Growth of epitaxial zirconium-doped indium oxide (222) at low temperature by rf sputtering

Abstract

Zr-doped In₂O₃ (Zr-In₂O₃) (222) epitaxial layers of thickness 210 nm were grown on yttria-stabilized zirconia (YSZ) (111) and Al₂O₃ (0001) substrates with rf magnetron sputtering at 350 °C in an atmosphere deficient in oxygen. X-Ray scattering and use of a transmission electron microscope (TEM) revealed Zr-In₂O₃ films to be deposited epitaxially on YSZ (111) and Al₂O₃ (0001). Images observed with an atomic-force microscope demonstrate that the substrate profoundly affected the topography of the Zr-In₂O₃ (222) epilayers. The large mismatch of the Zr-In₂O₃ (222)/Al₂O₃ (0001) heteroepitaxy was responsible for the surface structure of the epilayer being rougher than that on YSZ (111). Cross-sectional TEM images reveal dense crystalline films with no macroscopic imperfection; the crystalline order of Zr-In₂O₃ epilayers is preserved up to the top surface. The Zr-In₂O₃ (222)/YSZ (111) heteroepitaxy has a Hall mobility greater than that of Zr-In₂O₃ (222)/Al₂O₃ (0001), perhaps due to the greater lattice mismatch of the Zr-In₂O₃ (222)/Al₂O₃ (0001) heteroepitaxy that results in Zr-In₂O₃ having a poor crystalline quality. Domain boundaries on a nanometre scale were found in the heteroepitaxial Zr-In₂O₃ (222)/Al₂O₃ (0001) resulting from random nucleation and relaxation of misfit stress. The existence of these domain boundaries on a nanometre scale thus affects the electrical properties of the Zr-In₂O₃ epilayer.