Ab initio molecular dynamics simulations of properties of a-Al2O3/vacuum and a-ZrO2/vacuum vs a-Al2O3/Ge(100)(2x1) and a-ZrO2/Ge(100)(2x1) interfaces

The local atomic structural properties of a-Al2O3, a-ZrO2 vacuum/oxide surfaces, and a-Al2O3/Ge(100)(2x1), a-ZrO2/Ge(100)(2x1) oxide/semiconductor interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-Al2O3 and a-ZrO2 bulk samples were generated using a hybrid classical-DFT MD approach. The interfaces were formed by annealing at 700 and 1100 K with subsequent cooling and relaxation. The a-Al2O3 and a-ZrO2 vacuum/oxide interfaces have strong oxygen enrichment. The a-Al2O3/Ge interface demonstrates strong chemical selectivity with interface bonding exclusively through Al-O-Ge bonds. The a-ZrO2/Ge interface has roughly equal number of Zr-O-Ge and O-Zr-Ge bonds. The a-Al2O3/Ge junction creates a much more polar interface, greater deformation in Ge substrate and interface intermixing than a-ZrO2/Ge consistent with experimental measurements. The differences in semiconductor deformation are consistent with the differences in the relative bulk moduli and angular distribution functions of the two oxides.