The Growth and Characterization of Zinc Oxide Thin Film on Fused Silica and SiO 2 /Si(100) Substrates
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The Growth and Characterization of Zinc Oxide Thin Film on Fused Silica and SiO2/Si(100) Substrates C. Jin, A. Tiwari, H. Porter, M. Park, and J. Narayan Department of Materials Science and Engineering, North Carolina State University Raleigh, NC, 27695-7916
ABSTRATCT In this work, ZnO thin films were grown on amorphous fused silica and preoxidized silicon substrates by using pulsed laser deposition technique. X-ray diffraction patterns showed that the films were highly crystalline and c-axis oriented. The surface morphologies of the films were observed by using scanning electron microscope and optical microscope. Free exciton absorption was observed at room temperature for the film grown on fused silica substrate. The strong near-UV luminescence peaked at 380 nm were observed for all the films and was attributed to the phonon-related exciton emission. The effect of oxygen partial pressure on the luminescence intensity is also reported.
INTRODUCTION Encouraged by the potential applications, the growth and characterization of ZnO thin films have become a very active research field in the past years. As a II-VI semiconductor, ZnO has a wide direct bandgap of 3.39 eV at room temperature and a larger exciton binding energy up to 60 meV. These characteristics make the material an ideal candidate for light emitting diode (LED)1 and UV-blue semiconductor laser.2 ZnO has also the potentials for many other applications such as flat panel displays,3 solar cell,4 gas sensor,5 and surface acoustic wave devices.6 Many different techniques were used to develop ZnO thin films, for examples, chemical vapor deposition7, pulsed laser deposition,8 rf magnetron sputtering9, and spray pyrolysis.10 Most ZnO thin films were grown on α-Al2O3 substrates on which ZnO films can be grown epitaxially by domain matched epitaxial mechanism.8 Single crystalline ZnO thin films grown on a latticematched substrate was also reported.11 Another substrate that was frequently used is fused silica (glass).12 This is an amorphous substrate and is more practical for the future applications of planar displaying In this study, we report the growth and characterization of ZnO thin films on amorphous substrates. All films were deposited by using pulsed laser deposition technique. The resultant thin films were characterized by using x-ray diffraction, scanning electron microscope (SEM), Raman scattering, absorption, emission and excitation spectra. The effects of oxygen partial pressure on the optical properties of the films were also investigated.
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EXPERIMENTAL DETAILS An excimer KrF laser operated at 248 nm with the pulse width of 25 ns was used to ablate a sintered ZnO target made in our laboratory. Commercial fused silica slides (Alfa Aesar) and pre-oxidized silicon (100) wafers were used as substrates. The films were grown at the optimized temperature of 630 °C at different oxygen partial pressures from 2×10-5 to 4×10-1 Torr. The structure of the films was characterized by using x-ray diffraction technique with Cu Kα line. Surface morphol
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