Electronic properties of cesium-covered GaN(0001) surfaces

Cesium was deposited on clean n-GaN(0001)-1 x 1 surfaces at 150 K using Cs dispensers, X-ray photoemission spectroscopy showed that the Cs-films grow layer by layer. Cesium-induced variations of electronic surface properties were observed using photoemission spectroscopy with monochromatized HeI radiation (UPS) and a Kelvin probe (CPD), The UPS data recorded with clean GaN(0001) surfaces give their ionization energy as 6.8 +/- 0.1 eV, so that their electron affinity measures 3.35 +/- 0.1 eV. The work function of clean GaN(0001) surfaces was determined as 4 +/- 0.2 eV. Cesium deposition first reduces the work function by up to 2.7 eV and then increases it until eventually a work function of 2 eV is reached. A simple point-charge model easily explains this decrease of the work function by the formation of surface dipoles. The latter value is characteristic of bulk cesium. (C) 1998 Elsevier Science B.V.