Photoreflectance spectroscopy study of built-in electric fields in stressed GaAs/GaAsP superlattices

The photoreflectance spectroscopy method has been used to study stressed GaAs/GaAs$_{0.6}$P$_{0.4}$ superlattices grown along the [100] and [111] directions. An analysis of the Franz-Keldysh oscillations observed in photoreflectance spectra determines the built-in fields in these superlattices. The fields amount to 80 kV cm$^{-1}$ for the (100) orientation and 430 kV cm$^{-1}$ for the (111) orientation. The difference has been explained by the presence of a strain-induced piezoelectric field in stressed superlattices grown along the [111] direction.