期刊
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A
卷 29, 期 3, 页码 -出版社
A V S AMER INST PHYSICS
DOI: 10.1116/1.3549136
关键词
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资金
- State Key Program for Basic Research of China [2011CB302003]
- Project of High Technology Research and Development of China [2007AA03Z404]
- National Natural Science Foundation of China [61025020, 60776013, 60990312]
In this study, the authors investigate the evolution of the structural and electrical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The inserting of a low-temperature ZnO buffer layer not only significantly improves the structural quality of the high-temperature (HT)-grown ZnO epilayer on a sapphire substrate but also results in high background electron concentration in it from the Hall-effect measurement. After subtracting the conductive contribution from a thin degenerated layer mostly formed between the buffer layer and the substrate based on the two-layer model, the deduced electron-carrier concentration is still in the order of 10(18) cm(-3), which is much larger than the 10(16) cm(-3) obtained from capacitance-voltage measurement near the top surface. This indicates that a much thicker layer with high carrier concentration should be formed in the HT-grown ZnO epilayer, which is significantly different from that observed in GaN epitaxy, where only a thin degenerated interfacial layer is suggested to form in the GaN buffer layer. Al atoms' distribution acquired from secondary-ion mass spectrometry shows a strong dependence on the temperature of the ZnO growth process, indicating that a thermally enhanced diffusion mechanism should be responsible for the observation of the enhanced Al atom concentration in the HT-grown ZnO epilayer. As substituted Al atoms on the Zn site act as donors in ZnO, the one-to-one correspondence between Al content and the carrier concentration, as well as the analysis of temperature-dependent Hall-effect measurement, indicates that diffusion-induced gradient-distributed Al-Zn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3549136]
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