Effects of Ga doping on optical and structural properties of ZnO epilayers |
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| Authors: | IA Buyanova XJ Wang WM Wang CW Tu WM Chen |
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| Institution: | 1. Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden;2. Department of Electrical and Computer Engineering, UC California, La Jolla, USA;1. School of Materials Science and Engineering, Changsha University of Science and Technology, Changsha 410004, PR China;2. Hunan Provincial Engineering Research Center of Electric Transportation and Smart Distribution Network, Changsha University of Science and Technology, Changsha 410114, PR China;3. School of Metallurgy and Environment, Central South University, Changsha 410083, PR China;1. Physics Department, Faculty of Science, Suez Canal University, 41522 Ismailia, Egypt;2. Texas State University-San Marcos, Department of Chemistry and Biochemistry, 601 University Dr., San Marcos, TX 78666, USA;3. Department of Basic Science, Higher Technological Institute, 44629 10th of Ramadan City, Egypt;1. Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan;2. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan |
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| Abstract: | Effects of Ga incorporation on electrical, structural and optical properties of ZnO epilayers are systematically studied by employing structural and optical characterization techniques combined with electrical and secondary ion mass spectrometry measurements. A non-monotonous dependence of free electron concentrations on Ga content is observed and is attributed to defect formation and phase separation. The former process is found to dominate for Ga concentrations of around 2–3×1020 cm?3. The corresponding defects are suggested to be responsible for a broad red emission, which peaks at around 1.8 eV at 4 K. Characteristic properties of this emission are well accounted for by assuming intracenter transitions at a deep center, of which the associated Huang–Rhys factor and mean phonon energy are determined. For higher Ga doping levels, the phase separation is found to be significant. It is suggested that under these conditions only a minor fraction of incorporated Ga atoms form shallow donors, which leads to the observed dramatic decrease of carrier concentration. |
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