  The Schottky barrier heights (SBHs) of defect-free interfaces of ZnO, CdO,
MgO and SrO with various metals and different terminations are investigated by
density functional supercell calculations. The oxide bands are corrected for
their density functional band gap error by applying U-type treatment to their
metal-d and O-p states where necessary. The p-type SBHs are found to decrease
linearly with increasing metal work function. The pinning factor S of the
non-polar and polar interfaces are similar for each oxide. S is found to be
0.26, 0.56, 0.74 and 0.96 for CdO, ZnO, MgO and SrO, respectively, with S
increasing for increased oxide ionicity. The calculated pinning factors are
generally consistent with the metal-induced gap states (MIGS) model in terms of
variation with ionicity and dielectric constant. A significant shift of SBHs
from the non-polar to the polar interfaces of 0.4 eV, 1 eV and 0.5 eV for ZnO,
MgO and SrO, respectively, can be explained by an interfacial dipole. Our
results are also useful to describe Co,Fe|MgO interfaces in magnetic tunnel
junctions.
