Extended X-ray Absorption Fine Structure Studies of GaN Epilayers Doped in situ with Er and Eu During Molecular Beam Epi
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Y5.10.1
Extended X-ray Absorption Fine Structure Studies of GaN Epilayers Doped in situ with Er and Eu During Molecular Beam Epitaxy V. Katchkanov1, 2, J.F.W. Mosselmans2, S. Dalmasso1, K. P. O’Donnell1, R.W. Martin1, O. Briot3, N. Rousseau3, G. Halambalakis3 1 Department of Physics, Strathclyde University, 107 Rottenrow East, Glasgow, G4 0NG United Kingdom 2 Synchrotron Radiation Department, CCLRC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD United Kingdom 3 Groupe d’Études des Semiconducteurs, Université Montpellier Place Eugène Bataillon 34095 Montpellier Cedex 05, France ABSTRACT The local structure around Er and Eu atoms introduced into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure above the appropriate rare-earth X-ray absorption edge. The samples were doped in situ during growth by Molecular Beam Epitaxy. The formation of ErN clusters was found in samples with high average Er concentrations of 32±6% and 12.4±0.8%, estimated by Wavelength Dispersive X-ray analysis. When the average Er concentration is decreased to 6.0±0.2%, 1.6±0.2% and 0.17±0.02%, Er is found in localised clusters of ErGaN phase with high local Er content. Similar behaviour is observed for Eu-doped samples. For an average Eu concentration of 30.5±0.5% clusters of pure EuN occur. Decreasing the Eu concentration to 10.4±0.5% leads to EuGaN clusters with high local Eu content. However, for a sample with an Eu concentration of 14.2±0.5% clustering of Eu was not observed. INTRODUCTION Rare-earth (RE) doped semiconductors have attracted much interest due to the possibility of integrating intense narrow-band emission with existing semiconductor devices [1]. A range of semiconductors such as Si, GaAs has been studied as hosts for RE elements [2]. The discovery that temperature quenching of the emission is inversely proportional to the semiconductor band gap [3] makes wide band gap materials attractive as RE hosts. In the last decade GaN has emerged from the range of wide band gap semiconductors as a particularly significant material and has become the basis of a novel and rapidly advancing lighting technology [4]. GaN possesses a number of properties that make it a suitable host for visible- and infrared- emitting RE ions, including good chemical and thermal stability, and excellent high-field transport properties. The possibility of electroluminescent devices based on GaN doped with different RE elements has already been demonstrated [5] but their further development is hindered by a lack of understanding of the underlying excitation processes. The structure of the local environment of the RE ion in the host is believed to play a crucial role [6]. The efficiency of the RE emission strongly depends on the symmetry of site occupied by the RE ion through the relaxation of the selection rules for intra-4f shell transitions.
Y5.10.2
Different methods have been applied in order to get information about the lattice location of RE in GaN [7, 8]. Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool
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