INSITU MONITORING AND CONTROL OF ATOMIC LAYER EPITAXY BY SURFACE PHOTOABSORPTION

Surface photo-absorption (SPA) is a real-time optical probe for examining growth and gives us a microscopic insight into atomic processes occurring on a growth surface. SPA observations during GaAs and InP atomic layer epitaxy (ALE) using trimethyl Group III sources and Group V hydrides demonstrate that the adsorption of trimethyl source saturates during the trimethyl source supply period and that the saturated surface corresponds to a metastably methyl-terminated surface with a lifetime of several tens of seconds. In contrast, when the trimethyl source is supplied onto the Group III metal surface, an increase in the SPA reflectivity from the metal surface level is observed, indicating that the trimethyl source molecule decomposes on the Group III metal surface via adsorption. These observations give rise to the conclusion that the growth rate self-limitation in ALE is caused by the inhibited adsorption of excessively supplied Group III source molecules on the methyl-terminated surface, and not by a selective adsorption mechanism. SPA observation also makes it possible to determine readily and precisely the growth parameters for ALE which strongly depend on the reactor design and the gas flow condition.