title: Critical increase in Na-doping facilitates acceptor band movements that yields ~180 meV shallow hole conduction in ZnO bulk crystals.
abstract: Stable p-type conduction in ZnO has been a long time obstacle in utilizing its full potential such as in opto-electronic devices. We designed a unique experimental set-up in the laboratory for high Na-doping by thermal diffusion in the bulk ZnO single crystals. SIMS measurement shows that Na concentration increases by 3 orders of magnitude, to ~3 × 1020cm-3as doping temperature increases to 1200 °C. Electronic infrared absorption was measured for Na-acceptors. Absorption bands were observed near (0.20-0.24) eV. Absorption bands blue shifted by 0.04 eV when doped at 1200 °C giving rise to shallow acceptor level. NaZnband movements as a function of doping temperature are also seen in Photoluminescence emission (PL), Photoluminescence excitation (PLE) and UV-Vis transmission measurements. Variable temperature Hall measurements show stable p-type conduction with hole binding energy ~0.18 eV in ZnO samples that were Na-doped at 1200 °C.
authors.affiliation: Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Narendra S
authors.initials: NS
authors.lastname: Parmar
authors.affiliation: Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Haena
authors.initials: H
authors.lastname: Yim
authors.affiliation: Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Choi