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21 Jan 2013

Volume 102, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 033901 (2013); http://dx.doi.org/10.1063/1.4758300 (5 pages)

Marina S. Leite, Robyn L. Woo, Jeremy N. Munday, William D. Hong, Shoghig Mesropian, Daniel C. Law, and Harry A. Atwater
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Editorial

Nghi Q. Lam, Editor

Appl. Phys. Lett. 102, 030401 (2013); http://dx.doi.org/10.1063/1.4789587 (1 page)

Online Publication Date: 24 January 2013

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Abstract Unavailable
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99.10.Np Editorial note
01.10.-m Announcements, news, and organizational activities
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Quantifying the intrinsic amount of fabrication disorder in photonic-crystal waveguides from optical far-field intensity measurements

P. D. García, A. Javadi, H. Thyrrestrup, and P. Lodahl

Appl. Phys. Lett. 102, 031101 (2013); http://dx.doi.org/10.1063/1.4788709 (4 pages)

Online Publication Date: 22 January 2013

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Residual disorder due to fabrication imperfections has important impact in nanophotonics where it may degrade device performance by increasing radiation loss or spontaneously trap light by Anderson localization. We propose and demonstrate experimentally a method of quantifying the intrinsic amount of disorder in state-of-the-art photonic-crystal waveguides from far-field measurements of the Anderson-localized modes. This is achieved by comparing the spectral range where Anderson localization is observed to numerical simulations, and the method offers sensitivity down to ≃ 1 nm.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials

Gate controlled coupling of intersubband plasmons

A. Delteil, A. Vasanelli, Y. Todorov, B. Paulillo, G. Biasiol, L. Sorba, and C. Sirtori

Appl. Phys. Lett. 102, 031102 (2013); http://dx.doi.org/10.1063/1.4788753 (4 pages)

Online Publication Date: 22 January 2013

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The optical response of a heavily doped quantum well, with two occupied subbands, has been investigated as a function of the electronic density. It is shown that the two optically active transitions are mutually coupled by dipole-dipole Coulomb interaction, which strongly renormalizes their absorption amplitude. In order to demonstrate this effect, we have measured a set of optical spectra on a device in which the electronic density can be tuned by the application of a gate voltage. Our results show that the absorption spectra can be correctly described only by taking into account the Coulomb coupling between the two transitions. As a consequence, the optical dipoles originating from intersubband transitions are not independent, but rather coupled oscillators with an adjustable strength.
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78.67.De Quantum wells
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.21.Fg Quantum wells
78.30.Fs III-V and II-VI semiconductors

Large area sub-wavelength azo-polymer gratings by waveguide modes interference lithography

Xiangxian Wang, Douguo Zhang, Yikai Chen, Liangfu Zhu, Wenhai Yu, Pei Wang, Peijun Yao, Hai Ming, Wenxuan Wu, and Qijin Zhang

Appl. Phys. Lett. 102, 031103 (2013); http://dx.doi.org/10.1063/1.4788754 (4 pages)

Online Publication Date: 22 January 2013

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Except for the commonly used surface plasmon polaritons (SPPs), in this letter we demonstrate that waveguide modes (WMs) can realize the large area sub-wavelength gratings. Both transverse-magnetic (TM) and transverse-electric polarized beams can be used in this method, while for the lithography based on SPPs only TM polarized beam is applicable. The WMs interference lithography has the advantages of low heat loss and much suitable for thick photo-resist films. Large area gratings were inscribed on the azo polymer film at period of 187 nm and 189 nm, which are smaller than the half wavelength of the incident beam.
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42.79.Dj Gratings
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)
81.16.Nd Micro- and nanolithography

Non-rare earth white emission phosphor: Ti-doped MgAl2O4

J. H. Lim, B. N. Kim, Y. Kim, S. Kang, R. J. Xie, I. S. Chong, K. Morita, H. Yoshida, and K. Hiraga

Appl. Phys. Lett. 102, 031104 (2013); http://dx.doi.org/10.1063/1.4788929 (4 pages)

Online Publication Date: 22 January 2013

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White emission produced by Ti-doped MgAl2O4 phosphor powder is reported, which is in contrast to blue emission from most Ti-doped single crystals of MgAl2O4. The white emission peak consists of four deconvoluted peaks: 440, 490, 550, and 620 nm, when was excited by 260 nm wavelength. Ti4+ in octahedral sites was found to contribute mostly to greenish blue emissions at 490 and 550 nm. The red emission at 620 nm was produced by abundant Mg2+ and O2− vacancies in the spinel powder.
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78.55.Hx Other solid inorganic materials
61.72.jd Vacancies

Silicon sub-bandgap photon linear detection in two-photon experiments: A photo-assisted Shockley-Read-Hall mechanism

B. Vest, E. Lucas, J. Jaeck, R. Haïdar, and E. Rosencher

Appl. Phys. Lett. 102, 031105 (2013); http://dx.doi.org/10.1063/1.4788705 (5 pages) | Cited 1 time

Online Publication Date: 23 January 2013

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We investigate the linear response of silicon p-i-n diodes to sub-bandgap photons (1.4 μm-1.6 μm) that has been reported by many authors and left unexplored till then. The quantum efficiency of this mechanism is extremely low (typically 10−9) but has a drastic influence on silicon devices harnessing two-photon absorption. We show that this linear photonic current decreases with temperature, displaying an activation energy similar to the dark current one. We show that this behaviour is consistent with a photo-assisted Shockley-Read mechanism in which the occupancy factor of a defect state in the Si band gap is influenced by the sub-band gap photon flux.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Optical and electrical simulations of two-junction III-V nanowires on Si solar cell

Shaojiang Bu, Xinhua Li, Long Wen, Xuesong Zeng, Yufeng Zhao, Wenbo Wang, and Yuqi Wang

Appl. Phys. Lett. 102, 031106 (2013); http://dx.doi.org/10.1063/1.4788750 (5 pages) | Cited 1 time

Online Publication Date: 23 January 2013

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A coupled optoelectronic simulation was used to theoretically assess the performance of core-shell GaInP nanowires array (NWA)/Si thin-film two-junction solar cell. Outstanding light harvesting rooted from the strong light trapping and the formation of Fabry-Pérot optical cavity in the NWA enables the cell to produce high photocurrent. From the detailed balance calculation, above 32% of efficiency could be obtained at the current matching geometries. Coupled optoelectronic simulation shows that current matching can be easily achieved even under relatively high recombination rate. A promising efficiency of 27.1% is obtained for the proposed cell with appropriate nanowires surface passivation.
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88.40.jj Silicon solar cells
88.40.jm Thin film III-V and II-VI based solar cells
88.40.jp Multijunction solar cells
81.65.Rv Passivation
88.40.hj Efficiency and performance of solar cells

Application of self-assembled hemispherical microlasers as gas sensors

V. D. Ta, R. Chen, D. M. Nguyen, and H. D. Sun

Appl. Phys. Lett. 102, 031107 (2013); http://dx.doi.org/10.1063/1.4788751 (4 pages)

Online Publication Date: 23 January 2013

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Dye-doped hemispherical resonators are self-assembled on a distributed Bragg reflector based on hydrophobic effect. The size of hemispheres can be well-controlled with diameters ranging from 5 to 150 μm. Upon optical pumping, whispering gallery mode laser emission with transverse magnetic polarization is observed from the hemispheres. Application of the microlasers as refractive index gas sensors has been demonstrated by detecting the spectrum shift of the lasing mode, and the sensitivity higher than 130 nm/RIU is achieved. Our approach provides an effective technique to obtain high quality microlasers and opens an opportunity to employ the cost effective microlasers as high sensitive sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Hv Refractometers and reflectometers
42.55.Mv Dye lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Super-oscillatory optical needle

Edward T. F. Rogers, Salvatore Savo, Jari Lindberg, Tapashree Roy, Mark R. Dennis, and Nikolay I. Zheludev

Appl. Phys. Lett. 102, 031108 (2013); http://dx.doi.org/10.1063/1.4774385 (4 pages)

Online Publication Date: 23 January 2013

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Super-oscillatory optical lenses have recently been shown to achieve subwavelength focusing and have been used for super-resolution imaging. However, the subwavelength hotspots created by these lenses are always accompanied by sidebands containing a significant fraction of the optical energy and are highly localised in the axial direction. Here, we report a class of super-oscillatory lenses that form extended subwavelength optical needles on a 15λ field of view.
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42.79.Bh Lenses, prisms and mirrors

Experimental determination of electron-hole pair creation energy in 4H-SiC epitaxial layer: An absolute calibration approach

Sandeep K. Chaudhuri, Kelvin J. Zavalla, and Krishna C. Mandal

Appl. Phys. Lett. 102, 031109 (2013); http://dx.doi.org/10.1063/1.4776703 (4 pages)

Online Publication Date: 23 January 2013

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Electron-hole pair creation energy (ε) has been determined from alpha spectroscopy using 4H-SiC epitaxial layer Schottky detectors and a pulser calibration technique. We report an experimentally obtained ε value of 7.28 eV in 4H-SiC. The obtained ε value and theoretical models were used to calculate a Fano factor of 0.128 for 5.48 MeV alpha particles. The contributions of different factors to the ultimate alpha peak broadening in pulse-height spectra were determined using the calculated ε value and Monte-Carlo simulations. The determined ε value was verified using a drift-diffusion model of variation of charge collection efficiency with applied bias.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
29.40.Wk Solid-state detectors
68.55.ag Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.25.Dc Spin polarized transport in semiconductors
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Purple photochromism in Sr2SnO4:Eu3+ with layered perovskite-related structure

Sunao Kamimura, Hiroshi Yamada, and Chao-Nan Xu

Appl. Phys. Lett. 102, 031110 (2013); http://dx.doi.org/10.1063/1.4788752 (4 pages)

Online Publication Date: 24 January 2013

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We report photochromism (PC) in Sr2SnO4:Eu3+ with layered perovskite-related structure. The Sr2SnO4:Eu3+ turned purple upon irradiation with UV light (λ < 350 nm), and the colored Sr2SnO4:Eu3+ returned to its initial colorless state when visible light (λ = 400–700 nm) was irradiated. Furthermore, the PC was strongly dependent on the firing temperature; purple color upon UV irradiation can be enhanced by increasing the firing temperature, which was attributed to an increase of the Sr vacancies in the host lattice from the results of crystal structure analysis. This suggests that controlling the lattice defect plays an important role for enhancing the PC performance.
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78.20.-e Optical properties of bulk materials and thin films
78.40.Ha Other nonmetallic inorganics
61.72.jd Vacancies
61.72.-y Defects and impurities in crystals; microstructure

Millimeter scale electrostatic mirror with sub-wavelength holes for terahertz wave scanning

Hyeon-Cheol Park, Jung-Hwan Lee, Sang-Gil Park, Dae-Su Yee, and Ki-Hun Jeong

Appl. Phys. Lett. 102, 031111 (2013); http://dx.doi.org/10.1063/1.4788915 (4 pages)

Online Publication Date: 24 January 2013

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This work reports the design, microfabrication, and characterization of highly reflective electrostatic mirrors with sub-wavelength holes for scanning terahertz (THz) waves. The mirror consists of an aluminum coated silicon mirror plate precisely assembled on the top of two axis torsional microactuators. The mirror plate with sub-wavelength microholes not only provides high reflectivity over 98% at THz waves by decoupling the surface plasmon resonance but also reduces air damping by allowing air to flow through the mirror plate during the mirror scanning. The device can provide many opportunities for miniaturized THz time domain spectroscopic imaging systems.
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07.10.Cm Micromechanical devices and systems
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Generation of flat-spectrum wideband chaos by fiber ring resonator

Anbang Wang (王安帮), Yuncai Wang (王云才), Yibiao Yang (杨毅彪), Mingjiang Zhang (张明江), Hang Xu (徐航), and Bingjie Wang (王冰洁)

Appl. Phys. Lett. 102, 031112 (2013); http://dx.doi.org/10.1063/1.4789366 (5 pages)

Online Publication Date: 24 January 2013

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We present a simple method to generate spectrally uniform wideband chaos by injecting chaotic laser into a fiber ring resonator. The resonator is a single-coupler ring equipped with an optical filter and amplifier, which adjust the optical field circulating in the ring. The incoherent interference of the circulating fields produces wideband chaos with uniform power spectrum density distribution. We experimentally achieved a chaotic spectrum that extends over 26.5 GHz (limited by measurement bandwidth) and fluctuates within ±1.5 dB. In addition, tuning the filter frequency can control the spectral profile so as to meet different application needs.
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42.55.Wd Fiber lasers
42.81.Wg Other fiber-optical devices
42.79.Ci Filters, zone plates, and polarizers
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics

Thermal stress in silica-on-silicon disk resonators

Tong Chen, Hansuek Lee, and Kerry J. Vahala

Appl. Phys. Lett. 102, 031113 (2013); http://dx.doi.org/10.1063/1.4789370 (4 pages)

Online Publication Date: 24 January 2013

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The thermal expansion mismatch of thermal grown silica on a silicon wafer is well known to induce compressive stress upon cooling from the growth temperature to room temperature. In this Letter, we investigate how this stress impacts silica disk structures by comparison of measurements with both a finite element and an analytical model. The disk structures studied are also whispering gallery optical resonators, and proper control of stress is critical to obtain high-Q resonances. Based on our analysis, thicker oxide layers and proper control of undercut enable ultra-high-Q optical performance and mechanical stability.
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84.40.Az Waveguides, transmission lines, striplines
02.70.Dh Finite-element and Galerkin methods

Two-photon-absorption photodiodes in Si photonic-crystal slow-light waveguides

Ryo Hayakawa, Norihiro Ishikura, Hong C. Nguyen, and Toshihiko Baba

Appl. Phys. Lett. 102, 031114 (2013); http://dx.doi.org/10.1063/1.4789393 (3 pages) | Cited 3 times

Online Publication Date: 24 January 2013

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We demonstrate two-photon-absorption photodiodes in Si photonic-crystal waveguides, which shows wideband low-dispersion slow light. The device was fabricated on SOI substrate by CMOS-compatible process. The responsivity was improved by higher group indexes of slow light up to 0.052 A/W for pulses at wavelengths around 1550 nm with a 2.7 ps width and sub-watt peak powers. We applied this device to an optical correlator and dispersion detector. In the former, the correlation waveforms of 0.7−10 ps pulses were observed with small errors. In the latter, photocurrents inversely proportional to the pulse width were detected.
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85.60.Dw Photodiodes; phototransistors; photoresistors
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Impact of intermediate localized states on nonlinear optical absorption of Ga-Ge-Se nanocolloidal solutions

Indu Sebastian, S. Divya, V. P. N. Nampoori, P. Radhakrishnan, and Sheenu Thomas

Appl. Phys. Lett. 102, 031115 (2013); http://dx.doi.org/10.1063/1.4789436 (5 pages)

Online Publication Date: 25 January 2013

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We present the linear and nonlinear optical studies on nanocolloidal solutions of Ga9Ge27Se64 glass with varying concentrations. Optical bandgap of the material is found to vary with respect to the concentration of the solute in the solution. An intermediate peak in the band tail of the absorption spectra is observed due to the presence of energy band in the forbidden gap. The existence of fluorescence emission confirms the above argument. Nonlinear absorption is studied using open aperture Z-scan technique. The mechanism behind nonlinear absorption is predicted as two photon as well as two step photon absorption. Nonlinearity increases with decrease in optical bandgap which in turn depends on the concentration of the nanocolloidal solutions.
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42.65.-k Nonlinear optics
78.55.Qr Amorphous materials; glasses and other disordered solids
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.40.Fy Semiconductors
78.40.Pg Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Improved photovoltaic effects in InGaN-based multiple quantum well solar cell with graphene on indium tin oxide nanodot nodes for transparent and current spreading electrode

Tae Hoon Seo, Jae-Phil Shim, Seung Jin Chae, GangU Shin, Bo Kyoung Kim, Dong-Seon Lee, Young Hee Lee, and Eun-Kyung Suh

Appl. Phys. Lett. 102, 031116 (2013); http://dx.doi.org/10.1063/1.4789502 (4 pages)

Online Publication Date: 25 January 2013

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We implemented graphene network on indium tin oxide (ITO) nanodots to a transparent and current-spreading electrode in InGaN-based solar cell to improve power conversion efficiency. The external quantum efficiency and short circuit current density (Jsc) of solar cells with graphene network on ITO nanodots were enhanced compared to those of solar cells with ITO and bare graphene film. The increase of the power conversion efficiency is attributed to the high transmittance, internal light-scattering effect, and effective carrier absorption of ITO nanodots.
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88.40.jm Thin film III-V and II-VI based solar cells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
88.40.hj Efficiency and performance of solar cells
FREE

A light emitting device made from thin zirconium-doped hafnium oxide high-k dielectric film with or without an embedded nanocrystal layer

Yue Kuo and Chi-Chou Lin

Appl. Phys. Lett. 102, 031117 (2013); http://dx.doi.org/10.1063/1.4789531 (4 pages)

Online Publication Date: 25 January 2013

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A solid state light emitting device composed of the 10 nm thickness zirconium-doped hafnium oxide high-k gate dielectric with or without an embedded nanocrystalline ZnO layer has been fabricated and studied. The emission spectrum, which extended from visible light to IR, was broadened and the intensity was increased with the embedding of a nanocrystalline ZnO layer. The mechanisms of light emission and enhancement were investigated and explained with defect generation process in the film. This kind of device is easily prepared by the IC compatible process. There are many potential applications of this kind of device.
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85.60.Jb Light-emitting devices

Low-voltage electro-absorption optical modulator based on slow-light Bragg reflector waveguide

Xiaodong Gu, Shoki Shimizu, Toshikazu Shimada, Akihiro Matsutani, and Fumio Koyama

Appl. Phys. Lett. 102, 031118 (2013); http://dx.doi.org/10.1063/1.4789533 (4 pages)

Online Publication Date: 25 January 2013

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We report on slow-light GaInAs/GaAs electro-absorption modulators with a Bragg reflector waveguide. We fabricated 20∼100 μm long compact modulators composed of triple GaInAs/GaAs quantum wells sandwiched by highly reflective Bragg reflectors. A large group index of 20 enables us to reduce the size of the modulators. We demonstrated 6 dB intensity modulation with a voltage swing Vpp below 0.5 V for 50 μm long devices. Shorter devices, for example with a length of only 20 μm, also showed an extinction ratio over 4 dB for sub-volt driving. Characterizations on wavelength dependence were also carried out experimentally.
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42.79.Hp Optical processors, correlators, and modulators
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.65.Wi Nonlinear waveguides
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Single-mode surface-emitting concentric-circular-grating terahertz quantum cascade lasers

Guozhen Liang, Houkun Liang, Ying Zhang, Suraj P. Khanna, Lianhe Li, A. Giles Davies, Edmund Linfield, Dau Fatt Lim, Chuan Seng Tan, Siu Fung Yu, Hui Chun Liu, and Qi Jie Wang

Appl. Phys. Lett. 102, 031119 (2013); http://dx.doi.org/10.1063/1.4789535 (4 pages) | Cited 1 time

Online Publication Date: 25 January 2013

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We demonstrate single-mode surface-emitting terahertz frequency quantum cascade lasers utilising non-uniform second-order distributed feedback concentric-circular-gratings. The grating is designed for single-mode operation and surface emission for efficient and directional optical power out-coupling. The devices exhibit single-mode operation over the entire dynamic range with a side-mode-suppression-ratio of around 30 dB at 78 K, and a six-fold rotationally symmetric far-field pattern. In addition, the devices show a peak output power approximately three times higher than in ridge-waveguide lasers of similar size, whilst maintaining similar threshold current densities for the 3.8 THz emission and without remarkably sacrificing the maximum temperature operation performance. Owing to the high symmetry of the structure and the broad area light emission from surface, the devices are potentially very suitable for use as single-mode, high power emitters for integration into two-dimensional laser arrays.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Suppression of Auger-stimulated efficiency droop in nitride-based light emitting diodes

R. Vaxenburg, E. Lifshitz, and Al. L. Efros

Appl. Phys. Lett. 102, 031120 (2013); http://dx.doi.org/10.1063/1.4789364 (5 pages)

Online Publication Date: 25 January 2013

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We calculate the rate of nonradiative Auger recombination in InGaN/GaN quantum wells with rectangular and smooth confining potentials. The calculations show that the rate of Auger recombination in rectangular quantum wells is sufficiently high to explain the efficiency droop in nitride-based light emitting diodes (LEDs). This rate, however, can be reduced by softening of the confining potential and a three-fold suppression is demonstrated in the studied quantum wells. The suppression of the Auger recombination rate improves LED radiative efficiency and reduces the droop effect, as we show using the standard recombination (ABC) model.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Leaky-surface-wave generated acoustic beam displacement upon reflection in lithium tantalate crystals

R. Rimeika, J. Belovickis, and D. Čiplys

Appl. Phys. Lett. 102, 031601 (2013); http://dx.doi.org/10.1063/1.4788686 (4 pages)

Online Publication Date: 22 January 2013

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The non-specular reflection of a leaky surface acoustic wave radiated beam from the surface of piezoelectric lithium tantalate crystal has been investigated using an acoustoelectric and acousto-optic technique. The Schoch-type beam displacement upon reflection strongly depends on whether the surface is free or metalized. This effect is attributed to the excitation (on the reflecting surface) of the leaky surface wave, the acoustoelectric attenuation of which strongly depends on the surface conductivity.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.25.+i Surface conductivity and carrier phenomena

Adhesion of a fluorinated poly(amic acid) with stainless steel surfaces

Youngsuk Jung, Sunjin Song, Sangmo Kim, Yooseong Yang, Jungha Chae, Tai-Gyoo Park, and Myung Dong Cho

Appl. Phys. Lett. 102, 031602 (2013); http://dx.doi.org/10.1063/1.4776663 (4 pages)

Online Publication Date: 22 January 2013

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The authors elucidate an origin and probable mechanism of adhesion strength change at an interface of fluorinated poly(amic acid) and stainless steel. Fluorination provides favorable delamination with release strength weaker than 0.08 N/mm from a metal surface, once the amount of residual solvent becomes less than 35 wt. %. However, the release strength critically depends on film drying temperature. Characterization on stainless steel surfaces and thermodynamic analyses on wet films reveal a drying temperature of 80 °C fosters interaction between the metal oxides at stainless steel surface and the free electron donating groups in poly(amic acid).
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81.90.+c Other topics in materials science (restricted to new topics in section 81)
65.40.gp Surface energy
68.55.am Polymers and organics
68.35.Md Surface thermodynamics, surface energies

Electrical and chemical characteristics of probe-induced two-dimensional SiOx protrusion layers

Jin-Han Lin, Hsien-Che Chiu, Yu-Rong Lin, Teng-Kai Wen, Ranjit A. Patil, Rupesh S. Devan, Chia-Hao Chen, Hung-Wei Shiu, Yung Liou, and Yuan-Ron Ma

Appl. Phys. Lett. 102, 031603 (2013); http://dx.doi.org/10.1063/1.4776696 (5 pages)

Online Publication Date: 23 January 2013

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Three two-dimensional SiOx (x ≡ O/Si content ratio and x > 2) protrusion layers of ∼0.5, ∼4, and ∼6 nm high were induced on a native SiO2 layer by atomic force microscopy (AFM) probes. X-ray photoemission spectroscopy (XPS) was used to reveal the elemental quantity of the photoelectrons, Si 2p core-levels, and Si oxidation states in the three SiOx protrusion layers and native SiO2 layer. Pt-coated conductive AFM probes were also exploited to acquire the rectifying current-voltage (IV) characteristics of the three SiOx protrusion layers and the native SiO2 layer, indicating all the three SiOx protrusion layers to be good Schottky diodes.
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73.40.Ei Rectification
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Ps Atomic force microscopy (AFM)

Charge transfer in Sr Zintl template on Si(001)

Miri Choi, Agham B. Posadas, Hosung Seo, Richard C. Hatch, and Alexander A. Demkov

Appl. Phys. Lett. 102, 031604 (2013); http://dx.doi.org/10.1063/1.4788916 (4 pages)

Online Publication Date: 24 January 2013

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The formation of the half monolayer (ML) Sr Zintl template layer on Si(001) is investigated in a combined experimental and theoretical work consisting of in situ reflection high energy electron diffraction, in situ x-ray photoelectron spectroscopy (XPS), and density functional theory. Starting with clean 2 × 1 reconstructed Si(001), we demonstrate that Sr deposition leads to a charge transfer from the metal to the Si substrate resulting in the disappearance of the asymmetry of Si dimers—an essential structural change that enables direct perovskite epitaxy on Si, and likely, other semiconductors. XPS reveals an unexpected shift to higher binding energy of the Si 2p core-level components, including the bulk. This unusual behavior is attributed to final state effects using first principles calculations. As measured by ultraviolet photoelectron spectroscopy, the deposition of 0.5 ML of Sr lowers the work function of the system by 1.35 eV, and is in good agreement with our theoretical calculations.
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71.70.-d Level splitting and interactions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.at Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
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