Hard x-ray photoemission studied and band alignment in TiO2/HfO2/Ge heterojunctions

Novel high K oxides such as hafnium oxide and zirconium oxide have replaced silicon dioxide as gate oxide. Although titanium oxide has a high dielectric constant, the poor conduction band offset between titanium oxide and Si/Ge makes it a poor choice for gate oxide. One way to address this issue is to have a thin intermediate layer with appropriate band alignment between titanium oxide and the semiconductor. Here we present hard x-ray photoelectron spectroscopy (HAXPES) study on the band alignment between atomic layer deposited (ALD) TiO₂/HfO₂/Ge heterojunctions. The exact position of the valence band maximum was determined by convoluting theoretical calculated density of states from first-principles calculations and comparing with experimental valence band data. We will also discuss the dependence of the band alignment on the thickness of the intermediate layer.