The Characterization of N Interstitials and Dangling Bond Point Defects on Ion-Implanted GaN Nanowires Studied by Photoluminescence and X-Ray Absorption Spectroscopy Kuo-Hao Lee, z Jau-Wern Chiou, y Jin-Ming Chen, z Jyh-Fu Lee, z Alain Braud, J Katharina Lorenz, ww Eduardo Alves, ww and In-Gann Chen w,z z Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan y Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan z National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan J Centre de Recherche sur les Ions, les Mate´ riaux et la Photonique (CIMAP), CNRS-CEA-ENSICAEN, Universite´ de Caen, UMR 6252, 14050 Caen, France ww Instituto Tecnologico e Nuclear, Estrada Nacional 10, PT-2685-953 Sacave´ m, Portugal Photoluminescence and X-ray absorption spectroscopy (XAS) measurement were used to characterize the near-band edge (NBE) emission intensity and electronic structure of as- implanted GaN nanowires (NWs) that had been implanted with Eu ions to different fluences. The N K- and Ga L 3 -edge of total electron yield XAS spectra showed the formation of N interstitials (N i ) and dangling bond (N db ) point defects and the formation of metallic Ga layers on the surface of NWs. X-ray diffraction, Ga K- and L 3 -edge of total fluorescence yield XAS spectra consistently revealed the wurtzite structure of the as- implanted NWs up to the highest fluence. The ratio of absorp- tion intensity found in sp 3 and sp 2 environment and the NBE intensity were strongly affected by the implantation. It is sug- gested that the decrease of NBE intensity was closely related to the change from sp 3 to sp 2 environment. The absorption intensity ratio between the as-grown and as-implanted samples of N db and N i was directly proportional to the fluences indicating that these defects are preferentially formed during implantation. I. Introduction N ANOWIRES (NWs) have attracted a great attention of research interest in the past. Semiconductor NWs are promising candidates for applications in sensors, 1 nanoelectron- ics, 2 and light-emitting diodes. 3 NWs have been fabricated by many methods such as catalytic reactions 4 and molecular beam epitaxy. 5 GaN materials doped with rare earth elements allow the production of electroluminescence emitters that cover the visible entire wavelength range. 6–9 Ion implantation is an at- tractive doping method that provides precise control of the pro- file and concentration of the implant. For as-implanted GaN films, typical and common damage features such as planar and point defects were often found in the implanted region. 10 Dhara et al. 11,12 was the first group to investigate the bombardment surface damage of GaN NWs and reported the accumulation of Ga atoms on NW’s surface. However, the research on optical properties and bombardment-induced N-related point defects for GaN NWs is still limited. The aim of the present study was to investigate the impact of implantation on the photolumines- cence (PL) properties and the formation of N-related point defects for as-implanted GaN:Eu NWs. The X-ray absorption spectroscopy (XAS) analysis results not only show the coexis- tence of N interstitials (N i ) and N dangling bond (N db ) defects but also revealed the influence of both point defects on PL properties. II. Experimental Procedure The GaN NWs synthesis process was based on the chemical reaction of Ga vapor and NH 3 gas in the presence of Pt nano- particles. GaN NWs were grown by thermally reacting metallic Ga (3 g) with NH 3 (500 sccm) gas at 9501C and 260 torr for 30 min. 13 A Pt-coated Si substrate was placed 5 cm downstream from the Ga source in a horizontal tube furnace with a diameter of 80 mm and a length of 120 cm. At 9501C, the metallic Ga source evaporated and the Ga vapors diffused from the source area to the Si substrate surface, which was placed 5 cm down- stream from the source. The chemical reaction of Ga vapor and NH 3 gas can be expressed as Ga ðlÞ þ NH 3ðgÞ ! GaN ðsÞ þ 3 2 H 2ðgÞ (1) After the growth processes, the NWs were subsequently implanted with Eu ions at an energy of 300 keV and fluences of 10 13 , 10 14 , and 10 15 cm 2 , respectively. The corresponding concentration of the implant species is 1.9  10 4 , 1.9  10 3 , and 1.9  10 2 at.%, respectively. The typical diameter of NWs is B100 nm and the depth of implanted region is B100 nm. As-grown GaN NWs served as the reference sample for the fol- lowing analyses. Characterizations of the as-implanted GaN:Eu NWs were performed by X-ray diffraction (XRD) and high-res- olution transmission electron microscopy (HRTEM). PL mea- surements were performed using an He–Cd laser. The N K-, Ga K-, and L 3 -edge of XAS measurement were conducted at the high-energy spherical grating monochromator and Wiggler-C beamlines, respectively, of the National Synchrotron Radiation Research Center in Hsinchu, Taiwan. XAS spectra were mea- sured using both total electron yield (TEY) and total fluores- cence yield (TFY) signals, which probe the surface to a depth of o100 A ˚ and the regions deeper than 1000 A ˚ , respectively. C. Jagadish—contributing editor w Author to whom correspondence should be addressed. e-mail: ingann@mail.ncku.edu.tw Manuscript No. 28113. Received May 31, 2010; approved July 10, 2010. J ournal J. Am. Ceram. Soc., 93 [11] 3531–3534 (2010) DOI: 10.1111/j.1551-2916.2010.04059.x r 2010 The American Ceramic Society 3531