K-Dependence of the Electron Spin-Flip Time in GaAs

Abstract

The k‐dependence of the electron spin flip time (τsf) in undoped GaAs is experimentally determined for the first time. Time‐resolved optical orientation under strong optical injection is used to directly obtain τsf, which monotonically decreases by more than one order of magnitude when the electron k‐vector varies from 0 to 2.5×106 cm−1. Our results are well reproduced by a Monte‐Carlo simulation of the electron‐hole scattering and demonstrate that, at low lattice temperatures, the main spin flip mechanism of conduction band electrons is the Bir‐Aronov‐Pikus, i.e. a spin relaxation mechanism based in the exchange of spins between electrons and depolarized holes. We also show with the simulations that many body effects, such as phase space filling, result in an increase of τsf with excitation density.