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Al2O3 films 150 Å 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 (α-Al2O3) is calculated by the ab initio density functional method and compared with experimental results. The α-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 ⊥ * ≈ 6.3m 0 and m ‖ * ≈ 0.36m 0. The effective electron mass is independent of the direction m ‖ * ≈ m ⊥ * ≈ 0.4m 0.
Perevalov et al. (Sun,) studied this question.