Structural, optical, and electrical properties of orthorhombic κ -(In x Ga 1-x ) 2 O 3 thin films

Abstract

Material properties of orthorhombic κ-phase (In x Ga 1-x ) 2 O 3 thin films grown on a c-plane sapphire substrate by pulsed-laser deposition are reported for an indium content up to x ∼ 0.35. This extended range of miscibility enables band gap engineering between 4.3 and 4.9 eV. The c-lattice constant as well as the bandgap depends linearly on the In content. For x > 0.35, a phase change to the hexagonal InGaO 3 (ii) and the cubic bixbyite structure occurred. The dielectric function and the refractive index were determined by spectroscopic ellipsometry as a function of the alloy composition. We propose zirconium to induce n-type conductivity and have achieved electrically conducting thin films with a room temperature conductivity of up to 0.1 S/cm for samples with a low In content of about x = 0.01. Temperature-dependent Hall-effect measurements yielded a thermal activation energy of the free electron density of 190 meV. Schottky barrier diodes with rectification ratios up to 10 6 were investigated by quasi-static capacitance voltage and temperature-dependent current voltage measurements.