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28 Dec 2009

Volume 95, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 95, 261901 (2009); http://dx.doi.org/10.1063/1.3268436 (3 pages)

Weiqiang Wang, Richard Clark, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta
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Optimization of back reflector for high efficiency hydrogenated nanocrystalline silicon solar cells

Guozhen Yue, Laura Sivec, Jessica M. Owens, Baojie Yan, Jeffrey Yang, and Subhendu Guha

Appl. Phys. Lett. 95, 263501 (2009); http://dx.doi.org/10.1063/1.3279143 (3 pages) | Cited 30 times

Online Publication Date: 28 December 2009

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We have studied the effect of texture in Ag/ZnO back reflectors (BRs) on the performance of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells. While a larger texture provides superior light trapping, it also deteriorates the nc-Si:H quality. We have used total and diffused reflection and atomic force microscopy to evaluate the BR texture. A BR with textured Ag and thin ZnO layers has been found to give the best cell performance. Using the optimized BR, we have achieved an initial active-area efficiency of 10.2% in a nc-Si:H single-junction cell and a stable total-area efficiency of 12.5% in a hydrogenated amorphous silicon/nc-Si:H/nc-Si:H triple-junction cell.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

An assessment of the mobility degradation induced by remote charge scattering

Z. Ji, J. F. Zhang, W. Zhang, G. Groeseneken, L. Pantisano, S. De Gendt, and M. M. Heyns

Appl. Phys. Lett. 95, 263502 (2009); http://dx.doi.org/10.1063/1.3279146 (3 pages)

Online Publication Date: 29 December 2009

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Carrier mobility reduces when the gate SiON becomes thinner than 2 nm or high-k layer is used. Agreement has not yet been reached on the level of reduction and on the underlying mechanism. Remote charge scattering has been proposed to be responsible for the mobility reduction and this work assesses its importance. By increasing charge density at 0.56–1 nm from the substrate interface to the order of 1020 cm−3, it is found that both electron and hole mobility changes little.
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72.80.Sk Insulators
72.20.Fr Low-field transport and mobility; piezoresistance
77.55.D- High-permittivity gate dielectric films

Role of photovoltaic effects on characterizing emission properties of InGaN/GaN light emitting diodes

Jae-Ho Song, Ho-Jong Kim, Byung-Jun Ahn, Yanqun Dong, Sayong Hong, Jung-Hoon Song, Youngboo Moon, Hwan-Kuk Yuh, Sung-Chul Choi, and Sangkee Shee

Appl. Phys. Lett. 95, 263503 (2009); http://dx.doi.org/10.1063/1.3272679 (3 pages) | Cited 4 times

Online Publication Date: 30 December 2009

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Strong photovoltaic effects on photoluminescence (PL) spectra in InGaN/GaN blue light emitting diodes were investigated. Due to severe carrier escape from quantum wells, significant photovoltaic effects occur in PL measurement in open-circuit condition, which strongly affect the PL peak position and intensity. We reveal that proper correlation between electroluminescence and PL peak positions cannot be obtained without proper consideration of the photovoltaic effects. By changing sample temperature and the PL excitation power, the generated photovoltage varies in the range of 2.0 to 2.6 V. We show that in the open-circuit condition, which is the usual case, the determination of radiative efficiency by measuring the PL intensity ratio of low-and high-temperature cannot be accurate, and the excitation intensity dependent PL cannot be solely intrinsic either. Both the absorption of incident laser and the carrier escape from the quantum well are bias-sensitive. By a simple and straightforward method, we determined that 51% of photogenerated carriers escaped in short-circuit condition.
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85.60.Jb Light-emitting devices

Magnetic phase coupled to an electric memory state in d0 oxide ZrO2 films

Y. Jo, I. R. Hwang, B. H. Park, K. J. Lee, S. I. Lee, and M. H. Jung

Appl. Phys. Lett. 95, 263504 (2009); http://dx.doi.org/10.1063/1.3271980 (3 pages)

Online Publication Date: 30 December 2009

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It is quite interesting to develop a multifunctional device using a single material with a simple structure. One of the possible candidates could be multiferroics, which are both ferroelectric and magnetic. By taking advantage of the strong spin-charge coupling, the electric field can control the magnetic polarization and the magnetic field can control the electric polarization. However, these multiferroics are not yet attractive for practical applications because none of the existing materials combine large and robust electric and magnetic polarizations at room temperature. Here, we report an unusual functional material showing a magnetic phase strongly coupled to an electric memory state at room temperature. An oxygen-vacant ZrO2 thin film generates bistable resistive switching between high-resistance (HR) and low-resistance (LR) states by applying external voltage, and it is ferromagnetic at the HR state but nonmagnetic at the LR state. This unique feature is applicable to unusual functional devices, such as electric-field-controlled magnetic data storage devices.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
77.80.Fm Switching phenomena
77.80.B- Phase transitions and Curie point

Blue-enhanced thin-film photodiode for dual-screen x-ray imaging

Y. Vygranenko, A. Sazonov, G. Heiler, T. Tredwell, M. Vieira, and A. Nathan

Appl. Phys. Lett. 95, 263505 (2009); http://dx.doi.org/10.1063/1.3276288 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2009

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This article reports on a-Si:H-based low-leakage blue-enhanced photodiodes for dual-screen x-ray imaging detectors. Doped nanocrystalline silicon was incorporated in both the n- and p-type regions to reduce absorption losses for light incoming from the top and bottom screens. The photodiode exhibits a dark current density of 900 pA/cm2 and an external quantum efficiency up to 90% at a reverse bias of 5 V. In the case of illumination through the tailored p-layer, the quantum efficiency of 60% at a 400 nm wavelength is almost double that for the conventional a-Si:H n-i-p photodiode.
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85.60.Dw Photodiodes; phototransistors; photoresistors
07.85.-m X- and γ-ray instruments

Enhanced lateral photovoltaic effect in an improved oxide-metal-semiconductor structure of TiO2/Ti/Si

Chong Qi Yu, Hui Wang, and Yu Xing Xia

Appl. Phys. Lett. 95, 263506 (2009); http://dx.doi.org/10.1063/1.3280382 (3 pages) | Cited 4 times

Online Publication Date: 31 December 2009

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A greatly enhanced lateral photovoltaic effect (LPE) is achieved in an improved metal-semiconductor (MS) structure of TiO2(1.2 nm)/Ti(6.2 nm)/Si. Compared with the LPE in traditional MS structures of Ti(6.2 nm)/Si and other reported MS structures, this oxide-metal-semiconductor structure presents a much larger sensitivity of lateral photovoltage of 97 mV/mm. We ascribe this to the enhancement of lateral gradient of the density of excess carriers in the structure caused by the increase of surface resistivity.
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72.40.+w Photoconduction and photovoltaic effects
73.40.Ns Metal-nonmetal contacts
73.25.+i Surface conductivity and carrier phenomena
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