The formation of a rock-salt type ZnO thin film by low-level alloying with MgO

A high pressure form of ZnO with a rock-salt structure can be synthesized as a thin film by a pulsed laser deposition technique when greater than or equal to 15 mol% of MgO is alloyed. The phase is identified both by x-ray diffraction and near edge x-ray absorption fine structure (NEXAFS) measurements. NEXAFS is interpreted with the aid of first principles calculations employing a supercell composed of 108 atoms with a Zn-1s core-hole. The rock-salt phase can be formed only when an MgO(100) substrate is used because of a favourable lattice matching. As a result of the heteroepitaxy, the crystal is distorted tetragonally by c/a = 1.02. The energy increase due to the tetragonal deformation is estimated to be 2 meV/ZnO by a first principles calculation.