First-principles study of the structural and electronic properties of (100)Ge/Ge(M)O2 interfaces (M=Al, La, or Hf)

The structural and electronic properties of (100)Ge/Ge(M)O-2 interfaces, with M=Al, La, or Hf, are investigated using density functional theory. When a Ge atom is substituted by a Hf atom in the GeOx (suboxide) interfacial layer, a Ge-Hf bond is formed due to the fivefold coordination of Hf in the GeOx matrix. The formation of this bond gives rise to a defect level in the upper part of the Ge energy band gap. On the other hand, the incorporation of Al or La in the interfacial layer results only in the formation of Al-O-Ge or La-O-Ge bonds at/near the interface due to the fourfold coordination of these metals in the GeOx matrix. This gives rise to a surface-state free Ge energy band gap. These findings highlight the advantage of lower coordinated metal oxides that tend to form germanate layers in contact with Ge for their potential use as gate stacks in high performance metal-oxide-semiconductor field effect transistors. (C) 2008 American Institute of Physics.