Type B epitaxy of Ge on CaF2(111) surface

It was known experimentally that type B orientation, which is rotated 180° about the [111] axis, dominated the heteroepitaxial growth of Ge(111) on a CaF2(111) substrate at an elevated temperature. We performed first principles calculations using density functional theory to determine the energetics of the Ge(111)/CaF2(111) interface and found that the type B orientation of the Ge film is most likely a result of a direct bonding between Ge atoms and Ca2+ at the CaF2 surface with the top F− layer depleted. Our theoretical prediction is supported by our X-ray diffraction experiments on {111} < 121> biaxially textured Ge/CaF2 samples.