Surface photo-absorption (SPA) is a newly developed in situ optical monitoring technique for the epitaxial growth process. This method is based on the measurement of reflection intensity of p-polarized incident light at close to the Brewster angle. This letter describes use of SPA to investigate the decomposition of Ga organometals in metalorganic chemical vapor deposition during the growth of GaAs layers. Triethylgallium and trimethylgallium are used as the gallium sources, and the temperature range is 300°C-670°C. It is found that the SPA signal is very sensitive to chemical species on the growing surface, and that triethylgallium decomposes almost completely on the growisng surface above 500°C while trimethylgallium does not completely decompose even at 630°C. The results imply that the self-limiting characteristic of the growth rate in atomic layer epitaxy is caused by the formation of a molecular layer of methylgallium compounds.
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