Extrinsic photoluminescence from GaAs quantum wells

Abstract

Extrinsic photoluminescence has been observed from a number of undoped GaAs- ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}$ As multiquantum-well samples grown by molecular beam epitaxy. For quantum wells of width ${L}_{z}\ensuremath{\lesssim}300$ \AA{} this luminescence is typically only a few percent of the intrinsic luminescence and it decreases with decreasing ${L}_{z}$. Single quantum-well samples doped with [Be]\ensuremath{\sim}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ are found to exhibit extrinsic and intrinsic luninescence comparable in intensity. This extrinsic luminescence is believed due to the recombination of $n=1$ electrons with neutral acceptors in the quantum wells, carbon in the case of the undoped material. Estimates of the binding energy of the neutral acceptors $E({A}^{0})$ from the measured free heavy-hole exciton energy gap of the quantum wells, the heavy-hole exciton binding energy, and the energy of the peak of the extrinsic photoluminescence, show that $E({A}^{0})$ increases with decreasing ${L}_{z}$. These results on $E({A}^{0})$ are compared with the recent theoretical results of Bastard on the binding energy of hydrogenic acceptors as a function of ${L}_{z}$ and position in the well. Other data on the extrinsic photoluminescence of single and multiquantum samples are also presented.