Enhanced growth and photoluminescence properties of Sn x N y (x 4 y) nanowires grown by halide chemical vapor deposition Matthew Zervos a,n , Andreas Othonos b a Nanostructured Materials and Devices Laboratory, Materials Science Group, Department of Mechanical Engineering, University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus b Research Center of Ultrafast Science, Department of Physics, University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus article info Article history: Received 29 June 2010 Received in revised form 27 November 2010 Accepted 13 December 2010 Communicated by M. Tischler Available online 17 December 2010 Keywords: A1. Nanostructures A3. Chloride vapor phase epitaxy B1. Nanomaterials B1. Nitrides B2. Semiconducting materials abstract Tin nitride nanowires have been grown by halide chemical vapor deposition via the reaction of Sn with NH 4 Cl at 425 1C under a steady flow of NH 3 using small ramp rates o10 1C/min, which is critical for obtaining a high yield and uniform distribution of nanowires. Tin nitride nanowires with diameters o100 nm and lengths of 2–3 mm were grown on Si and exhibited pronounced peaks in the X-ray diffraction corresponding to Sn rich Sn x N y (x 4y) with a hexagonal structure, i.e. c ¼5.193 ˚ A, a ¼3.725 ˚ A. The excitation of the Sn x N y NWs with UV light of l ¼300 nm at T ¼300 and 77 K gave a broad photoluminescence (PL) spectrum covering 450–750 nm attributed to optical transitions between shallow and deep traps located within the band gap. These traps are most likely related to surface and nitrogen vacancy states. Time correlated, single photon counting PL measurements taken between 450 and 750 nm, showed that the PL decay has a multi-exponential structure, suggesting the existence of complex, non-radiative relaxation paths with relaxation times that are found to become shorter at smaller wavelengths. Finally no significant differences were observed between the PL spectra of the Sn x N y and In doped Sn x N y NWs most likely due to the low level of incorporation of In attributed to differences in the ionic radii of In and Sn but also the larger energy and growth temperatures required for the formation of In–N bonds. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Group III-Nitride (III-N) compound semiconductors such as GaN, InN and AlN have been investigated intensively in view of their applications as electronic and optoelectronic devices [1–3]. In particular group III-N semiconductors are attractive, since their band-gap can be tailored from 0.7 eV in InN [4] up to 6.2 eV in AlN [5,6]. In contrast there are only a few investigations on group IV-N compounds such as Ge 3 N 4 [7,8] and Sn 3 N 4 [9–21]. So far Sn 3 N 4 thin films have been grown by a variety of methods [11–18], including, atmospheric pressure chemical vapor deposition (APCVD) using halides [11,12], metal organic chemical vapor deposition (MOCVD) [13], sputtering [14–17] and ammonothermal synthesis [18,19]. Even fewer investigations have been carried out on nanostructured Sn 3 N 4 . To be specific Sn 3 N 4 nanoparticles (NPs) have been obtained by Nand et al. [20] via CVD using SnCl 4  5H 2 O as a solid precursor, while more recently Sn x N y nanowires (NWs) with average dia- meters of E200 nm and lengths of o5 mm were grown for the first time via the reaction of Sn with NH 4 Cl under a steady flow of NH 3 but their yield and uniformity was limited [21]. Here we show that a higher yield and uniform distribution of Sn x N y NWs can be obtained by controlling the sublimation of NH 4 Cl which leads to the growth of straight Sn x N y nanowires with diameters o100 nm and lengths of 2–3 mm exhibiting pronounced peaks in the X-ray diffraction, not previously observed and corresponding to hexagonal, Sn-rich Sn x N y (x 4y). More impor- tantly we have carried out for the first time photoluminescence (PL) measurements on these Sn x N y NWs and obtained a broad emission spectrum spanning 450–750 nm with a maximum at 530 nm. Time correlated single photon counting (TCSPC) measurements revealed that the PL decay has a multi-exponential structure, suggesting the existence of complex, non-radiative relaxation paths which are available to the photogenerated carriers and are most likely related to surface and nitrogen vacancy states. 2. Experimental method The Sn x N y NWs were grown using an atmospheric pressure chemical vapor deposition (APCVD) reactor which consists of four mass flow controllers (MFC’s) and a horizontal quartz tube furnace, capable of reaching a maximum temperature of 1100 1C. Initially, fine Sn powder (Aldrich, o150 mm, 99.5%) and NH 4 Cl (VWR Int 99.9%) were weighed and mixed thoroughly in a quartz boat and a square piece of Si(0 0 1) E7  7 mm 2 coated with 1–2 nm of Au was loaded Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.12.029 n Corresponding author. Tel.: + 357 22892194; fax: + 357 22892254. E-mail address: zervos@ucy.ac.cy (M. Zervos). Journal of Crystal Growth 316 (2011) 25–29