IN-SITU TECHNIQUE FOR MEASURING GA SEGREGATION AND INTERFACE ROUGHNESS AT GAAS ALGAAS INTERFACES/

We describe a method, based on electron diffraction, for measuring the Ga segregation and roughness at GaAs/AlGaAs interfaces. By monitoring the phase of reflection high energy electron diffraction intensity os cillations, we can deduce changes of alloy composition in real time. I n particular, we can relate the phase to the extent of As coverage and thereby explain the ''forbidden range'' for growth of GaAlAs. We have determined that segregation only occurs at the normal (AlAs on GaAs) interface and have detected Ga persisting on a nominal AlAs surface ev en after 20 monolayers.