Browsing by Author "Serpengüzel, A."
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Item Open Access Alteration of spontaneous emission in hydrogenated amorphous silicon nitride microcavities(Elsevier BV, 1998) Serpengüzel, A.; Aydınlı, Atilla; Bek, A.A Fabry-Perot microcavity is used for the alteration of the spontaneous emission spectrum in hydrogenated amorphous silicon nitride. The modified photon density of states of the Fabry-Perot microcavity are responsible for the alteration of the spontaneous emission spectrum. The Fabry-Perot microcavity enhances the intensity of the spontaneous emission signal by a factor of 4 at the photon energies corresponding to the microcavity resonances. The 0.075 eV wide spontaneous emission linewidth of the Fabry-Perot microcavity resonances is 7 times smaller than the 0.5 eV wide spontaneous emission linewidth of the bulk hydrogenated amorphous silicon nitride. © 1998 Elsevier Science B.V. All rights reserved.Item Open Access Controlled photoluminescence in amorphous-silicon-nitride microcavities(2001) Serpengüzel, A.; Tanriseven, S.Narrow-band and enhanced photoluminescence have been observed in hydrogenated amorphous-silicon-nitride microcavities. The distributed Bragg reflectors were fabricated using alternating layers of hydrogenated amorphous-silicon nitride and hydrogenated amorphous-silicon oxide. The microcavity resonance wavelength was designed to be at the maximum of the bulk hydrogenated amorphous-silicon-nitride luminescence spectrum. At the microcavity resonance, the phololuminescence amplitude is enhanced, while the photoluminescence linewidth is reduced with respect to the bulk hydrogenated amorphous-silicon nitride. © 2001 American Institute of Physics.Item Open Access Dependence of the photoluminescence of Tl2InGaS4 layered crystal on temperature and excitation intensity(Pergamon Press, 1998) Gasanly, N. M.; Serpengüzel, A.; Gürlü, O.; Aydınlı, A.; Yılmaz, I.The emission band spectra of Tl2InGaS4 layered crystals were investigated in the 10-120 K temperature range and in the 540-860 nm wavelength range using photoluminescence (PL). The peak energy position of the emission band is located at 1.754 eV (707 nm) at 10 K. The emission band has a half-width of 0.28 eV and an asymmetric Gaussian lineshape. The increase of the half-width of the emission band, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature is explained using the configuration coordinate model. The blue shift of the emission band peak energy and the sublinear increase of the emission band intensity with increasing excitation intensity is explained using the inhomogenously spaced donor-acceptor pair recombination model. © 1998 Elsevier Science Ltd. All rights reserved.Item Open Access Donor-acceptor pair recombination in AgIn5S8 single crystals(American Institute of Physics, 1999-03-15) Gasanly, N. M.; Serpengüzel, A.; Aydınlı, Atilla; Gürlü, O.; Yilmaz, I.Photoluminescence (PL) spectra of AgIn5S8 single crystals were investigated in the 1.44-1.91 eV energy region and in the 10-170 K temperature range. The PL band was observed to be centered at 1.65 eV at 10 K and an excitation intensity of 0.97 W cm(-2). The redshift of this band with increasing temperature and with decreasing excitation intensity was observed. To explain the observed PL behavior, we propose that the emission is due to radiative recombination of a donor-acceptor pair, with an electron occupying a donor level located at 0.06 eV below the conduction band, and a hole occupying an acceptor level located at 0.32 eV above the valence band. (C) 1999 American Institute of Physics.Item Open Access Enhanced coupling to microsphere resonances with optical fibers(Optical Society of America, 1997) Serpengüzel, A.; Arnold, S.; Griffel, G.; Lock, J. A.Morphology-dependent resonances (MDR's) of polystyrene microspheres were excited by an optical fiber coupler. For optical elimination of the air-cladding interface at the optical fiber coupler surface, the microsphere was immersed in an index-matching oil. MDR's were observed, even though the relative refractive index between the microsphere and the oil was only 1.09. The observed MDR spectra are in good agreement with the generalized Lorenz-Mie theory and the localization principle. The scattering efficiency into each MDR is estimated as a function of the impact parameter by means of generalized Lorenz-Mie theory. (C) 1997 Optical Society of America.Item Open Access Far-infrared elastic scattering proposal for the Avogadro Project's silicon spheres(Elsevier, 2018) Humayun, M. H.; Khan, I.; Azeem, F.; Chaudhry, M. R.; Gökay, U. S.; Murib, M. S.; Serpengüzel, A.Avogadro constant determines the number of particles in one mole of a substance, thus relating the molar mass of the substance to the mass of this substance. Avogadro constant is related to Système Internationale base units by defining the very concept of chemical quantity. Revisions of the base units created a need to redefine the Avogadro constant, where a collaborative work called the Avogadro Project is established to employ optical interferometry to measure the diameter of high quality 100 mm silicon spheres. We propose far-infrared spectroscopy for determining the Avogadro constant by using elastic scattering from the 100 mm Avogadro Project silicon spheres. Similar spectroscopic methods are already in use in the near-infrared, relating whispering gallery modes of the 1 mm silicon spheres to the diameter of the spheres. We present numerical simulations in the far-infrared and the near-infrared, as well as spatially scaled down elastic scattering measurements in the near-infrared. These numerical and experimental results show that, the diameter measurements of 100 mm single crystal silicon spheres with elastic scattering in the far-infrared can be considered as an alternative to optical interferometry.Item Open Access Low-temperature visible photoluminescence spectra of TlGaSe2 layered crystal(Elsevier Science Publishers B.V., Amsterdam, Netherlands, 2000) Gasanly, N. M.; Serpengüzel, A.; Aydınlı, A.; Baten, S. M. A.The photoluminescence (PL) spectra of TlGaSe2 layered single crystals were investigated in the 8.5-35 K temperature. 0.2-15.2 W cm-2 excitation laser intensity, and in the 600-700 nm wavelength range. The PL spectrum has a slightly asymmetric Gaussian lineshape with a peak position located at 1.937 eV (640 nm) at 8.5 K. The PL is quenched with increasing temperature. The blue shift of the PL peak and the sublinear increase of the PL intensity with increasing laser intensity is explained using the inhomogenously spaced donor-acceptor pair recombination model. Analysis of the data indicates that the PL band is due to donor-acceptor recombination. A shallow acceptor level and a moderately deep donor level are, respectively, introduced at 0.012 eV above the top of the valence band and at 0.317 eV below the bottom of the conduction band. An energy-level diagram for radiative donor-acceptor pair recombination in TlGaSe2 layered single crystals is proposed.Item Open Access Morphology Dependent Resonances of a microsphere/optical fiber system(Optical Society of America, 1996) Griffel, G.; Arnold, S.; Taskent, D.; Serpengüzel, A.; Connolly, J.; Morris, N.Morphology-dependent resonances of microspheres sitting upon an index-matched single-mode fiber half-coupler are excited by a tunable 753-nm distributed-feedback laser. Resonance peaks in the scattering spectra and associated dips in the transmission spectra for the TE and TM modes are observed. We present a new model that describes this interaction in terms of the fiber-sphere coupling coefficient and the microsphere's intrinsic quality factor Q0. This model enables us to obtain expressions for the finesse and the Q factor of the composite particle-fiber system, the resonance width, and the depth of the dips measured in the transmission spectra. Our model shows that index matching improves the coupling efficiency by more than a factor of 2 compared with that of a non-index-matched system. © 1996 Optical Society of America.Item Open Access Morphology-dependent resonances of a microsphere-optical fiber system(1996) Griffel G.; Arnold, S.; Taskent, D.; Serpengüzel, A.; Connolly J.; Morris, N.Morphology-dependent resonances of microspheres sitting upon an index-matched single-mode fiber half-coupler are excited by a tunable 753-nm distributed-feedback laser. Resonance peaks in the scattering spectra and associated dips in the transmission spectra for the TE and TM modes are observed. We present a new model that describes this interaction in terms of the fiber-sphere coupling coefficient and the microsphere's intrinsic quality factor Q0. This model enables us to obtain expressions for the finesse and the Q factor of the composite particle-fiber system, the resonance width, and the depth of the dips measured in the transmission spectra. Our model shows that index matching improves the coupling efficiency by more than a factor of 2 compared with that of a non-index-matched system. © 1996 Optical Society of America.Item Open Access Photoluminescence from a VCSEL structure a-SiNx:H microcavity(IEEE, 1999) Serpengüzel, A.; Darici, Y.Microcavity effects on the photoluminescence (PL) of porous Si has already been reported. Recently, we have observed visible and near infrared (IR) PL from hydrogenated amorphous Si nitride (a-SiNx:H) grown by low temperature PECVD. We have also reported the enhancement and inhibition of PL in an a-SiNx:H microcavity formed with metallic mirrors. The a-SiNx:H used in the microcavity was grown both with and without ammonia (NH/sub 3/). For the Si rich a-SiNx:H grown without NH/sub 3/, the PL is in the red-near IR. For the N rich a-SiNx:H grown with NH/sub 3/, the PL is in the blue-green. In this paper, we report on the bright and spectrally pure PL of a-SiNx:H in a VCSEL structure microcavity.Item Open Access Radiative donor-acceptor pair recombination in TlInS2 single crystals(Institute of Physics Publishing, 1999) Aydınlı, A.; Gasanly, N. M.; Yılmaz, I.; Serpengüzel, A.Photoluminescence (PL) spectra of TlInS2 layered single crystals were investigated in the 500-860 nm wavelength region and in the 11.5-100 K temperature range. We observed two PL bands centred at 515 nm (2.41 eV, A band) and 816 nm (1.52 eV, B band) at T = 11.5 K and an excitation intensity of 7.24 W cm-2. A detailed study of the A band was carried out as a function of temperature and excitation laser intensity. A red shift of the A band position was observed for both increasing temperature and decreasing excitation laser intensity in the range from 0.12 to 7.24 W cm-2. Analysis of the data indicates that the A band is due to radiative transitions from the moderately deep donor level located at 0.25 eV below the bottom of the conduction band to the shallow acceptor level located at 0.02 eV above the top of the valence band. An energy-level diagram for radiative donor-acceptor pair transitions in TlInS2 layered single crystals is proposed.Item Open Access Super-radiant surface emission from a quasi-cavity hot electron light emitter(Springer New York LLC, 1999) O'Brien, A.; Balkan, N.; Boland-Thoms, A.; Adams, M.; Bek, A.; Serpengüzel, A.; Aydınlı, A.; Roberts, J.The Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure (HELLISH-1) device is a novel surface emitter which utilises hot carrier transport parallel to the layers of a Ga1 - xAlxAs p-n junction incorporating a single GaAs quantum well on the n-side of the junction plane. Non-equilibrium electrons are injected into the quantum well via tunnelling from the n-layer. In order to preserve the charge neutrality in the depletion region, the junction undergoes a self-induced internal biasing. As a result the built-in potential on the p-side is reduced and hence the injection of non-equilibrium holes into the quantum well in the active region is enhanced. The work presented here shows that a distributed Bragg reflector grown below the active region of the HELLISH device increases the emitted light intensity by two orders of magnitude and reduces the emission line-width by about a factor of 3 in comparison with the original HELLISH-1 structure. Therefore, the device can be operated as an ultrabright emitter with higher spectral purity.Item Open Access Visible photoluminescence from low temperature deposited hydrogenated amorphous silicon nitride(Pergamon Press, 1996) Aydınlı, A.; Serpengüzel, A.; Vardar, D.Hydrogenated amorphous silicon nitride (a-SiNx:H) samples have been prepared by plasma enhanced chemical vapor deposition (PECVD) using a mixture of silane (SiH4), nitrogen and ammonia (NH3). Most films exhibit visible photoluminescence (PL) and some emit strong PL after annealing. While films grown without NH3 exhibit PL in the deep red, those grown with NH3 show PL in the green. The PL properties of these films with no oxygen (O) content are similar to those of silicon oxide (SiOx) films and porous Si. Using infrared and X-ray Photoelectron Spectroscopy, we suggest that PL from a-SiNx:H films originate from Si clusters which form during PECVD and crystallize upon annealing. We propose that the presence of O is not necessary for efficient PL.Item Open Access Visible photoluminescence from planar amorphous silicon nitride microcavities(Optical Society of America, 1998) Serpengüzel, A.; Aydınlı, Atilla; Bek, A.; Güre, M.Fabry-Perot microcavities were used for the enhancement and inhibition of photoluminescence (PL) in a hydrogenated amorphous silicon nitride (a-SiNx:H) microcavity fabricated with and without ammonia. A planar microcavity was realized that included a metallic back mirror and an a-SiNx:H-air or a metallic front mirror. The PL extends from the red part of the spectrum to the near infrared for the samples grown without ammonia. The PL is in the blue-green part of the spectrum for the samples grown with ammonia. The PL amplitude is enhanced and the PL linewidth is reduced with respect to those in bulk a-SiNx:H. The numerically calculated transmittance, reflectance, and absorbance spectra agree well with the experimentally measured spectra. (C) 1998 Optical Society of America [S0740-3224(98)00211-2] OCIS codes: 230.5750, 250.5230, 310.0310.