Surface photovoltage in semiconductors under pulsed optical excitation, and its relevance to synchrotron radiation spectroscopy

We used the SuperACO Free Electron Laser (FEL) to excite photocarriers in semiconductors at room temperature, and synchrotron radiation photoemission spectroscopy to measure the consequently induced surface photovoltage (SPV), The natural synchronization between the two sources allowed us to study with sub-nanosecond resolution the temporal dependence of the non-equilibrium charge carrier distribution for two prototype systems, Ag/GaAs(110) and Si(111)2 x 1. We found that to correctly interpret the effects of the SPV on the band position, the interplay between instrumental factors (pulse duration and repetition rate) and semiconductor parameters (such as surface and bulk recombination rates) must be taken into account. Since the FEL has the typical temporal structure of a synchrotron radiation source and a flux comparable to the one obtainable at third generation storage rings, these results are of relevance to the most advanced spectroscopic techniques used to study the electronic structure of semiconductors; therefore, in this paper we discuss the possible effects of intense synchrotron radiation beams on position and lineshape of photoemission features at semiconductor surfaces. (C) 1998 Elsevier Science B,V. All rights reserved.