NEGATIVE ELECTRON-AFFINITY OF CESIATED P-GAN(0001) SURFACES

The adsorption of cesium on clean n- and p-GaN(0001)- 1 X 1 surfaces a t 150 K was investigated using x-ray photoemission spectroscopy, photo emission spectroscopy with monochromatized He I radiation ultraviolet photoelectron spectroscopy (UPS) and a Kelvin probe (contact potential difference, CPD). The CPD measurements gave work functions of 3.88 +/ - 0.15 and 3.6 +/- 0.15 eV for clean n- and p-GaN(0001) surfaces, resp ectively. The widths of UPS energy distribution curves yield an ioniza tion energy of 6.8+/-0.15 eV. Thus, depletion and inversion layers exi st at clean surfaces of n- and p-GaN(0001) surfaces, respectively. As a function of Cs coverage, the work function displays the well-known b ehavior in that it first decreases, passes through a minimum, and even tually reaches a value of 2.1 eV, the work function of metallic cesium . In the submonolayer coverage regime, the ionization energy decreases by 2.3 +/- 0.15 eV. At clean p-GaN(0001) surfaces the vacuum level li es by only 0.3 eV above the conduction-band minimum in the bulk. Alrea dy minute amounts of Cs suffice to produce negative electron affinity. The Schottky barrier height of metallic Cs films on n-GaN(0001) is de termined as 0.2+/-0.15 eV. This value is in good agreement with what i s predicted by the MIGS and electronegativity model. (C) 1998 American Vacuum Society.