Band alignment of vanadium oxide as an interlayer in a hafnium oxide-silicon gate stack structure

Vanadium oxide (VO ₂) is a narrow band gap material (Eg 0.7 eV) with a thermally induced insulator-metal phase transition at ∼343 K and evidence of an electric field induced transition at T 343 K. To explore the electronic properties of VO ₂, a sandwich structure was prepared with a 2 nm VO ₂ layer embedded between an oxidized Si(100) surface and a 2 nm hafnium oxide (HfO ₂) layer. The layer structure was confirmed with high resolution transmission electron microscopy. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy, and the band alignment was deduced on both n-type and p-type Si substrates. The valence band offset between VO ₂ and SiO ₂ is measured to be 4.0 eV. The valence band offset between HfO ₂ and VO ₂ is measured to be ∼3.4 eV. The band relation developed from these results demonstrates the potential for charge storage and switching for the embedded VO ₂ layer.