THE DEPENDENCE OF THE STRUCTURE AND ELECTRONIC-PROPERTIES OF WURTZITEGAN SURFACES ON THE METHOD OF PREPARATION

The effects of in situ cleaning, thermal and chemical treatments on wu rtzite GaN surfaces have been studied using various electron spectrosc opies and low energy electron diffraction (LEED). Nitrogen-ion bombard ment or deposition of Ga metal, followed by annealing in UHV, yields c lean (1 X 1)-ordered surfaces, with the latter giving a somewhat bette r LEED pattern. Uniform heating during annealing appears important in avoiding facetting. Annealing an 'as-inserted' surface either in UHV o r in a flux of NH3 vapor is not completely effective in cleaning, but annealing a clean ion-bombarded surface in NH3 impedes the formation o f N vacancies which occurs in UHV. Surface band bending depends on ann eal temperature for both as-inserted and ion-bombarded samples, changi ng by up to 0.7 eV from 300 to 700 degrees C. This is tentatively expl ained by the accumulation of surface Ga vacancies which act as accepte rs. Adsorbed H removes a surface state near the valence band maximum b ut is very sensitive to desorption by impact of similar to 90 eV elect rons. (C) 1998 Elsevier Science B.V.