Langmuir evaporation from the (100), (111A), and (111B) faces of GaAs

We have measured the Langmuir evaporation of Ga and As from the (100), (111A), and (111B) faces of GaAs above and below the congruent evaporation temperature T_c. We have found that T_c is lowest for the (111B) face and highest for the (111A) face. These differences can be understood in terms of the different lifetimes of surface Ga on these faces. Furthermore, we have deduced that the evaporation processes are the rate limiting steps in the decomposition of GaAs. Below T_c, decomposition is controlled by the evaporation of Ga; above T_c it is controlled by the evaporation of As.