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10 Jan 2011

Volume 98, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 023701 (2011); http://dx.doi.org/10.1063/1.3518472 (3 pages)

Amit Choubey, Mohammad Vedadi, Ken-ichi Nomura, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Directional single mode quantum cascade laser emission using second-order metal grating coupler

G. Maisons, M. Carras, M. Garcia, B. Simozrag, and X. Marcadet

Appl. Phys. Lett. 98, 021101 (2011); http://dx.doi.org/10.1063/1.3535610 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2011

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We report on the design and experimental demonstration of a substrate emitting quantum cascade laser (QCL) with low beam divergence in the two directions. A low-loss, index-coupled, distributed feedback laser is coupled to a monolithic extraction area. Both functions are performed with a top metal grating spatially differentiated for improving the divergence of the QCL in the two directions. Spectrally single-mode InGaAs/AlInAs QCL emitting at a wavelength of 5.65 μm with a low beam divergence, represented by a full width at half maximum of 2.3° and 4°, is demonstrated at room temperature with a threshold current of 2.1 kA/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers

High internal and external quantum efficiency InGaN/GaN solar cells

Elison Matioli, Carl Neufeld, Michael Iza, Samantha C. Cruz, Ali A. Al-Heji, Xu Chen, Robert M. Farrell, Stacia Keller, Steven DenBaars, Umesh Mishra, Shuji Nakamura, James Speck, and Claude Weisbuch

Appl. Phys. Lett. 98, 021102 (2011); http://dx.doi.org/10.1063/1.3540501 (3 pages) | Cited 11 times

Online Publication Date: 10 January 2011

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High internal and external quantum efficiency GaN/InGaN solar cells are demonstrated. The internal quantum efficiency was assessed through the combination of absorption and external quantum efficiency measurements. The measured internal quantum efficiency, as high as 97%, revealed an efficient conversion of absorbed photons into electrons and holes and an efficient transport of these carriers outside the device. Improved light incoupling into the solar cells was achieved by texturing the surface. A peak external quantum efficiency of 72%, a fill factor of 79%, a short-circuit current density of 1.06 mA/cm2, and an open circuit voltage of 1.89 V were achieved under 1 sun air-mass 1.5 global spectrum illumination conditions.
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88.40.jm Thin film III-V and II-VI based solar cells
88.05.Tg Energy use in lighting
42.25.Bs Wave propagation, transmission and absorption

Temperature tunability of photonic crystal fiber filled with Fe3O4 nanoparticle fluid

Yinping Miao, Bo Liu, Kailiang Zhang, Yan Liu, and Hao Zhang

Appl. Phys. Lett. 98, 021103 (2011); http://dx.doi.org/10.1063/1.3540647 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2011

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Fe3O4 nanoparticles fluid has unique optical properties, which provides versatile possibilities to design state-of-the-art photonic devices. In this paper, by combining Fe3O4 nanoparticles fluid with the photonic crystal fiber (PCF), the spectral characteristics of fluid-filled PCF under different temperatures were experimentally demonstrated. Transmission power and the long wavelength edge of the dip are both found to become highly temperature dependent. The experimental results indicate the slope of this edge is adjustable by changing temperature and there is a linear relationship between transmission power and temperature. This suggests the potential application of this device as an intensity-modulated sensing element or a tunable all-in-fiber gain equalization filter with an adjustable slope.
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42.81.Wg Other fiber-optical devices
42.65.-k Nonlinear optics
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Deformation-immunized optical deposition of graphene for ultrafast pulsed lasers

Hyungseok Kim, Junhyun Cho, Sung-Yeon Jang, and Yong-Won Song

Appl. Phys. Lett. 98, 021104 (2011); http://dx.doi.org/10.1063/1.3536502 (3 pages) | Cited 3 times

Online Publication Date: 11 January 2011

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We demonstrate deformation-suppressed optical deposition of graphene onto an optical fiber by forming a graphene/polyvinyl acetate (PVAc) composite for ultrafast nonlinear photonics. With pure graphene, its nonlinear operation threshold is elevated by the optical deposition that cannot guarantee the intact two-dimensional nanoshape of graphene. The role of PVAc that provides immunity to graphene against deleterious degradation of morphology and optical nonlinearity is elucidated via electron microscope analysis, Raman characterization, and realizing passive mode-locking operation of fiber lasers. Resultant center wavelength, spectral width, and repetition rate of the laser pulses are 1572.6 nm, 0.6 nm, and 91.5 MHz, respectively.
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78.67.Sc Nanoaggregates; nanocomposites
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.47.J- Ultrafast spectroscopy (<1 psec)
78.30.Am Elemental semiconductors and insulators

Coupling of a surface plasmon with localized subwavelength microcavity modes

P. Jouy, Y. Todorov, A. Vasanelli, R. Colombelli, I. Sagnes, and C. Sirtori

Appl. Phys. Lett. 98, 021105 (2011); http://dx.doi.org/10.1063/1.3536504 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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Midinfrared photonic modes of a periodically patterned metal-dielectric-metal structure have been investigated theoretically and experimentally. We have observed an anticrossing behavior between cavity modes localized in the double-metal regions and the surface plasmon polariton, signature of a hybridization between the two modes.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
63.20.Pw Localized modes
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.Ac Multilayers

Midinfrared electroluminescence from PbTe/CdTe quantum dot light-emitting diodes

A. Hochreiner, T. Schwarzl, M. Eibelhuber, W. Heiss, G. Springholz, V. Kolkovsky, G. Karczewski, and T. Wojtowicz

Appl. Phys. Lett. 98, 021106 (2011); http://dx.doi.org/10.1063/1.3531760 (3 pages) | Cited 3 times

Online Publication Date: 11 January 2011

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Midinfrared electroluminescence of epitaxial PbTe quantum dots in CdTe with emission in the 2–3 μm wavelength range is demonstrated up to room temperature. The light-emitting diode structures were grown by molecular beam epitaxy with the active PbTe quantum dots embedded in the intrinsic zone of a CdTe/CdZnTe p-i-n junction on GaAs (100) substrates. The current and temperature dependences of the electroluminescence emission are presented. The comparison with photoluminescence measurements shows that midinfrared light-emission from the diodes originates from the quantum dots.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence
68.55.ag Semiconductors
78.55.Et II-VI semiconductors
85.30.Kk Junction diodes

Fully complementary metal-oxide-semiconductor compatible nanoplasmonic slot waveguides for silicon electronic photonic integrated circuits

Shiyang Zhu, T. Y. Liow, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 98, 021107 (2011); http://dx.doi.org/10.1063/1.3537964 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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Horizontal Al/SiO2/Si/SiO2/Al nanoplasmonic slot waveguides with the SiO2 width at each side of ∼ 15 nm and the Si core width of ∼ 136–43 nm were fabricated using a fully silicon complementary metal-oxide-semiconductor compatible technology. The propagation losses were measured to be ∼ 1.07–1.63 dB/μm at the telecommunication wavelength of 1550 nm, in agreement with those predicted from numerical simulation. A simple tapered coupler with length of ∼ 0.3–1 μm provides a high coupling efficiency of ∼ −0.6–−1.5 dB between the plasmonic waveguide and the conventional Si dielectric waveguide. The plasmonic slot waveguide can achieve a low-loss ultracompact bend. A direct 90° bend was demonstrated to have the pure bending loss as low as ∼ 0.2–0.4 dB. The losses of propagation, coupling, and bending depend weakly on wavelength in the c-band. These results demonstrate the potential for seamless integration of functional plasmonic devices in existing silicon electronic photonic integrated circuits.
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42.82.Et Waveguides, couplers, and arrays
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Tv Field effect devices

The effect of intensity of excitation on CdSe/ZnS quantum dots: Opportunities in luminescence sensing

Jens U. Sutter, David J. S. Birch, and Olaf J. Rolinski

Appl. Phys. Lett. 98, 021108 (2011); http://dx.doi.org/10.1063/1.3534784 (3 pages) | Cited 1 time

Online Publication Date: 11 January 2011

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We report changes in the photophysical properties of core-shell type CdSe/ZnS quantum dots (QDs) under optical irradiation. QDs either in aqueous solution or immobilized in a silica sol gel matrix have been excited at different wavelengths and fluxes. Illumination of the sample with 140 fs 700 nm Ti:sapphire laser pulses of the peak power of the order of 4 GW/cm2 caused gradual increase in the luminescence lifetime from an initial value of 3.5 increasing to 4.5 ns and an increase in luminescence intensity by ∼ 8%. Using about 16 GW/cm2 peak power resulted in a shortening of the luminescence lifetime to 3 ns and a decrease in intensity by ∼ 75%. Both photobrightening and photodarkening were fully reversible. We discuss the kinetics of photobrightening and photodarkening and investigate the suitability of QDs as luminescence lifetime sensors with tunable parameters.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors

Optical racetrack ring-resonator based on two U-bent microfibers

Yongmin Jung, Gilberto Brambilla, Ganapathy Senthil Murugan, and David J. Richardson

Appl. Phys. Lett. 98, 021109 (2011); http://dx.doi.org/10.1063/1.3540684 (3 pages)

Online Publication Date: 11 January 2011

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We experimentally demonstrate an optical racetrack ring-resonator with four optical ports constructed using two U-shaped bent microfibers placed into direct physical contact. Localized light is clearly observed along the closed loop path as a result of the resulting strong optical resonance. The resonator was embedded in a low-index polymer matrix to improve the long term mechanical and optical stability allowing a detailed study of its polarization characteristics.
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42.81.Wg Other fiber-optical devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.81.Gs Birefringence, polarization

Monolithic single GaN nanowire laser with photonic crystal microcavity on silicon

Junseok Heo, Wei Guo, and Pallab Bhattacharya

Appl. Phys. Lett. 98, 021110 (2011); http://dx.doi.org/10.1063/1.3540688 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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Optically pumped lasing at room temperature in a silicon based monolithic single GaN nanowire with a two-dimensional photonic crystal microcavity is demonstrated. Catalyst-free nanowires with low density ( ∼ 108 cm−2) are grown on Si by plasma-assisted molecular beam epitaxy. High resolution transmission electron microscopy images reveal that the nanowires are of wurtzite structure and they have no observable defects. A single nanowire laser fabricated on Si is characterized by a lasing transition at λ = 371.3 nm with a linewidth of 0.55 nm. The threshold is observed at a pump power density of ∼ 120 kW/cm2 and the spontaneous emission factor β is estimated to be 0.08.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Polarization-independent filters for luminescent solar concentrators

Dick K. G. de Boer, Chi-Wen Lin, Merijn P. Giesbers, Hugo J. Cornelissen, Michael G. Debije, Paul P. C. Verbunt, and Dirk J. Broer

Appl. Phys. Lett. 98, 021111 (2011); http://dx.doi.org/10.1063/1.3541543 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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The efficiency of luminescent solar concentrators could be enhanced by use of wavelength-selective filters, reducing the amount of luminescent light lost. To accomplish this, polarization-independent filters with reflectivity >97% were made by combining layers of cholesteric liquid crystals, either a right- with a left-handed layer, or two right-handed layers with a half-lambda waveplate. Normal cholesteric filters have a reflection bandwidth which is narrower than the spectral and angular range of the luminescent emission. The reflection band is broadened from 80 to 200 nm by employing a pitch gradient in the cholesteric layer. The measured transmission bands compare well with calculations.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Kr Display devices, liquid-crystal devices
85.60.Jb Light-emitting devices
42.79.Ek Solar collectors and concentrators

Topology optimized low-contrast all-dielectric optical cloak

Jacob Andkjær and Ole Sigmund

Appl. Phys. Lett. 98, 021112 (2011); http://dx.doi.org/10.1063/1.3540687 (3 pages) | Cited 2 times

Online Publication Date: 13 January 2011

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A systematic methodology for designing low-contrast all-dielectric cloaks operating in the optical range is presented. Topology optimization is used to find the layout of standard dielectric material that minimizes the norm of the scattered field in the surroundings of the cloak. Rotational symmetries are exploited to optimize for multiple angles based on the solution for a single angle of incidence. For a few discrete angles of incidences (1–4) the cloaking is shown to be nearly perfect in a limited frequency range, and even for a rotational symmetric design, cloak and object appear smaller than the noncloaked object.
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42.70.-a Optical materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.-e Optical elements, devices, and systems

Theoretical and experimental studies of surface plasmons excited at metal-uniaxial dielectric interface

Xiaolei Wang, Pei Wang, Junxue Chen, Yonghua Lu, Hai Ming, and Qiwen Zhan

Appl. Phys. Lett. 98, 021113 (2011); http://dx.doi.org/10.1063/1.3541653 (3 pages) | Cited 1 time

Online Publication Date: 13 January 2011

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In this letter, surface plasmons (SPs) excited at the metal-uniaxial dielectric interface are investigated both theoretically and experimentally. The dispersion relations of SPs are derived for the cases where the optical axis of uniaxial medium is parallel the interface or in the incident plane perpendicular to the interface. The theoretical predictions are verified by a Kretschmann–Raether [ W. L. Barnes, A. Dereux, and T. W. Ebbesen, Nature (London) 424, 824 (2003)] configuration with azobenzene polymer as photoinduced uniaxial medium. The attenuated total reflection spectra clearly show that the dependence of the SPs propagation properties on the orientations of optical axis, which is consistent with the theoretical analysis. The results of this study provide a useful approach to modulate SPs through adjusting the azobenzene molecular orientation.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)

Photo-Dember terahertz emitter excited with an Er:fiber laser

G. Klatt, B. Surrer, D. Stephan, O. Schubert, M. Fischer, J. Faist, A. Leitenstorfer, R. Huber, and T. Dekorsy

Appl. Phys. Lett. 98, 021114 (2011); http://dx.doi.org/10.1063/1.3543627 (3 pages) | Cited 2 times

Online Publication Date: 13 January 2011

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A terahertz emitter based on the lateral photo-Dember effect is shown to efficiently generate terahertz radiation with a peak frequency of 0.7 THz and an electric field amplitude up to 5 V/cm when excited by 90 fs pulses centered at 1.55 μm. A thin layer of In0.53Ga0.47As grown on InP provides the substrate material in which unidirectional lateral photo-Dember currents are excited. Since photo-Dember terahertz emitters do not require an external bias, they do not suffer from high dark currents limiting the application of biased InGaAs photoconductive terahertz emitters.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Gain of blue and cyan InGaN laser diodes

T. Lermer, A. Gomez-Iglesias, M. Sabathil, J. Müller, S. Lutgen, U. Strauss, B. Pasenow, J. Hader, J. V. Moloney, S. W. Koch, W. Scheibenzuber, and U. T. Schwarz

Appl. Phys. Lett. 98, 021115 (2011); http://dx.doi.org/10.1063/1.3541785 (3 pages) | Cited 2 times

Online Publication Date: 13 January 2011

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Experimental gain spectra of 450 and 490 nm laser diodes on c-plane GaN are analyzed by detailed comparison with the results of a fully microscopic theory. The gain calculation shows the importance of electron LO-phonon coupling. The whole spectral gain shape, not only the low energy tail, is strongly influenced by the LO-phonon contribution. The inhomogeneous broadening parameter increases by a factor of about two for the cyan laser diode in comparison with the blue laser structure. This indicates an increase in alloy and thickness fluctuations for the longer wavelength material.
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42.55.Px Semiconductor lasers; laser diodes
63.20.kd Phonon-electron interactions
78.66.Fd III-V semiconductors

Experimental observation of Fano resonance in a single whispering-gallery microresonator

Bei-Bei Li, Yun-Feng Xiao, Chang-Ling Zou, Yong-Chun Liu, Xue-Feng Jiang, You-Ling Chen, Yan Li, and Qihuang Gong

Appl. Phys. Lett. 98, 021116 (2011); http://dx.doi.org/10.1063/1.3541884 (3 pages) | Cited 3 times

Online Publication Date: 14 January 2011

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We experimentally observe Fano resonance in a single silica toroidal microresonator, in which two whispering-gallery modes (WGMs) are excited simultaneously through a fiber taper. By adjusting the fiber-cavity coupling strength and the polarization of incident light, the Fano-like resonance line shape can be engineered and further convert to the electromagnetically induced transparency (EIT) like line shape. Our theoretical analysis reveals that both the Fano and EIT resonances originate from an indirect-coupling of two originally orthogonal WGMs, which is mediated by the common fiber taper waveguide. The sharp Fano line shape holds great potential in optical switching and sensitivity-enhanced biochemical sensing.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.40.Az Waveguides, transmission lines, striplines
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.25.-b Spin polarized transport
42.25.Ja Polarization
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Atmospheric pressure cold plasma as an antifungal therapy

Peng Sun, Yi Sun, Haiyan Wu, Weidong Zhu, Jose L. Lopez, Wei Liu, Jue Zhang, Ruoyu Li, and Jing Fang

Appl. Phys. Lett. 98, 021501 (2011); http://dx.doi.org/10.1063/1.3530434 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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A microhollow cathode based, direct-current, atmospheric pressure, He/O2 (2%) cold plasma microjet was used to inactive antifungal resistants Candida albicans, Candida krusei, and Candida glabrata in air and in water. Effective inactivation (>90%) was achieved in 10 min in air and 1 min in water. Antifungal susceptibility tests showed drastic reduction of the minimum inhibitory concentration after plasma treatment. The inactivation was attributed to the reactive oxygen species generated in plasma or in water. Hydroxyl and singlet molecular oxygen radicals were detected in plasma-water system by electron spin resonance spectroscopy. This approach proposed a promising clinical dermatology therapy.
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87.53.-j Effects of ionizing radiation on biological systems
87.85.-d Biomedical engineering
52.77.-j Plasma applications

Influence of annular magnet on discharge characteristics in enhanced glow discharge plasma immersion ion implantation

Liu He Li, Zhuo Wang, Qiu Yuan Lu, En Jing Pang, Dan Dan Dun, Fu Shun He, Fen Li, Ricky K. Y. Fu, and Paul K. Chu

Appl. Phys. Lett. 98, 021502 (2011); http://dx.doi.org/10.1063/1.3537962 (3 pages)

Online Publication Date: 11 January 2011

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A permanent annular magnet positioned at the grounded anode alters the discharge characteristics in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). The nonuniform magnetic field increases the electron path length and confines electron motion due to the magnetic mirror effect and electron-neutral collisions thus occur more frequently. The plasma potential and ion density measured by a Langmuir probe corroborate that ionization is improved near the grounded anode. This hybrid magnetic field EGD-PIII method is suitable for implantation of gases with low ionization rates.
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52.80.Hc Glow; corona
52.77.Dq Plasma-based ion implantation and deposition
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.70.Ds Electric and magnetic measurements

Diffuse discharge, runaway electron, and x-ray in atmospheric pressure air in an inhomogeneous electrical field in repetitive pulsed modes

Tao Shao (邵涛), Cheng Zhang (章程), Zheng Niu (牛铮), Ping Yan (严萍), Victor F. Tarasenko, Evgenii Kh. Baksht, Alexander G. Burahenko, and Yuliya V. Shut’ko

Appl. Phys. Lett. 98, 021503 (2011); http://dx.doi.org/10.1063/1.3540504 (3 pages) | Cited 12 times

Online Publication Date: 13 January 2011

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This letter reports on experimental studies of a pulsed discharge in an inhomogeneous electric field at a pressure of 1 atm for varying voltage pulse parameters. The amplitude of voltage pulses applied to point-to-plane and point-to-point gaps was 12–140 kV and the full width at half maximum was 1–40 ns. It is shown that in a wide range of experimental conditions, a diffuse discharge is ignited due to preionization of the gap by runaway electrons and x-rays. With all gaps, the runaway electrons are produced in response to electric field amplification near the electrodes and in the gap.
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52.80.-s Electric discharges
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Evidence of tetragonal nanodomains in the high-pressure polymorph of BaTiO3

L. Ehm, L. A. Borkowski, J. B. Parise, S. Ghose, and Z. Chen

Appl. Phys. Lett. 98, 021901 (2011); http://dx.doi.org/10.1063/1.3535611 (3 pages) | Cited 1 time

Online Publication Date: 10 January 2011

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The pressure induced P4mm→Pmmathm phase transition in BaTiO3 perovskite was investigated by x-ray total scattering. The evolution of the structure was analyzed by fitting pair distribution functions over a pressure range from ambient pressure up to 6.85(7) GPa. Evidence for the existence of tetragonal ferroelectric nanodomains at high pressure was found. The average size of the nanodomains in the high-pressure phase decreases with increasing pressure. Extrapolation of the domain size to pressures higher than studied experimentally suggests a disappearance of the ferroelectric domains at about 9.3(5) GPa and a cubic symmetry of BaTiO3 high-pressure phase.
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77.80.B- Phase transitions and Curie point
61.46.-w Structure of nanoscale materials
62.50.-p High-pressure effects in solids and liquids
78.70.Ck X-ray scattering
77.80.Dj Domain structure; hysteresis
64.70.K- Solid-solid transitions

Hybrid exchange-correlation functional study of the structural, electronic, and mechanical properties of the MAX phases

M. Ramzan, S. Lebègue, and R. Ahuja

Appl. Phys. Lett. 98, 021902 (2011); http://dx.doi.org/10.1063/1.3536513 (3 pages)

Online Publication Date: 10 January 2011

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In this letter, we report on our results obtained with the hybrid functional HSE06 on the structural, electronic, and mechanical properties of the MAX phases. As a sample, we choose Ti2AlN, Ti2AlC, V2AlC, Nb2AlC, Ta2AlC, V2GeC, Ti3SiC2, and Ti4AlN3, which cover all the known types of MAX phases. From our calculations, we have found that V2GeC has the magnetically ordered ground state. Our results are compared to available experimental data, and it is shown that the HSE06 functional can be used as a predictive tool to study the properties of this family of compounds.
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71.70.Gm Exchange interactions
61.66.Fn Inorganic compounds
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Correlating structure, strain, and morphology of self-assembled InAs quantum dots on GaAs

D. P. Kumah, J. H. Wu, N. S. Husseini, V. D. Dasika, R. S. Goldman, Y. Yacoby, and R. Clarke

Appl. Phys. Lett. 98, 021903 (2011); http://dx.doi.org/10.1063/1.3535984 (3 pages) | Cited 1 time

Online Publication Date: 11 January 2011

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We report on the use of a direct x-ray phase retrieval method, coherent Bragg rod analysis, to characterize self-assembled InAs quantum dots (QDs) grown epitaxially on GaAs substrates. Electron density maps obtained close to the x-ray absorption edges of the constituent elements are compared to deconvolute composition and atomic spacing information. Our measurements show no evidence of a wetting layer and reveal bowing of the atomic layers throughout the QD, extending from the QD-substrate interface. This leads to a half-layer stacking shift which may act to partially decouple the QDs electronically from the substrate.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.70.Dm X-ray absorption spectra

Bond-specific reaction kinetics during the oxidation of (111) Si: Effect of n-type doping

B. Gokce, D. E. Aspnes, G. Lucovsky, and K. Gundogdu

Appl. Phys. Lett. 98, 021904 (2011); http://dx.doi.org/10.1063/1.3537809 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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It is known that a higher concentration of free carriers leads to a higher oxide growth rate in the thermal oxidation of silicon. However, the role of electrons and holes in oxidation chemistry is not clear. Here, we report real-time second-harmonic-generation data on the oxidation of H-terminated (111)Si that reveal that high concentrations of electrons increase the chemical reactivity of the outer-layer Si-Si back bonds relative to the Si-H up bonds. However, the thicknesses of the natural oxides of all samples stabilize near 1 nm at room temperature, regardless of the chemical kinetics of the different bonds.
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81.65.Mq Oxidation
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
78.47.N- High resolution nonlinear optical spectroscopy
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si

Low aspect-ratio hemispherical nanopit surface texturing for enhancing light absorption in crystalline Si thin film-based solar cells

Junshuai Li, HongYu Yu, Yali Li, Fei Wang, Mingfei Yang, and She Mein Wong

Appl. Phys. Lett. 98, 021905 (2011); http://dx.doi.org/10.1063/1.3537810 (3 pages) | Cited 3 times

Online Publication Date: 11 January 2011

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In this letter, we report light absorption enhancement in crystalline Si thin film-based solar cells through introducing low aspect-ratio hemispherical nanopit surface textures. Optical characteristics of the system are systematically investigated in terms of the structural parameters including nanopit diameter (D) and array periodicity (P) via simulation. An ultimate efficiency of ∼ 35.7% is predicted when both D and P are ∼ 700 nm, which is more than double of that ( ∼ 15.9%) of the flat Si film with the same thickness of 2 μm. An understanding on the light absorption enhancement is provided based on the optical processes in the subwavelength structures.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Fourier transformation infrared spectrum studies on the role of fluorine in SnO2:F films

B. Zhang, Y. Tian, J. X. Zhang, and W. Cai

Appl. Phys. Lett. 98, 021906 (2011); http://dx.doi.org/10.1063/1.3533801 (3 pages)

Online Publication Date: 11 January 2011

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Show Abstract
In this letter we employed Fourier transform infrared spectroscopy (FTIR) to study fluorine-doped SnO2 films deposited by spray pyrolysis. The role of oxygen vacancy and substitution of fluorine for oxygen are demonstrated by FTIR. It is found that at low doping levels, fluorine ions prefer to occupy oxygen positions in SnO2 lattice. While beyond a certain doping level, fluorine ions start to occupy interstitial positions, which has a negative effect on carrier concentration that, in turn, affects the infrared reflectivity of SnO2 films. FTIR also shows the increase of the disorder of SnO2 films with increasing fluorine doping.
Show PACS
78.66.Li Other semiconductors
73.61.Le Other inorganic semiconductors
78.30.Hv Other nonmetallic inorganics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.72.jd Vacancies
61.72.jj Interstitials
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