High-density-excitation states in GaAs/AlAs type-II superlattices

GaAs/AlAs II 型超晶格中的高密度激发态

基本信息

批准号：
09640404
负责人：
NAKAYAMA Masaaki
金额：
$ 1.86万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640404/
关键词：
superlattice GaAs AlAs type-II photoluminescence exciton high-density-excitation state biexciton electron-hole droplet

项目摘要

High-density-excitation effects on photoluminescence (PL) properties in GaAs/AlAs type-II superlattices (SLs) have been investigated from the aspects of biexcitons and electron-hole droplets. The structures of (GaAs)_m/(AlAs)_n SL samples are as follows : (m, n)=(10, 10), (12, 12), (13, 13), (10, 14), and (10, 20), where m and n indicate the thickness of the GaAs and AlAs layers in monolayer (ML) units (1 ML=0.283 nm), respectively. In the SLs, the lowest-energy exciton consists of the X electron and F heavy hole which are confined in the AlAs and the GaAs layers, respectively : so-called the type-II exciton. The lifetime of the type-Il exciton is of the order of *is : This leads to the advantage for the formation of the high-density-excitation state. Following results have been obtained.1. The biexciton formation is observed under the very low excitation-power condition around 10 mW/cm^2. From the line-shape analysis of the PL bands, the biexciton binding energies are estimated to be 2.5-3.5 mV.The layer-thickness dependence of the biexciton binding energy reveals the following facts : The quantum confinement of the electron and hole increases the binding energy, while the spatial separation decreases it. From time-resolved PL spectra, the transient processes of the formation and decay of the type-II biexciton are clearly detected.2. Under the excitation-power condition three-orders higher than that for the biexciton formation, a novel PL band with a threshold nature in the excitation is observed on the low-energy side of the biexciton band. The shape of the PL band dose not change with the excitation power, and its lifetime is much faster than that of the biexciton PL.These results suggest that the PL band results from the formation of electron-hole droplets. The PL-band shape is explained by a conventional model for electron-hole droplets used in indirect-transition-type semiconductors.

从双激子和电子空穴液滴的角度研究了高密度激发对 GaAs/AlAs II 型超晶格 (SL) 光致发光 (PL) 性能的影响。 (GaAs)_m/(AlAs)_n SL样品的结构如下： (m, n)=(10, 10), (12, 12), (13, 13), (10, 14), 和 ( 10, 20)，其中m和n分别表示单层(ML)单元中的GaAs和AlAs层的厚度(1 ML=0.283 nm)。在 SL 中，最低能量的激子由 X 电子和 F 重空穴组成，它们分别被限制在 AlAs 和 GaAs 层中：即所谓的 II 型激子。 II型激子的寿命为*is量级：这导致有利于形成高密度激发态。得到如下结果： 1．在 10 mW/cm^2 左右的极低激发功率条件下观察到双激子的形成。根据 PL 带的线形分析，双激子结合能估计为 2.5-3.5 mV。双激子结合能的层厚度依赖性揭示了以下事实：电子和空穴的量子限制增加了结合能量，而空间分离会降低能量。从时间分辨PL光谱中，可以清楚地检测到II型双激子的形成和衰变的瞬态过程。 2．在比双激子形成高三个数量级的激发功率条件下，在双激子带的低能侧观察到具有激发阈值性质的新PL带。 PL带的形状不随激发功率的变化而变化，并且其寿命比双激子PL的寿命快得多。这些结果表明PL带是电子空穴液滴形成的结果。 PL 带形状可以通过间接跃迁型半导体中使用的电子空穴液滴的传统模型来解释。