Real-time optical diagnostics for measuring and controlling epitaxial growth

Abstract We summarize recent applications of two real-time optical diagnostic techniques, reflectance difference spectroscopy (RDS) and spectroellipsometry (SE), to epitaxial growth on GaAs and atomic layer epitaxy (ALE) in particular. Using RDS, we obtain the first real-time spectroscopic data of the evolution of the (001) GaAs surface to cyclic and non-cycle exposures of atmospheric pressure H 2 , H 2 and trimethylgallium, and H 2 and arsine, which simulate growth by ALE. None of our observations is consistent with any previously proposed simple model, emphasizing the necessity of real-time measurements for the analysis of complex surface reactions. Using SE we have constructed a closed-loop system for controlling the compositions of Al x Ga 1− x As layers grown by chemical beam epitaxy. We have produced various graded-compositional structures, including parabolic quantum wells 200 A wide where the composition was controlled by analysis of the running outermost 3 A (about 1 monolayer) of depositing material.