Arsenic on cubic GaN surfaces: surfactant effect versus incorporation

The presence of arsenic during the Molecular Beam Epitaxy growth of cubic GaN changes the structure of the growing surface and influences the structural and optical properties of the cubic epilayers. The transition between the surface reconstructions obtained when arsenic is present on the (001) β GaN has been followed as a function of the As flux. It could be demonstrated that, below a certain critical As flux, arsenic atoms sitting on the surface smooth the growth front and exchange with nitrogen atoms, thus acting as surfactant for cubic growth, whereas above this value As is incorporated in the lattice. This critical As flux value depends on the growth temperature. A comparison has been carried out of the optical properties of cubic GaN layers grown with or without arsenic during growth and for different As fluxes. It was shown that better layers are obtained when arsenic is present, if growth is carried out at high enough temperatures. At lower temperatures, the incorporation of arsenic in the GaN lattice degrades the quality of the cubic GaN layers, possibly because of isoelectronic doping.