1ST-PRINCIPLES STUDY OF ZN-STABILIZED AND SE-STABILIZED ZNSE(100) SURFACE RECONSTRUCTIONS

We have carried out first-principles pseudopotential calculations to s tudy the formation energies of various ZnSe(100) surface reconstructio ns. Both Zn- and Se-terminated models are treated, using as a guide th e satisfaction of the electron counting rule (i.e., charge compensatio n at the surface by the filling of all the Se dangling bonds and the e mptying of the Zn dangling bonds). In order to treat structures with d ifferent stoichiometries, we determine the surface energy as a functio n of the Zn chemical potential, which is allowed to vary in a range de termined by the energies of bulk Zn, Se, and ZnSe. A c(2 X 2) reconstr uction with half-monolayer coverage of twofold coordinated Zn atoms is stable in the Zn-rich limit. Under moderately Se-rich conditions, the surface adopts a (2 X 1) Se-dimer phase. In the extreme Se-rich limit we predict the stability of a reconstruction with one and a half mono layer coverage of Se. The new structure can account for the high growt h rates observed in atomic layer epitaxy and migration enhanced epitax y experiments at relatively low temperatures.