Abstract
The changes in the chemical composition, atomic structure, and electronic properties of the p-GaN(0001) surface upon chemical treatment in an HCl-isopropanol solution and vacuum annealing are investigated by x-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, and low-energy electron diffraction. It is demonstrated that a considerable part of the surface gallium oxide is removed upon chemical treatment of the GaN surface. Subsequent annealing of the surface under vacuum at temperatures of 400–450°C leads to a decrease in the residual carbon and oxygen contamination to 3–5% of the monolayer. The preparation of a clean p-GaN(0001) surface with a (1×1) structure identical to that of the bulk unit cells is confirmed by the low-energy electron diffraction data. The cesium adsorption on the clean p-GaN surface results in a decrease in the work function by ∼2.5 eV and the appearance of an effective negative electron affinity on the surface. The quantum efficiency of the GaN photocathode at a wavelength of 250 nm is equal to 26%.
Published Version
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