PHOTOREFLECTANCE CHARACTERIZATION OF CDTE THIN-FILMS GROWN BY MOLECULAR-BEAM EPITAXY ON GAAS(100)

CdTe films have been grown on top of GaAs(100) by means of Molecular B eam Epitaxy (MBE) at 300-degrees-C substrate temperature. Different pr ocedures for the CdTe growth and for the preparation of the GaAs subst rates resulted in diverse crystalline qualities of the CdTe films. We present the results obtained from PhotoReflectance (PR) measurements o f these films employing HeNe and Ar-ion lasers as modulating excitatio n. For Ar excitation, the ratio of CdTe to GaAs signal strength for th e E0 transition is enhanced, allowing a differentiation of the contrib utions from film and substrate. Both the PR line shape and intensity a re correlated to the structural quality of the CdTe films. One of the samples presented a below-band-gap transition of the GaAs substrate ar ound 30 +/- 5 meV from E0 which is attributed to donor states produced by Te atoms diffused in the interface; this result demonstrates the h igh sensitivity of the photoreflectance technique to the structural pr operties of interfaces.