Extended wide band gap amorphous aluminium-doped zinc oxide thin films grown at liquid nitrogen temperature

Abstract

Amorphous aluminium-doped zinc oxide (AZO) thin films are grown by standard RF sputtering at low temperatures on glass substrates. Due to poor thermal conductivity and thermal energy generated by the sputter gun, controlling the substrate surface temperature is the key to controlling the growth of amorphous and nanocrystalline films. The ratio of grains and amorphous part of the films can be controlled by selective growth conditions. During a transmission electron microscope (TEM) inspection process, the amorphous films react immediately and strongly with an electron beam and transform to a mixture of amorphous and nanocrystalline phases. The films having a mixture of amorphous and nanocrystalline phases, either as-grown or after transformation by irradiation of the electron beam, are stable in the TEM inspection, indicating that the low interface energy stabilizes the mixture phase. The optical band gap increases with the content of amorphous phase and is 4.3 eV for pure amorphous AZO films.