Investigation of Nonequilibrium Many-Body Effects in Semiconductors

本征半导体的光谱光学性质 它们的基本吸收边附近由 光子和元激发之间的相互作用， 材料 最重要的过程之一是吸收 光子通过同时激发一个电子从 原本满的价带进入原本空的传导 乐队 导带电子和价带空穴是量子的， 机械准粒子 这项建议的目的是 非平衡性质的实验和理论研究 共振产生高密度电子-空穴对系统 通过飞秒激光激发。 一个高密度 半导体中的非热载流子分布非常复杂， 目前所知甚少。 这些研究将使用最先进的 飞秒激光，并将重点放在获得信息的 （1）如何有效的筛查归因于 电子-空穴的非平衡分布， 从准热平衡分布的筛选;（2） 我们如何描述与 从非平衡态到准平衡态载流子的演化 （3）人口的时间尺度是什么？ 热化，以及多体库仑效应何时变得 （4）在什么条件下可以观察到光学 增益（非平衡增益），以及相关的时间尺度是什么 实现人口反转。 使用大约10倍的激光脉冲 fs，半导体的动力学将从 从初始非平衡态到准热平衡态。 的 将要研究的半导体包括CdS（或CdSe），GaAs， 和GaAs-Al GaAs多量子威尔斯阱。

The optical properties of intrinsic semiconductors in the spectral vicinity of their fundamental absorption edge are determined by the interaction between photons and elementary excitations with the material. One of the most important processes is the absorption of a photon by means of simultaneous excitation of an electron from the originally full valence band into the originally empty conduction band. Conduction-band electrons and valence-band holes are quantum- mechanical quasi-particles. The aim of this proposal is an experimental and theoretical study of nonequilibrium properties of a high-density elecron-hole-pair system, which is generated resonantly by femtosecond laser excitation. The behavior of a high-density nonthermal carrier distribution in semiconductors is very complex and presently little is known. The studies will use state-of-the-art femtosecond laser and will focus on obtaining information on the following topics: (1) how effective is the screening attributable to a nonequilibrium electron-hole distribution, and how does it differ from the screening of a quasi-thermal equilibrium distribution; (2) how does one describe the dynamics of screening associated with the evolution from nonequilibrium to quasi-equilibrium carrier distributions; (3) what is the time scale for population thermalization, and when do the many-body Coulomb effects become dominant; (4) under what conditions is it possible to observe optical gain (non-equilibrium gain), and what are the relevant time scales to obtain a population inversion. Using laser pulses of approximately 10 fs, the dynamics of the semiconductors will be followed from the initial nonequilibrium state to quasi-thermal equilibrium. The semiconductors that will be investigated include CdS (or CdSe), GaAs, and GaAs-A1GaAs multiple quantum wells.