共查询到20条相似文献,搜索用时 0 毫秒
1.
研究了非掺GaAs半绝缘单晶的液封垂直梯度凝固法(VGF)生长技术,解决了Si沾污和C浓度的控制问题,得到了直径2英寸非掺半绝缘低位错单晶。测试表明:该单晶的位错密度较LEC单晶下降近一个数量级,电学参数与LEC单晶类似,接近国个VGF单晶的的参数指标。 相似文献
2.
3.
P. Reuvekamp F. S. Razavi C. Hoch J. S. Kim R. K. Kremer A. Simon 《Journal of Superconductivity and Novel Magnetism》2009,22(4):353-356
To prevent the loss of K in growing single crystals of Ba1−x
K
x
Fe2As2 we developed a rapid-heating Sn-flux method. Large single crystals with the optimal superconducting transition temperature
T
C≈38 K were obtained and their structural, chemical and superconducting properties were investigated. Additionally, the effect
of post-growth annealing on these crystals at different temperatures was examined. Scanning electron microscopy microprobe
studies on a crystal with the composition goal of Ba0.25K0.75Fe2As2 revealed a well defined separation of two phases with compositions that are suggestive of rational ratios of the K and Ba
content. 相似文献
4.
We investigated the opportunities to increase the electric uniformity of GaAs and InGaAs films grown by molecular-beam epitaxy (MBE) technique on monocrystalline (single crystal) GaAs: both on porous and conventional so-called “monolithic” (without pores) GaAs (100) substrates. The basic attention was given to study the electrically active defects in films by using scanning electron microscope (SEM) with new technique which is called “Rau-detector” [E.I. Rau, A.N. Zhukov and E.B. Yakimov, Solid-State Phenomena, 1998, v. 53-54, 327.]. We compared the main properties of epitaxial GaAs and InGaAs films grown on above mentioned substrates. The films grown on porous substrates had higher structural perfection including the following advantages: (a) smoother surface due to lateral growth mechanism; (b) less density of structural defects (without dislocation walls), the density of pyramidal defects was ∼ 2 × 105 cm− 2 as compared with the density 2 × 107 cm− 2 in the films grown on monolithic substrates; (c) less electrical activity of various structural defects and increased electric uniformity of grown films. The electrical activity of defects in films grown on porous substrates was essentially lowered due to gettering properties of porous substrate. 相似文献
5.
谱共轭梯度法含有两个方向调控参数,是求解无约束优化问题的一类有效方法.本文给出一对参数公式以构建新的谱共轭梯度法,该方法在精确线搜索下与标准FR方法等价,在Wolfe线搜索下具有类似标准DY方法的内在性质.我们证明了采用Wolfe线搜索的新算法在每一次迭代中均产生下降方向,并且具有全局收敛性.数值实验结果表明,新算法数值稳定、有效,适合于求解大规模无约束优化问题. 相似文献
6.
7.
8.
9.
GaOOH crystals were synthesized by a simple hydrothermal method at 90-200 °C for 18 h. The products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscope (HRTEM). The rods synthesized at 110-150 °C exhibited intersecting morphology and regular diamond-like cross section with a diagonal length ratio of 2:1, and those synthesized at 180-200 °C exhibited nunchakus-like architecture. The formation of diamond-like cross section was due to homogeneous growth of lattice planes, namely {1 1 0}, along [4 1 0], [4 1¯ 0], [4¯ 1 0], and [4¯ 1¯ 0] directions of orthorhombic GaOOH. Moreover, the formation of the trunk was due to the growth along [0 0 1] direction. 相似文献
10.
It is well-known that the properties of semiconductor materials including gallium arsenide are controlled by defects and impurities.
The characterization of these defects is important not only for better understanding of the solid state phenomena but also
for improved reliability and performance of electronic devices. We have been investigating the defects in gallium arsenide
for several years using deep level transient spectroscopy, photoconductivity, transient photoconductivity, photoluminescence
etc. Results drawn from our recent studies are presented here to illustrate some of the problems concerning transition metal
impurities, process-induced defects, occurrence of intracentre transitions and metastability of deep levels in gallium arsenide. 相似文献
11.
Neng-Hui Zhang 《Thin solid films》2007,515(23):8402-8406
The functionality and reliability of multilayered systems are strongly influenced by thermoelastic stresses. Recently Hsueh formulated a closed-form solution [Hsueh, Thermal stresses in elastic multilayer systems, Thin Solid Films 418 (2002) 182] by decomposing the total strain into a uniform strain component and a bending strain component in order to overcome the complexity of the traditional analytical models. The present study develops an alternative analytical model in terms of the curvature radius of the neutral axis for zero normal strain and the normal strain at the interface between the substrate and the films. Numerical results are calculated for thermoelastic stresses in five-layer (AlGa)As laser diodes. Also two approximate models for the case of multilayered films on a thick substrate are obtained. 相似文献
12.
A. Christou 《Quality and Reliability Engineering International》1989,5(1):37-46
A review of the reliability status of GaAs discrete devices and integrated circuits is given. In the present survey of new devices and circuits it is shown that a significant number of reliability problems continue to persist. 相似文献
13.
We generate spin-polarized carrier populations in GaAs and low temperature-grown GaAs (LT-GaAs) by circularly polarized optical beams and pull them by external electric fields to create spin-polarized currents. In the presence of the optically generated spin currents, anomalous Hall currents with an enhancement with increasing doping are observed and found to be almost steady in moderate electric fields up to 120 mV μm−1, indicating that photo-induced spin orientation of electrons is preserved in these systems. However, a field 300 mV μm−1 completely destroys the electron spin polarization due to an increase of the D’yakonov–Perel’ spin precession frequency of the hot electrons. This suggests that high field carrier transport conditions might not be suitable for spin-based technology with GaAs and LT-GaAs. It is also demonstrated that the presence of the excess arsenic sites in LT-GaAs might not affect the spin relaxation by Bir–Aronov–Pikus mechanism owing to a large number of electrons in n-doped materials. 相似文献
14.
W. T. Anderson D. V. Morgan F. A. Buot A. Christou 《Quality and Reliability Engineering International》1988,4(3):255-268
This paper reviews the present knowledge on subsurface burnout mechanisms in Gallium Arsenide (GaAs) electronic devices. The results of the work should assist in the creation of more reliable devices with greater radiation hardness. 相似文献
15.
16.
17.
The synthesis of single-crystalline GaN nanowires on c-Al2O3 substrates using a vapor phase epitaxy process was studied. The GaN nanowires synthesized at a high NH3 gas flow rate and thus with a sufficient supply of the N source grew via the vapor-solid mechanism, while those synthesized at a low NH3 gas flow rate grew via the vapor-liquid-solid mechanism. The internal stress between the nanowires and the substrate was investigated using micro-Raman spectroscopy. The X-ray diffraction indicated that the triangular GaN nanowires have a single-crystalline hexagonal structure. 相似文献
18.
用晶体生长动力学考察了籽晶法气相生长C60单晶体的生长工艺,得出关键在于处理成核与长大两个因素之间的矛盾。对管状炉的温度场进行了重新设计,将冷端的最低温度点移至合适部位,有效地控制了成核的数目。通过不断地优化实验,经选出恰当的冷、热端温度及生长周期,生长出的C6。单晶的最大钱度超过6mm,且有较高的结晶品质。同一单晶的劳厄像显示出C60的生长暴露面有(111)和(100)两种。 相似文献
19.
Al-Si eutectic growth mechanism was investigated in a directionally-solidified AI-1 3 wt% Si alloy with different strontium (Sr) and magnesium (Mg) additions, growth velocities and temperature gradients. Macro- and micro- scale metallographic analyses revealed that addition level of Sr and Mg, temperature gradient and growth velocity are important factors affecting stability of solidifying AI-Si eutectic front and the final morphology of eutectic grains in the solidified A1-13 wt% Si alloys. By varying (tailoring) these factors, a variety of eutectic grain structures and morphologies such as planar front, cellular structure, a mix of cellular and columnar, or equiaxed dendrites, can be obtained. Increasing temperature gradient, reducing growth velocity, or decreasing Sr and Mg contents is beneficial to stabilizing planar growth front of eutectic grains, which is qualitatively in accordance with constitutional supercooling criterion for binary eutectic growth. In contrast, adding more Sr and Mg, increasing growth velocity, or decreasing temperature gradient produces large constitutional supercooling, leading to columnar-equiaxed transition (CET) of eutectic structure, which can be interpreted on the basis of Hunt's Model. It is also found that both solute concentration and solidification variables have significant impact not only on eutectic growth, but also on gas porosity formation. 相似文献
20.