Abstract
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 1018 cm−3, which is much larger than the 1016 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 AlZn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.