Electron-spin relaxation in p-type quantum wells via the electron-hole exchange interaction: The effects of the valence-band spin mixing and of an applied longitudinal electric field

The spin-relaxation time of the photogenerated electrons in p-doped quantum wells of GaAs is calculated. The spin-flip mechanism investigated is due to the electron-hole scattering by the exchange interaction. We have shown that the inclusion of the spin mixing of the valence holes has a dual effect. On one hand, it increases the spin-flip scattering rate by enlarging the hole density of states. On the other hand, the exchange strength weakens due to the valence spin mixing. The combined effect is a partial compensation, leaving the spin-relaxation times of the electrons similar to those obtained assuming holes having pure-spin states. We have also investigated the changes on the spin relaxation brought about by an applied electric field along the quantum well growth direction, and we have calculated longer spin relaxation as the field strength increases. Such behavior is characteristic of the exchange spin-flip channel and, if experimentally observed, it will indicate the dominant role played by the type of spin relaxation we have studied in this work.