Electron micro-probe analysis and cathodoluminescence spectroscopy of rare earth - implanted GaN
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Electron micro-probe analysis and cathodoluminescence spectroscopy of rare earth - implanted GaN S. Dalmassoa, R.W. Martina, P.R. Edwardsa, V. Katchkanova, K.P. O’Donnella, K. Lorenzb, E. Alvesb, U. Wahlb, B. Pipeleersc, V. Matiasc, A. Vantommec, Y. Nakanishid, A. Wakaharad, A. Yoshidad a
Department of Physics, University of Strathclyde, Glasgow G4 0NG, U.K. Dept. Física, Instituto Tecnológico e Nuclear, Sacavém PT-2685-953, Portugal c Katholieke Universiteit Leuven, B-3001 Leuven, Belgium d Dept. of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, 441-8580, Japan b
ABSTRACT GaN films doped with rare earth (RE) elements have attracted considerable attention due to the unique optical luminescent properties of the RE intra 4f(n)-shell electron transitions which lead to sharp blue (Tm), green (Er) and red (Eu) emissions. This paper presents an overview of investigations of GaN films implanted with each of these ions using a combination of electronbeam and optical techniques. The ion implantations were performed under a wide range of conditions, covering variations in fluences, energies and temperatures and followed by different high-temperature annealing steps. The resulting RE:GaN films were analysed using an electron probe micro-analyser modified to allow cathodoluminescence (CL) spectroscopy. Elemental microanalysis data obtained by wavelength dispersive X-ray analysis (WDX) is correlated with simultaneously collected room temperature CL spectra. WDX allows the quantification of the RE elemental concentrations in GaN down to ~ 0.03 at. % in very thin layers (~ 100 nm deep). Furthermore, by varying the incident electron beam energy, details concerning the depth profile of RE implants can be determined. The effects of both implantation conditions and rapid thermal annealing on the depth profile and on the luminescence properties are reported. CL measurements performed on annealed samples reveal sharp visible and near IR emission lines characteristic of the RE3+ intra-4f(n) atomic shell transitions. INTRODUCTION The utilisation of rare earth (RE) ions for optoelectronics applications such as luminescent phosphors and solid-state lasers has a long history. Doping GaN with RE is attractive for two different reasons. The first concerns the specific optical properties of the RE, with very sharp visible and IR transitions due to intra 4f(n)-shell electron transition. By choosing the appropriate elements, blue (Tm), green (Er) and red (Eu) emission can be obtained. Secondly, GaN is particularly attractive as a host due to its unique properties, such as its large band gap, radiation hardness, and high thermal and chemical stability Therefore, RE-doped GaN represents an interesting alternative route to the production of large-scale outdoor displays. Recent progress in this area has led to the demonstration of blue, green and red electroluminescent devices, [1]. However the physical mechanisms and structures that are responsible for the luminescence
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continue to be poorly
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