EFFECTS OF LASER WAVELENGTH AND FLUENCE ON THE GROWTH OF ZNO THIN-FILMS BY PULSED-LASER DEPOSITION

Transparent, electrically conductive and c-axis oriented ZnO thin film s have been grown by the pulsed laser deposition (PLD) technique on si licon and Coming glass substrates employing either a KrF excimer laser (lambda = 248 nm) or a frequency-doubled Nd:YAG laser (lambda = 532 n m). The crystalline structure, surface morphology, optical and electri cal properties of the deposited films were found to depend not only on the substrate temperature and oxygen partial pressure, but also on th e irradiation conditions. The quality of the ZnO layers grown by the s horter wavelength laser was always better than that of the layers grow n by the longer wavelength, under otherwise identical deposition condi tions. This behaviour was qualitatively accounted for by the results o f the numerical solution of a one-dimensional heat diffusion equation which indicated a strong superheating effect of the melted target mate rial for the case of frequency-doubled Nd:YAG laser irradiations. By o ptimizing the deposition conditions we have grown, employing the KrF l aser, very smooth c-axis oriented ZnO films having a full-width at hal f-maximum value of the (002) X-ray diffraction Value less than 0.16 de grees and optical transmittance around 85% in the visible region of th e spectrum at a substrate temperature of only 300 degrees C.