A study of Franz–Keldysh oscillations of GaAs/Si/GaAs and AlAs/Si/AlAs heterostructures

Abstract
We have carried out a detailed study of Franz–Keldysh oscillations observed in the photoreflectance spectra of molecular beam epitaxy grown GaAs/Si/GaAs and AlAs/Si/AlAs heterostructures with a Si nominal thickness of two monolayers. The oscillations in the photoreflectance spectra were due to internal electric fields generated by graded pn junctions created by Si diffusion. The data were analyzed employing the asymptotic Franz–Keldysh theory. It is concluded that different contributions from degenerate heavy and light hole bands, to transitions around the Γ 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.