Optical properties of the plasma hydrogenated ZnO thin films

We have optimized the deposition of the highly electrically resistive undoped (intrinsic) polycrystalline ZnO thin layers on fused silica substrates by the DC reactive magnetron sputtering of metallic zinc target in argonne/oxide atmosphere and we introduced the post-deposition hydrogen plasma doping. The thickness of thin film was evaluated by reflectance interferometry using the metallographic optical microscope fiber coupled to the CCD spectrometer operating in 400-1000 nm spectral range. The optical absorption was measured by photothermal deflection spectroscopy operating in 300-1600 nm spectral range. The change of the optical absorption edge and the increase of the infrared optical absorption was detected in hydrogenated ZnO. The increase of the infrared optical absorption goes with the increase of the electrical conductivity. We conclude that the plasma hydrogenation of the intrinsic ZnO thin films is related to increase of the free carrier concentration.