Delivered by Ingenta to: Rice University IP: 46.243.173.175 On: Mon, 13 Jun 2016 16:11:09 Copyright: American Scientific Publishers RESEARCH ARTICLE Copyright © 2013 American Scientiﬁc Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 13, 6231–6235, 2013 Luminance Behavior of Lithium-Doped ZnO Nanowires with p-Type Conduction Characteristics Won Bae Ko 1 , Jun Seok Lee 1 , Sang Hyo Lee 1 , Seung Nam Cha 2 , Jung Inn Sohn 2 , Jong Min Kim 2 , Young Jun Park 3 , Hyun Jung Kim 4 , and Jin Pyo Hong 1 ∗ 1 Novel Functional Materials and Device Laboratory, Department of Physics, Research Institute for Natural Science, Hanyang University, Seoul 133-791, Korea 2 Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, United Kingdom 3 Frontier Research Laboratory, Samsung Institute of Advanced Technology, Yongin-si 446-712, Korea 4 Department of Semiconductor Science, Dongguk University, Seoul 100-715, Korea The present study describes the room-temperature cathodeluminescence (CL) and temperature- dependent photoluminescence (PL) properties of p-type lithium (Li)-doped zinc oxide (ZnO) nanowires (NWs) grown by hydrothermal doping and post-annealing processes. A ZnO thin ﬁlm was used as a seed layer in NW growth. The emission wavelengths and intensities of undoped ZnO NWs and p-type Li-doped ZnO NWs were analyzed for comparison. CL and PL observations of post-annealed p-type Li-doped ZnO NWs clearly exhibited a dominant sharp band-edge emis- sion. Finally, a n-type ZnO thin ﬁlm/p-type annealed Li-doped ZnO NW homojunction diode was prepared to conﬁrm the p-type conduction of annealed Li-doped ZnO NWs as well as the structural properties measured by transmission electron microscopy. Keywords: Zinc Oxide, p-Type Characteristics, Lithium, Nanowires. 1. INTRODUCTION The wide-bandgap semiconductor ZnO is increasingly becoming a leading candidate for next generation opto- and microelectronics due to its high exciton binding energy, thermochemical stability, environmental compati- bility, and potential applications for light-emitting devices and photovoltaics. 1 2 However, the synthesis of a stable and reproducible p-type ZnO material with satisfactory concentration and high mobility still remains a challenging problem. The most often studied dopants are the group-V atoms: N, 2 P, 3 As, 4 and Sb. 5 6 As an alternative, group-I dopants have been proposed. 7–10 The difﬁculties in obtaining p-ZnO have been recognized to be related to several factors, such as limited dopant solubility, compensation by native donors, and the unintentional incorporation of hydrogen as a shallow donor. Simple theoretical calcu- lations suggest that Li interstitials (Li i  inside ZnO host materials can behave as donors and also work as shallow ∗ Author to whom correspondence should be addressed. acceptors on zinc sites (Li Zn . 11–13 In general, Li-doped ZnO is highly resistive due to self-compensation and a low energy barrier for Li to switch between interstitial and substitutional sites. Previous analyses by other research groups have indicated that Li concentration and the elec- trical properties of the ZnO host material can be manip- ulated by vacancy cluster gettering or high-temperature treatments. 14 15 However, despite major progress over the last few years, the understanding of the role of dopants and other impu- rities, as well as of native defects, is still incomplete. The effect of post-annealing on ZnO nanostructures has also not yet been addressed in detail, even though recent studies have suggested that post-annealing can raise the near-band emission efﬁciency of ZnO ﬁlms and nanostructures. Cathodeluminescence (CL) and photoluminescence (PL) are well known to excite individual nanosized materials and are widely used to characterize their luminescence properties. In particular, CL measurements provide use- ful information regarding the excitation and de-excitation mechanisms of doped-ZnO nanomaterials, as well as the optimum acceleration range and current densities. J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 9 1533-4880/2013/13/6231/005 doi:10.1166/jnn.2013.7700 6231