Explanation of multiplet spots in low-energy electron diffraction patterns of clean GaN surfaces

Abstract:

Clean, ordered, and stoichiometric GaN surfaces are obtained after exposure to a Ga-flux followed by annealing in ultrahigh vacuum (UHV), after desorption of a Ga layer deposited at room-temperature or after nitrogen ion-bombardment and annealing in UHV. Samples annealed at temperatures above approximately display low-energy electron diffraction patterns. As a function of electron energy, the normal-order spots split into circular sextets. These multiplet rings periodically expand and coalesce. This observation is explained by oppositely oriented, regular step arrays in the [1000]-, [0100]- and [0010]-directions on the GaN surfaces. Quantitative analysis of the data gives terrace widths of Å and step heights of Å. The observations suggest faceting or the “development” of growth spirals with steps heights of two Ga-N bilayers by thermal etching.