Extrinsic photoluminescence from GaAs quantum wells

Extrinsic photoluminescence has been observed from a number of undoped GaAs- AlₗGa₁-ₗ As multiquantum-well samples grown by molecular beam epitaxy. For quantum wells of width Lₙ300 this luminescence is typically only a few percent of the intrinsic luminescence and it decreases with decreasing Lₙ. Single quantum-well samples doped with Be10^17 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 (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 Lₙ. 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 Lₙ and position in the well. Other data on the extrinsic photoluminescence of single and multiquantum samples are also presented.