Temperature dependence studies of Er optical centers in GaN epilayers grown by MOCVD
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Temperature dependence studies of Er optical centers in GaN epilayers grown by MOCVD V. X. Ho,1 S. P. Dail,1 T. V. Dao,1 H. X. Jiang,2 J. Y. Lin,2 J. M. Zavada,3 and N. Q. Vinh1 1
Department of Physics & Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, Virginia 24061, U.S.A. 2 Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409, U.S.A. 3 Department of Electrical and Computer Engineering, New York University, Brooklyn, New York 11201, U.S.A.
ABSTRACT We report the temperature dependence of Er optical centers in GaN epilayers prepared by metalorganic chemical vapor deposition under the resonant excitation (4I15/2 ΔΊ4I9/2) excitation using a Ti:Sapphire laser (Oexc = 809 nm). High resolution infrared spectroscopy and temperature dependence measurements of photoluminescence intensity from Er ions in GaN have been performed to identify the crystal filed splitting of the first excited state, 4I13/2. Here, we have employed a simple approach to determine activation energies which are related to the thermal population of electrons from the lowest level to the higher level of the crystal field splitting of the first excited state. INTRODUCTION Rare earth doped wide-bandgap semiconductor is of significant interest for optoelectronic device applications, because of their temperature independent, atomic-like and stable emission together with the possibility of optical or electrical excitation [1-3]. Much of the research has focused on the element Er with the emission from the first excited state (4I13/2) to the ground state (4I15/2) at 1.54 Pm that is the minimum loss window of silica fibers for optical communications and in the eye-safe wavelength region [4-10]. GaN with the direct bandgap semiconductor appears to be excellent host materials for Er ions, not only due to their structural and thermal stability [11, 12] but also to the recent advancements in growth techniques of high-quality crystals of both n- and p-type [2]. While light emitting diodes based on GaN:Er have been demonstrated [13], the realization of GaN:Er materials for optical amplification is still under investigation. For this reason, it is necessary to determine important factors which influence the optical performance of Er embedded in GaN. The information would provide us with the direction to optimize the optical properties of GaN:Er material. Previous work has revealed that a number of Er optical centers as well as a variety of energy transfer routes take place in GaN [14, 15]. The existence of various Er optical centers depends on preparation methods, such as ion implantation [16, 17], metal-organic chemical vapor deposition (MOCVD) [18] and molecular beam epitaxy (MBE) [19], as well as growth and annealing conditions [16]. The absorption and emission studies together with the crystal field calculation provided an understanding of energy transfer mechanism to Er ions and the Er related luminescence process [20]. Non-radiative recombination channels were also investigated to understand
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