ISSN - 10637834, EISSN - 10906460, Physics of the Solid State, 2004, vol. 46, p. 1949-1953
Low-temperature method of cleaning p-GaN(0001) surfaces for photoemitters with effective negative electron affinity
The changes in the chemical composition, atomic structure, and electronic properties of the p-GaN(001) 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%. © 2004 MAIK "Nauka/Interperiodica".