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Direct bandgap InxGa1-xP/GaAs heterostructure has received increased attention as an alternative to AlyGa1-yAs/GaAs system, due to the attractive properties of InxGa1-xP, e.g., it is lattice- matched to GaAs and is more superior to AlyGa1-yAs in terms of number of deep level traps and susceptibility of surface oxidation. For the fundamental and applied purposes, knowledge of anisotropic effect on the optical properties of InxGa1-xP is often important. Spectroscopic ellipsometry (SE) is known as a sensitive optical tool for nondestructive characterization of semiconductor materials. In this research, SE was used to investigate anisotropic effect on the optical properties of InxGa1-xP. Each of the two samples used contained an undoped and ordered (100) In0.48Ga0.52P thin layer grown on a semi-insulating (100) GaAs substrate by metal-organic chemical vapor deposition. SE measurements were carried out in room-air with the sample cross-sections [011] and [-011] oriented parallel to the normal of the incidence plane, respectively. In the data analysis, the optical properties of InxGa1-xP were extracted via a fitting model which included the effects of the native oxide overlayer. We determined the critical point (CP) energies of InxGa1-xP by fitting the second derivative of the measured dielectric function spectra to a standard analytic lineshape. For each sample studied, our results clearly show a shift in energy for each chosen CP, when the sample cross sections [011] and [-011] were oriented parallel to the normal of the incidence plane, respectively. We believe that this shift is directly related to the anisotropic effect on the optical properties of InxGa1-xP.
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