Effects of hydrogen on the structural and electro-optical properties of zinc oxide thin films

Hydrogen doped zinc oxide (ZnO:H) films have been deposited by radio-frequency reactive magnetron sputtering and then heat treated at fixed temperature. The roles of hydrogen on transparent conducting properties as well as on microstructural evolution have been investigated. It is identified from X-ray diffraction patterns that, as hydrogen contents increase in the sputtering gas, the ZnO:H films have a mixed orientation composed of(10 (1) over bar0), (10 (1) over bar1), and (11 (2) over bar0) peaks rather than the (0002) preferred orientation, regardless of heat-treatment. As the contents increase, the films also exhibit increasingly irregular surface morphology and collapsed columnar subsurface regions. In so far as bonding characteristics are concerned, X-ray photoelectron spectroscopy analyses show that O-H hydroxy] bonds are formed during hydrogen doping and the bonds are retained after heat-treatment at 500 degreesC. In the range of 0-8% hydrogen in the sputtering gas, it is observed from a Hall measurement that electrical resistivity decreases sharply with increasing amount of hydrogen. A main factor improving the electrical properties is found to be hydrogen incorporation, rather than oxygen vacancies or zinc interstitials. Beyond 8 vol Fb hydrogen, the electrical properties are again deteriorated due to the decrease of electron mobility, which may be understood in terms of the degradation of structural properties caused by hydrogen. Meanwhile, it is also found that average optical transmittance values show a similar trend as the electrical resistivity values I vs. hydrogen contents. (C) 2000 The Electrochemical Society. S0013-4651(00)05-017-5. All rights reserved.