Semiconductor Photonics: Nano-Structured Materials and Devices

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Authors: Thomas Prevenslik
Abstract: High quantum dot (QD) efficiency may be explained by excitons generated in the quantum electrodynamics (QED) confinement of electromagnetic (EM) radiation during the absorption of the laser radiation. There is general agreement that by the Mie theory laser photons are fully absorbed by QDs smaller than the laser wavelength. But how the absorbed laser photons are conserved by a QD is another matter. Classically, absorbed laser radiation is treated as heat that in a body having specific heat is conserved by an increase in temperature. However, the specific heats of QDs vanish at frequencies in the near infrared (NIR) and higher, and therefore an increase in temperature cannot conserve the absorbed laser photons. Instead by QED, the laser photon energy is first suppressed because the photon frequency is lower than the EM confinement frequency imposed by the QD geometry. To conserve the loss of suppressed EM energy, an equivalent gain must occur. But the only EM energy allowed in a QED confinement has a frequency equal to or greater than its EM resonance, and therefore the laser photons are then up-converted to the QD confinement frequency - the process called cavity QED induced EM radiation. High QD efficiency is the consequence of multiple excitons generated in proportion to very high QED induced Planck energy because at the nanoscale the EM confinement frequencies range from the vacuum ultraviolet (VUV) to soft x-rays (SXRs). Extensions of QED induced EM radiation are made to surface enhanced Raman spectroscopy (SERS) and light emission from porous silicon (PS).
Authors: Harry L. Kwok
Abstract: Hall measurement is an effective means to measure carrier density and mobility in metals and semiconductors. This work examined the carrier mobility determined in the accumulation layer of organic field-effect transistors (OFETS) and proposed a method to explain data taken from rubrene single-crystal devices. The model was used to extract information on the trap states and the properties of the transport layer at different temperature.
Authors: A. Soltani Vala, J. Barvestani, M. Kalafi
Abstract: An analytical direct matching procedure within the Kronig-Penney model applied to analyze the dispersion behavior of the localized surface states supported in the surface of a semiinfinite one-dimensional photonic crystals truncated with air. The photonic crystal containing alternating layers of positive and negative media. In the case of the conventional indices, as the incident light changes from normal to oblique incidence, the surface modes shifts into higher frequencies. For this reason, the phenomenon of photonic band gap has been used only under a narrow range of frequencies of light incident at a particular angle or in a particular angular range. We have showed that by choosing some proper value for the PC parameters, zero and negative dispersion of surface modes emerge in a large range of k|| , and, due to the different nature of the band structure the surface modes are more localized compared to those appeared in the conventional PC.
Authors: Wen Xiu Que, M. Sun, C.Y. Jia, L. Cheng, Zhuo Sun, L.L. Wang, X. Hu
Abstract: Titania/organically modified silanes (ormosils) organic-inorganic hybrid thin films doped with azobenzene small molecules are prepared by a low temperature sol-gel spin-coating process for optical switch applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrapropyl orthotitanate are used as matrix precursors. Atomic force microscopy is used to study the morphological properties of the hybrid thin films. Results indicate that crack-free thin films with a thickness of about 1.3μm can be obtained by a single spin-coating process after a low heat treatment temperature. The propagation mode properties of the hybrid thin films are also studied by employing a prism coupling technique. The photo-responsive properties of the hybrid films baked at different temperatures are induced by an irradiation with UV light and subsequent visible light.
Authors: Wen Xiu Que, X.M. Ren, W. Zhang, W.J. Jiang, Y. Gao, X. Hu
Abstract: Titania/organically modified silane hybrid thin films for photonic applications were prepared by combining a low temperature sol-gel technique and a spin-coating process from an organic-inorganic hybrid system. Effects of the titanium content and heat treatment temperature on the structural and optical properties of the hybrid thin films were characterized by atomic force microscopy and UV-visible spectroscopy. It is found that the optical and microstructural properties of the hybrid thin films depend on the heat-treatment temperature and titanium molar contents. The thickness and the refractive index of the hybrid thin films were also measured and found to be related to the heat treatment temperature and titanium molar content. These results indicate that a dense and high transparent hybrid thin film can be obtained at a low heat treatment temperature. Potential photonic device structural patterns can easily fabricated from the as-prepared hybrid thin films by using etching process.
Authors: Zong You Yin, Xiao Hong Tang, Ji Xuan Zhang, Deny Sentosa, Jing Hua Teng, An Yan Du, Mee Koy Chin
Abstract: Morphology and crystal-quality of InAs/In0.53Ga0.47As/InP quantum dots (QDs) grown by metal-organic vapor phase epitaxy (MOVPE) in N2 ambient using different growth modes have been studied. It is found that the morphology and crystal-quality of InAs QDs are dependant on the growth modes. After optimizing the dots’ growth modes, dots’ size dispersion and crystal-quality are both improved greatly, resulting in the enhancement factor of ∼ 2.9 in the photoluminescence (PL) peak-intensity from single QD. When the dots are buried, the dot size decrease compared with the free-standing dots due to the soon capping layer deposition during dots’ being buried. The thermal activation energy measured is comparable to the valence-band offset in the QD system calculated by 8 kp theory model. This indicates the PL quenching induced by the interface defects is suppressed due to the defect density lowering in the QDs grown by such optimized growth mode.
Authors: Y.P. Liu, Y.P. Guo, Z.J. Yan, C.M. Huang, Y.Y. Wang
Abstract: Three dimensional (3D) SiO2 photonic crystals films were fabricated on quartz substrate by vertical deposition method. The effects of various preparation parameters on optical properties were studied by optical transmission measurements. Bragg reflection on parallel sets of (111) planes were observed in all the samples. The center wavelength of [111] photonic band gap (PBG) varied from 450 nm to 680 nm with the increasing sphere size. For a given sphere size, the (111) Bragg reflection of as-deposited sample shifted towards lower wavelengths as the sintering temperature T increased. The role of evaporation temperature on the optical properties of the film was also investigated. The PBG can be correspondingly modulated in visible region by changing various preparation parameters.
Authors: N. Begum, A.S. Bhatti, M. Piccin, G. Bais, F. Jabeen, S. Rubini, F. Martelli, A. Franciosi
Abstract: Self-assembled nanowires have attracted much attention due to their potential applications in electronics and optoelectronics. A recent interest in Mn catalyzed GaAs nanowires are due to their potential use in spintronic devices at nanoscale. High densities of Au- and Mncatalyzed self-assembled GaAs nanowires (NWs) with diameter in the range of 20 to 200 nm and length of few microns were synthesized by molecular beam epitaxy (MBE) on different substrates at varied substrate temperatures. These nanowires were investigated by means of μ-Raman spectroscopy at room temperature. The Raman spectra from NWs show an energy downshift and a broadening of the LO and TO phonon lines that differ from those of epitaxial GaAs. We suggest that those downshift and broadening are due to the relaxation of the q=0 selection rule in the presence of structural defects in the nanowires. The results indicate that the use of Mn instead of Au as growth catalyst does not affect the structural quality of the nanowires drastically.
Authors: Ming Wu, Hai Rong Liu, Wei Jun Tong, De Xiu Huang
Abstract: In this paper we have proposed a photonic crystal structure to enhance the coupling efficiency between photonic crystal waveguide (PCW) and the conventional dielectric waveguide. The proposed waveguide characterized with employing the taper structure and varying the holes’ radius in the taper. Two-dimensional (2D) finite-difference time-domain (FDTD) method has been used to analyze the structure. The simulation results show that the coupling efficiency can be achieved as high as 81.6% at the wavelength of 1.55um.

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