Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) substrates by pulsed laser deposition

Abstract

Transparent p-type conducting ${\mathrm{CuGaO}}_{\mathrm{2}}$ thin films were prepared on $\mathrm{\alpha -}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ (001) single-crystal substrates by pulsed laser deposition. The films were grown epitaxially on the substrates in an as-deposited state. X-ray pole figure analysis revealed that the films were composed of two types of epitaxial grains, both with c axes oriented perpendicular to the surface and a axes rotated 60° with respect to each other around the c axis. Observation of the ${\mathrm{CuGaO}}_{\mathrm{2}}$ thin films by atomic force microscopy and high-resolution transmission electron microscopy substantiated this conclusion. The films have high optical transparency (∼80%) in the visible region, and the energy gap of ${\mathrm{CuGaO}}_{\mathrm{2}}$ for direct allowed transition was estimated to be 3.6 eV. p-type conductivity was confirmed by Seebeck and Hall measurements. The electrical conductivity, carrier (positive hole) density, and Hall mobility of the films at room temperature were ${\text{6.3×10}}^{\text{−2}} {\mathrm{S cm}}^{\mathrm{-1}},$ ${\text{1.7×10}}^{18} {\mathrm{cm}}^{\mathrm{-3}},$ and 0.23 cm² V⁻¹ s⁻¹, respectively.