Mobility vs thickness in n+-ZnO films: Effects of substrates and buffer layers |
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| Affiliation: | 1. University of Oslo, Centre for Materials Science and Nanotechnology, 0318 Oslo, Norway;2. Department of Applied Physics, Aalto University, P.O. Box 15100, Aalto, 00076 Espoo, Finland;1. State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China;2. Huize Cigarette Factory, Hongyun Honghe Tobacco (Group) Co. Ltd, Huize 654200, China;1. The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch 8043, New Zealand;2. Department of Electrical and Computer Engineering, Western Michigan University, Kalamazoo, MI 49008-5329, USA;1. College of Physics & State Key Laboratory, Qingdao University, No. 308, Ningxia Road, Qingdao 266071, People’s Republic of China;2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China;1. University of Sfax, Research Unit: PMISI, Sfax, Tunisia;2. University Lille North of France, ULCO, UDSMM, 62228 Calais, France;3. University Lille North of France, ULCO, UDSMM, 59140 Dunkerque, France;4. Hebei Union University, Electrical Engineering, 46 Xinhua Road, Tangshan 063009, Hebei, China |
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| Abstract: | We review recent work on thickness effects in thin films of Ga- and Al-doped ZnO (GZO and AZO, respectively) grown by pulsed laser deposition (PLD), RF sputtering (RFS), or molecular beam epitaxy (MBE), and comprising four, distinct types of structures: (1) films grown directly on lattice-mismatched substrates; (2) films grown on buffer layers on lattice-mismatched substrates; (3) films grown on lattice-matched bulk substrates; and (4) homoepitaxial films with nearly perfect interfaces. Representative examples of each type include: 1a) PLD-GZO/Si; 1b) RFS-AZO/quartz; 2) RFS-AZO/ZnON/quartz; 3) PLD-GZO/bulk-ZnO; and 4) MBE-GZO/MBE-ZnO/GaN. Samples 1a, 1b, 2, and 3 can all be well described by a simple, phenomenological model for the thickness (d) dependence of sheet concentration ns and mobility μ: ns(d)=n(∞)(d - δd), and μ(d)=μ(∞)/[1+d*/(d-δd)], where n(∞) is the predicted volume carrier concentration at d=∞ (i.e., the bulk value), δd is the thickness of the dead layer (if any) between film and substrate, μ(∞) is the predicted mobility at d=∞, and d* is a figure of merit for the electrical properties of the interface. Samples 1a, 1b, 2, and 3, are well explained by the model with d*=23, 22, 7, and 3 nm, respectively. However, sample 4 does not obey the d* model at all and must be explained by entirely different physics. The films are characterized by Hall-effect, X-ray reflectance, X-ray photoelectron spectroscopy, reflectance, and transmittance measurements. |
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| Keywords: | Mobility Thickness dependence Substrates Buffer layers Hall effect Reflectance |
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