Theoretical and experimental energy barriers associated with the incorporation of excess As into GaAs(0 0 1)

We present the results of calculations on the incorporation process of an As atom into a tetrahedral interstitial position of the GaAs lattice. To model this particular step of the As-incorporation process, the interactions between an As2 molecule and an As-terminated, partially relaxed GaAs(0 0 1) surface represented by a Ga24As25H44 cluster are studied. We use quantum chemical ab initio methods for these simulations. From the interaction characteristics we obtain an energy barrier that governs the thermally activated escape of an As2 molecule from an interstitial surface site. On this basis a Langmuir-adsorption-like model can be formulated which describes the experimentally determined excess As concentration in a GaAs crystal grown at low temperatures rather well.