Ionization Energy and Electron Affinity of Clean and Oxidized Al{sub}xGa{sub}(1-x)N(0001) Surfaces

摘要

Ionization energies and electron affinities of clean Al{sub}xGa{sub}(1-x)N(0001) surfaces were investigated by ultraviolet photoemission spectroscopy over the whole composition range. The samples were cleaned with cycles of N{sup}+-ion sputtering and annealing partly within a Ga atom flux. The ionization energy is measured as 6.5 eV and is almost independent of the aluminum content in good agreement with the general chemical trend. The electron affinity decreases linearly with composition from 3.1 eV for GaN to 0.25 eV for AlN. No evidence for negative electron affinity at AlN(0001) surfaces was found. Adsorption of oxygen at room temperature leads to a significant increase of the ionization energy and electron affinity. With AlN(0001) surfaces, an oxygen uptake of 0.6 monolayers is observed after exposures of 10{sup}8 Langmuirs and the ionization energy increases by approximately 2 eV.