Modulated-beam studies of the layer-by-layer etching of GaAs(001) using AsBr3: identification of the reaction mechanism

Modulated-beam mass spectroscopy (MBMS) has been used to study the reaction mechanism of the layer-by-layer etching of GaAs(001) using AsBr3 under molecular beam epitaxy conditions. It is shown that GaBr is the main etching product and its ''delay'' time with respect to the incident AsBr3 flux exhibits a strong dependence on substrate temperature, changing from 12 ms in the reaction limited regime at 387 degrees C to less than 0.5 ms at 560 degrees C. Desorbing As-containing species appear to have very short surface lifetimes throughout the temperature range investigated and the additional As-2 flux supplied from a solid source has no effect on the etching rate. The results suggest a reaction pathway where the rate limiting step is the formation or description of GaBr and not the decomposition of AsBr3.