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  Physics Express 2013, 3: 9
  Research Article
Studies on optical and electrical characteristics of ZnO thin films grown by atomic layer deposition
  D. Saha, Vikas K. Sahu, Amit K. Das, R. S. Ajimsha, P. Misra, L. M. Kukreja  
Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
  The optical and electrical characteristics and chemical composition of highly transparent ZnO thin films grown on (00.1) sapphire substrates by atomic layer deposition (ALD) technique at different growth temperatures were studied. Substrate temperature was varied from room temperature to ~ 275°C and the ALD window for the growth of ZnO was observed in the range of ~ 140-200°C with a constant growth rate of ~ 0.2 nm/cycle. Near band edge emission (NBE) due to excitonic transitions was observed in the UV spectral region at room temperature in all the films having peak at ~ 380 nm along with deep level emission (DLE) in the visible spectral range. The position of DLE peak was found to shift from orange to green spectral region on increasing growth temperature. The ALD grown ZnO thin films were found to be highly resistive when grown below ALD window and n-type conducting with decreasing resistivity on increasing growth temperature when grown within and above ALD process window. The XPS studies on these films revealed presence of acceptor type point defects such as oxygen interstitials and/or–OH groups which act as free carrier traps in the films grown at low temperatures and oxygen vacancy related donor type point defects when grown above 140°C. The concentrations of these point defects were found to vary with growth temperature. Based on these studies a correlation has been established between photoluminescence, carrier concentration, mobility and native point defects in ALD grown ZnO thin films.
  Atomic layer deposition; Self-limiting growth; Photoluminescence; X-ray photoelectron spectroscopy  

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