Thermal Decomposition of Gallium Arsenide

Single crystals of GaAs containing Ga{111}, As{111}, and {110} faces decomposed at rates between 4×10−2 and 1×10−3 times the free evaporation rates were examined microscopically. At these high values, the decomposition rate is observed to be orientation dependent in the order As{111}>Ga{111}, as previously reported. The {110} face decomposes at a rate intermediate between the As{111} and the Ga{111} faces. At our high decomposition rates, the As{111} faces are completely corroded in a noncrystallographic manner, while crystallographic decomposition pits are produced on the Ga{111} face. At low decomposition rates, the degree of decomposition on all three faces appears equal and decomposition pits made up of {111} faces are formed. Surface kinks produced by mechanical damage and chemical etch pitting act as nucleation sites for decomposition pits. Dislocations do not serve as nucleation sites for decomposition pits. A model that accounts for the experimental observation is presented.