Surface atomic process of incorporation of excess arsenic in molecular-beam epitaxy of GaAs

The surface atomic process that leads to the incorporation of extremely high concentrations of excess arsenic into GaAs layers during growth by moelcular-beam epitaxy at low temperatures is investigated. A model of the surface atomic process is derived on the basis of the results of growth experiments where the dependence of the concentration of excess arsenic in the GaAs layer on the flux condition and growth temperature has been examined. In the model, arsenic atoms that are chemisorbed on the arsenic-terminated GaAs(100) surface serve as precursors of excess arsenic, and, hence, the concentration of excess arsenic depends directly on the steady-state coverage of the chemisorbed arsenic atoms. The model is developed quantitatively on the basis of the Langmuir adsorption model, which explains the majority of experimental results but leads to an extremely low activation energy for desorption of adsorbed arsenic atoms.