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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

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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From circular to triangular alumina nanopore arrays via simple replication

Guiduk Yu and Kyusoon Shin

Appl. Phys. Lett. 102, 021601 (2013); http://dx.doi.org/10.1063/1.4775667 (4 pages)

Online Publication Date: 14 January 2013

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We found inverse-hexagonal packing pattern from self-assembled anodic aluminum oxide and exploited the pattern to obtain triangular pore array. By replicating the curved interface between aluminum and porous alumina, we fabricated a pattern with the opposite packing structure as well as the inversed pattern curvature. Anodization from the replicated structure formed triangular pores in inverse-hexagonal packing, whereas that from the original pattern produces circular pores in hexagonal packing. Our finding highlights the importance of the curvature as well as packing structure of pre-patterns in pore formation and achievement in the control via a simple replication process.
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81.16.Rf Micro- and nanoscale pattern formation
61.43.Gt Powders, porous materials
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
81.16.Dn Self-assembly

Controlling interfacial states in amorphous/crystalline LaAlO3/SrTiO3 heterostructures by electric fields

D. V. Christensen, F. Trier, Y. Z. Chen, A. Smith, J. Nygård, and N. Pryds

Appl. Phys. Lett. 102, 021602 (2013); http://dx.doi.org/10.1063/1.4775669 (4 pages) | Cited 1 time

Online Publication Date: 14 January 2013

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The tunable metal-insulator transition in crystalline LaAlO3/SrTiO3 heterostructures constitutes a central element in the range of remarkable interface properties that has made this oxide system subject to extensive research. Recently, metallic interfaces have also been realized when depositing amorphous LaAlO3 films on SrTiO3. Here, we present a non-volatile and reversible tuning of the interface conductivity by more than 3 orders of magnitude at room temperature by applying an electric field to such amorphous/crystalline heterostructures with amorphous LaAlO3 film thicknesses of ∼2 nm. We show that the tunability is strongly temperature dependent, and demonstrate a simple protocol for enhancing the tunability.
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73.61.Ng Insulators
68.35.Ct Interface structure and roughness
71.30.+h Metal-insulator transitions and other electronic transitions

Formation and development of dislocation in graphene

Gun-Do Lee, Euijoon Yoon, Nong-Moon Hwang, Cai-Zhuang Wang, and Kai-Ming Ho

Appl. Phys. Lett. 102, 021603 (2013); http://dx.doi.org/10.1063/1.4775671 (4 pages)

Online Publication Date: 16 January 2013

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The formation and development processes of dislocation in graphene are investigated by performing tight-binding molecular dynamics (TBMD) simulation and ab initio total energy calculation. It is found that the coalescence of pentagon-heptagon (5-7) pairs with vacancy defects induces the formation of dislocation due to the separation of two 5-7 pairs. In TBMD simulations, adatoms are ejected and evaporated from graphene surface so that the dislocation is developed. It is observed that diffusing carbon atoms nearby dangling bonds help non-hexagonal rings change into stable hexagonal rings. These results might give some ideas for the control of structural properties by inducing defect structures.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.jd Vacancies
71.55.Ht Other nonmetals
66.30.Lw Diffusion of other defects

Silicon surface texturing with a combination of potassium hydroxide and tetra-methyl ammonium hydroxide etching

Sindhuja Sridharan, Navakanta Bhat, and K. N. Bhat

Appl. Phys. Lett. 102, 021604 (2013); http://dx.doi.org/10.1063/1.4776733 (4 pages)

Online Publication Date: 16 January 2013

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A two step silicon surface texturing, consisting of potassium hydroxide (KOH) etching followed by tetra-methyl ammonium hydroxide etching is presented. This combined texturing results in 13.8% reflectivity at 600 nm compared to 16.1% reflectivity for KOH etching due to the modification of microstructure of etched pyramids. This combined etching also results in significantly lower flat-band voltage (VFB) (−0.19 V compared to −1.3 V) and interface trap density (Dit) (2.13 × 1012 cm−2 eV−1 compared to 3.2 × 1012 cm−2 eV−1).
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68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces
81.65.Cf Surface cleaning, etching, patterning

Molecular organization in organic semiconductor thin films observed in real time

D. A. Evans, O. R. Roberts, A. R. Vearey-Roberts, G. T. Williams, A. C. Brieva, and D. P. Langstaff

Appl. Phys. Lett. 102, 021605 (2013); http://dx.doi.org/10.1063/1.4775762 (5 pages)

Online Publication Date: 17 January 2013

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Post-deposition molecular rearrangement in thin organic films is revealed by in situ real-time photoelectron spectroscopy during organic molecular beam deposition. Agreement between real time spectroscopy and Monte Carlo modeling confirms the role of nearest-neighbor molecular attraction in driving a time-dependent morphology for oriented films of tin phthalocyanine (SnPc) on a range of substrates. The time-dependent molecular self-organization occurs over timescales comparable to the growth rates and is therefore an important factor in the degradation of thin films of organic semiconductors typically considered for the fabrication of multilayer semiconductor devices.
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68.55.ag Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

An in situ x-ray photoelectron spectroscopy study of the initial stages of rf magnetron sputter deposition of indium tin oxide on p-type Si substrate

M. H. Rein, M. V. Hohmann, A. Thøgersen, J. Mayandi, A. O. Holt, A. Klein, and E. V. Monakhov

Appl. Phys. Lett. 102, 021606 (2013); http://dx.doi.org/10.1063/1.4774404 (4 pages)

Online Publication Date: 17 January 2013

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The interface between indium tin oxide and p-type silicon is studied by in situ X-ray photoelectron spectroscopy (XPS). This is done by performing XPS without breaking vacuum after deposition of ultrathin layers in sequences. Elemental tin and indium are shown to be present at the interface, both after 2 and 10 s of deposition. In addition, the silicon oxide layer at the interface is shown to be composed of mainly silicon suboxides rather than silicon dioxide.
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68.55.ag Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Cd Deposition by sputtering
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Effect of polarity on Ni/InN interfacial reactions

K. C. Kragh-Buetow, X. Weng, E. D. Readinger, M. Wraback, and S. E. Mohney

Appl. Phys. Lett. 102, 021607 (2013); http://dx.doi.org/10.1063/1.4781768 (4 pages)

Online Publication Date: 18 January 2013

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Ni films on (0001) and (000math) InN exhibited different reaction kinetics upon annealing at 673K. Structural and chemical analysis using grazing incidence X-ray diffraction, transmission electron microscopy, and X-ray energy dispersive spectrometry indicated that an interfacial reaction did not occur between the Ni film and the In-polar (0001) InN layer. However, the N-polar face reacted with Ni to form the Ni3InNx ternary phase with an anti-perovskite structure. The difference in reactivity for Ni on In-face and N-face InN indicates that polarity alters the reaction and may also affect interactions between other metals and group III-nitride semiconductors.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.Cc Kinetics of defect formation and annealing
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Intrinsic bandgap of cleaved ZnO(11math0) surfaces

A. Sabitova, Ph. Ebert, A. Lenz, S. Schaafhausen, L. Ivanova, M. Dähne, A. Hoffmann, R. E. Dunin-Borkowski, A. Förster, B. Grandidier, and H. Eisele

Appl. Phys. Lett. 102, 021608 (2013); http://dx.doi.org/10.1063/1.4776674 (4 pages)

Online Publication Date: 18 January 2013

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The existence of intrinsic surface states, the position of the Fermi level, and the size of the surface bandgap of the non-polar ZnO(11math0) cleavage surfaces were investigated by scanning tunneling microscopy and spectroscopy. The comparison of spectroscopic measurements performed on atomically flat and stepped surfaces reveals the absence of intrinsic surface states within the fundamental bulk bandgap, but shows the occurrence of step-induced gap states. These states lead to a pinning of the Fermi level at the surface within the bandgap and generate a significant defect-related tunnel current, narrowing the measured apparent bandgap.
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73.20.At Surface states, band structure, electron density of states
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
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Structural and mechanical stability of dilute yttrium doped chromium

Jialin Lei, Bin Chen, Shengmin Guo, Kaiyang Wang, Liuxi Tan, Ebrahim Khosravi, Jinyuan Yan, Selva Vennila Raju, and Shizhong Yang

Appl. Phys. Lett. 102, 021901 (2013); http://dx.doi.org/10.1063/1.4775596 (4 pages)

Online Publication Date: 14 January 2013

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Rare earth element doping of chromium is much desired for various applications, but is technically difficult because of dopant segregation. Using a room temperature mechanical alloying method, dilute yttrium doping into nanosized chromium was achieved. Synchrotron-based high-pressure X-ray diffraction indicated that the Cr-Y alloy (Cr0.97Y0.03) was stable at up to 39 GPa, and the bulk modulus was 203 ± 2.6 GPa. The experimental results were consistent with first-principles density functional theory simulation. The diffraction line broadening profiles indicated the deformation anisotropy of the nanoalloy. This study suggests that Cr0.97Y0.03 alloy is promising for ultrahigh stress applications such as airplane engines and land-based turbines.
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81.40.Lm Deformation, plasticity, and creep
62.20.de Elastic moduli
62.20.F- Deformation and plasticity
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Jj Elasticity and anelasticity, stress-strain relations

12% magnetic field-induced strain in Ni-Mn-Ga-based non-modulated martensite

A. Sozinov, N. Lanska, A. Soroka, and W. Zou

Appl. Phys. Lett. 102, 021902 (2013); http://dx.doi.org/10.1063/1.4775677 (5 pages) | Cited 1 time

Online Publication Date: 14 January 2013

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Magnetic field-induced strain (MFIS) of 12% is reported in ferromagnetic Ni46Mn24Ga22Co4Cu4 martensite exhibiting non-modulated (NM) tetragonal crystal structure with lattice parameter ratio c/a>1. The strain was measured at ambient temperature in a magnetic field of the order of 1 T. The twinning stress σTW and the magnetic stress σMAG were also measured and the condition for a giant MFIS observation σTW<σMAG was confirmed. The MFIS was achieved in NM Ni46Mn24Ga22Co4Cu4 martensite by considerable lowering of the σTW value as compared to the values for NM martensites in ternary Ni-Mn-Ga system.
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61.66.Dk Alloys
61.72.Mm Grain and twin boundaries
75.50.Cc Other ferromagnetic metals and alloys

Monolayer graphene oxide as a building block for artificial muscles

Geoffrey W. Rogers and Jefferson Z. Liu

Appl. Phys. Lett. 102, 021903 (2013); http://dx.doi.org/10.1063/1.4775597 (4 pages)

Online Publication Date: 15 January 2013

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The electromechanical actuation of a highly ordered compound of graphene oxide (GO) is shown via ab initio simulations to produce high-performance quantum-mechanical responses, which mimic the behaviour of mammalian skeletal muscle. In addition to large expansive strains (∼10%), this GO compound (asymmetrically unzipped C4O) exhibits large contractive strains of −4.8% upon −0.15 e/C-atom electron injection. Furthermore, as these contractive strains are coupled with equally high stresses (∼100 GPa) and short response times ( ∼ 1 ns), we show that this GO material meets all of the functional requirements of an artificial muscle building block.
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82.45.Mp Thin layers, films, monolayers, membranes
87.19.Ff Muscles
61.48.Gh Structure of graphene
81.05.ue Graphene
71.15.-m Methods of electronic structure calculations
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Fabrication of stereo metallic resonant structures with polymer droplets as template

Xiao-Chun Chen, Yuan-Wei Wu, Yu-Hui Hu, Hong-Min Li, Ru-Wen Peng, Xi-Ping Hao, and Mu Wang

Appl. Phys. Lett. 102, 021904 (2013); http://dx.doi.org/10.1063/1.4775765 (4 pages)

Online Publication Date: 15 January 2013

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Using polymer droplets formed in dewetting of polymer film on silicon surface as template, the silicon columns capped with circular polymer plates are fabricated via plasma etching. By blanket deposition of a gold layer on the structure, an array of metallic microcavities featured by a metal circular plate separated by a silicon column with the bottom metallic film is achieved. The geometrical parameters of the stereo structures can be tuned. We show that the electric field at the edge of the cap is greatly enhanced, which can be used as the hot spot for trace amount of chemical detection.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
81.65.Cf Surface cleaning, etching, patterning
68.55.-a Thin film structure and morphology
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Surface plasmon modulation induced by a direct-current electric field into gallium nitride thin film grown on Si(111) substrate

Arnaud Stolz, Suk-Min Ko, Gilles Patriarche, Elhadj Dogheche, Yong-Hoon Cho, and Didier Decoster

Appl. Phys. Lett. 102, 021905 (2013); http://dx.doi.org/10.1063/1.4776671 (3 pages) | Cited 1 time

Online Publication Date: 16 January 2013

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We report here the experimental results on a field effect refractive index change into gallium nitride (GaN) structures. This effect is characterized through the common prism-coupling technique with the application of a vertical direct-current electric field. Surface plasmon propagation was used to increase the sensitivity of the electro-optic measurements. We have obtained a large refractive index variation for GaN epilayer, around 1.4×10−2 at 1.55μm wavelength. In order to understand the origin of the index modulation, we have conducted a scanning transmission electron microscopy analysis and discussed the influence of threading dislocations density acting as traps and thermo-optic effect. According to recent works, we observed experimentally the optical response of a non-linear electro-optic effect on GaN on Si(111) substrate and estimated a Kerr coefficient of about 2.14×10−16m2 V−2.
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78.20.nd Thermophotonic effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Nonlocal electro-optic effects for transverse electric modes in quantum well Mach-Zehnder modulators

Guanghui Wang and Ruiqiang Wang

Appl. Phys. Lett. 102, 021906 (2013); http://dx.doi.org/10.1063/1.4776688 (3 pages)

Online Publication Date: 16 January 2013

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We develop a microscopic nonlocal theory for the electro-optic effect (Pockels effect) and report its effective electrorefractive modulation for transverse electric (TE) waves in a quantum well (QW) waveguide Mach-Zehnder modulator. A general expression for the dielectric function with spatial dispersion for TE modes is derived. Furthermore, it is desirable that a low absorption loss (α<9.0 cm−1) and a large refractive index change (Δn ∼ 0.00137) are obtained by an optimal bias electric field and QW width. These properties may have extensive applications in the field of optoelectronics.
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78.20.Jq Electro-optical effects
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