Sub-picosecond raman spectroscopy of semiconductors

Abstract

Recent advances in laser and optical detector technology have made it possible to perform time resolved Raman scattering experiments on opaque semiconductors with sub-picosecond temporal resolution. This has allowed us to directly study the initial stages in the relaxation of energetic carriers in 111-V semiconductors such as GaAs and Gal1-xAlxAs. The generation of a non-equilibrium population of longitudinal optic (LO) phonons by a well characterized population of energetic carriers has been temporally resolved in GaAs. Changes in the screening of the LO phonons due to the creation of a high density of hot carriers and their cooling have also been observed. These studies have been extended to the alloy system Gal1-xAlxAs to characterize the changes introduced into the hot carrier relaxation processes by alloy disorder effects. The modification of the carrier relaxation processes due to the presence of strong carrier-carrier scattering was observed using the hot luminescence which accompanied the Raman scattering at high excitation levels. © 1987 SPIE.