Stimulated Opticaltransitions in Er-Doped Silicon Nanostructures
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STIMULATED OPTICAL TRANSITIONS IN ER-DOPED SILICON NANOSTRUCTURES B. V. KAMENEV Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 V. I. EMEL’YANOV, V. Yu. TIMOSHENKO, P. K. KASHKAROV M.V.Lomonosov Moscow State University, Moscow, Russia E. I. TERUKOV, V. Kh. KUDOYAROVA Ioffe Physico-Technical Institute, St.Petersburg, Russia ABSTRACT Photoluminescence (PL) of Er3+ ions in nanocrystalline (amorphous) silicon matrix has been investigated under a high level of optical excitation. A superlinear increase of the PL intensity, a shortening of the PL decay time, and strong angular dependence were found at the excitation intensity above 200 kW/cm2. These effects are observed only in samples with presence of silicon nanocrystalls and explained by stimulated optical transitions. INTRODUCTION A trivalent Er3+ ion possesses promising properties for optoelectronic applications because the transition in the f -shell of the Er3+ ion leads to a luminescence at 1.54 µm, which corresponds to minimal optical losses in optical fibers. Despite many attempts to achieve room temperature operating device by implanting Er3+ ions into crystalline silicon (c-Si) (see for instance [1]), the photoluminescence (PL) of Er3+ ions in c-Si demonstrates a strong temperature quenching [2]. Better results were obtained in the case of Er3+ ions introduced in an amorphous [3, 4] and nanocrystalline [5, 6] silicon matrix where an efficient emission at 1.54 µm was found at room-temperature. Recently, a superlinear growth of the intensity of PL at 1.54 µm and a shortening of its lifetime with increasing intensity of the pulsed laser excitation have been observed in a(nc)-Si(Er), and it was explained by stimulated optical transitions [7,8]. In this work, we significantly extended our previous understanding and show that the presence of Si nanocrystals is a key feature for silicon based laser structures.
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EXPERIMENTAL SETUP The samples used in this study were prepared by co-sputtering of silicon and erbium onto a quartz substrate using a magnetron-assisted silane decomposition technique. The concentrations of Er and oxygen in the samples were about 1020 cm-3. The PL was excited by pulses of a nitrogen laser (hν=3.7 eV, τ=10 ns, pulse energy up to 50 µJ, repetition rate 20 Hz). The laser beam is focused on a sample within a spot of a diameter ~ 500 µm. PL was dispersed with a 1 m focal length grating monochromator. InGaAs photodiodes with a time resolution of 100 µs and 100 ns were used to detect the PL spectra and the PL transients, respectively. Raman spectra were taken under CW excitation of an Ar+ laser using a 1 m focal length double spectrometer. RESULTS
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Fig.1 Typical spectra of Er-related PL in studied samples. Inset shows the PL temperature dependence.
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