EXCITONIC ABSORPTION IN CDTE-BASED PIEZOELECTRIC QUANTUM-WELLS

We have investigated excitonic effects in piezoelectric quantum wells by using a two-parameter variational approach. One parameter is used to describe the spatial extension of the exciton, and the other one to characterize its anisotropy. It is shown that in wide piezoelectric quantum wells, all excitonic effects are controlled by the quantum-confined Stark effect, which tends to localize electrons and holes on opposite interfaces of the quantum well. Hence, in contrast to the case of square quantum wells, excitons in wide piezoelectric quantum wells have an enhanced two-dimensional character, with a binding energy inversely proportional to the well width. We have also calculated exciton absorption using one or two variational parameters, or simply electron-hole overlap integrals. It is found that only the two-parameter variational approach can provide a good quantitative agreement with exciton absorption data we have measured in CdTe square quantum wells and piezoelectric quantum wells.