温度对GaSb/GaAs量子点尺寸分布的影响

采用低压金属有机物化学气相沉积 (LP-MOCVD) 法制备GaSb/GaAs量子点。通过对不同生长温度的样品进行分析发现温度的变化对GaSb/GaAs量子点的相位角无明显影响,量子点的形状是透镜型。由于量子点特殊的应力分布,可实现量子点的"自限制"生长。量子点的化学势不连续性以及Ostwald熟化机制的影响使得量子点尺寸分布在一定范围内不连续,会出现两种尺寸模式的量子点生长。Sb原子的表面迁移率对GaSb/GaAs量子点生长有较大的影响。升高温度可有效改善量子点的分立性,在升温过程中量子点体现出其熟化过程,高温时表面原子的解析附作用对量子点尺寸和密度的影响较大。     

High-crystalline GaSb epitaxial films grown on GaAs(001) substrates by low-pressure metal–organic chemical vapor deposition

Orthogonal experiments of Ga Sb films growth on Ga As(001)substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition(LP-MOCVD)system.The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters.It was demonstrated that the optimized Ga Sb thin film has a narrow full width at half maximum(358 arc sec)of the(004)ω-rocking curve,and a smooth surface with a low root-mean-square roughness of about 6 nm,which is typical in the case of the heteroepitaxial single-crystal films.In addition,we studied the effects of layer thickness of Ga Sb thin film on the density of dislocations by Raman spectra.It is believed that our research can provide valuable information for the fabrication of high-crystalline Ga Sb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices.     

稀土对WC颗粒增强铁基体复合涂层组织结构的影响

采用氩弧熔覆技术在45号钢表面制备一层稀土WC颗粒增强铁基体耐磨复合涂层。通过扫描电镜(SEM)、X射线衍射(XRD)和能谱仪(EDS)等测试分析手段研究了稀土的引入对复合涂层中基体组织及碳化物的影响,并与未加稀土进行了比较。结果表明:引入稀土后,一方面优化了熔覆层组织中碳化物颗粒分布,降低了熔覆层组织中碳化物颗粒的团聚、桥接,且颗粒分布均匀;另一方面改善了熔覆层的组织,细化晶粒,减弱了熔覆过程中产生的树状晶,抑制了WC颗粒的溶解和鱼骨状碳化物的生成。在熔覆层组织中碳化物颗粒相主要有三种存在形式:原始未熔WC颗粒、与基体形成的复式碳化物及在凝固过程中重新结晶的W2C(或WC)。     

Nucleation of GaSb on GaAs （001） by low pressure metal-organic chemical vapor deposition

The initial growth stage of GaSb on GaAs(001) by low pressure metal–organic chemical vapor deposition(MOCVD)is investigated. The dependence of the nucleation on growth temperature, growth pressure, and vapor V/III ratio is studied by means of atomic force microscopy. The nucleation characteristics include the island density, size, and size uniformity distribution. The nucleation mechanism is discussed by the effects of growth temperature, growth pressure, and vapor V/III ratio on the density, size, and size uniformity of GaSb islands. With the growth temperature increasing from 500℃ to610℃ and the growth pressure increasing from 50 mbar to 1000 mbar(1 mbar = 105Pa), the island density first increases and then decreases; with the V/III ratio increasing from 0.5 to 3, the trend is contrary.     

The design and numerical analysis of tandem thermophotovoltaic cells

In this paper, numerical analysis of GaSb （Eg = 0.72 eV）/Gao.84Ino.16Aso.14Sbo.86 （Eg = 0.53 eV） tandem thermopho- tovoltaic （TPV） cells is carried out by using Silvaco/Atlas software. In the tandem cells, a GaSb p-n homojunction is used for the top cell and a GalnAsSb p-n homojunction for the bottom cell. A heavily doped GaSb tunnel junction connects the two sub-cells together. The simulations are carried out at a radiator temperature of 2000 K and a cell temperature of 300 K. The radiation photons are injected from the top of the tandem cells. Key properties of the single- and dual-junction TPV cells, including I-V characteristic, maximum output power （Pmax）, open-circuit voltage （Voc）, short-circuit current （/~sc）, etc. are presented. The effects of the sub-cell thickness and carrier concentration on the key properties of tandem cells are investigated. A comparison of the dual-TPV cells with GaSb and GalnAsSb single junction cells shows that the Pmax of tandem cells is almost twice as great as that of the single-junction cells.