Abstract

There has been a great deal of interest in the physics of spin relaxation in III-V semiconductors[1, 2, 3]. Much of the attention has been focused on spin polarized conduction band electrons, which relax relatively slowly in comparison with spin polarized holes and are, therefore, more accessible to experimental studies. Because of the strong spin-orbit interaction and coupling of the quasi-momentum and the angular momentum of the holes in III-V compounds[1, 2], the spin relaxation of holes in a undeformed cubic crystal of the GaAs type is extremely fast — on the scale of the momentum relaxation time or in the femtosecond time domain. Direct observation of optical orientation and relaxation of spin-polarized holes in bulk GaAs is, therefore, very difficult. On the other hand, in quantum wells [4, 5, 6, 7], because of the modification of the valence band structure, a significant change in the hole-spin relaxation dynamics near the zone center leading to a substantial increase in the spin relaxation time is expected. Hole spin relaxation times in quantum wells ranging from 4 ps[6] to as long as 1 nsec[7], depending upon the doping levels, temperature, and quantum well structures, have been reported. In this paper, we report the direct observation of optical orientation and the subsequent relaxation of spin-polarized holes in undoped bulk GaAs at room temperature, using time-and polarization-resolved femtosecond spectroscopy.

© 2002 Optical Society of America