Domain matching epitaxy of cubic In2O3 on r-plane sapphire

Abstract

Undoped, Sn-doped, and Mg-doped In2O3 layers were grown on rhombohedral r-plane sapphire (α-Al2O3 (10.2)) by plasma-assisted molecular beam epitaxy. X-ray diffraction and Raman scattering experiments demonstrated the formation of phase-pure, cubic (110)-oriented In2O3 for Sn- and Mg-concentrations up to 2 × 1020 and 6 × 1020cm-3, respectively. Scanning electron microscopy images showed facetted domains without any surface-parallel (110) facets. High Mg- or Sn-doping influenced surface morphology and the facet formation. X-ray diffraction Φ-scans indicated the formation of two rotational domains separated by an angle Φ = 86.6° due to the substrate mirror-symmetry around the in-plane-projected Al2O3 c-axis. The in-plane epitaxial relationships to the substrate were determined for both domains. For the first domain it is Al2O3[01.0]∥In2O3[334]. For the second domain the inplane epitaxial relation is Al2O3[01.0]∥In2O3[334]. A low-mismatch coincidence lattice of indium atoms from the film and oxygen atoms from the substrate rationalizes this epitaxial relation by domain-matched epitaxy. Cross-sectional transmission-electron microsopy showed a columnar domain-structure, indicating the vertical growth of the rotational domains after their nucleation. Coincidence structure of In2O3 (110) (In atoms in red) grown on Al2O3 (10.2) (O atoms in blue) showing two rotational domians. (Figure Presented).