MOCVD grown GaAs and InP epitaxial layers have been studied using photoreflectance spectroscopy. Homogeneous and heterogeneous structures were employed to investigate the influence of the mismatch induced strain and dislocations. All the tested spectra contained a sharp peak related to the fundamental absorption edge and a pronounced Franz-Keldysh oscillation. The data analysis revealed a consistent difference in bandgap, temperature coefficients of the bandgap, and surface electric
field, in the order of the degree of mismatch. For GaAs/GaAs and GaAs/Si samples, the bandgaps derived from the three point method were 1.436 and 1.324eV, respectively. Values of 1.334, 1.325, and 1.294 eV for the bandgap were found for InP/InP, InP/GaAs, and InP/GaAs/Si, respectively. For GaAs epitaxial layers, the intensity of the surface
field bore a ratio of 1.18:1 between GaAs and Si substrates. For InP epitaxial layers, the ratio was 1.23:1.12:1 in the sequence of InP, GaAs, and GaAs/Si substrates. Such a measure must be related to the mismatch in the heteroepitaxy structures. A shoulderlike peak, 18-23 meV below the gap-energy peak (Eo), was found for GaAs samples, which could be impurity related. A broad shoulder-like peak 30 meV below the fundamental absorption edge was also observed only for InP/GaAs/Si and hence attributed to some shallow defect levels induced by antiphase disorder.