Properties of TiO₂-based transparent conducting oxide thin films on GaN(0001) surfaces

Anatase Nb-doped TiO₂ transparent conducting oxide has been formed on GaN(0001) surfaces using a sputtering method. Amorphous films deposited at room temperature were annealed at a substrate temperature of 500 °C in vacuum to form single-phase anatase films. Films with a thickness of 170 nm exhibited a resistivity of 8× 10^-4 Ωcm with absorptance less than 5% at a wavelength of 460 nm. Furthermore, the refractive index of the Nb-doped TiO₂ was well matched to that of GaN. These findings indicate that Nb-doped TiO₂ is a promising material for use as transparent electrodes in GaN-based light emitting diodes (LEDs), particularly since reflection at the electrode/GaN boundary can be suppressed, enhancing the external quantum efficiency of blue LEDs.