Effects of hot electron nonlinear transport in ultrafast photoretractive response

本研究的目的是研究半绝缘半导体中的超快光折变（PR）响应。特别是，我们专注于热电子的非线性输运的光激发空间电荷场的动力学的影响。本研究的主要结果如下.我们对直流偏置半绝缘GaAs中包含热电子非线性输运的皮秒PR效应进行了理论推导和数值计算。有人发现，空间电荷场的大小增加了一个因素，由于电子温度的大幅增加。研究还发现，超热电子的非线性输运引起了高电场畴的集体太赫兹振荡，导致了空间电荷场相位的同样振荡行为.从理论和实验两方面阐明了晶体温度对皮秒光折变效应的影响。实验结果表明，虽然光生自由载流子光栅引起的瞬态能量转移具有较弱的温度依赖性，但在皮秒光折变效应和双光子吸收中没有观察到这种依赖性。这一实验结果也得到了理论分析的支持。

The purpose of this study is to investigate ultrafast photorefractive (PR) responses in semiinsulating semiconductors. In particular, we focus on the effect of hot electron nonlinear transport on the dynamics of photoexcited space-charge fields. The main results of this study are listed below.1. We carried out formulation and numerical calculation of the picosecond PR effect that includes the hot electron nonlinear transport in DC-biased semi-insulating GaAs. It was found that the magnitude of the space-charge field is increased by a factor of one owing to a large increase of the electron temperature. It was also found that the hot electron nonlinear transport gives rise to a collective teraherz oscillation of high electric field domains, leading to the same oscillatory behavior in the space-charge field's phase.2. We clarified the effect of crystal-temperature on the picosecond PR effect, both theoretically and experimentally. Experimental results showed that although the transient energy transfer caused by photo-induced free carrier gratings had a week temperature dependence, such a dependence was not observed in the picosecond PR effect and two-photon absorption. This experimental finding was also supported by the theoretical analysis.