Hole polarization and slow hole-spin relaxation in an n-doped quantum-well structure

We present a study of the dependence of the hole-spin relaxation on the electron density in an n-modulation-doped 75-Å GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum well by using cw and time-resolved photoluminescence techniques, at low temperature. The electron concentration has been continuously varied from ${10}^{11}$ to ${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$. A slow hole-spin relaxation time has been found (≊1 ns). A polarization decrease has also been observed when the in-plane wave vector of the photocreated holes increases. Calculations are presented which qualitatively support the latter experimental findings.