Spin relaxation of holes in the split-hole band of InP and GaSb

Abstract
We report spin-orientation experiments for photoexcited holes in the spin-orbit-split valence band created by optical pumping with circularly polarized light near k=0. The degree of circular polarization of the E0+Δ0 luminescence, which measures directly the spin orientation of the thermalized holes, is studied as a function of the excitation energy for n-type InP (with different doping levels ranging from 5×1015 to 5×1017 cm3) and for n-type GaSb (1.8×1018 cm3). We observe no dependence of the polarization degree on doping in InP. The degree of polarization decreases similarly with increasing photon energy in InP and GaSb, materials with very different spin-orbit splittings. Several spin-relaxation mechanisms are discussed. The data are analyzed on the basis of the Dyakonov-Perel spin-relaxation mechanism. The effect of scattering between split-hole, light-hole, and heavy-hole bands is also considered. The Dyakonov-Perel mechanism seems to be dominant for hole excitations up to 0.5 eV above the E0+Δ0 gap. From a fit of the experimental depolarization curves we obtain reasonable momentum relaxation times for holes of the order of 100200 fs in InP and 200300 fs in GaSb.