Reflection high-energy electron diffraction techniques were used to study the stability of the 2 x 2 reconstruction, on the (00•1) surface of the hexagonal phase, as a function of the growth parameters. The relationship between the critical conditions for the existence of the reconstruction, which corresponded to a unique surface stoichiometry, was used to demonstrate the interdependence of the growth parameters. A model was proposed which described the stoichiometric balance of species arriving at the surface with regard to the critical conditions for the observation of the reconstruction. Transition curves which demarcated the 2 x 2 reconstruction regime were characterized, and were shown to be a reference point for a particular surface stoichiometry. A flux balance model was proposed which was based upon the relationship between the substrate temperature, the Ga flux, the N supply, and the appearance of the 2 x 2 reconstruction. The 2 x 2 reconstruction also provided a method for in situ  monitoring of the stoichiometry at the sample surface.

P.Hacke, G.Feuillet, H.Okumura, S.Yoshida: Applied Physics Letters, 1996, 69[17], 2507-9