Picosecond and subpicosecond laser spectroscopy experiments in semiconductors have recently allowed the probing of the ultrafast relaxation dynamics of photogenerated electron hole plasmas. These experiments provide information germane to the temporal evolution of the hot carrier distributions. This knowledge is important, both for the understanding of the fundamental physics of the relaxation processes involved and for the technology of device development.
The luminescence of weakly photoexcited heavily doped semiconductors has been studied, where the number of photogenerated electron hole pairs is small with respect to the number of ionised donors or acceptors. In this case, the time resolved luminescence is directly related to the evolution of the distribution of the minority carriers and theorectical difficulties are considerably reduced as both the lattice and the majority carrier bath are at thermodynamic equilibrium. Luminescence spectroscopy of p-doped indium phosphide has been undertaken on a femtosecond time scale in order to elucidate the dynamics of the electrons photoexcited high in the Gamma valley by an ultrashort optical pulse.
The work has enable the elucidation of several relaxation mechanisms for hot electrons produced by ultrashort optical excitation in the Gamma of both intrinsic and doped indium phosphide. It provides an experimental and theoretical foundation for ongoing and planned studies of doped quantum confined semiconductor structures using tunable femtosecond laser techniques.