Optical and hall properties of ZnO thin films fabricated by using the pulsed laser deposition method at various oxygen pressures and substrate temperatures

Zinc oxide (ZnO) thin films are fabricated on sapphire substrates at various oxygen pressures (100 mTorr similar to 250 mTorr) and substrate temperatures (200 degrees C similar to 600 degrees C) by using pulsed laser deposition in order to investigate the microstructure, as well as the optical and the Hall-effect properties of the Zno thin films. All ZnO thin films are shown to be c-axis oriented, exhibiting only a (002) diffraction peak. The ZnO thin film fabricated at 200 mTorr and 500 degrees C shows the highest (002) orientation, and the full width of half maximum (FWHM) of the (002) diffraction peak is 0.36 degrees. In the photoluminescence (PL) spectra at room temperature, a strong ultraviolet emission and a weak yellow emission are observed. The deposition conditions affect the UV emission properties more than the deep-level emission properties. Also, we suggest that UV emissions have a close relation to the crystallinity of thin films. On the other hand, the center of the deep-level emission shows a yellow emission band in most of the thin films. However, the center of the deep-level emission shifts from the yellow region to the green region at a deposition condition of 200 mTorr and 600 degrees C. The Hall-effect measurement indicates that the highest carrier concentration (4.46 x 10(18) cm(-3)) and the lowest resistivity (0.336 ohm cm) are obtained in the ZnO thin film fabricated at 200 mTorr and 500 degrees C.