The dependence of the structure and electronic properties of wurtzite GaN surfaces on the method of preparation

The effects of in situ cleaning, thermal and chemical treatments on wurtzite GaN surfaces have been studied using various electron spectroscopies and low energy electron diffraction (LEED). Nitrogen-ion bombardment or deposition of Ga metal, followed by annealing in UHV, yields clean (1 X 1)-ordered surfaces, with the latter giving a somewhat better LEED pattern. Uniform heating during annealing appears important in avoiding facetting. Annealing an 'as-inserted' surface either in UHV or in a flux of NH3 vapor is not completely effective in cleaning, but annealing a clean ion-bombarded surface in NH3 impedes the formation of N vacancies which occurs in UHV. Surface band bending depends on anneal temperature for both as-inserted and ion-bombarded samples, changing by up to 0.7 eV from 300 to 700 degrees C. This is tentatively explained by the accumulation of surface Ga vacancies which act as accepters. Adsorbed H removes a surface state near the valence band maximum but is very sensitive to desorption by impact of similar to 90 eV electrons. (C) 1998 Elsevier Science B.V.