High Temperature Implantation of Tm in GaN
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High Temperature Implantation of Tm in GaN K. Lorenz1, U. Wahl1, E. Alves1, S. Dalmasso2, R.W. Martin2, K.P. O`Donnell2 1 ITN, Estrada Nacional 10, 2686-953 Sacavém, Portugal 2 Department of Physics, University of Strathclyde, Glasgow, G4 0NG, U.K. ABSTRACT Thulium ions were implanted into MOCVD grown GaN films with a fluence of 2.5×1015 at/cm2 at temperatures between 20 and 500 °C. The lattice damage introduced by the implantation and the effect of post-implant annealing were investigated using the Rutherford backscattering/channeling (RBS/C) technique. Whereas for room temperature implantation the implanted layer becomes amorphous, high temperature implantation inhibits amorphisation. For implantation temperatures higher than 300 °C the RBS/C results clearly show two different damage regions - one at the surface and the second deeper in the crystal coinciding with the Tm depth profile. Annealing causes a decrease of the surface damage as well as initiating regrowth from the unimplanted bulk GaN. For the samples that were not completely amorphous a large part of the Tm atoms were found to be incorporated in Ga-sites. The optical properties of the ion implanted GaN films have been studied by room temperature cathodoluminescence. Directly following the implantation no Tm-related luminescence was observed. Subsequent annealing of the samples achieved optical activation, revealing well-defined emissions due to intra-4f-shell transitions of the Tm3+ ions in the blue spectral range at 477 nm and in the near infra-red at 804 nm. INTRODUCTION Optical doping of GaN with rare earth (RE) ions has been the subject of intense investigation due to its promising luminescence characteristics. Light emission spanning the entire visible spectral range opens the possibility to develop integrated, all-nitride light-emitting devices for several applications in display technology [1]. Doping has been performed during growth [2-5] or by ion implantation into GaN films [6-9], resulting in red (Eu, Pr), green (Er) and blue (Tm) luminescence. 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 which is difficult to obtain by growth techniques [10]. However, the influence of the correlated lattice damage and the required post-implant annealing on the luminescence properties needs further investigation. The combination of the Rutherford backscattering (RBS)/channeling technique and optical measurements provides a powerful tool allowing determination of the lattice site of the RE ions as well as the level of incorporated damage and the correlation of these structural features with the optical properties of the system. High temperature implantation has been shown to decrease the radiation damage during Tm implantation into GaN [11]. This work presents detailed studies of the effect of high temperature implantation on the structural and optical properties of Tm-implanted GaN.
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