Papers by Keyword: Quantum Well

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Authors: V. Dixit, H.F. Liu, N. Xiang
Abstract: Blueshifts of photoluminescence (PL) peak wavelength from GaInNAs/GaAs quantum well (QW) at various annealing temperatures have been studied. Our results indicate that as-grown GaInNAs/GaAs QW sample has N-Ga3In1 phase, which changes to a mixture of N-Ga3In1 and NGa2In2 after annealing. The activation energy characterized for short range order is 2.38 eV, which is smaller than that for the diffusion process (3.196 eV). This indicates that the short range order is the dominant mechanism for PL blueshift at relatively low annealing temperature and for short time annealing.
Authors: Robert S. Okojie, Ming Xhang, P. Pirouz, Sergey P. Tumakha, Gregg Jessen, Leonard J. Brillson
Authors: Teddy Robert, Maya Marinova, Sandrine Juillaguet, Anne Henry, Efstathios K. Polychroniadis, Jean Camassel
Abstract: A new type of 6H zigzag faults has been identified from high resolution transmission electron microscopy (HRTEM) measurements performed on low-doped 4H-SiC homoepitaxial layer grown on off-axis substrates in a hot-wall CVD reactor. They are made of half unit cells of 6H with corresponding low temperature photoluminescence (LTPL) response ranging from about 3 eV to 2.5 eV at liquid helium temperature.
Authors: Teddy Robert, Sandrine Juillaguet, Maya Marinova, Thierry Chassagne, Ioannis Tsiaousis, N. Frangis, Efstathios K. Polychroniadis, Jean Camassel
Abstract: The electronic structure of in-grown 8H stacking faults in 4H-SiC matrix has been investigated in detail. After assessment of the structural properties by high resolution transmission electron microscopy, we focus on the electronic structure. We show that one unit cell of 8H does not behave like a single type-II quantum well but, rather, like two type-II quantum wells of 3C coupled by a thin hexagonal barrier. Using a transfer matrix method, we compute the corresponding transition energies, taking into account the effect of the valence band offset and built-in electric field. A good agreement is found with the experimental data collected from low temperature photoluminescence spectroscopy.
Authors: M.A. Humayun, M.A. Rashid, F. Malek, A. Yusof, F.S. Abdullah, N.B. Ahmad
Abstract: This paper presents a comparative analysis of some of the important characteristics of the carriers of quantum well and quantum dot based laser. Among the characteristics of the carriers, confined carrier concentrations in the gain medium as well as the carrier concentrations at the threshold have been studied extensively by using InxGa1-xN based quantum well and InxGa1-xN based quantum dot in the active layer of the laser structure. The numerical results obtained are compared to investigate the superiority of the quantum dot over quantum well. It is ascertained from the comparison results that InxGa1-xN based quantum dot provides higher density of confined carrier and lower level of carrier concentration required for lasing action. This paper reports the enhancement of confined carrier density and minimization of carrier concentration at threshold of laser using InxGa1-xN based quantum dot as the active layer material. Hence, it is revealed that better performances of lasers have been obtained using InxGa1-xN based quantum dot than that of quantum well in the active medium of the device structure.
Authors: I. Ostrovskii, O.A. Korotchenkov
Authors: Paul K.L. Yu, Edward T. Yu, De Li Wang
Abstract: In this paper we present the concept and demonstration of novel photovoltaic and electro-optic devices, and photoelectrochemical cells based on various semiconductor nanostructures, specifically compound semiconductor quantum wells and nanowires, and the use of plasmonic and related scattering effects from metal or dielectric nanoparticles to increase efficiency of optical absorption. Quantum-well solar cells were fabricated with scattering from metallic or dielectric nanostructures incorporated to direct incident photons into lateral, optically confined paths with high electromagnetic field intensity within relatively thin multiple-quantum-well regions to maximize quantum efficiency of photon absorption. The internal structure of quantum wells in quantum-well solar cells was also analyzed and characterized; the incorporation of a suitable potential step within each quantum well was explored for improvement in power conversion efficiency. Vertical nanowire arrays were engineered to optimize optical confinement within the nanowires, and core-shell heterostructures were employed to achieve broad-spectrum absorption while maintaining high open-circuit voltages. Large linear electro-optic effect is observed in the nanowire arrays. Branched nanowire photoelectrochemical cells were also made and characterized for their spectral incident photon-to-current conversion efficiency. These works have been sponsored by U.S. Department of Energy and National Science Foundation.
Authors: Dnyaneshwar S. Patil, E.P. Samuel
Abstract: The Quantum well structures have exhibited significant utility in the fabrication of advanced laser devices. The Gallium nitride semiconductor and its alloy particularly AlGaN based quantum structures are having important applications in optical data storage systems and the visible displays. Due to tailoring of wide band gap energy the spectrum obtained is from visible to ultraviolet wavelength range. We had thoroughly investigated the influence of Aluminum mole fraction variation in AlxGa1-xN under a biased condition for GaN/AlGaN based quantum heterostructure optical properties. Here, we had used 6X6 Hamiltonian to realize these properties. The 6X6 Hamiltonian has been chosen to include the many body effect in the calculation and to enhance the accuracy of the optimized results. The paper is focused to reveal the Aluminum mole fraction dependence of near and far filed intensities, peak optical gain, carrier concentration, and optical confinement factor. The effective index method has been used in determination of the optical field intensity in the near and far regimes. The variation in Aluminum mole fraction produces disparity in carrier concentration; hence, we have obtained the spontaneous emission and optical gain as a function of photon energy for different carrier density. The piezoelectric effect on GaN quantum well due to AlGaN barriers has been included through Poisson equation. This Poisson equation has been solved in a self-consistent manner along with Schrödinger and subsequently carrier concentrations have been deduced with a high accuracy using our simulation tools developed in MATLAB.
Authors: A. Wulfes, J. Gutowski, E. Kurtz, D. Hommel, M. Scholl, M. Heuken
Authors: C. Ivan Cabrera, J.C. Rimada, Luis Hernandez, Agustin Enciso, David Armando Contreras-Solorio
Abstract: Strain-balanced quantum well solar cells (SB-QWSC) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a pin device. The strain-balanced quantum well solar cell benefits from a fundamental efficiency enhancement due to anisotropic emission from the quantum wells. This anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. We have also demonstrated that the photo-generated carriers can escape from the QWs with near unity efficiency, via a thermally-assisted tunneling process, because gain is several orders greater than radiative recombination.
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