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Abstract

Molecular AsH₃, adsorbed on Ga‐rich GaAs(100) at 115 K, dissociates readily upon uv irradiation with 193, 248, and 351 nm excimer laser light. In the initial photodissociation step one As-H bond cleaves, leaving all the AsH₂, and a large fraction of the H, adsorbed to As. The AsH₂ further photodissociates to give As-H and Ga-H. The final steps, photochemical removal of hydrogen from Ga-H and As-H, lead to As deposition. The photodissociation cross section decreases sharply with the extent of photolysis. The wavelength dependence, compared to the gas‐phase absorption cross section, extends to much lower photon energies and indicates that substrate‐mediated excitation dominates the observed chemistry. There are strong isotope effects in all the cross sections; these are related to mass‐dependent substrate‐mediated quenching of the excited states. Implications for photon‐assisted organometallic chemical vapor deposition are discussed.