路电流密度减少的原因,为有机太阳能电池性能的改善提供了研究方法.     

锐钛矿型TiO2(101)面原子几何及弛豫结构的第一性原理计算

采用平面波超软赝势方法计算了锐钛矿型TiO₂(101)面的表面能和表面原子弛豫结构.首先对TiO₂(101)面的6种不同的表面原子终止结构的体系总能量进行了计算,结果表明终止原子为两配位的O原子、次层为五配位的Ti原子的表面结构最为稳定.针对该表面研究了表面能和原子弛豫与模型中原子层数和真空厚度的关系,当原子层数为12层,真空厚度为0.4nm时,表面能收敛度小于0.01J/m².研究发现:表面上两配位的O原子向里移动约0.0012nm,五配 关键词： 第一性原理 2')" href="#">TiO₂ 表面结构 弛豫     

Performance limits of the mid-wave InAsSb/AlAsSb nBn HOT infrared detector

InAsSb ternary alloy is considered to be an alternative to HgCdTe (MCT) in mid-wavelength infrared spectral region. The high operation temperature conditions are successfully reached with $\hbox {A}^{\mathrm{III}}\hbox {B}^{\mathrm{V}}$ bariodes, where InAsSb/AlAsSb system is playing dominant role. Since there is no depletion region in the active layer, the generation-recombination and trap-assisted tunneling mechanisms are suppressed leading to lower dark currents in comparison with standard photodiodes. As a consequence, the bariodes operate at a higher temperature than standard photodiodes which could be used in wide range of system applications, especially where the size, weight, and power consumption are crucial. The paper presents detailed analysis of the bariode’s performance (such as dark and photocurrent, differential resistance area product, and detectivity) versus applied voltage, operating temperatures and structural parameters. The optimal working conditions are calculated. The theoretical predictions of bariode’s performance are compared with experimental data published in the literature. Finally, the nBn InAsSb/AlAsSb performance is compared to the MCT “Rule 07”.