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15 Apr 2012

Volume 111, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 084701 (2012); http://dx.doi.org/10.1063/1.3698319 (11 pages)

Xerxes Lopez-Yglesias, Jason M. Gamba, and Richard C. Flagan
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back to top Lasers, Optics, and Optoelectronics

Light scattering at textured back contacts for n-i-p thin-film silicon solar cells

K. Bittkau, W. Böttler, M. Ermes, V. Smirnov, and F. Finger

J. Appl. Phys. 111, 083101 (2012); http://dx.doi.org/10.1063/1.3703572 (5 pages) | Cited 2 times

Online Publication Date: 16 April 2012

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The angular resolved light scattering at textured back contacts for n-i-p thin-film silicon solar cells is investigated experimentally in air. These results are compared to simulations performed by a scalar model for reflection with excellent agreement. Furthermore, light scattering is modeled for the transmission and reflection inside the silicon solar cell. It is found that the reflection at the back contact dominates the light scattering in the absorber layer. From these simulations, a quantity is derived that successfully predicts the external quantum efficiencies of solar cells on different textures.
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88.40.jj Silicon solar cells

Optically optimal wavelength-scale patterned ITO/ZnO composite coatings for thin film solar cells

Antoine Moreau, Rafik Smaali, Emmanuel Centeno, and Christian Seassal

J. Appl. Phys. 111, 083102 (2012); http://dx.doi.org/10.1063/1.3703670 (6 pages)

Online Publication Date: 17 April 2012

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A methodology is proposed for finding structures that are, optically speaking, locally optimal: a physical analysis of much simpler structures is used to constrain the optimization process. The obtained designs are based on a flat amorphous silicon layer (to minimize recombination) with a patterned anti-reflective coating made of ITO or ZnO, or a composite ITO/ZnO coating. These latter structures are realistic and present good performances despite very thin active layers.
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81.65.-b Surface treatments

Modeling of current gain compression in common emitter mode of a transistor laser above threshold base current

Rikmantra Basu, Bratati Mukhopadhyay, and P. K. Basu

J. Appl. Phys. 111, 083103 (2012); http://dx.doi.org/10.1063/1.4703926 (7 pages)

Online Publication Date: 18 April 2012

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We have obtained the expressions for the terminal currents in a heterojunction bipolar transistor laser the base of which contains a quantum well (QW). The emitter-base junction is assumed to be abrupt, leading to abrupt discontinuity in quasi-Fermi level at the interface. The expressions for the terminal currents as a function of collector-emitter and base-emitter voltages are obtained from the solution of the continuity equation. The current density in the QW located at an arbitrary position in the base is related to the virtual state current density. The threshold current density in the QW is calculated by using the expression for gain obtained from Fermi golden rule. The plot of collector current (IC) versus collector-emitter voltage (VCE) for different values of base current shows the usual transistor characteristics, i.e., a rising portion after a cut-in VCE, and then a saturation behavior. The dc current gain remains constant. However, as the base current exceeds the threshold, a stimulated recombination rate is added to the spontaneous recombination rate and the plots of collector currents become closer for the same increase in base current. This current gain compression is in agreement with the experimental observation. Our calculated values qualitatively agree with other experimental findings; however some features like Early effect do not show up in the calculation.
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85.30.Pq Bipolar transistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Molecular beam epitaxial growth and characterization of InSb1 − xNx on GaAs for long wavelength infrared applications

Nimai C. Patra, Sudhakar Bharatan, Jia Li, Michael Tilton, and Shanthi Iyer

J. Appl. Phys. 111, 083104 (2012); http://dx.doi.org/10.1063/1.3702453 (8 pages) | Cited 1 time

Online Publication Date: 19 April 2012

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Recent research progress and findings in InSbN have attracted great attention due to its use in long wavelength infrared applications. A large bandgap reduction in InSb resulting from high N incorporation with minimal crystal defects is challenging due to relatively small atomic size of N. Hence optimization of growth conditions plays an important role in the growth of high-quality InSbN epilayers for device purposes. In this paper, we report on the correlation of structural, vibrational, electrical, and optical properties of molecular beam epitaxially grown InSbN epilayers grown on GaAs substrates, as a function of varying growth temperatures. Two dimensional growths of InSb and InSbN were confirmed from dynamic reflection high energy electron diffraction patterns and growth parameters were optimized. High crystalline quality of the epilayers is attested to by a low full width at half maximum of 200 arcsec from high resolution x-ray diffraction (HRXRD) scans and by the high intensity and well-resolved InSb longitudinal optical (LO) and 2nd order InSb LO mode observed from micro-Raman spectroscopy. The N incorporation in these InSbN epilayers is estimated to be 1.4% based on HRXRD simulation. X-ray photoelectron spectroscopy (XPS) studies reveal that most of the N present in the layers are in the form of In-N bonding. Variation of the lattice disorder with growth temperature is correlated with the types of N bonding present, the carrier concentration and mobility, observed in the corresponding XPS spectra and Hall measurements, respectively. XPS analysis, HRXRD scans, and Raman spectral analysis indicate that lower growth temperature favors In-N bonding which dictates N incorporation in the substitutional sites and lattice disorder, whereas, high growth temperature promotes the formation of In-N-Sb bonding. The best room temperature and 77 K electrical transport parameters and maximum redshift in the absorption edge have been achieved in the InSbN epilayer grown in the 290 °C ∼ 330 °C temperature range.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

Non-equilibrium Green’s function calculation for GaN-based terahertz-quantum cascade laser structures

H. Yasuda, T. Kubis, I. Hosako, and K. Hirakawa

J. Appl. Phys. 111, 083105 (2012); http://dx.doi.org/10.1063/1.4704389 (4 pages) | Cited 1 time

Online Publication Date: 19 April 2012

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We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green’s function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.-x Radiowave and microwave (including millimeter wave) technology

Cavity suppression in nitride based superluminescent diodes

A. Kafar, S. Stańczyk, S. Grzanka, R. Czernecki, M. Leszczyński, T. Suski, and P. Perlin

J. Appl. Phys. 111, 083106 (2012); http://dx.doi.org/10.1063/1.4704147 (6 pages)

Online Publication Date: 20 April 2012

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We have fabricated two types of InGaN superluminescent diodes applying two different concepts of cavity suppression: a tilted waveguide geometry and passive absorber solution. Both types of devices showed superluminescence behavior, but both eventually lased under the application of high enough current. The lasing threshold turned out to be higher for tilted waveguide devices. By using long (2 mm) waveguides, we managed to demonstrate the power in superluminescent mode exceeding 100 mW in blue/violet part of the spectrum.
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85.60.Jb Light-emitting devices

Homogeneous and elongation-free 3D microfabrication by a femtosecond laser pulse and hologram

M. Yamaji, H. Kawashima, J. Suzuki, S. Tanaka, M. Shimizu, K. Hirao, Y. Shimotsuma, and K. Miura

J. Appl. Phys. 111, 083107 (2012); http://dx.doi.org/10.1063/1.4705286 (7 pages)

Online Publication Date: 23 April 2012

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A new 3D microfabrication method has been developed, which uses only a single femtosecond laser pulse and a hologram. For the microfabrication inside transparent materials, the optical axial elongation of the fabricated structure is a major problem that has thus far limited design flexibility, especially for the direction along the optical axis. By controlling the light intensity distribution profile and using the adequate focal length of the hologram, this problem was solved and homogeneous and elongation-free 3D microfabrication was achieved.
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81.16.-c Methods of micro- and nanofabrication and processing
42.62.-b Laser applications
42.40.Kw Holographic interferometry; other holographic techniques
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

A scattering model for nano-textured interfaces and its application in opto-electrical simulations of thin-film silicon solar cells

K. Jäger, M. Fischer, R. A. C. M. M. van Swaaij, and M. Zeman

J. Appl. Phys. 111, 083108 (2012); http://dx.doi.org/10.1063/1.4704372 (9 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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We present a scattering model based on the scalar scattering theory that allows estimating far field scattering properties in both transmission and reflection for nano-textured interfaces. We first discuss the theoretical formulation of the scattering model and validate it for nano-textures with different morphologies. Second, we combine the scattering model with the opto-electric asa simulation software and evaluate this combination by simulating and measuring the external parameters and the external quantum efficiency of solar cells with different interface morphologies. This validation shows that the scattering model is able to predict the influence of nano-textured interfaces on the solar cell performance. The scattering model presented in this manuscript can support designing nano-textured interfaces with optimized morphologies.
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68.35.Ct Interface structure and roughness
88.40.jj Silicon solar cells

Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

M. Baibarac, F. Massuyeau, J. Wery, I. Baltog, and S. Lefrant

J. Appl. Phys. 111, 083109 (2012); http://dx.doi.org/10.1063/1.4705403 (5 pages)

Online Publication Date: 27 April 2012

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In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials.
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78.66.Sq Composite materials
81.07.Pr Organic-inorganic hybrid nanostructures
81.16.-c Methods of micro- and nanofabrication and processing
78.30.-j Infrared and Raman spectra
78.55.-m Photoluminescence, properties and materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
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