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14 Jan 2013

Volume 102, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 102, 023901 (2013); http://dx.doi.org/10.1063/1.4773526 (4 pages)

Yoshihiro Gohda and Shinji Tsuneyuki
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Optical conductivity of highly mismatched GaP alloys

Yoshihiro Gohda and Shinji Tsuneyuki

Appl. Phys. Lett. 102, 023901 (2013); http://dx.doi.org/10.1063/1.4773526 (4 pages)

Online Publication Date: 14 January 2013

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Highly mismatched alloys are promising for applications to intermediate-band (IB) solar cells. Here, we report first-principles prediction of intermediate bands in GaP on the basis of hybrid-density-functional theory, which enables to handle large supercells including defects with much better accuracy than semilocal functionals. Calculated optical conductivity reveals that the intermediate states due to co-doped Mg and O have sufficiently high optical transition probability. The multiple gaps are robust against thermalization. Intermediate-band states become more delocalized by hybridization with phosphorus-vacancy states, increasing the optical transition probability.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Influence of Pb doping on the electrical transport properties of BiCuSeO

Lin Pan, David Bérardan, Lidong Zhao, Céline Barreteau, and Nita Dragoe

Appl. Phys. Lett. 102, 023902 (2013); http://dx.doi.org/10.1063/1.4775593 (5 pages) | Cited 3 times

Online Publication Date: 14 January 2013

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The effect of Pb doping on the thermoelectric properties of p-type BiCuSeO from 25 K to 873 K has been studied. The electrical resistivity and Seebeck coefficient of Bi1−xPbxCuSeO both decreased monotonically in all temperature range with increasing Pb content due to the increased carrier concentration. The power factor of Bi1−xPbxCuSeO (x = 0.03) reaches 5.3 μW cm−1 K−2 at 873 K. The influence of Pb2+ doping on the electronic structure is the same as the one obtained with Sr2+, however, the decrease of the holes mobility is reduced as compared to Sr2+ doping, which could be beneficial to the thermoelectric performances.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.up Other materials

Cross sections of operating Cu(In,Ga)Se2 thin-film solar cells under defined white light illumination analyzed by Kelvin probe force microscopy

Zhenhao Zhang, Michael Hetterich, Uli Lemmer, Michael Powalla, and Hendrik Hölscher

Appl. Phys. Lett. 102, 023903 (2013); http://dx.doi.org/10.1063/1.4775679 (5 pages)

Online Publication Date: 15 January 2013

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The contact potential of cross sections of operating Cu(In,Ga)Se2 thin-film solar cells is analyzed by Kelvin probe force microscopy under defined illumination intensities with white light. The potential drop through the solar cell heterojunction is found to decrease with increasing illumination intensity up to flat-band conditions and the decrease of the potential drop correlates with the increase of the photovoltage induced by the illumination. Interestingly, we observe that potential variations at Cu(In,Ga)Se2 grain boundaries decrease to less than 50 mV under illumination. With this finding, the often claimed beneficial effect of Cu(In,Ga)Se2 grain boundaries is critically discussed.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
88.40.jp Multijunction solar cells

Bistable springs for wideband microelectromechanical energy harvesters

Son D. Nguyen, Einar Halvorsen, and Igor Paprotny

Appl. Phys. Lett. 102, 023904 (2013); http://dx.doi.org/10.1063/1.4775687 (4 pages)

Online Publication Date: 15 January 2013

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This paper presents experimental results on a microelectromechanical energy harvester with curved springs that demonstrates an extremely wide bandwidth. The springs display an asymmetrical bistable behavior obtained purely through their geometrical design. The frequency down-sweep shows that the harvester 3-dB bandwidth is about 587 Hz at 0.208-g acceleration amplitude. For white noise excitation at 4×10−3 g2/Hz, we found that the bandwidth reaches 715 Hz, which is more than 250 times wider than in the linear-spring regime. By varying the bias voltage, an output power of 3.4 μW is obtained for frequency down-sweep at 1-g amplitude and 150-V bias.
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84.60.-h Direct energy conversion and storage
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Photothermally activated motion and ignition using aluminum nanoparticles

Jacques E. Abboud, Xinyuan Chong, Mingjun Zhang, Zhili Zhang, Naibo Jiang, Sukesh Roy, and James R. Gord

Appl. Phys. Lett. 102, 023905 (2013); http://dx.doi.org/10.1063/1.4776660 (5 pages)

Online Publication Date: 17 January 2013

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The aluminum nanoparticles (Al NPs) are demonstrated to serve as active photothermal media, to enhance and control local photothermal energy deposition via the photothermal effect activated by localized surface plasmon resonance (LSPR) and amplified by Al NPs oxidation. The activation source is a 2-AA-battery-powered xenon flash lamp. The extent of the photothermally activated movement of Al NPs can be ∼6 mm. Ignition delay can be ∼0.1 ms. Both scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements of motion-only and after-ignition products confirm significant Al oxidation occurs through sintering and bursting after the flash exposure. Simulations suggest local heat generation is enhanced by LSPR. The positive-feedback effects from the local heat generation amplified by Al oxidation produce a large increase in local temperature and pressure, which enhances movement and accelerates ignition.
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78.20.nb Photothermal effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.33.Vx Reactions in flames, combustion, and explosions
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Phase transitions and thermal expansion in pyroelectric energy conversion

Ian M. McKinley and Laurent Pilon

Appl. Phys. Lett. 102, 023906 (2013); http://dx.doi.org/10.1063/1.4776668 (5 pages)

Online Publication Date: 18 January 2013

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This paper elucidates dynamic effects of phase transitions and thermal expansion on pyroelectric energy conversion. The Olsen cycle was performed on [001]-oriented 0.72PbMg1/3Nb2/3O3−0.28PbTiO3 (PMN-28PT) single crystals at different frequencies with electric field cycled between 0.2 and 0.75 MV/m and temperature between 22 and 140 ∘C. The measured energy density more than doubled as frequency increased from 0.0173 to 0.0211 Hz. This was attributed to secondary pyroelectric effect caused by thermal expansion. At 0.0211 Hz, the samples transitioned from pseudocubic to highly polarized tetragonal phase during cooling. At lower frequency, it underwent additional phase transition from tetragonal to less polarized monoclinic phase.
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84.60.-h Direct energy conversion and storage
05.70.Fh Phase transitions: general studies
77.70.+a Pyroelectric and electrocaloric effects
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