Mg in GaN: Incorporation of a volatile species at high temperatures during molecular beam epitaxy

We examine the epitaxial incorporation behavior of the volatile $p$ -type dopant Mg at high growth temperatures during the molecular beam epitaxy of GaN on the [0001] surface, and report interesting doping behavior. The net Mg incorporation is independent of the arriving Mg flux over a flux variation of two decades, and dependent strongly on the growth temperature of the epilayer, limiting the net hole concentrations obtainable to the low ${10}^{17}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}$ range. These results are explained in terms of incorporation either through a surface Mg phase, or via the availability of specific sites on the surface for Mg incorporation.