Effect of barrier thickness on the luminescence properties of AlAs/GaAs multiple quantum wells grown by molecular beam epitaxy

Abstract

The influence of barrier layer thickness LB for LB >3 nm on the optical properties of all-binary AlAs/GaAs multiple quantum well heterostructures (MQWH) is studied by photoluminescence and excitation spectroscopy measurements at 2 K. In contrast to expectation for a simple coupling between the constituent GaAs quantum wells, MQWH samples with thinner barrier layers show excitonic peaks shifted to higher energies and exhibit a larger splitting between the electron to heavy-hole and electron to light-hole free excitons. This feature remains for different values of the otherwise constant well width within different series and when a small amount of Al is added to the well. Our detailed experimental data indicate that the mechanism responsible for the high-energy shift is intrinsic in nature. This unusual feature demonstrates the inadequacy of photoluminescence and excitation spectroscopy to determine well widths accurately.