Beneficial effect of La on band offsets in Ge/high-κ insulator structures with GeO_2 and La_2O_3 interlayers

摘要

The electron energy band alignment between (100)Ge and high-κ oxide insulators (ZrO_2, Gd_2O_3, La_2Hf_2O_7) grown by the atomic beam deposition method is analyzed using photoemission of electrons from the Ge valence band. Formation of a thin GeO_2 passivation layer before the high-κ deposition is found to significantly reduce the barrier for electrons. However, when La_2O_3 is deposited as an interlayer, it strongly reacts with the Ge substrate to form a La-Ge-O germanate at the interface, which is found to retain a high barrier for the carriers in Ge.