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14 Jan 2013

Volume 102, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

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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Enhanced external quantum efficiency in rectangular single nanowire solar cells

Xiaofeng Li and Yaohui Zhan

Appl. Phys. Lett. 102, 021101 (2013); http://dx.doi.org/10.1063/1.4775578 (4 pages) | Cited 2 times

Online Publication Date: 14 January 2013

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Single-nanowire solar cells (SNSCs) in lying configuration can have external quantum efficiency (EQE) over 100% but always in narrowbands with EQE peaks slightly exceeding unit. We presented a rectangular gallium arsenide (GaAs) SNSC, which provides light absorption efficiency (Qabs) and EQE far beyond 100% for both transverse electric and magnetic illuminations, by optimally engineering the nanowires and introducing an advanced nanoshell design. Electromagnetic and carrier transport calculations show that Qabs and EQE peaks of the designed SNSCs can both be over 200% with averaged EQE ∼ 150% in most of the active spectral band of GaAs.
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88.40.jj Silicon solar cells
88.40.H- Solar cells (photovoltaics)

Surface-normal second harmonic emission from AlGaAs high-contrast gratings

T. Tran, V. Karagodsky, Y. Rao, W. Yang, R. Chen, C. Chase, L. C. Chuang, and C. J. Chang-Hasnain

Appl. Phys. Lett. 102, 021102 (2013); http://dx.doi.org/10.1063/1.4775664 (4 pages)

Online Publication Date: 14 January 2013

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Second harmonic (SH) generation from AlGaAs near-wavelength high-contrast gratings was studied in polarization-dependent reflection measurements. The grating design is critical in determining the strength and polarization of the second harmonic signal. The second harmonic response was enhanced by more than 3 orders of magnitude compared to flat AlGaAs surfaces without the gratings. These enhancements are due to the diffractive nature of the gratings, specifically their ability to change the direction of light waves.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Dj Gratings
78.66.Fd III-V semiconductors
FREE

Active terahertz quantum-cascade composite right/left-handed metamaterial

Amir A. Tavallaee, Philip W. C. Hon, Qi-Sheng Chen, Tatsuo Itoh, and Benjamin S. Williams

Appl. Phys. Lett. 102, 021103 (2013); http://dx.doi.org/10.1063/1.4775666 (4 pages) | Cited 1 time

Online Publication Date: 14 January 2013

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We report the demonstration of a composite right/left-handed (CRLH) metamaterial waveguide for terahertz quantum-cascade (QC) lasers. By incorporating gap capacitors ( ∼ 250 nm) in the top metallization of a metal-metal waveguide operating in a higher order lateral mode, we have realized a CRLH transmission line that supports traveling modes with negative effective phase indices (i.e., left-handed or backward-wave propagation). The CRLH metamaterial waveguide is employed as an active leaky-wave antenna for a terahertz QC-laser. Directional single-lobed beams launched in the backwards direction at angles of −4° and −63° were experimentally observed at excitation frequencies 2.59 and 2.48 THz, respectively.
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42.70.-a Optical materials
84.40.Az Waveguides, transmission lines, striplines
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Two-path solid-state interferometry using ultra-subwavelength two-dimensional plasmonic waves

Kitty Y. M. Yeung, Hosang Yoon, William Andress, Ken West, Loren Pfeiffer, and Donhee Ham

Appl. Phys. Lett. 102, 021104 (2013); http://dx.doi.org/10.1063/1.4775668 (4 pages) | Cited 1 time

Online Publication Date: 14 January 2013

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We report an on-chip solid-state Mach-Zehnder interferometer operating on two-dimensional (2D) plasmonic waves at microwave frequencies. Two plasmonic paths are defined with GaAs/AlGaAs 2D electron gas 80 nm below a metallic gate. The gated 2D plasmonic waves achieve a velocity of ∼c/300 (c: free-space light speed). Due to this ultra-subwavelength confinement, the resolution of the 2D plasmonic interferometer is two orders of magnitude higher than that of its electromagnetic counterpart at a given frequency. This gigahertz proof-of-concept at cryogenic temperatures can be scaled to the terahertz–infrared range for room temperature operation, while maintaining the benefits of ultra-subwavelength confinement.
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07.60.Ly Interferometers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Photoresponse mechanisms of ultraviolet photodetectors based on colloidal ZnO quantum dot-graphene nanocomposites

Dong Ick Son, Hee Yeon Yang, Tae Whan Kim, and Won Il Park

Appl. Phys. Lett. 102, 021105 (2013); http://dx.doi.org/10.1063/1.4776651 (3 pages)

Online Publication Date: 16 January 2013

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Ultraviolet (UV) photodetectors were fabricated using the wet spin-coating for ZnO quantum dots (QDs) and the transfer method for the graphene sheet. High-resolution transmission electron microscopy images showed that the ZnO QDs were uniformly distributed between the voids of the surface circumferences on the graphene layers. Current-voltage measurements on the UV photodetector at 300 K showed that the ratio of the photocurrent to the dark current was about 1.1 × 104. The rise and the decay times of the UV photodetector were approximately 2 and 1 s, respectively. The photoresponse mechanisms are described on the basis of the experimental results.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
79.60.-i Photoemission and photoelectron spectra

The silicon Schottky diode on flexible substrates by transfer method

Tae-Yeon Oh, Shin Woo Jeong, Seongpil Chang, Kookhyun Choi, Hyun Jun Ha, and Byeong Kwon Ju

Appl. Phys. Lett. 102, 021106 (2013); http://dx.doi.org/10.1063/1.4776685 (3 pages)

Online Publication Date: 16 January 2013

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A flexible silicon barrier diode was fabricated by the transfer printing method. Micro-line patterned p-type single crystalline silicon membranes were created from a silicon on insulator wafer. The dark current of our device was very low, about 1 pA for reverse bias voltages up to 5 V, and showed rectifying behavior with an ideality factor of 1.05. The photo-response and the responsivity was 32 and 0.3 A/W, respectively, for light intensity of 1.2 mW/cm2. Also, the current of the photodetector changed under compressive stress or tensile stress. Our device is functional as the piezotronic sensor as well as the photodetector.
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85.30.Kk Junction diodes
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Heterojunction photodiode fabricated from multiwalled carbon nanotube/ZnO nanowire/p-silicon composite structure

Dali Shao, Mingpeng Yu, Jie Lian, and Shayla Sawyer

Appl. Phys. Lett. 102, 021107 (2013); http://dx.doi.org/10.1063/1.4776691 (3 pages) | Cited 1 time

Online Publication Date: 16 January 2013

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A heterojunction photodiode was fabricated from multiwalled carbon nanotubes (MWCNTs)/ZnO nanowires/p-Si (100) substrate composite structure. The heterojunction photodiode demonstrated a faster transient response and higher responsivity than the reference sample without deposition of MWCNTs, which is attributed to improved carrier collection and transport efficiency through the MWCNTs network. The high photoresponsivities of the devices are explained in terms of operation as a hybrid of photodiode and photoconductor modes. The spectral response of the devices showed dependence on voltage polarity and is attributed to the high valance band offset in the interfacial region of ZnO and p-Si substrate.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.35.Kt Nanotube devices

Light-emitting devices based on erbium-doped TiO2/p+-Si heterostructures: Engineering of electroluminescence via aluminum co-doping

Yang Yang, Yunpeng Li, Lu Jin, Xiangyang Ma, and Deren Yang

Appl. Phys. Lett. 102, 021108 (2013); http://dx.doi.org/10.1063/1.4788679 (5 pages) | Cited 1 time

Online Publication Date: 18 January 2013

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We have recently reported erbium (Er)-related visible and infrared (∼1540 nm) electroluminescence (EL) from the light-emitting device (LED) based on Er-doped TiO2 (TiO2:Er)/p+-Si heterostructure, triggered by the energy transferred from oxygen-vacancy-related self-trapped excitons (STEs) to Er3+ ions in anatase TiO2. Herein, we further co-dope aluminum (Al) into the TiO2:Er film, which is also used to form heterostructure with p+-Si. The LED based on such heterostructure features the Er-related EL with the substantially suppressed visible emissions and the remarkably enhanced ∼1540 nm emission. The Al co-doping is proved not to substantially affect the amounts of oxygen-vacancy-related STEs and Er3+ ions in anatase TiO2. In this context, the above-mentioned engineering of Er-related EL is tentatively ascribed to the modification of crystal field around the Er3+ ions in anatase TiO2 by the Al co-doping.
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85.60.Jb Light-emitting devices

Random lasing and weak localization of light in transparent Nd+3 doped phosphate glass

Jingwen Zhang, Long Xu, Hao Wang, Feng Huang, Xiudong Sun, Hua Zhao, and Xuesheng Chen

Appl. Phys. Lett. 102, 021109 (2013); http://dx.doi.org/10.1063/1.4788682 (4 pages)

Online Publication Date: 18 January 2013

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Random lasing action and weak localization of light were observed in multiple visible wavelengths with highly transparent, Nd+3 doped phosphate glass gain media, with strong energy redistribution between different frequencies under different pumping powers. A tentative model based on photoinduced scattering was proposed and verified with a He-Ne laser beam in probing the lasing zone. The remarkable coherency and intensity changes of the probing laser beam confirmed the local, random scattering behind the photoinduced random lasing and the localization of light.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Ce Glasses, quartz
42.70.Hj Laser materials
78.45.+h Stimulated emission

Cavity piezooptomechanics: Piezoelectrically excited, optically transduced optomechanical resonators

Chi Xiong, Linran Fan, Xiankai Sun, and Hong X. Tang

Appl. Phys. Lett. 102, 021110 (2013); http://dx.doi.org/10.1063/1.4788724 (4 pages) | Cited 1 time

Online Publication Date: 18 January 2013

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We present a monolithic integrated aluminum nitride (AlN) optomechanical resonator in which the mechanical motion is actuated by piezoelectric force and the displacement is transduced by a high-Q optical cavity. The AlN optomechanical resonator is excited from a radio-frequency electrode via a small air gap to eliminate resonator-to-electrode loss. We observe the electrically excited mechanical motion at 47.3 MHz, 1.04 GHz, and 3.12 GHz, corresponding to the 1st, 2nd, and 4th radial-contour mode of the wheel resonator, respectively. An equivalent circuit model is developed to describe the observed Fano-like resonance spectrum.
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42.79.-e Optical elements, devices, and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Improving imaging resolution of shaking targets by Fourier-transform ghost diffraction

Cong Zhang, Wenlin Gong, and Shensheng Han

Appl. Phys. Lett. 102, 021111 (2013); http://dx.doi.org/10.1063/1.4788727 (5 pages) | Cited 1 time

Online Publication Date: 18 January 2013

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For conventional imaging, shaking of the imaging system or the target leads to the degradation of imaging resolution. The influence of the target's shaking to Fourier-transform ghost diffraction (FGD) is investigated and phase-retrieval method is used to recover the target's imaging. The analytical results, which are backed up by numerical simulation and experiments, demonstrate that the quiver of target has no effect on the resolution of FGD and high-resolution imaging can be always achieved by phase-retrieval method from FGD patterns. This approach can be applied in high-precision imaging systems, to overcome the influence of the system's shaking to imaging resolution.
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42.30.Va Image forming and processing
42.30.Kq Fourier optics
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