The hydrogen plasma doping of ZnO thin films and nanoparticles

The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped (intrinsic) ZnO thin films and aligned nanocolumns grown on the nucleated glass substrate by the hydrothermal process in an oil bath containing a flask with ZnO nutrient solution. The localized defect states at 2.3 eV below the optical absorption edge were detected by photothermal deflection spectroscopy (PDS) in a broad spectral range from near UV to near IR. The optical absorptance spectroscopy shows that hydrogen doping increases free electron concentration changing ZnO to be electrically conductive (hydrogen doping). The high Dc current flow degrades the optical and electronic properties. Photoluminescence spectroscopy shows that after plasma hydrogenation, the exciton related emission band centered near the optical absorption edge at the wavelength 375 nm (3.3 eV) is partly deteriorated but fully recovers after the subsequent plasma oxidation. Therefore, the exciton related photoluminescence is influenced significantly by the plasma treatment and it correlates with free electron concentration.