JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 16 (2 0 0 5 ) 397 – 401 Synthesis and photoluminescence of ZnO nanowires/nanorods J. GRABOWSKA, K. K. NANDA † , E. MCGLYNN ∗ , J.-P. MOSNIER, M. O. HENRY, A. BEAUCAMP, A. MEANEY School of Physical Sciences & National Centre for Plasma Science & Technology, Dublin City University, Ireland E-mail: enda.mcglynn@dcu.ie We report growth of ZnO nanowires on various substrates using a vapour phase transport method and show that the growth mechanism is vapour-liquid-solid growth. We present photoluminescence data for samples grown on a-plane sapphire at room and low temperatures indicating that the optical quality of these structures is potentially excellent, with intense emission and narrow bound exciton linewidths. The intensity decays rapidly with increasing temperature, indicating a strong temperature-activated non-radiative mechanism whose origin is unclear. We observe a high energy excitonic emission close to the band edge which we assign to the “surface” exciton in ZnO at ∼3.368 eV. This assignment is consistent with the large surface to volume ratio of the nanowire systems under consideration and also indicates that this large ratio has a significant effect on the luminescence even at low temperatures. These surface effects may also be responsible for the rapid decay of the luminescence with increasing temperature via a temperature-activated surface recombination. The nanowire systems appear to offer the prospect of extremely efficient excitonic emission for device applications, and we note that one of the important aspects of achieving this potential will be control of the surface effects via passivation or other means. C  2005 Springer Science + Business Media, Inc. 1. Introduction ZnO is receiving renewed attention for wide band-gap device applications due to a number of advantages it presents in comparison with GaN, e.g. larger exciton binding energy, availability of large area substrates for homo-epitaxy etc. [1]. ZnO is a wide bandgap semicon- ductor (∼3.37 eV at room temperature), which is suit- able for short-wavelength optoelectronic applications. The high exciton binding energy of 60 meV (which is larger than the thermal energy at room tempera- ture) promises an efficient excitonic emission at room temperature under low excitation intensity [2]. In this regard ZnO is a promising photonic material for the UV/blue devices such as short wavelength light emit- ting diodes and laser diodes in optoelectronics, but also is promising material in spintronics, if doped with mag- netic impurities. One-dimensional (1-D) nanoscale materials, such as nanotubes [3], nanowires [4], and nanobelts [5] and other structures [6, 7], have attracted much atten- tion because of their interesting properties for under- standing fundamental physical concepts and for poten- tial applications [6, 7]. The growth of single-crystal semiconductor hollow nanotubes would be advanta- geous in potential nanoscale electronics, optoelectron- ics and biochemical-sensing applications. As the lumi- † Present address: Materials Research Centre, Indian Institute of Science, Bangalore 560012, India. ∗ Author to whom all correspondence should be addressed. nescence of ZnO is very sensitive to its surface state, ZnO whiskers with a high surface to bulk ratio are ex- pected to make possible novel practical applications for electro-optical devices and chemical sensors. The fabrication of nanometer-sized 1-D materials has at- tracted considerable attention because of their funda- mental importance in the understanding of mesoscopic phenomenon as well as their potential in the develop- ment of nanodevices. In this paper we study the low temperature lumines- cence properties of ZnO nanowires grown on sapphire with particular attention to their excitonic structure and the influence of the large surface to volume ratio. 2. Experimental details ZnO nanowires in our experiments are grown on var- ious substrates (Si, SiO 2 , Al 2 O 3 ) with a vapour phase transport (VPT) process using Au as a catalyst on the substrate [4, 8]. In this process, Au (in thin film form) was first deposited on a substrate and subsequently an- nealed, causing it to bead into droplets, and ZnO powder was vaporized and condensed on the particles, result- ing in catalysed epitaxial growth of the ZnO nanowires. The diameter of the nanowires can be tuned by con- trolling the size of the Au particles through control 0957–4522 C  2005 Springer Science + Business Media, Inc. 397