High Resolution Site-Selective Studies of Erbium-Centers in GaN and GaN:Mg
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High Resolution Site-Selective Studies of Erbium-Centers in GaN and GaN:Mg. V. Glukhanyuk1, H. Przybylińska, A. Kozanecki, Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland. W. Jantsch, Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Altenberger str. 69, A-4040 Linz, Austria.
ABSTRACT In this work the high resolution optical spectroscopy is used in order to determine the positions of the Stark split 4I15/2, 4I11/2 and 4I9/2 energy levels of Er3+ in GaN and GaN:Mg. Photoluminescence and photoluminescence excitation spectra were measured at energies corresponding to the 4I15/2→4I9/2 and 4I15/2→4I11/2 absorption transitions. Low Er implant doses were applied to reduce the number of possible defects. In undoped GaN only a single Er-center was observed and no influence of Mg doping on the energy level splittings of this center in GaN:Mg was found. Numerical analysis based on point charge model was used to calculate parameters of the local crystal field (CF) acting on Er3+ ions. The splittings of the 4 I9/2 and 4I11/2 energy levels were calculated in weak CF approach and good agreement with experimental results was obtained. The calculations confirmed that the symmetry of the erbium center in hexagonal GaN is C3v. INTRODUCTION Erbium doped semiconductors are considered as possible candidates for application in infrared optoelectronic devices, such as optical amplifiers, optical memory devices, and lasers [1-4]. The transitions from the 4I13/2 first excited state of Er3+ to the 4I15/2 ground state occur at 1.54 µm, which wavelength corresponds to low loss and low dispersion window of silica fibers used in telecommunication. Erbium doped gallium nitride (3.5 eV band gap) is particularly interesting because of simultaneous emission in the visible and infrared range of wavelengths and possible application in full color displays [2,5,6]. Moreover, due to the wide band gap the temperature quenching of Er luminescence is less effective than in Si or GaAs [7]. Ion implantation is the main technique used for incorporation of erbium into the semiconductor host. However, implantation creates many defects which may form complexes with erbium, beside complexes with native impurities. Kim et. al. [8,9] in their studies of photoluminescence (PL) in Er-implanted GaN as a function of excitation wavelength and annealing temperature have revealed nine different Er3+ emitting centers on the basis of characteristic differences in their PL spectra and PL excitation (PLE) spectra. They also found that the dominant excitation mechanism for above band-gap and near band-gap excitation is trap mediated. Surprisingly enough, only approx. 1 % of Er-centers could be effectively excited via the indirect mechanism, whereas 99% of centers seemed to be excited only directly. On the other hand, we have shown that in high purity GaN implanted with low Er doses only one Er3+ center dominates in the PL, independent of excitation wavelength [10]. 1
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