Raman scattering from In1-x-yGaxAlyAs quaternary alloys

Raman scattering studies were reported of In1-x-yGaxAlyAs/InP lattice matched quaternary alloys. The quaternary alloys a.ere grown on (100) oriented InP substrates by MBE method. The composition and intensity dependence of optical phonon mode frequencies show that the quaternary alloys exhibit three-mode behavior, i.e. InAs-like, GaAs-like and AlAs-like modes. Polarization analysis of the Raman spectra shows that the LO phonon modes are Raman active in the depolarized configuration and Raman inactive in the polarized configuration. TO phonon modes were also observed due to disorder effects, resulting in the asymmetrical shapes of the Raman peaks of the optical phonons.

Low Temperature Deposited Nano-structured Vanadium Oxide Thin Films for Uncooled Infrared Detectors

A novel process of room temperature ion beam sputtering deposition of vanadium oxide films and low temperature post annealing for uncooled infrared detectors was proposed in this work. VOx thin films with relatively low square resistance (70 K Omega / square) and large temperature coefficient of resistance (more than 3%/K) at room temperature were fabricated using this low temperature process which was very compatible with the process of uncooled infrared detectors based on micromachined technology. Furthermore, chemical composition and film surface have been characterized using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) respectively. The results showed that the main composition of the processed thin films was V2O5 and the thin films were in the process of crystallization.

Electrical and Optical Phase Transition Properties of Nano Vanadium Dioxide Thin Films

Nano-vanadium dioxide thin films were prepared through thermal annealing vanadium oxide thin films deposited by dual ion beam sputtering. The nano-vanadium dioxide thin films changed its state from semiconductor phase to metal phase through heating by homemade system. Four point probe method and Fourier transform infrared spectrum technology were employed to measure and anaylze the electrical and optical semiconductor-to-metal phase transition properties of nano-vanadium dioxide thin films, respectively. The results show that there is an obvious discrepancy between the semiconductor-to-metal phase transition properties of electrical and optical phase transition. The nano-vanadium dioxide thin films' phase transiton temperature defined by electrical phase transiton property is 63 degrees C, higher than that defined by optical phase transiton property at 5 mu m, 60 degrees C; and the temperature width of electrical phase transition duration is also wider than that of optical phase transiton duration. The semiconductor-to-metal phase transiton temperature defined by optical properties increases with increasing wavelength in the region of infrared wave band, and the occuring temperature of phase transiton from semiconductor to metal also increases with wavelength increasing, but the duration temperature width of transition decreases with wavelength increasing. The phase transition properties of nano-vanadium dioxide thin film has obvious relationship with wavelength in infrared wave band. The phase transition properties can be tuned through wavelength in infrared wave band, and the semiconductor-to-metal phase transition properties of nano vanadiium dioxide thin films can be better characterized by electrical property.

Tunable optical properties of nano-Au on vanadium dioxide

The optical properties of Au nanoparticles deposited on thermochromic thin films of VO2 are investigated using spectroscopy. A localized modification on the transmittance spectrum of VO2 film is formed due to the presence of Au nanoparticles which exhibit localized surface plasmon resonance (LSPR) in the visible-near IR region. The position of the modification wavelength region shows a strong dependence on the Au mass thickness and shifts toward the red as it increases. On the other hand, it was found that the LSPR of Au nanoparticles can be thermally tunable because of the thermochromism of the supporting material of VO2. The LSPR wavelength, lambda(SPR), shifts to the blue with increasing temperature, and shifts back to the red as temperature decreases. A fine tuning is achieved when the temperature is increased in a stepwise manner.

Nano-Ag on vanadium dioxide. I. Localized spectrum tailoring

We report on the utilization of localized surface plasmon resonance (LSPR) of Ag nanoparticles to tailor the optical properties Of VO2 thin film. Interaction of nano-Ag with incident light yields a salient absorption band in the visible-near IR region and modifies the spectrum Of VO2 locally. The wavelength of modification occurs in a limited spectral region rather than affects the full spectrum. The wavelength of modification shows a strong dependence on the metal nanoparticle size and shifts toward the red as the particle size or the mass thickness of nano-Ag increases. Also, we found that the wavelength can be shifted into the IR further by introducing a thin layer of TiO2 onto the nano-Ag. Interestingly, with the help of LSPR effects the VO2 film exhibits an anomalous thermochromic behavior in the modification wavelength region, which may be useful in optical switching applications.

Nano-Ag on vanadium dioxide. II. Thermal tuning of surface plasmon resonance

Thermal tuning of the localized surface plasmon resonance (LSPR) of Ag nanoparticles on a thermochromic thin film of VO2 was studied experimentally. The tuning is strongly temperature dependent and thermally reversible. The LSPR wavelength lambda(SPR) shifts to the blue with increasing temperature from 30 to 80 degrees C, and shifts back to the red as temperature decreases. A smart tuning is achievable on condition that the temperature is controlled in a stepwise manner. The tunable wavelength range depends on the particle size or the mass thickness of the metal nanoparticle film. Further, the tunability was found to be enhanced significantly when a layer of TiO2 was introduced to overcoat the Ag nanoparticles, yielding a marked sensitivity factor Delta lambda(SPR)/Delta n, of as large as 480 nm per refractive index unit (n) at the semiconductor phase of VO2.

Growth and characterization of InAsSb alloys by metalorganic chemical vapour deposition

Low pressure metalorganic chemical vapour deposition (LP-MOCVD) growth and characteristics of InAssb on (100) Gasb substrates are investigated. Mirror-like surfaces with a minimum lattice mismatch are obtained. The samples are studied by photoluminescence spectra, and the output is 3.17 mu m in wavelength. The surface of InAssb epilayer shows that its morphological feature is dependent on buffer layer. With an InAs buffer layer used, the best surface is obtained. The InAssb film shows to be of n-type conduction with an electron concentration of 8.52 x 10(16) cm(-3).

富钇稀土-铝合金制取的研究Study on Preparation of Yttrium-Rich RE-Al Alloys

我国江西龙南稀土矿是目前世界上储量最大的富钇稀土矿、研制具有多种用途的钇（Y）-铝（Al）或富钇混合稀土（Ymm）-铝中间合金，对于开拓我国龙南稀土矿的应用领域扩大稀土合金出口具有重要意义。基于这一背景并针对目前氟化物体系制取Ymm-Al合金时存在着电解温度高，腐蚀现象严重，电效偏低等缺点，本文系统开展了在氯化物熔盐体系中电解制取Ymm-Al合金的研究工作。本工作由三部分组成：在第一部分工作中，开展了熔盐电解所需要基本原料-无水稀土氯化物制取的工艺研究。利用化学分析和结构分析手段，弄清了干法氯化过程中YmmCl_3水解的机理，提出了减弱水解的措施，即YmmCl_3先在850-900 ℃灼烧1.5 + 0.2hr，脱掉吸附水并将碱式碳酸盐转化为氧化物，增加稀土氧化物的比表面。通过条件试验得到最佳工艺条件为：采用NH_4 Cl:Ymm_2 O_3 = 14:1（摩尔比）的配料比，每次投入氯化装置的原料量为0.26 - 0.36 kg, 在400-450 ℃氯化反应激烈开始后迅速降温至400 ℃以下，待物料粘结现象消失后，再行升温氯化。出料及后期控制温在475 ± 25 ℃。经过3.8 ± 0.2hr氯化，可制得水不溶物小于1%并符合熔盐电解要求的YmmCl_3原料。此新工艺与原有干法工艺相比，流程短，装置简单，不需密闭抽真空，成本低，适于制取任何量的优质熔盐电解所需氯化稀土原料。在第二部分工作中，利用上述YmmCl_3原料，以液态铝为阴极，在氯化物体系中进行熔盐电解，通过试验得出在小型试验规模制取Ymm-Al合金的最隹工艺条件为：电解质组成（重量比）40%YmmCl_3-1%NaF-59%等摩尔的NaCl-KCl；电解温度为790 ± 5 ℃；阴极电流密为0.7 - 0.02A/cm~2；电解电量为333 ± 5库仑/克铝，制得钇铝合金中Ymm含量为10 ± 2%。添加1%的NaF可消除阴极表面生成枝状物，减少合金中夹渣和熔盐中沉渣。在电解工作中，将方差分析应用于试验数据处理，方差分析结果表明，各种试验因素对电效有明显影响，试验数据可靠，试验误差在允许范围以内。在第三部分工作中，利用线性扫描伏安法测定了在最隹电解工艺条件下Y~（3+）和Ymm在液态铝及钼电极上的析出电位。测定结果表明：Y~（3+）和Ymm~（3+）在液态铝阴极上的析出电位比在钼阴极上偏正0.2 ～ 0.8伏，氟离子的加入要比不加氟时析出电位不有同程度的负移，但考虑到氟离了具有消渣作用，加入少量氟比物添加剂对提高电效有利。

Band crossing in isovalent semiconductor alloys with large size mismatch: First-principles calculations of the electronic structure of Bi and N incorporated GaAs

For large size- and chemical-mismatched isovalent semiconductor alloys, such as N and Bi substitution on As sites in GaAs, isovalent defect levels or defect bands are introduced. The evolution of the defect states as a function of the alloy concentration is usually described by the popular phenomenological band anticrossing (BAC) model. Using first-principles band-structure calculations we show that at the impurity limit the N-(Bi)-induced impurity level is above (below) the conduction- (valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

GROWTH OF WIDE-BAND GAP IMMISCIBLE II-VI ALLOYS BY METALORGANIC VAPOR-PHASE EPITAXY

Although metalorganic vapor phase epitaxy (MOVPE) is generally regarded as a non-equillibrium process, it can be assumed that a chemical equilibrium is established at the vapor-solid interface in the diffusion limited region of growth rate. In this paper, an equilibrium model was proposed to calculate the relation between vapor and solid compositions for II-VI ternary alloys. Metastable alloys in the miscibility gap may not be obtained when the growth temperature is lower than the critical temperature of the system. The influence of growth temperature, reactor pressure, input VI/II ratio, and input composition of group VI reactants has been calculated for ZnSSe, ZnSeTe and ZnSTe. The results are compared with experimental data for the ZnSSe and ZnSTe systems.

Electronic properties of zinc-blende GaN, AlN, and their alloys Ga1-xAlxN

The electronic properties of wide-energy gap zinc-blende structure GaN, A1N, and their alloys Ga(1-x)A1(x)N are investigated using the empirical pseudopotential method. Electron and hole effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Gamma and those of the conduction band at Gamma and X are obtained for GaN and AIN, respectively. The energies of Gamma, X, L conduction valleys of Ga(1-x)A1(x)N alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices based on these materials in the blue light range application. (C) 1995 American Institute of Physics.

Band structure parameters of zinc-blende GaN, AlN and their alloys Ga1-xAlxN

The electronic properties of wide energy gap zinc-blende structure GaN, AlN and their alloys Ga1-xAlxN are investigated using the empirical pseudopotential method. Electron and hole Effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Gamma and those of the conduction band at Gamma and X are obtained. The energies of Gamma, X, L conduction valleys of Ga1-xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices in the blue light range.