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Pseudodirect Excitons in GaAs/AlAs Type-II Superlattices

GaAs/AlAs II 型超晶格中的赝直接激子

基本信息

批准号：
05640382
负责人：
NAKAYAMA Masaaki
金额：
$ 1.41万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

I have investigated optical properties of a pseudodirect exciton consisting of an AlAs-X_Z electron and a GaAs-G heavy hole in GaAs/AlAs type-II superlattices (SLs) from the following viewpoints : (1) the oscillator strength of the pseudodirect exciton resulting from a G-X mixing effect in the conduction band, and (2) high density excitation effects such as the formation of biexcitons.All samples were grown on a (001) semi-insulating GaAs substrate grown by molecular-beam epitaxy : (GaAs)_m/(AlAs)_m[(m, m)]SLs with m=8-13 monolayrs and (GaAs)_<10>/(AlAs)_n[(10, n)]SLs with n=10-20 monolayrs.I have obtained the following research results.(1) The relative oscillator strength of the pseudodirect exciton to the direct exciton as a function of the layr thickness is estimated from the experimental results obtained by photoluminescence (PL), PL-excitaion, and PL-decay-time measurements. The values of the relative oscillator strength in the (m, m) SLs are around 1x10^<-4> and independent of the layr thickness.In the (10, n) SLs the relative oscillator strength decreases from-1x10^<-4> to -1x10^<-5> with the increase of n.The G-X mixing factor producing the oscillator strength is estimated by using a first order perturbation theory.It is concluded that the G-X mixing factor is determined by the overlap of the envelope functions of the G and X_z electrons.(2) From the excitation-power dependence of the pseudodirect-exciton PL,it has been found for the first time that the biexcitons (exciton molecules) are sufficiently formed at an extremely low excitation power (-1 mW/cm^2) which is two-or three-order lower than in direct-transition-type GaAs quantum wells.The line shape analysis of the biexction PL band indicates that the biexciton-binding energy is about 3 me V.The observed decay time of the biexciton PL is about a half of that of the free exciton, whitch is a typical property of the biexciton dynamics.

我从以下角度研究了GaAs/AlAs II型超晶格（SL）中由AlAs-X_Z电子和GaAs-G重空穴组成的赝直接激子的光学性质：（1）导带中G-X混合效应产生的赝直接激子的振荡强度，以及（2）高密度激发效应，例如形成双激子。所有样品均生长在通过分子束外延生长的 (001) 半绝缘 GaAs 基板上：(GaAs)_m/(AlAs)_m[(m, m)]SL，m=8-13 单层和 (GaAs)_<10>/(AlAs)_n[(10, n)]SL，n=10-20 单层。获得了以下研究成果。（1）根据光致发光（PL）、PL-激发和PL-衰减时间测量获得的实验结果估计了赝直接激子与直接激子的相对振荡强度作为层厚度的函数。 (m, m) SL 中的相对振荡强度值约为 1x10^<-4> 且与层厚度无关。在 (10, n) SL 中，相对振荡强度随着 n 的增加从-1x10^<-4> 减小到 -1x10^<-5>。使用一阶微扰理论估计产生振荡强度的 G-X 混合因子。得出的结论是 G-X混合因子由G和X_z电子包络函数的重叠决定。(2)从赝直接激子PL的激发功率依赖性中,首次发现双激子(激子分子)在比激发功率低两到三数量级的极低激发功率(-1 mW/cm^2)下充分形成。双激子PL带的线形分析表明，双激子结合能约为3 me V。观察到的双激子PL衰减时间约为自由激子衰减时间的一半，这是双激子动力学的典型特性。