Paper EM-WeM4
Density-Functional Theory Molecular Dynamics Simulations of a-HfO₂/Ge(100)(2x1) and a-ZrO₂/Ge(100)(2x1) Interface Passivation

Wednesday, October 21, 2015, 9:00 am, Room 210E

: The structural properties of a-HfO₂/Ge(2x1)-(001) and a-ZrO₂/Ge(2x1)-(001) interfaces were investigated with and without a GeOx interface interlayer using density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic amorphous a-HfO₂ and a-ZrO₂ samples were generated using a hybrid classical-DFT MD “melt-and-quench” approach and tested against experimental properties. The oxide/Ge stacks were annealed at 800K, cooled to 0K, and relaxed providing system with enough freedom to form realistic interfaces. For each high-K/Ge stack type, two systems with single and double interfaces were investigated. All stacks were free of midgap states; however, stacks with an GeOx interlayer had band-edge states which decreased the band gaps by 0-30 %. These band-edge states were mainly produced by under-coordinated Ge atoms in GeOx layer or its vicinity due to deformation, intermixing, and bond-breaking. The DFT-MD simulations show that electronically passive interfaces can be formed either directly between high-K dielectrics and Ge or with a monolayer of GeO₂ if the processing does not create or properly passivates under-coordinated Ge atoms and Ge’s with significantly distorted bonding angles. Comparison to the charge states of the interfacial atoms from DFT to experimental XPS results show that while most studies of gate oxide on Ge(001) have a GeO_x interfacial layer, it is possible to form a oxide/Ge interface without a GeO_x interfacial layer. Comparison to experiments is consistent with the dangling bonds in the suboxide being responsible for midgap state formation.