The changes in the free-carrier concentration in polycrystalline ZnO films during exposure to H 2 and O 2 plasmas were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. The carrier concentration and mobility were extracted from the free-carrier absorption in the infrared using a model for the dielectric function. The electron density in polycrystalline zinc oxide films may be significantly increased by > 10 19 cm -3 by brief exposures to hydrogen plasma at room temperature and decreased by exposure to O 2 plasmas. Room-temperature oxygen plasma removes a fraction of the H at donor sites but both elevated temperatures (∼225 °C) and O 2 plasma were required to remove the rest. We demonstrate that combinations of O 2 and H 2 plasma treatments can be used to manipulate the carrier density in ZnO films. However, we also show the existence of significant drifts (∼15%) in the carrier concentrations over very long time scales (hours). Possible sites for H incorporation in polycrystalline films and reasons for the observed carrier-concentration changes are proposed.
ASJC Scopus subject areas
- Physics and Astronomy(all)