Optical characterization of hexagonal CdS layers grown on GaAs(111) by MBE: application of phase-shift-difference spectroscopy

摘要

Excitonic properties of hexagonal CdS epilayers grown on GaAs(111)A and B substrates by MBE have been investigated by means of a phase-shift-difference (PSD) spectroscopy in which the phase-shift of light upon reflection was measured. It is confirmed that the peak energy positions of the PSD spectrum correspond to the excitonic resonance energies by using CdS bulk crystal. The distinct transitions of A- and B-excitons were observed in the PSD spectra for the hexagonal CdS epilayers. Furthermore, new excitonic transition was found for the epilayers at the energy slightly below the resonance energy of the A-exciton. This transition was observed clearly for the epilayer on GaAs(111)A compared with that on GaAs(111)B, and was not observed for CdS bulk. Thus the new transition can be explained by a model of the exciton bound to staking faults that form a quantum well of cubic structure in the hexagonal epilayer. It is shown that stacking faults are potential well for electrons and potential barriers for holes.