Structural and Optical Properties of ZnS:Mn Films Grown by Pulsed Laser Deposition
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Structural and Optical Properties of ZnS:Mn Films Grown by Pulsed Laser Deposition
K. M. Yeung, S. G. Lu, C. L. Mak* and K. H. Wong Department of Applied Physics and Materials Research Centre, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China. * corresponding author: [email protected] ABSTRACT
High-quality manganese-doped zinc sulfide (ZnS:Mn) thin films have been deposited on various substrates using pulsed laser deposition (PLD). Effects of back-filled Ar pressure and substrate temperature on the structural as well as optical properties of ZnS:Mn films were studied. Structural properties of these films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Photoluminescence (PL) and optical transmittance were used to characterize the optical properties of these films. Our results reveal that ZnS:Mn films were polycrystalline with a mixed phase structure consisting of both wurtzite and zinc-blende structure. The ratio of these two structures was strongly depended on the change of substrate temperature. Low substrate temperature facilitated the formation of zinc-blende structure while the wurtzite phase became dominant at high substrate temperature. ZnS:Mn films with preferred wurtzite structure were obtained at a substrate temperature as low as 450°C. An orange-yellow emission band was observed at ∼590 nm. As the substrate temperature increased, the peak of this PL band shifted to a shorter wavelength. Furthermore, shifts in the absorption edge and the energy gap due to the change in substrate temperature were also observed. The variation in these optical properties will be correlated to their structural change.
INTRODUCTION
Zinc sulfide (ZnS) thin films have received much attention in view of their wide applications to opto-electronic devices, in particular, electroluminescent (EL) devices. Different techniques have been employed to prepare ZnS films, such as sputtering [1], metallo-organic chemical vapour deposition [2], molecular beam epitaxy [3], atomic layer epitaxy[4], sol-gel[5], spray pyrolysis[6] and pulsed laser deposition (PLD)[7, 8]. Among various techniques, PLD is a promising method for thin film deposition because of its low substrate temperature, good stoichiometry, fast deposition rate and relative simple setup. In this study, high quality ZnS:Mn films were fabricated by PLD method. Effects of different processing parameters (back-filled Ar pressure and substrate temperature) on the structural properties of these ZnS:Mn films were investigated. Changes in optical transmittance and photoluminescence properties associated with the structural change were also studied.
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EXPERIMENTAL DETAILS
Laser ablation of ZnS:Mn was carried out with an ArF excimer laser (Lambda Physik, 193 nm, 20 ns) focused on the rotating target at an incidence angle of 45°. The laser fluence was ~ 2 J/cm2. The ZnS target used in this work were doped with Mn of 1% by weight and obtained from Target Materials, Inc. Deposition experiments were performed in a vacuum cham
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