Structure and photoluminescence investigations of Er doped GaN layers grown by MBE
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Structure and photoluminescence investigations of Er doped GaN layers grown by MBE T. Wojtowicz1, H.M. Ng2, and P. Ruterana1* 1 SIFCOM, UMR6176, CNRS-ENSICAEN, 6, Bld Maréchal Juin, 14050 Caen, France 2 Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ, U.S.A. Abstract In this work, we carry out TEM analysis on GaN layers grown on sapphire and doped in situ by MBE. In parallel, photoluminescence and electroluminescence experiments are used to determine the possible emission of the grown layers. It has been shown previously that the emission peaks at Er concentrations of about 1% and that their intensity dramatically decreases with increasing Er concentration probably due to compositional quenching. We report on the evolution of the microstructure versus composition and try to explain the quenching effects that can be related to the microstructure. 1. Introduction For a few years now, it has been possible to dope GaN layers using molecular beam epitaxy (MBE). This aims to use the wide band gap semiconductors as hosts to the rare earth and exploit the sharp emission lines from intra 4f shell transitions. It was shown that the whole visible spectrum can be covered by changing the rare earth or exciting different levels. It is also suspected that like in some systems for instance Si(nano)/SiO2, the energy coupling could involve defects. The aim of this work is to help in the development of rare earth doped GaN electroluminescent devices for use in optical communication systems. Er-doped GaN is currently being widely studied because of its possible optical applications [1]. Due to the characteristic 1.54 µm infrared emission from Er3+ ions and minimum light absorption at this wavelength in silica, Er-doped silica based optical fibers are now generally used [2]. Er has also transitions in the visible range; green emission from Er-doped GaN thin films grown by MBE has been previously reported [3]. Many other materials, such as Si and various II–VI and III–V semiconductors, have been studied in order to find good Er host material. The advantages of GaN include a direct and wide band gap, which results in very low thermal quenching of rare earth ion emission [4,5]. There is still a lot of work to do in this field, starting from optimising growth conditions, to understanding the interactions between Er atoms and the structural defects in the host crystal (GaN). In this work, we discuss results from investigations of MBE grown GaN layers doped with Er using different growth conditions. PL and EL measurements were carried out for optical and TEM, HRTEM for structural characterizations. 2. Experimental Prior to growth of GaN layers, a high temperature AlN buffer layer was grown at 720 °C on (0001) sapphire. This was followed by a thick Si doped GaN (1 micron) before the deposition of Er doped layers. The growth temperature was around 720 °C and growth rate *
Author for Correspondence email: [email protected], Tel: +33 2 31 45 26 53, Fax: +33 2 31 45 26 60
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was 0.3–0.4 µm/hr. The above
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