RBS ion channeling study of low concentrations of ion implanted samarium in GaN David C. Ingram a, * , Henryk Lozykowski b , Wojciech M. Jadwisienczak b a Condensed Matter and Surface Science Program, John E. Edwards Accelerator Laboratory, Department of Physics and Astronomy, Ohio University, Athens, OH 45701-2979, USA b Condensed Matter and Surface Science Program, School of Electrical Engineering and Computer Science, Ohio University, Athens, OH 45701, USA Abstract Thepurposeofthisworkistodeterminethelocationanddepthprofileofsamariumimplantedintogalliumnitride. The concentrations of the dopant are extremely low (100 ppm) which means that the measurements take a large integratedchargetocompletesothatapulsepileupsystemmustbeemployedtoenablecountratesupto100kHztobe used.Althoughthedopantsaremoremassivethanthesubstratetheyarestilldifficulttoresolvewith2MeVRBS.By takingadvantageofthe a-particleenergyavailablefroma4.5MVtandem,spectrahavebeenobtainedwheretherare earth dopants are easily visible. Using ion channeling angular scans across more than one axis it is possible to confirm the extent to which an impurity is substitutional, interstitial or randomly located in the host lattice. For the GaN wurtzite lattice with the c-axis Æ1000æ perpendicular to the surface the alternative axes are Æ1  101æ and the Æ11  21æ. The data show that samariumissubstitutionaltoalevelofabout80%withtheremainderrandomlylocatedinthelattice.Althoughthereis ahigherconcentrationoftherareearthclosertothesurface,thesubstitutionalfractiondoesnotchangesignificantlyas a function of depth. The samarium concentration in the sample varied from about 100 ppm at 300 nm below the surface to about 300 ppm at the surface. Ó 2004 Elsevier B.V. All rights reserved. Keywords: RBS channeling; GaN rare earth dopants; Atom location 1. Introduction As a direct wide band gap semiconductor gal- lium nitride is an ideal candidate to be a host of optically active elements. To this end there have been many studies of the properties of rare earth elements, or elements from the lanthanide group, where the 4f orbits may be useful in producing light in the 380–1000 nm range of wavelengths [1,2]. These studies involved the ion implantation of these optically active dopants and the sub- sequentannealingofthesamples.Inthispaperwe report, for the first time, the samarium concen- tration profile and substitutional fraction as a function of depth, and the crystallinity of the substrate. * Corresponding author. Tel.: +1-740-593-1705; fax: +1-740- 593-1436. E-mail address: ingram@ohio.edu (D.C. Ingram). 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.01.145 Nuclear Instruments and Methods in Physics Research B 219–220 (2004) 699–702 www.elsevier.com/locate/nimb