Papers by Keyword: Superlattice

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Authors: Jun Feng Chen, Xiang Zhen Yu
Abstract: The tradition energy dispersion model can not match the experiment results of the AlGaN/GaN superlattice with strong polarization effect. Thus we propose a new dispersion model from the improved tight binding method. In this model, the couple of wavefunctions from more potential wells are considered. To a AlGaN/GaN superlattice with 1.5nm well length, 1nm barrier length and 25% Al content, the calculation result shows that the improved model are much more precise than the tradition model. This improved dispersion model can be used in the study of the nonlinear transport of AlGaN/GaN superlattice.
Authors: Fu Ling Tang, F.C. Wan, X.Q. Dai, W.J. Lu
Abstract: We studied in detail the lattice transition and local lattice structure (including Jahn-Teller distortion) in LaMnO3/SrMnO3 surperlattices by classical atomistic simulation. For a certain doping density, it is found that the superlattices with short modulation period have small lattice energies and larger differences among lattice parameters a, b/√2 and c. The average La-Mn (Mn3+-O) distance is larger than the average Sr-Mn (Mn4+-O) distance for all doping densities and superlattice configurations at certain doping density. The standard deviation of Mn-O bond lengths and Jahn-Teller distortion of MnO6 octahedra have been calculated. Both the standard deviation and Jahn-Teller distortion of Mn3+O6 octahedra in the superlattices are much smaller than those of Mn3+O6 octahedra in LaMnO3, while Mn4+O6 octahedra in the superlattices have the smallest lattice distortion, but larger than those in SrMnO3.
Authors: Jie Guo, Rui Ting Hao, Qian Run Zhao, Shi Qing Man
Abstract: The energy band structure of InAs/GaSb superlattice can be tailored by changing the thickness of InAs or GaSb layer thickness. Different superlattice as InAs/GaSb (4ML/8ML, 8ML/8ML and 16ML/7ML) for cut-off wavelengths from short to long IR wavelength were designed and deposited on GaSb substrates by melocular beam epitaxy system. The lattice mismatch was below 1000ppm under the careful Ga1-xInx- type interface control. The responsitivity revealed the band structure in InAs/GaSb superlattice can be tailored and the cutoff wavelength was from 2.5μm to 11μm. The current-voltage relation and the differential resistance in infrared photodiode were also measured and studied.
Authors: L. Hart, B.R. Davidson, J.M. Fernández, R.C. Newman, C.C. Button
Authors: Amal A. Kabalan, Pritpal Singh
Abstract: Tuning the bandgap of superlattice structures creates devices with unique optical, electronic and mechanical properties. Designing solar cells with superlattice structures increases the range of light energy absorbed from the solar spectrum in the device. A superlattice is a nanostructure composed of alternating thin layers of two materials. The thickness of the constituent materials alters the optical bandgap of the superlattice. This paper discusses a mathematical model which computes the effective bandgap of a CdTe/PbTe superlattice based on a given thickness of the CdTe and PbTe films. The output of this model is verified by fabricating superlattices with different thickness and measuring their effective bandgaps. The electrochemical atomic layer deposition method is used to fabricate the superlattice structures. The advantage of this method over other vacuum techniques is that it is inexpensive and operates at room temperature. This paper also discusses a method to mitigate the lattice mismatch between the substrate and the superlattice. The optical bandgaps, crystallinity, grain size and chemical composition of the structures are measured using a spectrometer, diffractometer, transmission electron microscope and scanning electron microscope, respectively. The bandgaps of the fabricated superlattices were in agreement with the simulated values. This model can be used for designing the bandgaps of superlattices which can be incorporated in solar cells.
Authors: Zs. Makkai, Béla Pécz, M.A. di Forte-Poisson, F. Huet
Authors: V.A. Ignatchenko, D.S. Tsikalov
Abstract: The dynamic susceptibility and the one-dimensional density of states (DOS) of an initially sinusoidal superlattice (SL) with simultaneous presence of two-dimensional (2D) phase inhomogeneities that simulate the deformations of the interfaces between the SL’s layers and three-dimensional (3D) amplitude inhomogeneities of the layer material of the SL were investigated. An analytical expression for the averaged Green’s function of the sinusoidal SL with 2D phase inhomogeneities was obtained in the Bourret approximation. It was shown that the effect of increasing asymmetry of heights of the dynamic susceptibility peaks at the edge of the Brillouin zone of the SL, which was found in [6] at increasing the rms fluctuations of 2D inhomogeneities, also takes place at increasing the correlation wave number of such inhomogeneities. It was also shown that the increase of the rms fluctuations of 3D amplitude inhomogeneities in the superlattice with 2D phase inhomogeneities leads to the suppression of the asymmetry effect and to the decrease of the depth of the DOS gap.
Authors: L.K. Orlov, A.V. Potapov, N.L. Ivina, E.A. Steinman, V.I. Vdovin
Authors: P.S. Clegg, J.P. Goff, G.J. McIntyre, R.C.C. Ward, M.R. Wells
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