Negative electron affinity at the Cs/AlN(0001) surface

The effects of cesium (Cs) adsorption on band bending and electron affinity at the AlN(0001)-1X1 surface are investigated via ultraviolet and x-ray ph otoemission spectroscopy. The movement of the Fermi level indicates an init ial interaction between Cs and empty surface states, followed by an increas e in band bending presumably linked to metallization. The electron affinity , chi, of the clean AlN surface is positive and equal to 1.9+/-0.3 eV. The Cs-surface dipole layer decreases chi by 2.6+/-0.3 eV, leading to evidence of true negative electron affinity at the surface of this important materia l. (C) 1999 American Institute of Physics. [S0003-6951(99)03210-6].