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This paper describes the application of two surface sensitive optical techniques to the study of III-V growth under MOVPE conditions. The first technique, optical second harmonic generation, is shown to be well suited to in-situ MOVPE studies of III-V growth, despite the fact that typical substrates should give rise to intense bulk SHG signals. Model SHG studies of GaAs (100) are described which allow the proposal of a suitable experimental geometry for the application of this technique to a substrate in an MOVPE reactor. Reflectance anisotropy measurements have been made from a GaAs (100) surface in an MOVPE reactor during a series of pump-purge cycles commonly used to remove volatile contaminants from the reactor prior to MOVPE growth. The RA response observed from the substrate at 300 K varies in intensity with both the number of pump-purge cycles and the extent of evacuation reached in each cycle, suggesting that a change in surface structure or composition may be induced via evacuation in an increasingly cleaner reactor environment. RA data recorded during a pre- growth substrate bake in arsine clearly show the onset of the formation of an As-stabilized surface at temperatures around 670 K, where the decomposition of arsine becomes appreciable. Temperature-programmed desorption from the resulting As-stabilized surface reveals an initial loss of As from the surface commencing at low temperatures (470 K) followed by recovery of the As-stabilization at higher temperatures (670 K) due to arsine decomposition. These data are compared with data for As-desorption from GaAs (100) recorded during MBE growth and it is shown that inflection in the RA traces could relate to surface reconstruction changes occurring under these high overpressure conditions.
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