Picosecond and femtosecond spectroscopy of highly excited charge carriers in semiconductors: theory

Abstract

Time-resolved luminescence, absorption and four-wave-mixing spectroscopy in the picosecond and femtosecond regimes are currently the most efficient experimental methods for studying energy and phase relaxation rates of highly excited charge carriers in solids. Here most of the effort concerns semiconductors, as these relaxation rates will determine and limit the efficiency of future generations of ultrafast electronic and optoelectronic devices. The following survey describes some attempts at a detailed analysis of recent experimental luminescence and absorption data covering a representative range of materials, spectral regimes and excitation densities. In spite of the fact that nanostructures are at the focus of present-day technological developments our discussion is limited to experiments on unstructured semiconductors, because the much simpler electronic structure of bulk materials will make it easier to realize the essentials of an extremely transient generation and relaxation dynamics of charge carriers and its description by appropriate Monte Carlo or quantum transport techniques.