Pulsed Laser Deposition of High Quality ZnO Thin Films

Abstract

Thin films of ZnO have been grown on silicon and glass substrates by the pulsed laser deposition method. The effects of the oxygen partial pressure, substrate temperature and laser wavelength on the structural and optical properties of the films have been studied. The KrF excimer laser (at 248 nm) was found to produce better quality thin films than the frequency doubled Nd:YAG laser (532 nm). Layers produced at substrate temperatures as low as 300°C were c-axis oriented with a FWHM value for the 002 XRD reflection less than 0.2° and exhibited optical transmission higher than 80% in the visible region.

Effects of laser wavelength and fluence on the growth of ZnO thin films by pulsed laser deposition

“…However, the absence of any structure in the shoulders of the Zn 2p3/2 and Zn2pl/2 XPS peaks recorded for these films indicates that they do not contain, within the XPS resolution limit (< 0.1%), metallic Zn. The binding energies of the Ols and Zn2p3/a and Zn2pl/z peaks, measured with respect to that of C ls situated at 284.6 eV, closely correspond to O and Zn in ZnO [8,20] and confirm our previous Rutherford backscattering measurements which showed that the PLD grown films, regardless of the laser employed, were essentially stoichiometric ZnO [13,14]. Narrow XRD lines and refractive index values around 1.97-2.0 were recorded for all the films grown by the KrF laser at fluences in the 1.5-2.5 J/cm 2 range, when keeping substrate temperatures around 300-350°C and oxygen partial pressures in the low 10 .3 Torr range.…”

“…around (1-2)X 10 -3 Tort. This result, although different from that obtained when growing ZnO thin films using a frequency-doubled Nd: YAG laser [13,14], is similar to data published for indium tin oxide films prepared by PLD with an excimer laser [16]. It has been suggested [16,17] that a relatively high oxygen pressure (i.e.…”

“…ZnO targets (99.9% purity) prepared by the usual sintering techniques were ablated within our PLD set-up [13,14] either by a KrF laser or a frequencydoubled Nd:YAG laser. The incident laser fluence was adjusted within the 0.4-4.0 J/cm 2 range by varying the energy contained in each laser pulse.…”

Low temperature growth of highly transparent c-axis oriented ZnO thin films by pulsed laser deposition

“…Using the Scherrer equation [23] the grain size dimensions were estimated for the thicker films to be around 20 nm.…”

“…The experimental set-up employed for PLD and the preparation route of the targets have already been described in detail elsewhere [23]. Cylindrical ZnO pellets of 99.9 % purity were ablated either by a frequency-doubled Nd:YAG laser (h=532 nm, pulse duration rwHM=4 ns) or by a KrF excimer laser (x=248 nm, pulse duration rmB~=20 ns).…”