Optical Pumping and Photoluminescence Detection of Spin-polarized Electrons in Uniaxially Stressed Gallium Arsenide*

This work describes the development and application of an optical pumping and photoluminescence experiment for electron spin polarization measurements on semiconductor photocathode materials. We discuss the spin polarization increase that is produced by applying a uniaxial compression to a gallium arsenide crystal and selectively optically pumping the transition between the upper strain-split valence band and the conduction band. The electron spin polarization is measured by analysing the circular polarization of the photoluminescence. The relation between luminescence and spin polarizations is given by T P S u = 'h's rS + rr where P o is the luminescence circular polarization+ Ps is the spin polarization, and Ph is the hole coupling factor. For band edge excitation Ph is identical to Ps. In this expression, rs and rr are the spin relaxation and luminescence recombination times, respectively. From our data we infer an increase in Ps from 50% at zero stress to 70% for an applied COO11 stress of 4.0 x 10' -2 dyn cm in a 1 x 10 18 p-type GaAs crystal at T = lOOoK. For comparison, the maximum theoretical polarization at infinite stress is 80%.