Electronic structure of α-Al₂O₃: Ab initio simulations and comparison with experiment

Al2O3 films 150 angstrom thick are deposited on silicon by the ALD technique, and their x-ray (XPS) and ultraviolet (UPS) photoelectron spectra of the valence band are investigated. The electronic band structure of corundum (alpha-Al2O3) is calculated by the ab initio density functional method and compared with experimental results. The alpha-Al2O3 valence band consists of two subbands separated with an ionic gap. The lower band is mainly formed by oxygen 2s states. The upper band is formed by oxygen 2p states with a contribution of aluminum 3s and 3p states. A strong anisotropy of the effective mass is observed for holes: m(h perpendicular to)* approximate to 6.3m(0) and m(h parallel to)* approximate to 0.36m(0). The effective electron mass is independent of the direction m(e parallel to)* approximate to m(e perpendicular to)* = 0.4m(0).