Accurate band alignment at the amorphous Al2O3 /p-Ge(100) interface determined by hard x-ray photoelectron spectroscopy and density functional theory

We have investigated the band alignment at the interface of amorphous aluminum oxide (am-${\mathrm{Al}}₂{\mathrm{O}}₃$) grown by atomic layer deposition on p-Ge(100) and the effects of postgrowth annealing using hard x-ray photoelectron spectroscopy and density function theory (DFT). Accurate determination of the valence-band offsets was obtained by comparing the experimentally measured valence bands with DFT-calculated densities of states. The am-${\mathrm{Al}}₂{\mathrm{O}}₃$ density of states calculated from a weighted ensemble of crystalline ${\mathrm{Al}}₂{\mathrm{O}}₃$ structures gives excellent agreement with experiment, sufficiently capturing the nonlinear shape of the valence-band edge. We report a valence-band offset of $2.60\ifmmode\pm\else\textpm\fi{}0.1$ eV for am-${\mathrm{Al}}₂{\mathrm{O}}₃$/p-Ge, which is reduced by 0.20 eV upon annealing as interfacial ${\mathrm{GeO}}_x$ is formed.