Negative electron affinity and electron emission at cesiated GaN and AlN surfaces

The electronic structure of GaN and AlN (0001) surfaces and modification by cesium (Cs) adsorption are investigated via ultra-violet and X-ray photoem ission spectroscopy (UPS, XPS) and total yield spectroscopy. The electron a ffinity (EA) of the clean and ordered 1 X 1 surfaces is found to be equal t o 3.3 and 1.9 eV for GaN and AlN, respectively. Cs adsorption (with the hel p of oxygen pre-treatment in the case of GaN) reduces EA on both surfaces b y about 2.6-2.8 eV, leading to true negative electron affinity (NEA) in the case of AlN and effective NEA in the case of GaN. Total yield spectroscopy confirms NEA on both surfaces. (C) 2000 Elsevier Science B.V, All rights r eserved.