Challenges in controlling the electrical conductivity in ZnO:
Diffusion of Ion Implanted elements and self-diffusion
Vishnukanthan Venkatachalapathy1
Department of Physics/ Centre for Materials Science and Nanotechnology, University of Oslo, P.O.Box 1048 Blindern, NO-0316 Oslo, Norway
Rediscovered in the last decade, zinc oxide (ZnO) shows a great potential for a variety of optoelectronics and microelectronics applications, owing to its unique electronic and optical properties. However, most of the device structures explored have so far been based on hetero-epitaxial ZnO films grown on other substrates due to non-availability of high quality ZnO substrates. Regrettably, the hetero-epitaxial structures suffer from high density of threading dislocations due to lattice-parameter and thermal-expansion mismatch. Doping technologies for mass production of n- and p-type highly conductive ZnO substrates need to be developed for device applications. Importantly, P-type doping is difficult and is a narrow bottle-neck issue as ZnO is intrinsically n-type. In relation to the doping problems, concentrations and types of point defects acting as donors and acceptors in bulk ZnO produced by different techniques should be assessed accurately. It is also worth mentioning that the lack of mid-gap donor/acceptors would hamper efforts to obtain high resistivity wafers. More insight on the defects in bulk ZnO can be obtained by controlled defect introduction. Influence of different dopants on the formation of intrinsic defects and its complexes can be systematically studied by combining (i) Ion implantation followed by post-anneals and (ii) Doping in ZnO by different thin film growth techniques. Influence of different dopants on the formation of defect complexes, electrical properties and diffusion of these dopants will be discussed. Another important issue of ZnO as transparent conducting oxide replacing commercial ITO/FTO is conductivity limitations in n+-ZnO due to self-compensation. Arguably, Zinc vacancy (VZn) is a defect of paramount importance in ZnO due to its potential acceptor action and involvement in acceptor-like complexes. Arrhenius analysis of self-diffusion is a direct method probing intrinsic defect energetics as long as the atomic jumps are mediated by defects. Thus, assuming that Zn self-diffusion occurs via vacancy assisted mechanism, the energetics of Zn vacancies can be estimated. Effects of chemical potential (μ) and Fermi level position (EF) on Zn self-diffusion in isotopically modulated ZnO hetero-structures will also be presented.
Time: 10:00-11:00, October 28th
Location: Seminar Room 326, Chao KuangPiu Building
Coordinator: Prof. Jingyun Huang
