Processing of rare earth doped GaN with ion beams
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Processing of rare earth doped GaN with ion beams K. Lorenz1, U. Wahl1, E. Alves1, T. Wojtowicz2, P. Ruterana2, S. Dalmasso3, R.W. Martin3, K.P. O`Donnell3, S. Ruffenach4, O. Briot4, A. Vantomme5 1 Instituto Tecnológico e Nuclear, EN10, 2686-953 Sacavém, Portugal 2 LERMAT, FRE 2149, CNRS-ENSICAEN, 1450 Caen, France 3 Department of Physics, University of Strathclyde, Glasgow, G4 0NG, U.K. 4 GES, Université de Montpellier II, 34095 Montpellier, France 5 Instituut voor Kern- en Stralingsfysica, KULeuven, 3001 Leuven, Belgium ABSTRACT GaN epilayers grown by MOCVD were implanted with different fluences of thulium at room temperature and at 500 oC in order to find the optimum implantation conditions. Rutherford backscattering spectrometry in the channeling mode was used to monitor the damage evolution in the Ga-sublattice and to establish the lattice site location of the thulium ions. The nature of structural defects was studied with transmission electron microscopy and the optical properties of the samples with room temperature cathodoluminescence. The introduced damage could be significantly reduced by implantation at high temperature for fluences up to 5×1015 Tm/cm2. Annealing was necessary for optical activation of the implanted samples, in all cases. After annealing, sharp rare earth related emissions were observed in the blue and in the near infra-red spectral region. INTRODUCTION Doping of GaN with rare earth (RE) elements allows the production of electroluminescent emitters that cover the entire visible wavelength range. This represents an alternative route to develop integrated, all-nitride light-emitting devices for several applications in display technology. Doping GaN-films by ion implantation resulted in red (Eu, Pr), green (Er) and blue (Tm) luminescence [1-4]. The implantation technique has the advantage of an exact control of the concentration and depth distribution of the incorporated ions as well as the possibility of producing a lateral patterning. However, the influence of the retained implantation damage and the required post implant annealing on structural and luminescence properties needs further investigation. Although GaN is very stable against radiation damage and reveals a high capacity of dynamic annealing during the implantation as compared to other compound semiconductors like e.g. GaAs [5], the high RE concentrations necessary for electroluminescent devices cause considerable lattice damage. Annealing of GaN is known to be difficult because at the high temperatures needed to remove the lattice damage the crystal already starts to dissociate due to out-diffusion of nitrogen. Therefore it is convenient to develop implantation methods that already diminish the damage produced during the implantation such as implanting along major crystal directions (channeled implantation) or at elevated temperatures [6-8]. In this work we study structural and optical properties of Tm-implanted GaN for different implantation fluences and implantation temperatures.
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EXPERIMENTAL DETAILS Thulium
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