OPTICAL-PROPERTIES OF ULTRATHIN GAAS-LAYERS EMBEDDED IN ALXGA1-XAS

We present a comparison between the predictions of two theoretical mod els and experimental results on ultrathin GaAs layers with a thickness in the range from 1 to 8 ML embedded in bulk (AlxGa1-x)As, 0.30 less than or equal to x less than or equal to 0.34. The theoretical predict ions, obtained from an empirical tight-binding Green's-function approa ch and from the usual effective-mass approximation, are compared to ph otoluminescence and photoluminescence excitation data of a set of mult iple quantum-well samples grown by metal-organic vapor-phase epitaxy o n substrates with different misorientations. We find that the optical transitions are narrower in samples with slightly misoriented substrat es, although their spectral position remains unchanged. This suggests that the substrate misorientation favors a good quality of the ternary alloy. The observed optical transitions of our thin layers compare we ll with the predictions of both models. However, the lack of a reliabl e exciton theory for such ultrathin layers becomes apparent.