Self-heating effect in 1.3 mu m p-doped InAs/GaAs quantum dot vertical cavity surface emitting lasers

The self-heating effect in 1.3 mu m p-doped InAs/GaAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) has been investigated using a self-consistent theoretical model. Good agreement is obtained between theoretical analysis and experimental results under pulsed operation. The results show that in p-doped QD VCSELs, the output power is significantly influenced by self-heating. About 60% of output power is limited by self-heating in a device with oxide aperture of 5x6 mu m(2). This value reduces to 55% and 48%, respectively, as the oxide aperture increases to 7x8 and 15x15 mu m(2). The temperature increase in the active region and injection efficiency of the QDs are calculated and discussed based on the different oxide aperture areas and duty cycle.

Scattering of linear water waves by a fixed and infinitely long rectangular structure parallel to a vertical wall in oblique seas

The scattering of linear water waves by an infinitely long rectangular structure parallel to a vertical wall in oblique seas is investigated. Analytical expressions for the diffracted potentials are derived using the method of separation of variables. The unknown coefficients in the expressions are determined through the application of the eigenfunction expansion matching method. The expressions for wave forces on the structure are given. The calculated results are compared with those obtained by the boundary element method. In addition, the influences of the wall, the angle of wave incidence, the width of the structure, and the distance between the structure and the wall on wave forces are discussed. The method presented here can be easily extended to the study of the diffraction of obliquely incident waves by multiple rectangular structures.

田间含碎石土壤水分入渗及再分布试验研究

为探明碎石存在于田间土壤中如何改变土壤水分运移通道、影响土壤水分运动,揭示田间含碎石土壤水分运动的复杂过程,采用便携式针头降雨器在铜川崾岘梁修建的临时小区进行模拟降雨实验,测定含碎石浅层土体的入渗和水分再分布过程,采用土壤水分运动通量法计算浅层土体不同深度各截面面积的水量在雨后不同时间段的变化,分析含碎石土壤再分布特征及碎石含量对浅层土体入渗和水分再分布的影响。结果表明:碎石有利于田间浅层土壤入渗和蓄存;室内较田间测定的含碎石土壤入渗率小一个数量级以上;降雨后较短时段,碎石含量相对高的林地小区的浅层土体水分在降雨停止后呈增加趋势,表现了蓄水过程,碎石含量较低的撂荒地则表现了释水过程;降雨后较长时段,多数小区浅层土体(0-30 cm)水量变化呈现了"排水-存储交换-排水"过程,少数小区仅呈现了"排水"过程;雨后16 h左右的土体各截面面积的水量与碎石含量呈现了以直线y=0.4873为轴对称的递增和递减的指数为1/2的幂函数关系,说明碎石对黄土区典型土石区土体水分运动具有促进和阻滞双面影响。本文的研究结果可为含碎石土壤的水分利用及水分循环提供参考。

山地红枣林地滴灌水分运移规律试验研究

在米脂山地微灌枣树示范基地研究了一定流量范围、不同灌水量条件下,地表滴灌水分在水平和垂直方向上的运移规律及滴灌结束后的水分再分布特征。试验结果表明:在流量稳定条件下,湿润体的水平和垂直扩散距离均与时间有显著的幂函数关系;在4.6~5.0 L/h的流量范围内,湿润体的水平和垂直扩散距离与灌水量也存在显著的幂函数关系;滴灌停止后24 h内的土壤湿润体扩散很大,湿润体平均含水量降低很快,24 h后的扩散较小,平均含水量下降较小,确定滴灌停止后24 h时的湿润体特征值可作为滴灌系统设计的依据。

COMPARISON BETWEEN THE INFLUENCES OF LAYER THICKNESSES AND ALAS MOLE FRACTION-X ON VERTICAL-CAVITY SURFACE-EMITTING LASERS

Based on the n(x, lambda), the calculation of the reflection spectrum for vertical cavity surface emitting lasers shows that the deviation of the central wavelength caused by the change of layer thickness is much more than that caused by the change of AlAs mole fractions. Therefore the control of the MBE growth rate is very important.

Interfacial behaviour of quantum well electrode/electrolyte: effect of redox species on EER spectra of a single quantum well GaAs vertical bar AlxGa1-xAs electrode

The EER spectra of a single quantum well GaAs\AlxGa1-xAs electrode were studied as a function of applied reverse bias in ferrocene, p-methyl nitrobenzene and hydroquinone+benzoquinone non-aqueous solutions. EER spectra were compared for different redox species and showed that a pronounced quantum-confined Stark effect and a Franz-Keldysh oscillation for a single quantum well electrode were obtained in the p-methyl-nitrobenzene- and hydroquinone+benzoquinone-containing solutions. A surface interaction of the single quantum well electrode with ferrocene led to fewer changes in the electric field of the space charge layer for reverse bias; this was suggested to explain the weak quantum-confined Stark effect and Franz-Keldysh oscillation effect observed for the single quantum well electrode in the ferrocene-containing solution. (C) 1997 Elsevier Science S.A.

Far-field and beam characteristics of vertical-cavity surface-emitting lasers

We have determined the far-field patterns and beam parameters of vertical-cavity surface-emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active-layer aperture of VCSELs strongly influence laser far-field distributions and beam characteristics; for VCSELs with small window omega=5 mu m, only one dominant lobe has been observed in the far-field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active-layer aperture, the larger is the far-field divergence. The laser structure dependence of the K factor has also been studied. (C) 1996 American Institute of Physics.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

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 threshold gain. Some experiment results are demonstrated, showing the agreement of theoretical analysis with experiment.

PULSED ELECTRICAL OPERATION OF 1.5-MU-M VERTICAL-CAVITY SURFACE-EMITTING LASERS

Vertical cavity surface emitting lasers operating in the 1.3- and 1.5-mu m wavelength ranges are highly attractive for telecommunications applications. However, they are far less well-developed than devices operating at shorter wavelengths. Pulsed electrically-injected lasing at 1.5 mu m, at temperatures up to 240 K, is demonstrated in a vertical-cavity surface-emitting laser with one epitaxial and one dielectric reflector. This is an encouraging result in the development of practical sources for optical fiber communications systems.