Extrinsic photoluminescence from GaAs quantum wells

Abstract

Extrinsic photoluminescence has been observed from a number of undoped GaAs- ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}$ As multiquantum-well samples grown by molecular beam epitaxy. For quantum wells of width $L_z\lesssim 300$ Å 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]∼${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are found to exhibit extrinsic and intrinsic luninescence comparable in intensity. This extrinsic luminescence is believed due to the recombination of $n=1\mathrm{}$ 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 $E\left(A^0\right)$ 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 $E\left(A^0\right)$ increases with decreasing $L_z$. These results on $E\left(A^0\right)$ 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.