Time-Resolved Observation of Photo-Generated Carrier Transport Dynamics on Semiconductor Surface Based on Femtosecond Core-Level Photoelectron Spectroscopy

Abstract

Time-resolved photoelectron spectroscopy based on high-order harmonic source is a promising technique for directly measuring ultrafast electron dynamics in various solid state materials. In this article, we review the recent technological progress of this technique, and introduce our study of ultrafast photogenerated carrier dynamics on a semi-insulating GaAs surface using femtosecond time-resolved corelevel surface photoelectron spectroscopy. We observed a transient change in surface potential where the Ga 3d-core level photoelectron peak instantaneously shifted by about 350 meV towards a higher binding energy within 2 ps of a 100-fs laser irradiation. A comparison of the experimental result with numerical simulations based on a drift-diffusion model of a semi-insulating semiconductor revealed that the transient surface potential change is mainly due to the dynamical photo-Dember effect, in which the large difference in the carrier diffusion between electron and hole instantaneously induces surface photovoltage.