STUDIES AND MODELING OF GROWTH UNIFORMITY IN MOLECULAR-BEAM EPITAXY

We have developed a numerical model for the flux distribution in molecular beam epitaxy over stationary and rotating substrates. The existence of a temperature profile along the crucible and accumulation of material at the crucible orifice is taken into account. The influence of melt level tilt on the flux distribution is discussed in detail, and, in contrast to previous reports, is found to be small for the cases considered. Accurate thickness maps of GaAs wafers grown with two different types of effusion cells on stationary substrates were obtained using a scanning reflectance system. Excellent agreement of these experimental results with predictions of the model is demonstrated. We explain some of the deficiencies of the present arrangement and calculate the optimum system conditions for obtaining uniformity across a wafer to better than +/- 0.3%.