Effect of InxGa1-xAs (0 <= x <= 0.4) capping layer on self-assembled 1.3 mu m wavelength InAs/GaAs quantum islands

We report the effect of InchiGa1-chiAs (0 less than or equal to chi less than or equal to0.4) capping layer on photoluminescence (PL) properties of 1.3 mum wavelength self-assembled InAs quantum islands, which are formed via depositing 3.5 monolayers (ML) InAs on GaAs (1 0 0) substrate by molecular beam epitaxy (MBE). Compared with the InchiGa1-chiAs capping layer containing a larger In mole fraction chi greater than or equal to0.2 and the GaAs capping layer (chi = 0), the InAs islands covered by the In0.1Ga0.9As layer show PL with lower emission energy, narrower full-width at half-maximum (FWHM), and quite stronger intensity. The PL peak energy and FWHM become more temperature dependent with the increase of In content in the InchiGa1-chiAs capping layer (chi greater than or equal to0.2), while the InAs islands covered by the In0.1Ga0.9As layer is much less temperature sensitive. In addition, the InAs islands covered by the In0.1Ga0.9As capping layer show room temperature PL wavelength at about 1.3 mum. (C) 2001 Published by Elsevier Science B.V.

Structural anisotropy and optical properties of InxGa1-xAs quantum dots on GaAs(001)

InAs and InxGa1-xAs (x = 0.2 and 0.5) self-organized quantum dots (QDs) were fabricated on GaAs(0 0 1) by molecular beam epitaxy (MBE) and characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), acid photoluminescence polarization spectrum (PLP). Both structural and optical properties of InxGa1-xAs QD layer are apparently different from those of InAs QD layer. AFM shows that InxGa1-xAs QDs tend to be aligned along the [1 (1) over bar 0] direction, while InAs QDs are distributed randomly. TEM demonstrates that there is strain modulation along [1 1 0] in the InxGa1-xAs QD layers. PLP shows that In0.5Ga0.5As islands present optical anisotropy along [1 1 0] and [1 (1) over bar 0] due to structural and strain field anisotropy for the islands. (C) 2001 Elsevier Science B.V. All rights reserved.

Study of rapid carrier capture and relaxation in InAs/GaAs heterostructures

The rapid carrier capture and relaxation processes in InAs/GaAs quantum dots were studied at 77K by using a simple degenerate pump-probe technique. A rising process was observed in the transient reflectivity, following the initial fast relaxation associated with GaAs bulk matrix, and this rising process was assigned to be related to the carrier capture from the GaAs barriers to InAs layers. The assignment was modeled using Kramers-Kronig relation. By analyzing the rising process observed in the transient reflectivity, the carrier capture time constants were obtained. The measured capture times decrease with the increase of carrier concentration.

New progress of studies on semiconductor materials

This paper is a review of research and development on semiconductor materials, which covers main scientific activities in this field. The present status acid future prospects of studies on semiconductor materials, such as silicon crystals, GaAs related III-V compound semiconductor materials and GaAs, InP and silicon based quantum well and superlattice materials, quantum wires and quantum dots materials, microcavity and photonic crystals, materials for quantum computation and wide band gap materials, are briefly discussed.

Effect of buffer layer growth conditions on the secondary hexagonal phase content in cubic GaN films on GaAs(001) substrates

In this letter, we investigated the effect of the buffer layer growth conditions on the secondary hexagonal phase content in cubic GaN films on GaAs(0 0 1) substrate. The reflection high-energy electron diffraction (RHEED) pattern of the low-temperature GaN buffer layers shows that both the deposition temperature and time are important in obtaining a smooth surface. Four-circle X-ray double-crystal diffraction (XRDCD) reciprocal space mapping was used to study the hexagonal phase inclusions in the cubic GaN (c-GaN) films grown on the buffer layers. The calculation of the volume contents of the hexagonal phase shows that higher temperature and longer time deposition of the buffer layer is not preferable for growing pure c-GaN film. Under optimized condition, 47 meV FWHM of near band gap emission of the c-GaN film was achieved. (C) 2000 Elsevier Science B.V. All rights reserved.

Asymmetry in the vertically aligned growth induced InAs islands in GaAs

A 10-InAs-island-layer vertically coupled quantum dot structure on (001) GaAs was grown and investigated by molecular beam epitaxy and transmission electron microscopy. The result shows that the vertically aligned InAs islands are asymmetrical along the two < 110 > directions on the (001) growth plane. Such an asymmetry in the vertically coupled quantum dot structure can be explained with the chemical polarity in the III-V compound semiconductors.

Alignment of threading dislocations in the In0.3Ga0.7As/GaAs superlattice

Threading dislocations in the III-V heterostructure system are investigated based on the observation of dislocations in the In0.3Ga0.7As/GaAs superlattice with transmission electron microscope. To explain both the presence and orientation of threading dislocations in the epilayers an alloy effect on the dislocation lines in ternary III-V compounds is proposed, and, in addition, a pseudo-stable state for threading dislocations in binary compounds is recognized. (C) 1998 Elsevier Science B.V. All rights reserved.

Abnormal alignment of misfit dislocations in In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure that misfit dislocation lines deviate from the [110] directions at a certain angle depending on the indium content x. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on the misfit dislocations in the interface between the III-V ternary compounds.

Alignment of misfit dislocations in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As system grown on the (001) InP substrate that misfit dislocation lines deviate [110] directions at an angle with its value depending on the gallium content. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on misfit dislocations in the interface between the III-V ternary compounds. (C) 1998 American Institute of Physics.

Calculation of valence subband structures for strained GaInP/AlGaInP quantum wells without axial approximation

Usually in the calculation of valence subband structure for III-V direct bandgap material, axial approximation had been used in the Luttinger-Kohn model to simplify the computational efforts. In this letter, the valence subband structure for the GaInP/AlGaInP strained and lattice-matched quantum wells was calculated without axial approximation, on the basis of 6x6 Luttinger-Kohn Hamiltonian including strain and spin-orbit splitting effects. The numerical simulation results were presented with help of the finite-difference methods. The calculation results with/without axial approximation were compared and the effect of axial approximation on the valence subband structure was discussed in detail. The results indicated that there was a strong warping in the GaInP valence band, and axial approximation can lead to an error when k was not equal to zero, especially for compressively strained and lattice-matched GaInP/AlGaInP quantum wells.

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.

Delay of the excited state lasing of 1310 nm InAs/GaAs quantum dot lasers by facet coating

In this letter, we present a facet coating design to delay the excited state (ES) lasing for 1310 nm InAs/GaAs quantum dot lasers. The key point of our design is to ensure that the mirror loss of ES is larger than that of the ground state by decreasing the reflectivity of the ES. In the facet coating design, the central wavelength is at 1480 nm, and the high- and low-index materials are Ta2O5 and SiO2, respectively. Compared with the traditional Si/SiO2 facet coating with a central wavelength of 1310 nm, we have found that with the optimal design the turning temperature of the ES lasing has been delayed from 90 to 100 degrees C for the laser diodes with cavity length of 1.2 mm. Furthermore, the characteristic temperature (T-0) of the laser diodes is also improved.

复杂无机离子晶体晶格能的研究

对于简单二元晶体（I-VII，II-VI，III-V族晶体），我们发现了它们的晶格能、德拜温度、等离子体能量、体变模量间的一些简单关系，分析发现了德拜模型的局限性，得到离子品体晶格能最小可能值为546kjmol-1，也发现碱金属卤化物的晶格能与格波的纵、横光学支的波数都呈线性关系，相同阳离子及相同阴离子的碱金属卤化物的LEELS、HEELS，ORS的谱峰能量值也与晶格能呈线性关系，说明这些量都与离子间的｛妾合强度有一定的关系。基于复杂靛．体化学键介电理论，并考虑到晶格能和键性的关系，我们发展了一种新的经验地计算晶．格能的方法，晶格能被视为是由各类键贡献的，对于每类键，其对晶格能的贡献被分为离子性和共价性两部分，复杂离子晶体被分解后得到的各类键可做相似处理。我们又基于Born理论模型，考虑到离子晶体中离子间主要作用是库仑作用及电子壳层的排斥作用，发展了另一种简单的计算晶格能的方法。对于很多静电键为主的功能材料（如巨磁阻材料、超导体等），用这两种方法计算的晶格能值与实验值及他人的计算结果相当接近，它们可以作为复杂离子晶体晶格能可信I均估算方法。我们还计算了YBCO体系的晶格能，并得到其与氧浓度的函数关系。

分光光度法测定钛和钒的价态

本论文“分光光度法则测定钛和钒的价态”包括互相独立的两部分工作：一、关于钛，经比较选用2－噻吩甲酰三氟丙酮作为Ti(III)的显色剂。在含二氯化锡的盐酸介质中，形成具有M:R = 1:3的稳定络合物，在685和485nm处有两个吸收峰，摩尔吸光系数分别为1.10 * 10~3和1.79 * 10~3。在685nm处测定Ti(III)有很高的选择性，百倍量的Ti(IV)和除氧化剂外的毫克量的多数常见离子无影响。0－300微克Ti(III)/10毫升范围内遵守比尔定律。应用本法测定了三氯化钛氧化剂和异丙橡胶中的Ti(III)和Ti(IV)。另外建立了新的配制和保存Ti(III)标准溶液的方法。二、关于钒、用磷钼杂多酸－罗丹明B作试剂，在存在聚乙烯醇的情况下，水相分光光度测定了三、四、五价钒。V（▽）与试剂形成四元络合物R_4[Mo_(11)V(▽)PO_(40)], V(IV)无显色反应，V(III)还原磷钼杂多酸成磷钼等，再与罗凡明B形成三元络合物R_5[Mo_(10)(VI)Mo_2(▽)PO_(40)]，过剩磷钼杂多酸由加入柠檬酸掩蔽。当V(IV)与V(▽)共存时，将其氧化成V(▽)，测合量后减去V(▽)而得V(IV)含量；当V(IV)与V(III)共存时，将其还原成V(III)，测合量后减去V(III)而得V(IV)含量。试剂最大吸收峰在555nm，两种络合物最大吸收峰都在586nm处，络合物的摩尔吸光系数分别为2.80 * 10~5和2.16 * 10~5。0-3.0微克V(▽)和0-4.0微克V(III)/25毫升遵守比尔定律。仅钛、锆、铌和钽及氧化、还原剂有影响。一个体系能高灵敏的测定三、四、五价钒，本工作还是首次。

砷的化学形态分析方法的研究

本论文由三部分组成。第一部分是天然水中痕量砷（III）和无机砷总量的测定。我们提出了用硼氢化钾片作还原剂，在柠檬酸铵介质中选择还原砷（III），在洒石酸介质中还原无机砷总量，还原生成的砷化氢与同时生成的氢气一起通过吸收液显色，再用分光光度计分别测定砷（III）和无机砷总量的分析方法，并且对几种天然水样进行了分析和标准加入加收试验。本方法具有较好的精密度和较高的灵敏度，砷（III）的检出限为0.16ppb，无机砷总量的检出限为0.36ppb，而且分析速度快，操作简便，易于推广。第二部分是无机砷和有机胂的分离与测定。我们选用砷（III）和砷（v-bar）代表无机砷，二甲基胂酸和苯基胂酸代表有机胂，利用氢氧化铁对无机砷和有机胂的共沉淀能力的差异分离无机砷和有机胂，再用高氯酸—硝酸消化有机胂，以分光光度法分别测定。通过对水、土壤，特别是药物样品的分析，并把分析结果与高氯酸—硝酸消化测定的总砷量进行比较表明，本方法确实具有很好的实用价值。该方法的建立对于一些含砷量高的药物建立除砷方法和砷对人体毒害机理的进一步研究具有重要的意义。第三部分是对氢氧化铁吸附砷机理的探讨。文中讨论了氢氧化铁吸附砷的机制，认为溶液中砷离子是与不同水解度的铁的羟基化合物形成了离子缔合物而被氢氧化铁共沉淀的。同时观察到，随着砷的形态不同，氢氧化铁对它们的吸附能力也不相同。通过比较几种氢氧化物对不同形态砷吸附能力的差异和氢氧根离子对吸附能力的影响等试验，初步证明，三价铁离子水解过程中的某些产物以及不同形态砷离子的空间构型的氢氧化铁吸附不同形态砷的能力解产生很大的影响。文中还通过实验，确定了氢氧化铁吸附砷（III）和砷（v-bar）的等温吸附经验公式中的常数，并对砷（III）和砷（v-bar）在氢氧化铁上的吸附速率作了比较和讨论。