Investigations on the growth and optical properties of one dimensional ZnO nanostructures grown by radio frequency magnetron sputter deposition P. Sundara Venkatesh a , V. Ramakrishnan b , K. Jeganathan a, * a Centre for Nanoscience and Nanotechnology, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamilnadu, India b Department of Laser Studies, School of Physics, Madurai Kamaraj University, Madurai 625 021, Tamilnadu, India 1. Introduction Various deposition techniques [1–7] have been employed for the fabrication of one dimensional (1D) zinc oxide (ZnO) nanostructures. Among the various physical vapor deposition techniques, the magnetron sputter deposition has received a great attention due to its high throughput and high quality of deposition at low cost. It is widely used, because of the large area deposition of thin films/ nanostructures under various sputtering conditions such as substrate temperature, sputtering pressure and sputtering power. ZnO is a well known compound semiconductor with a wide band gap of 3.37 eV and a large exciton binding energy (60 meV) at room temperature which attracted considerable attention as a promising material for the fabrication of optoelectronic devices such as light emitting diodes and laser diodes with high operating temperature. The main advantage of ZnO in the field of optoelectronic applications is its large exciton binding energy as compared to other materials such as GaN and ZnSe [8]. This value is approximately equal to 2.4 times the room temperature thermal energy. Hence, it is a very suitable material for the fabrication of optoelectronic devices with high optical efficiency. Nevertheless, the understanding of exciton recombination and point defects in 1D ZnO nanostructures are very important for the applications perspective. Low temperature photoluminescence (LTPL) studies are essen- tial to analyze the point defects, because the room temperature photoluminescence (PL) spectra may exhibit dominant ultraviolet (UV) and no defect mediated emissions in the visible region even in presence of considerable point defects in the nanostructures [9]. The point defects will affect the electrical and optical properties of the materials which will reduce the efficiency of the devices. Hence, many research groups have paid more attention on the analysis of point defects and correlate them with the visible emissions to divulge the origin of transitions [10]. Therefore, a careful analysis of point defects and their correlation with the emissions are very essential. In the sputter deposition technique, the composition of argon and oxygen plays a major role in the quality and morphology of the nanostructures. It was observed that the crystalline nature of the nanowires was enhanced from polycrystalline to single crystalline by the introduction of oxygen into the chamber, but there is no noticeable change in the surface morphology of the nanowires [6]. Furthermore, the argon sputtering pressure plays an important role in the microstructure formation of the thin films and the high crystallinity of the films with larger grains are ascribed to the decrease in the collisions under low argon sputtering pressure [11]. Materials Research Bulletin xxx (2013) xxx–xxx A R T I C L E I N F O Article history: Received 28 January 2013 Received in revised form 3 May 2013 Accepted 27 May 2013 Available online xxx Keywords: A. Nanostructures A. Semiconductors B. Sputtering C. Raman spectroscopy D. Luminescence A B S T R A C T We report the fabrication of one dimensional ZnO nanostructures under various argon sputtering pressures by radio frequency magnetron sputter deposition technique. The transition of the nanostructures from vertical to inclined is monotonously increased with the argon sputtering pressure owing to the decrease in migration length of the adatoms by the increased number of collisions. The blue shift, intensity quenching and peak broadening of A 1 (LO) phonon mode in the Raman spectra indicates the increase of free carrier concentration with the argon sputtering pressure due to the enhancement of point defects such as zinc and oxygen vacancies. The dominant neutral donor to bound exciton emission with narrow full width at half maximum implies the high optical quality of the nanostructures irrespective of argon sputtering pressure. The characteristic of visible emission at 3.01 and 2.28 eV provides a strong evidence for the existence of zinc and oxygen vacancies in ZnO nanostructures. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Fax: +91 431 2497 045/2407 020. E-mail addresses: kjeganathan@yahoo.com, jagan@physics.bdu.ac.in (K. Jeganathan). G Model MRB-6774; No. of Pages 6 Please cite this article in press as: P.S. Venkatesh, et al., Mater. Res. Bull. (2013), http://dx.doi.org/10.1016/j.materresbull.2013.05.089 Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.05.089