GeSn合金的晶格常数对Vegard定律的偏离

在Si (001)衬底上, 以高质量的弛豫Ge薄膜作为缓冲层, 先后生长Sn组分x分别为2.5%, 5.2%和7.8%的完全应变的三层Ge_1-xSn_x合金薄膜. 在Si (001)衬底上直接生长了x分别为0.005, 0.016, 0.044, 0.070和0.155的五个弛豫Ge_1-xSn_x样品. 通过卢瑟福背散射谱、高分辨X射线衍射和X射线倒易空间图等方法测量了Ge_1-xSn_x合金的组分 与晶格常数. 实验得到的晶格常数相对Vegard定律具有较大的正偏离, 弯曲系数b=0.211 Å.     

EFFECTIVE CAVITY LENGTH IN VERTICAL CAVITY SURFACE EMITTING LASER

Effective cavity length method is introduced to vertical cavity surface emitting laser for characterizing some properties, including reflectivity, FWHM, mode wavelength and thresh-old gain. Some experiment results are demonstrated, showing the agreement of theoretical analysis with experiment.     

卫星姿态的开关式控制

<正> 在人造地球卫星的飞行控制中,一个重要的问题是控制卫星的姿态,即卫星相对某坐标系的定向和角速度.例如使卫星某个轴指向地球,或让卫星绕一轴旋转.某些时候,卫星姿态是用固定在卫星上的喷咀喷气的反作用力矩控制的.在工程上,喷咀只能有两种状态:喷或不喷,而喷气的速度是不加调节的.因此,卫星受到的控制力矩是开关式的,     

关于数学科学研究的报告

该文是由国家科委委托中国科学院组织的数学基础研究和应用基础研究调研专题小组起草的一份报告,现经作者同意发表于此,以期引起讨论。     

甲酸及其二聚体质子转移n→π~*跃迁的分子轨道研究

用MINDO/3和INDO/S法研究了甲酸及其二聚体的质子转移行为,得到基态和激发态质子转移的位能曲线,解释了二体UV光谱中n→π~*吸收带的蓝移现象,并求得了过渡态的结构和能量。     

半导体激光器的进展（Ⅱ）

５量子阱半导体激光器量子阱的概念早在量子力学的教科书中就作为基本的教材来讨论，两个高势能的阱壁夹住一个低势能阱底，构成了一个势阱，落入阱中的自由电子将在空间中被定域在阱内运动．如果是一维的势阱，则阱壁平面是无限大的，阱中的电子在阱壁平面仍然可以自由运动，然而在垂直阱壁方向却受到了阱壁的定域限制．电子将不断在二阱壁间来回反射，如果阱壁势能很高又很厚，则阱中电子就完全被约束在阱内．半导体双异质结构就是这样一个半导体势阱．如果把阱的宽度缩小到１００Ａ以下的量级，它与电子的德布罗意波长（或电子自由程）相…     

A ministop band in a single-defect photonic crystal waveguide based on silicon on insulator

This paper reports that a two-dimensional single-defect photonic crystal waveguide in the Г-K direction with triangular lattice on a silicon-on-insulator substrate is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. A ministop band （MSB） is observed by the measurement of transmission characteristics. It results from the coupling between the two modes with the same symmetry, which is analysed from the stimulated band diagram by the effective index and the two-dimensional plane wave expansion methods. The parameter working on the MSB is the ratio of the radius of air holes to the lattice constant, fla. It is obtained that the critical τ/a value determining the occurrence or disappearance of MSB is 0.36. When τ/a is larger than or equal to 0.36, the MSB occurs. However, when τ/a is smaller than 0.36, the MSB disappears.     

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55μm： physics,design and simulation

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30μm could absorb 90% of the incident light at 1.55μm wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.     

Zero biased Ge-on-Si photodetector with a bandwidth of 4.72~GHz at 1550~nm

High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8~μm Ge, with responsivities as high as 0.38 and 0.21~A/W at 1.31 and 1.55~μ m, respectively. The dark current density is 0.37~mA/cm² and 29.4~mA/cm² at 0~V and a reverse bias of 0.5~V. The detector with a diameter of 30~μ m, a 3~dB-bandwidth of 4.72~GHz at an incident wavelength of 1550~nm and zero external bias has been measured. At a reverse bias of 3~V, the bandwidth is 6.28~GHz.     

High-speed waveguide-integrated Ge/Si avalanche photodetector

Waveguide-integrated Ge/Si heterostructure avalanche photodetectors(APDs) were designed and fabricated using a CMOS-compatible process on 8-inch SOI substrate. The structure of the APD was designed as separate-absorption-chargemultiplication(SACM) using germanium and silicon as absorption region and multiplication region, respectively. The breakdown voltage(V_b) of such a device is 19 V at reverse bias and dark current appears to be 0.71 μA at 90% of the V_b. The device with a 10-μm length and 7-μm width of Ge layer shows a maximum 3-dB bandwidth of 17.8 GHz at the wavelength of 1550 nm. For the device with a 30-μm-length Ge region, gain-bandwidth product achieves 325 GHz.