Electron spin relaxation and photoluminescence of Zn-doped GaAs

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The luminescence generated by circularly polarized light has been analyzed to yield a number of characteristics of epilayers of GaAs covered with ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ and doped with Zn to give ${N}_{A}=5\ifmmode\times\else\texttimes\fi{}{10}^{17}$ to 2 \ifmmode\times\else\texttimes\fi{} ${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The measurements on these epilayers were obtained over a temperature range $T\ensuremath{\sim}6$ to 200 K. The main emphasis was on the electron spin relaxation time ${\ensuremath{\tau}}_{s}$ and the electron lifetime $\ensuremath{\tau}$, both determined via the depolarization of the circularly polarized luminescence in a transverse magnetic field (Hanle effect). Other observations include the photoluminescent spectrum along with its polarization dependence and the integrated photoluminescent intensity plus its dependence on the excitation intensity. In marked contrast to earlier work, we find ${\ensuremath{\tau}}_{s}$ essentially independent of ${N}_{A}$ and \ensuremath{\sim} 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ sec, an order of magnitude larger than previously reported for ${N}_{A}=4\ifmmode\times\else\texttimes\fi{}{10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. These observations and the insensitivity of ${\ensuremath{\tau}}_{s}$ to temperature at low $T$ are attributed to a resonant virtual photon electron-hole exchange mechanism for a degenerate hole distribution. Furthermore, $\ensuremath{\tau}$ is nearly independent of $T$ at low temperatures and ${N}_{A}$ for high doping levels. The experimental value of $\ensuremath{\tau}$ in this region, \ensuremath{\sim} 4.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ sec, is believed to be mainly radiative and is in agreement with theoretical expectations. Other aspects of the data presented are also discussed.