Plasma-Assisted MOCVD Growth of ZnO Thin Films
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Plasma-Assisted MOCVD Growth of ZnO Thin Films Maria Losurdo, Maria M. Giangregorio, Pio Capezzuto, Giovanni Bruno Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, and INSTM, UdR Bari, via Orabona, 4 – 70126 Bari, Italy Graziella Malandrino, Manuela Blandino, Ignazio L. Fragalà Dipartimento di Scienze Chimiche, Università di Catania, and INSTM, UdR Catania, Viale A. Doria 6, I-95125 Catania, Italy ABSTRACT ZnO thin films have been grown by metalorganic chemical vapor deposition (MOCVD) also plasma assisted (PA-MOCVD) on c-axis oriented sapphire (0001) and Si(001) substrates using the alternative Zn(TTA)2•tmed (HTTA=2-thenoyltrifluoroacetone,TMED=N,N,N’,N’tetramethylethylendiamine) precursor. The structural, morphological and optical properties of ZnO films have been investigated. The results show that the O2 plasma assisted growth results in an improvement of the structure, in smoother morphologies and in a better optical quality with a sharp and intense exciton of ZnO films. INTRODUCTION ZnO is a wide band gap (Eg = 3.37 eV) semiconductor material that has recently attracted much interest because of its high photocatalytic activity, and its applications in optoelectronic devices, such as short- wavelength lasers and light-emitting diodes, due to its strong excitonic feature and lasing properties even at room temperature [1]. ZnO nanostructures have also numerous applications in different areas including piezoelectric transducers, phosphors, sensors and transparent conducting films. In the past decade, research efforts have focused on the growth of ZnO thin films using a large variety of deposition techniques such as sputtering, spray pyrolysis, sol-gel, electron-beam deposition. However, the importance of metalorganic chemical vapor deposition (MOCVD) also plasma-assisted (PA-MOCVD) [2] for the growth of ZnO should be re-considered, since this technique has enabled the commercial application of GaN and related materials. In the particular case of ZnO, the high molecular bonding energy of 5.16eV [3] prevents thermal dissociation of oxygen at the substrate surface at growth temperatures
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