自组织InAs/GaAs量子点的X射线双晶衍射研究

用X射线双晶衍射方法测定了自组织生长的InAs／GaAs量子点的摇摆曲线，根据Takagi-Taupin方程对曲线进行了拟合。在考虑量子点层晶格失配的情况下，理论曲线和实验曲线符合得很好，从而确定了量子点垂直样品表面的失配度，约为4～6％，这与宏观连续体弹性理论的预测相近。结合电镜、原子力显微镜的观察结果表明对子单层沉积方法获得的量子点层采用化合物构层进行拟合所得结果是合理的。     

应力补偿技术在InAs/GaAs量子点中的研究现状

通过在多层量子点体系中引入应变补偿层,改变量子点系统的应力场分布,可以控制生长过程中量子点的大小均匀性和密度,最终获得高质量、高密度的多层量子点体系,应用到量子点光电器件中,可改善器件的电学和光学性能。介绍了应变补偿层在量子点体系中作用的原理,常用的应变补偿材料体系,以及目前国内外对应变补偿技术的研究状况,最后提出了现存的问题和今后的发展方向。     

自组织InAs/GaAs与InGaAs/GaAs量子点生长及退火情况的比较

本文采用MBE进行InAs/GaAs与InGaAs/GaAs量子点的生长,利用RHEED进行实时监测,并利用RHEED强度振荡测量生长速率。对生长的InAs/GaAs和InGaAs/GaAs两种量子点生长过程与退火情况进行对比,观察到当RHEED衍射图像由条纹状变为网格斑点时,InAs所需要的时间远小于InGaAs;高温退火下RHEED衍射图像恢复到条纹状所需要的时间InAs比InGaAs要长。     

1.08μmInAs/GaAs量子点激光器光学特性研究

介绍了ＩｎＡｓ／ＧａＡｓ量子点激光器的材料生长,器件制备及其光学特性的研究。器件为条宽１００μｍ,腔长１６００μｍ未镀膜激器。室温阈值电流密度为２２１Ａ／ｃｍ＾２,激射波长为１．０８μｍ,连续波工作最大光功率输出为２．７４Ｗ（双面）,外微分效率为８８％,经５０℃,１０００ｈ老化,仍有〉１．２Ｗ的光功率输出。     

GaInP应力补偿层在InAs/GaAs量子点中的初步应用

利用金属有机化合物气相沉积(MOCVD)技术生长了双层InAs/GaAs量子点,并将GaInP作为应力补偿层引入到其中,采用原子力显微镜(AFM)对量子点的结构和生长质量进行了表征与分析。实验结果表明,应变补偿层的采用可有效改善第二层量子点质量:(1)面密度最高可达7.5×1010 cm-2,而没有应变补偿层的样品的面密度仅为5.8×1010 cm-2;(2)缺陷岛密度可从不采用应变补偿时的9.6×107 cm-2降低至2.8×107 cm-2;(3)量子点的均匀性和尺寸也明显改善。此外,不同应变补偿层厚度比较实验结果显示,厚度过高或过低的应变补偿层都不能起到很好的补偿作用,取1~3nm之间为佳;不同GaInP补偿层组分的比较实验结果表明,Ga组分为0.566的样品补偿效果比0.606的样品更好。     

延长自组织InAs／GaAs量子点发光波长的研究进展

在近几年的InAs／GaAs自组织量子点的研究中，如何荻得1．3～1．55μm。长波长量子点材料是一个很热门的课题。本文综述了各种延长自组织InAs／GaAs量子点发光波长的方法，并提出了实用化的最佳途径。     

InP(001)基衬底上自组织生长InAs量子点(线)的光学性质研究

在InP(001)基衬底上用分子柬外延方法生长InAs纳米结构材料，通过衬底的旋转与否及混合生长模式，得到了两种InAs量子点和量子线，并研究了量子点、线的光学性质，结果表明，两种方式都可生长出较强发光的量子点(线)；由量子点排列构成的量子线的光致发光光谱呈现出多峰结构，分析和理论计算表明这是InAs量子线上各量子点在垂直方向上不同高度分布和非连续性而造成的。     

Ge基GaAs薄膜和InAs量子点MBE生长研究

采用分子束外延(MBE)法,在优化Ge衬底退火工艺的基础上,通过对比在(001)面偏<111>方向分别为0°、2°、4°和6°的Ge衬底上生长的GaAs薄膜,发现当Ge衬底的偏角为6°时有利于高质量GaAs薄膜的生长;通过改变迁移增强外延(MEE)的生长温度,发现在GaAs成核温度为375℃时,可在6°偏角的Ge衬底上获得质量最好的GaAs薄膜。通过摸索GaAs/Ge衬底上InAs量子点的生长工艺,实现了高效的InAs量子点光致发光,其性能接近GaAs衬底上直接生长的InAs量子点的水平。     

温度对InAs/GaAs量子点生长影响的动力学蒙特卡罗模拟

采用动力学蒙特卡罗模型模拟了GaAs应变弛豫图形衬底上InAs量子点阵列生长早期阶段,温度对浸润层之上第一层亚单原子层阶段的影响.通过对生长表面形态、岛平均大小、岛大小分布及其标准差等方面的研究,证明了通过控制温度能够得到大小均匀、排列有序的岛阵列,这对后续量子点生长的定位和尺寸控制有重要影响.     

InAs自组织量子点(线)的制备和表征

在InP(001)基衬底上用分子束外延方法生长了InAs纳米结构材料，通过改变生长方式，得到了InAs量子点和量子线。根据扫描电镜和透射电镜观测结果的分析，认为衬底旋转时浸润层三角形状的台阶为InAs量子线的成核提供了优先条件，停止衬底旋转时InAlAs缓冲层沿[11^-0]方向分布的台阶促使InAs优先形成量子点。讨论了量子点和量子线的形成机理。     

Thermal-induced intermixing effects on the optical properties of long wavelength low density InAs/GaAs quantum dots

The effect of post-growth rapid thermal annealing on the photoluminescence properties of long wavelength low density InAs/GaAs (001) quantum dots (QDs) with well defined electronic shells has been investigated. For an annealing temperature of 650 °C for 30 s, the emission wavelength and the intersublevel spacing energies remain unchanged while the integrated PL intensity increases. For higher annealing temperature, blue shift of the emission energy together with a decrease in the intersublevel spacing energies are shown to occur due to the thermal activated In–Ga interdiffusion. While, this behaviour is commonly explained as a consequence of the enrichment in Ga of the QDs, the appearance of an additional exited state for annealing temperatures higher than 650 °C suggests a variation of the intermixed QDs's volume/diameter ratio toward QDs's enlargement.     

Effect of temperature on the growth of InAs/GaAs quantum dots grown on a strained GaAs layer

We have studied the effect of temperature on the growth of InAs quantum dots (QDs) grown on a strained GaAs layer. The 2.0 nm thick, strained GaAs was obtained by growing it on a relaxed In0.15Ga0.85As layer. We observed that the density of QDs grown in this manner strongly depends on the growth temperature. A change in the growth temperature from 510 degrees C to 460 degrees C resulted in a large increase in the QD density from 2.3 x 10(10) cm(-2) to 6.7 x 10(10) cm(-2) and a sharp reduction in their height from 8.0 nm to 3.0 nm. Photoluminescence (PL) results from these QDs are also presented.     

Structural characterization of GaSb-capped InAs/GaAs quantum dots with a GaAs intermediate layer

GaSb incorporation to InAs/GaAs quantum dots is considered for improving the opto-electronic properties of the systems. In order to optimize these properties, the introduction of an intermediate GaAs layer is considered a good approach. In this work, we study the effect of the introduction of a GaAs intermediate layer between InAs quantum dots and a GaSb capping layer on structural and crystalline quality of these heterostructures. As the thickness of the GaAs intermediate layer increases, a reduction of defect density has been observed as well as changes of quantum dots sizes. This approach suggests a promising method to improve the incorporation of Sb to InAs heterostructures.     

InAs/GaAs multiple quantum dot structures grown by LP-MOVPE

Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal–organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence and atomic force microscopy were used as the main characterisation methods for the growth optimisation. The properties of multiple-stacked quantum dot structures are influenced by the thickness of the GaAs separation layers (spacers) between quantum dot-containing InAs layers, by the InAs layer thickness, by arsine partial pressure during growth, and by group III precursor flow interruption time.     

Site-controlled growth of InP/GaInP quantum dots on GaAs substrates

A technology platform for the epitaxial growth of site-controlled InP quantum dots (QDs) on GaAs substrates is presented. Nanoholes are patterned in a GaInP layer on a GaAs substrate by electron beam lithography and dry chemical etching, serving as QD nucleation centers. The effects of a thermal treatment on the structured surfaces for deoxidation are investigated in detail. By regrowth on these surfaces, accurate QD positioning is obtained for square array arrangements with lattice periods of 1.25?μm along with a high suppression of interstitial island formation. The optical properties of these red-emitting QDs (λ?～?670?nm) are investigated by means of ensemble- and micro-photoluminescence spectroscopy at cryogenic temperatures.     

Optimizing the spacer layer thickness of vertically stacked InAs/GaAs quantum dots

Vertically stacked multilayers of self-organized InAs/GaAs quantum dots (QDs) structures with different GaAs intermediate layer thicknesses varying between 2.8 and 17 nm are grown by solid source molecular beam epitaxy (SSMBE) and investigated by photoluminescence spectroscopy (PL). For 17 nm thick GaAs spacer, the PL spectra show two well separated features attributed to the formation of two QDs family with a bimodal size distribution indicating no correlation between the dots in different layers. In the meanwhile, the structures having thinner spacer thickness demonstrate single PL peaks showing an enhancement of high energy side asymmetrical broadening when increasing the excitation power. The corresponding emission energies exhibit a red shift when the spacer layer thickness decreases and correlated with the enhancement of the vertical electronic coupling as well as the rise of the QD's size in the upper layers induced by the build up of the strain field along the columns. The spacer thickness of 8.5 nm is found to yield the best optical properties.     

Effect of the bimodal size distribution on the optical properties of self-assembled Ge/Si(001) quantum dots

In situ reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy have been combined to investigate the effects of a bimodal size distribution and of the pyramid/dome transition on the optical properties of related Ge/Si layers. It is shown that the wetting layers are inhomogeneous in thickness due to the lateral diffusion of Ge from 2D layers towards islands, while no change is observed in the island-related photoluminescence. These results obtained indicate that 3D islands are, in their early nucleation stages, formed by consuming Ge from 2D layers, and that island luminescence energy is not sensitive to the vertical confinement inside islands.