The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Doyeol Ahn - One of the best experts on this subject based on the ideXlab platform.
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Structural dependence of Optical Gain in dip-shaped InGaN/GaN quantum wells
Semiconductor Science and Technology, 2010Co-Authors: Seoung-hwan Park, Doyeol Ahn, Bun-hei Koo, Jongwook KimAbstract:The structural parameter dependence of the Optical Gain of dip-shaped InGaN/GaN quantum well (QW) structures was investigated using the multiband effective-mass theory. In the case of the QW structure with a relatively smaller In composition (0.05) in the shallow well, the Optical Gain is larger than that with a larger In composition (0.1) in the shallow well. This is mainly due to the fact that the former has a smaller internal field than the latter. In the case of the QW structure with a thin dip well width and a relatively smaller In composition (0.05) in the shallow well, the Optical Gain rapidly increases with increasing In composition in the dip well because the internal field effect is negligible and a quasi-Fermi level separation becomes larger. On the other hand, the increasing rate of the Optical Gain is greatly reduced with increasing well width due to the internal field effect.
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Effects of strain distribution on the Optical Gain of
2009Co-Authors: Doyeol Ahn, B. H. KooAbstract:Effects of the strain distribution on the Optical Gain of InGaN-AlInGaN QW light-emitting diodes (LEDs)is investigated. The amount of stress and strain in the multilayer quantum well structures are calculated taking into account the difference between crystalline parameters. Siginificant enhancement of Optical Gain is expected with the introduction of strain distribution layers. I. INTRODUNCTION It is well known that for III-V nitride quantum well based optoelectronic devices, strong built-in polarization fields caused by the strain exist in the active layers, which degrade the performance of the device significantly. Especially, the wurtzite GaN-based quantum wells grown along (0001) direction possess the piezoelectric (PZ) and spontaneous polarization (SP) fields of an order of MV/m 1,2). These built- in internal fields reduce the Optical Gain and the luminescence by an order of magnitude as compared with other III-V semiconductors. Here, we present an investigation of the strain distribution effect on the Optical Gain of InGaN-AlInGaN QW light- emitting diodes (LEDs) using the 6x6 Pikus-Bir Hamiltonian for wurtzite semiconductors (3) and the non-Markovian Gain model with many-body effects (4). The amount of stress and strain in the multilayer quantum well structures are calculated taking into account the difference between crystalline parameters such as lattice constant and thermal expansion coefficient of the composed multilayer structures (5). In this strained multilayered structure where the i-th layer is characterized by the thickness i d and the lattice constant i a .
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Optical Gain and luminescence of a ZnO-MgZnO quantum well
IEEE Photonics Technology Letters, 2006Co-Authors: Doyeol Ahn, Seoung-hwan Park, Eun-hyun Park, Tae-kyung YooAbstract:The Optical Gain and the luminescence of a ZnO quantum well with MgZnO barriers is studied theoretically. We calculated the non-Markovian Optical Gain and the luminescence for the strained-layer wurtzite quantum well taking into account the excitonic effects. It is predicted that both Optical Gain and luminescence are enhanced for the ZnO quantum well when compared with those of the InGaN-AlGaN quantum well structure due to the significant reduction of the piezoelectric effects in the ZnO-MgZnO systems.
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Optical Gain in GaN Quantum Well Lasers with Quaternary AlInGaN Barriers
Japanese Journal of Applied Physics, 2005Co-Authors: Seoung-hwan Park, Hwa-min Kim, Doyeol AhnAbstract:Optical Gain in GaN quantum-well (QW) lasers with quaternary AlInGaN barriers lattice-matched to GaN is investigated on the basis of the multiband effective-mass theory and is compared with that of conventional GaN/AlGaN QW structures. GaN/AlInGaN QW lasers are expected to have enhanced Optical Gain compared with GaN/AlInGaN QW lasers. However, the Optical Gain is shown to be reduced markedly with increasing band gap of the AlInGaN barrier. This is because the spontaneous polarization effect is increased significantly for the QW structures with a larger AlInGaN band gap. We find that the threshold current density of the GaN/AlInGaN QW structure can be reduced using a quarternary AlInGaN barrier.
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Optical Gain of CdZnSe/ZnSe quantum well lasers
Applied Physics Letters, 1991Co-Authors: Doyeol Ahn, Tae-kyung Yoo, H. Y. LeeAbstract:Polarization‐dependent Optical Gain of recently demonstrated CdZnSe/ZnSe quantum well lasers is calculated for the first time. Our analysis is based on the multiband effective mass theory (k⋅p theory) and the density matrix formalism with intraband relaxation taken into account. It is shown theoretically that the TE mode Gain is significantly larger than the TM mode Gain for a wide range of carrier density. Comparison of the room‐temperature TE mode Gain of CdZnSe/ZnSe quantum well with that of GaAs/AlGaAs quantum well gives disappointing results for the II‐VI semiconductor lasers. It is expected that the Optical Gain of the ZnSe‐based semiconductor lasers would be substantially smaller than the Optical Gain of the GaAs‐based semiconductor lasers for a same quantum well width and carrier density.
Nelson Tansu - One of the best experts on this subject based on the ideXlab platform.
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Ultra-Broadband Optical Gain in III-Nitride Digital Alloys
Scientific Reports, 2018Co-Authors: Jonathan J. Wierer, Nelson TansuAbstract:A novel III-Nitride digital alloy (DA) with ultra-broadband Optical Gain is proposed. Numerical analysis shows a 50-period InN/GaN DA yields minibands that are densely quantized by numerous confined states. Interband transitions between the conduction and valence minibands create ultra-broadband Optical Gain spectra with bandwidths up to ~1 μm that can be tuned from the red to infrared. In addition, the ultra-broadband Optical Gain, bandwidth, and spectral coverage of the III-Nitride DA is very sensitive to layer thickness and other structural design parameters. This study shows the promising potential of the III-Nitride DAs with tunable ultra-broadband interband Optical Gain for use in semiconductor Optical amplifiers and future III-Nitride photonic integration applications.
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Optical Gain characteristics of staggered ingan quantum wells lasers
Journal of Applied Physics, 2010Co-Authors: Hongping Zhao, Nelson TansuAbstract:Staggered InGaN quantum wells (QWs) are analyzed as improved Gain media for laser diodes (LDs) lasing at 440 and 500 nm. The calculation of band structure is based on a 6-band k⋅p method taking into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to enhance the Optical Gain as well as to reduce the threshold current density for LDs emitting at 440 and 500 nm. Our analysis shows that the Optical Gain is enhanced by 1.5–2.1 times by utilizing the staggered InGaN QW active region emitting at 440 nm, which leads to a reduction of the threshold current density up to 24% as compared to that of the conventional InGaN QW laser. Staggered InGaN QWs with enhanced Optical Gain shows significantly reduced blue-shift as carrier density increases, which enables nitride QWs with high Optical Gain in the green spectr...
Jimmy Xu - One of the best experts on this subject based on the ideXlab platform.
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Optical Gain and stimulated emission in periodic nanopatterned crystalline silicon
Nature Materials, 2005Co-Authors: Sylvain G. Cloutier, Pavel A Kossyrev, Jimmy XuAbstract:Persistent efforts have been made to achieve efficient light emission from silicon in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects. Enhanced light emission from silicon is known to be theoretically possible, enabled mostly through quantum-confinement effects. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides. Here we report on Optical Gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask. In edge-emission measurements, we observed threshold behaviour, Optical Gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured Optical Gain and stimulated emission and provides a new pathway to enhance light emission from silicon.
Lorenzo Pavesi - One of the best experts on this subject based on the ideXlab platform.
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Polarized Optical Gain and polarization-narrowing of heavily oxidized porous silicon.
Physical review letters, 2004Co-Authors: Massimo Cazzanelli, Luca Dal Negro, Zeno Gaburro, Dmitri Kovalev, Lorenzo PavesiAbstract:We report on a polarization-sensitive Optical Gain in a blue-emitting Si/SiO(2) nanocrystalline system having a high degree of emission polarization memory. This system can show a positive Optical Gain or Optical loss depending on the polarization state of the pump and emitted light. Under Optical Gain conditions, the degree of polarization of the amplified spontaneous emission increases with the pumping fluence. This effect has been attributed to an increase in the stimulated emission efficiency occurring for the linearly polarized emission component characterized by high photon occupation numbers (stimulating photon flux). This finding is independently supported by other experimental observations. The occurrence of polarization dependent stimulated emission strongly indicates the relevance of morphological effects in light emission from ultrasmall elongated silicon nanostructures.
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Optical Gain in monodispersed silicon nanocrystals
Journal of Applied Physics, 2004Co-Authors: Massimo Cazzanelli, Lorenzo Pavesi, Daniel Navarro-urrios, Francesco Riboli, Nicola Daldosso, J. Heitmann, R. Scholz, Margit Zacharias, Ulrich GöseleAbstract:Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO∕SiO2 superlattices is presented. Under high power pulsed excitation, positive Optical Gain can be observed once a good Optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large Gain values are explained by the small size dispersion in these silicon nanocrystals.
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Optical Gain in PECVD silicon nanocrystals
Optical Properties of Nanocrystals, 2002Co-Authors: Luca Dal Negro, Lorenzo Pavesi, Massimo Cazzanelli, Zeno Gaburro, Domenico Pacifici, F. Priolo, G. Franzò, Fabio IaconaAbstract:Optical Gain has been recently observed in ion implanted Si nanocrystals (nc). Critical issues to the observation of Optical Gain are the formation of a waveguide structure to improve the mode confinement and a large nanocrystal area den-sity in the samples. Here we confirm these results by measuring Optical Gain by the variable stripe length (VSL) method on a set of silicon nanocrystals (nc) formed by plasma enhanced chemical vapor deposition (PECVD) and annealing treatments. Time resolved VSL measurements with ns pulses at high pumping fluencies have revealed fast component in the recombination dynamics under Gain conditions. Lifetime shortening and superlinear emission have been unambi-guously observed. The spectral shape of the fast luminescence is consistent with the amplified spontaneous emission lineshape (ASE) observed under CW pumping conditions and overlaps the Gain spectral band. The observation of light amplification is critically dependent on a very delicate balance among the nc Gain cross sections, the Optical mode losses of the waveguide structure, and the fast non radiative Auger processes. Within a four levels model we quantify the strong competition among all these processes and we obtain a satisfactory agreement with the experiments.
Massimo Cazzanelli - One of the best experts on this subject based on the ideXlab platform.
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Polarized Optical Gain and polarization-narrowing of heavily oxidized porous silicon.
Physical review letters, 2004Co-Authors: Massimo Cazzanelli, Luca Dal Negro, Zeno Gaburro, Dmitri Kovalev, Lorenzo PavesiAbstract:We report on a polarization-sensitive Optical Gain in a blue-emitting Si/SiO(2) nanocrystalline system having a high degree of emission polarization memory. This system can show a positive Optical Gain or Optical loss depending on the polarization state of the pump and emitted light. Under Optical Gain conditions, the degree of polarization of the amplified spontaneous emission increases with the pumping fluence. This effect has been attributed to an increase in the stimulated emission efficiency occurring for the linearly polarized emission component characterized by high photon occupation numbers (stimulating photon flux). This finding is independently supported by other experimental observations. The occurrence of polarization dependent stimulated emission strongly indicates the relevance of morphological effects in light emission from ultrasmall elongated silicon nanostructures.
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Optical Gain in monodispersed silicon nanocrystals
Journal of Applied Physics, 2004Co-Authors: Massimo Cazzanelli, Lorenzo Pavesi, Daniel Navarro-urrios, Francesco Riboli, Nicola Daldosso, J. Heitmann, R. Scholz, Margit Zacharias, Ulrich GöseleAbstract:Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO∕SiO2 superlattices is presented. Under high power pulsed excitation, positive Optical Gain can be observed once a good Optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large Gain values are explained by the small size dispersion in these silicon nanocrystals.
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Optical Gain in PECVD silicon nanocrystals
Optical Properties of Nanocrystals, 2002Co-Authors: Luca Dal Negro, Lorenzo Pavesi, Massimo Cazzanelli, Zeno Gaburro, Domenico Pacifici, F. Priolo, G. Franzò, Fabio IaconaAbstract:Optical Gain has been recently observed in ion implanted Si nanocrystals (nc). Critical issues to the observation of Optical Gain are the formation of a waveguide structure to improve the mode confinement and a large nanocrystal area den-sity in the samples. Here we confirm these results by measuring Optical Gain by the variable stripe length (VSL) method on a set of silicon nanocrystals (nc) formed by plasma enhanced chemical vapor deposition (PECVD) and annealing treatments. Time resolved VSL measurements with ns pulses at high pumping fluencies have revealed fast component in the recombination dynamics under Gain conditions. Lifetime shortening and superlinear emission have been unambi-guously observed. The spectral shape of the fast luminescence is consistent with the amplified spontaneous emission lineshape (ASE) observed under CW pumping conditions and overlaps the Gain spectral band. The observation of light amplification is critically dependent on a very delicate balance among the nc Gain cross sections, the Optical mode losses of the waveguide structure, and the fast non radiative Auger processes. Within a four levels model we quantify the strong competition among all these processes and we obtain a satisfactory agreement with the experiments.