Electric field effects in photoreflectance spectra of ZnSe epilayers grown on GaAs by molecular beam epitaxy

Photoreflectance (PR) is used to investigate the internal electric field of a series of ZnSe/GaAs heterostructures having different layer thicknesses. The room and low temperature PR spectra exhibited Franz-Keldysh oscillations at energies above the ZnSe band gap. From the period of these oscillations, the electric field at the ZnSe/GaAs interface was determined and behaviour decreasing with temperature was observed. The calculated values for the electric field (10-50 kV cm-1) are in agreement with the typical values in semiconductors. The dependence of the electric field on the layer thickness is attributed to the presence of additional states introduced by the misfit dislocations that are formed to relieve the epilayer strain