Dislocation density and band structure effects on spin dynamics in GaN

Abstract

We present experimental results obtained on wurtzite epitaxial GaN layers grown on sapphire and SiC substrates. Thanks to a set of samples with different values of the residual strain, we demonstrate that the high dislocation density enhances the spin relaxation rate through the Elliott–Yafet mechanism. This fact is validated by the T−1 temperature dependence of the spin-relaxation times. The influence of the valence-band structure on the hole-spin relaxation is also highlighted. In particular, a decrease in the hole-spin relaxation rate, accompanied by a strong polarization rate (∼50%) of the differential reflectivity signal (ΔR/R), is observed when the splitting ΔEAB between the heavy-hole and the light-hole bands is larger than the broadening ΓA of the A excitonic transition. On the contrary, the overlap of the A and B resonances for ΓA>ΔEAB is responsible for a decrease in the ΔR/R polarization rate (∼10%) and an enhancement of the spin relaxation rate.