Kinetic analysis of surface adsorption layer in GaAs(001) metalorganic vapor phase epitaxy by in situ reflectance anisotropy spectroscopy

A kinetic analysis of the surface adsorption layer of III/V semiconductors in metalorganic vapor phase epitaxy (MOVPE) was carried out by monitoring the temporal behavior of surface reconstruction that is assumed to be maintained during growth with the adsorption layers. A GaAs(001) surface was observed in situ using reflectance anisotropy spectroscopy (RAS), and both spectroscopic and kinetic analyses were performed when trimethylgallium (TMGa) was supplied intermittently while the supply of tertiarybutylarsine (TBAs) was continuous. When the flow of TMGa was switched on/off, the transient RA signal exhibited time constants of 0.2-20s. By observing the dependence of these time constants on the partial pressure of TMGa and substrate temperature, we considered that the time constant (t₀) at the start of TMGa supply corresponds to the adsorption of Ga from the gas phase to the adsorption layer, and two constants (i.e., t₁ and t₂) at the end of TMGa supply are associated with the crystallization of adsorbed Ga and the recovery of surface reconstruction, respectively. The equivalent thickness of the adsorption layer was estimated to be 0.19 monolayer thickness at 550°C.