A STUDY OF FRANZ-KELDYSH OSCILLATIONS OF GAAS SI/GAAS AND ALAS/SI/ALAS HETEROSTRUCTURES/

We have carried out a detailed study of Franz-Keldysh oscillations obs erved in the photoreflectance spectra of molecular beam epitaxy grown GaAs/Si/GaAs and AlAs/Si/AlAs heterostructures with a Si nominal thick ness of two monolayers. The oscillations in the photoreflectance spect ra were due to internal electric fields generated by graded p-n juncti ons created by Si diffusion. The data were analyzed employing the asym ptotic Franz-Keldysh theory. It is concluded that different contributi ons from degenerate heavy and light hole bands, to transitions around the Gamma point of the Brillouin zone, must be expected for different heterostructures depending upon the particular characteristics of the internal electric fields present in the sample.