Study of deposition parameters for the fabrication of ZnO thin films using femtosecond laser

Abstract

Femtosecond (fs) pulsed laser deposition (fs-PLD) of ZnO thin film on borosilicate glass substrates is reported in this work. The effect of important fs-PLD parameters like targetsubstrate distance, laser pulse energy, and substrate temperature on structure, morphology, optical transparency and luminescence of as deposited films is discussed.XRD analysis reveals that all the films grown using the laser energy range 120 J to 230 J are polycrystalline when they are deposited at room temperature in a ~ 10 -5 Torr vacuum. Introducing 0.7 mTorr oxygen pressure, the films show preferred c-axis growth and transforms into a single crystal like film when the substrate temperature is increased to 100 °C. The Scanning Electron Micrographs show the presence of sma ll nano size grains at 25 °C, which grow in size to the regular hexagonal shape particles at 100 °C.Optical transmission of the ZnO film is found to increase with an increase in crystal quality.Maximum transmittance of 95% in the wavelength range 400-1400 nm is achieved for films deposited at 100 °C employing a laser pulse energy of 180 J. The luminescence spectra show a strong UV emission band peaked at 377 nm close to the ZnO band gap.The shallow donor defects increase at higher pulse energies and higher substrate temperatures, which give rise to violet-blue luminescence. The results indicate that nanocrystalline ZnO thin films with high crystalline quality and optical transparency can be fabricated by using pulses from fs lasers.

Ultra-Short Pulsed Laser Deposition of Oxides, Borides and Carbides of Transition Elements

“…This was different to the approach of Hashmi et al, who studied the role of a dopant in the growth of ZnO films [63]. The laser source was the same as already used by the same group [61], while the dopant was samarium. The results indicated that with a Sm percentage of 1 wt %, the films retained the structure of crystalline ZnO with a preferential c-axis orientation, while for higher amounts of Sm, the formation of mixed oxides took place.…”

“…In the same year, Hashmi et al also studied the deposition of ZnO by fs PLD [61]. The laser source (Ti:sapphire) had a wavelength of 800 nm, a pulse duration of 100 fs and a repetition rate of 1 kHz.…”

The role of samarium incorporated structural defects in ZnO thin films prepared by femtosecond pulsed laser deposition

“…In our study these reasons are supported by XRD and AFM results which show that crystallite size is very small that increases number of grain boundaries. Furthermore, the samarium ions and atoms are also considered responsible for deep level emissions in SZO thin films because our previous work on undoped ZnO thin film using similar conditions of femto-PLD [21] did not show these VISIBLE range emission wavelengths.…”

“…Therefore a fs pulsed, regenerative amplified Ti:sapphire laser is used in the present research to fabricate samarium doped ZnO thin films at room temperature by using optimized PLD parameters [21]. Effect of samarium concentration on the structural, optical and electrical properties is investigated by analyzing the phase, topography, optical response, photoluminescence and electrical resistivity of these thin films.…”