Extrinsic photoluminescence from GaAs quantum wells

Extrinsic photoluminescence has been observed from a number of undoped GaAs- AlₓGa_1-x As multiquantum-well samples grown by molecular beam epitaxy. For quantum wells of width Lz300 {} this luminescence is typically only a few percent of the intrinsic luminescence and it decreases with decreasing Lz. Single quantum-well samples doped with [Be]{~}10¹⁷ cm^-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(A⁰) 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(A⁰) increases with decreasing Lz. These results on E(A⁰) are compared with the recent theoretical results of Bastard on the binding energy of hydrogenic acceptors as a function of Lz and position in the well. Other data on the extrinsic photoluminescence of single and multiquantum samples are also presented.