Experimental and theoretical study of excitonic transition energies in GaAs/AlxGa1-xAs quantum wells.

Abstract

High-quality molecular-beam-epitaxy-grown decoupled GaAs-(Al,Ga)As multiple quantum wells (MQW) of various well thickness (2.7 \ensuremath{\le}${\mathit{L}}_{\mathit{W}}$\ensuremath{\le}11.9 nm; x\ensuremath{\approxeq}0.3) and different barrier compositions (0.12\ensuremath{\le}x=1; ${\mathit{L}}_{\mathit{W}}$\ensuremath{\approxeq}11 nm) have been studied by x-ray diffraction (XRD), photoluminescence excitation, and emission (PL). The temperature dependence of the MQW properties has also been studied. The well width and barrier composition of the MQW were obtained by XRD and PL, respectively. 2s-excitonic features and the free electron-hole sublevel transitions can be resolved. We compare the 1s-2s energy difference and the ground-state binding energies of the heavy- and light-hole excitons with a recent accurate theory of exciton binding energies, taking the structure parameters from an independent determination. Experimental and theoretical values of the heavy- and light-hole exciton binding energies are found to agree within 1 meV. The theoretically predicted and experimentally observed excitonic transition energies associated with the lowest (n=1) electron, heavy-hole, and light-hole sublevels agree well, if the theoretical approach includes the split-off valence band. Interpolation formulas for the heavy- and light-hole ground-state exciton binding energies and for the n=1 electron, heavy-, and light-hole sublevel energies are given.