Pulsed laser deposited nanocrystalline ZnO thin films
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Pulsed laser deposited nanocrystalline ZnO thin films R. K. Thareja,1, 2 A. Mitra,1 V. Ganesan,3 A. Gupta,3 P. K. Sahoo,1 and V.N.Kulkarni1 1
Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208 016 (UP), India,
2
Department of Electrical and Computer Engineering, Kumamoto University, Japan, Inter University Consortium, University Campus, Khandwa Road, Indore
3
(MP) India.
ABSTRACT We report on random laser emission in pulsed laser deposited nanocrystalline ZnO thin films. The deposition was done on silicon and glass substrates in ambient oxygen pressure ranging from 10 mTorr to 1 Torr at room temperature. The deposited films were characterized using XRD, RBS, PL and AFM. The films grown at pressures less than 300 mTorr are found to be preferentially oriented along (002) plane. Morphology of the films deposited at different background pressures showed that the films deposited at lower pressures are significantly smoother than those at higher back ground pressure. PL intensity depends on the stoichiometry of the films and hence on oxygen pressure. Laser action was observed on optically pumping the films with 355 nm radiation. At excitation intensity above threshold, very narrow peaks are observed in the emission spectrum. The dependence of the laser emission on the size of nanocrystallites at different pressures of the ambient gas is presented. INTRODUCTION Wide band gap materials such as GaN and its alloys have been a focal point of research in semiconductor and opto-electronics since the demonstration of high quality GaAlInN based hetrostructures. Besides GaN, ZnO is also being considered as a promising material for UV and blue light emitting devices [1-4]. ZnO, like indium oxide and tin oxide is transparent in the visible and electrically conductive when doped with aluminum or gallium. This property has been widely studied for its practical applications such as transparent conducting electrodes for flat panel displays, solar cells and organic light emitting diodes. Several techniques are being used to produce ZnO films; e.g. Metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), sol-gel deposition, electron plasma P3.37.1
sputtering, reactive evaporation, spray pyrolysis, and pulsed laser deposition (PLD). The main advantages [5] of PLD are its ability to create energetic species of target, ability to reproduce the target composition, permitting high quality film growth at low substrate temperatures. Commercially available compound semiconductor lasers are made of single crystalline films fabricated by epitaxial growth on lattice-matched substrates. However, epitaxial growth techniques are not only expensive but also restricted to the type of substrates used [6]. The substrate restriction and fabrication cost has restricted the application of semiconductor lasers. Recent demonstration of lasing action from polycrystalline zinc oxide thin film on glass substrate as well as powder [7,8], motivated us to study the properties of pulsed laser deposited ZnO thin films
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