Reflectivity of high-energy electron beams at an MBE growing surface is calculated for varying layer thicknesses and glancing angles of the electron beam. In order to investigate some fundamental behaviors of RHEED intensity oscillations during MBE growth, we introduce a ''simple potential model'', which is a step-like potential for each uncompleted growing layer. The depth of the growing layer potential is assumed to be in direct proportion to the coverage of the layer. We also introduce a realistic crystal potential in the calculation to check the ''simple potential model''. A birth-death growth model is assumed in these calculations. It is found that the potential of the growing surface layer plays an important role in the phase-shift and frequency-doubling phenomena which are observed in experimental RHEED intensity oscillation curves. These phenomena can be explained by the averaged potential in the growing layer instead of the realistic potential.
