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8 Mar 2010

Volume 96, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 96, 101501 (2010); http://dx.doi.org/10.1063/1.3352316 (3 pages)

Bomi Gweon, Daeyeon Kim, Dan Bee Kim, Heesoo Jung, Wonho Choe, and Jennifer H. Shin
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Anisotropic heat propagation velocity in quantum cascade lasers

Miriam S. Vitiello and Gaetano Scamarcio

Appl. Phys. Lett. 96, 101101 (2010); http://dx.doi.org/10.1063/1.3352121 (3 pages) | Cited 1 time

Online Publication Date: 8 March 2010

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We report on the time-resolved measurement of the in-plane (v∥) and cross-plane (v┴) components of the heat transfer velocity in GaAs/Al0.15Ga0.85As quantum-cascade heterostructures. We compared the heating and cooling stages both in the active region and in the substrate with models of heat transfer in nanostructures. We found that v⊥ is reduced by a factor of ∼ 6.5 with respect to that of the corresponding bulk material due to the additional thermal resistance of each interface and to the phonon interference effects in the multilayered structure. The v∥ component is reduced by ∼ 30% due to interface roughness.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media

Improvement of quantum efficiency by employing active-layer-friendly lattice-matched InAlN electron blocking layer in green light-emitting diodes

Hee Jin Kim, Suk Choi, Seong-Soo Kim, Jae-Hyun Ryou, P. Douglas Yoder, Russell D. Dupuis, Alec M. Fischer, Kewei Sun, and Fernando A. Ponce

Appl. Phys. Lett. 96, 101102 (2010); http://dx.doi.org/10.1063/1.3353995 (3 pages) | Cited 15 times

Online Publication Date: 8 March 2010

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Improvement of the internal quantum efficiency in green-light emitting diodes has been achieved using lattice-matched InAlN electron-blocking layers. Higher electroluminescence intensities have been obtained due to better electron confinement in the device active region. The device efficiency has also been found to significantly depend on the InAlN growth temperature. Optimized InAlN growth at ∼ 840 °C results in a lower growth rate and longer growth times than at ∼ 780 °C. The observed reduction in emission efficiency for InAlN layers grown at higher temperatures is possibly attributed to thermal damage in the green active region.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

All-silicon sub-Gb/s telecom detector with low dark current and high quantum efficiency on chip

Takasumi Tanabe, Hisashi Sumikura, Hideaki Taniyama, Akihiko Shinya, and Masaya Notomi

Appl. Phys. Lett. 96, 101103 (2010); http://dx.doi.org/10.1063/1.3357427 (3 pages) | Cited 14 times

Online Publication Date: 8 March 2010

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We demonstrate channel selective 0.1-Gb/s photoreceiver operation at telecom wavelength using a silicon high-Q photonic crystal nanocavity with a laterally integrated p-i-n diode. Due to the good crystal property of silicon the measured dark current is only 15 pA. The linear and nonlinear characteristics are investigated in detail, in which we found that the photocurrent is enhanced of more than 105 due to the ultrahigh-Q (Q ≃ 105). With the help of two-photon absorption, which is visible at a surprisingly low input power of 10−8 W, the quantum efficiency of this device reaches ∼ 10%.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Uniform-field transverse electroreflectance using a mode-locked laser and a radio-frequency bias

J. K. Wahlstrand, H. Zhang, and S. T. Cundiff

Appl. Phys. Lett. 96, 101104 (2010); http://dx.doi.org/10.1063/1.3354078 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2010

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We describe a technique for transverse electroreflectance that uses broadband optical pulses from a mode-locked laser and a rapidly oscillating bias with a frequency near half the laser repetition rate. Since the electrodes are electrically isolated from the sample, highly nonuniform trap-enhanced fields do not occur. Because the time-averaged electric field is zero, space charges do not build up. Experimental results are presented for semi-insulating GaAs. The technique is also useful in ultrafast experiments that require a uniform transverse electric field.
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78.20.Jq Electro-optical effects
42.60.Fc Modulation, tuning, and mode locking
77.22.Jp Dielectric breakdown and space-charge effects

An electrically injected quantum dot spin polarized single photon source

Pallab Bhattacharya, Ayan Das, Debashish Basu, Wei Guo, and Junseok Heo

Appl. Phys. Lett. 96, 101105 (2010); http://dx.doi.org/10.1063/1.3357426 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2010

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The characteristics of an electrically injected spin polarized single photon source have been investigated. The GaAs-based microcavity diode consists of a single InAs/GaAs self-organized quantum dot as the single photon source and a MnAs/Al0.1Ga0.9As Schottky tunnel barrier for the ferromagnetic contact to inject spin polarized electrons. The measured output circular polarization of the biexciton emission at λ ∼ 1130 nm exhibits a switching behavior as a function of magnetic field, in the Faraday geometry, the value remaining near-zero for B<1 T and ∼ 6%–8% for B ≥ 1 T. The linear polarization shows a complementary trend. The results are explained in the framework of the exciton fine structure in the quantum dot and the effects of electron-hole exchange splitting, due to in-plane quantum dot anisotropy, and Zeeman splitting on the spin eigenstates and their coupling to the photon field.
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73.21.La Quantum dots
73.30.+y Surface double layers, Schottky barriers, and work functions
71.35.-y Excitons and related phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.67.Hc Quantum dots
81.07.Ta Quantum dots
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Phase-locked arrays of surface-emitting terahertz quantum-cascade lasers

Tsung-Yu Kao, Qing Hu, and John L. Reno

Appl. Phys. Lett. 96, 101106 (2010); http://dx.doi.org/10.1063/1.3358134 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2010

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We report the demonstration of phase-locked arrays of surface-emitting distributed-feedback (DFB) terahertz quantum-cascade lasers with single-mode operations. Carefully designed “phase sector” locks several surface-emitting DFB laser ridges in-phase, creating tighter beam-patterns along the phased-array direction with full width at half maximum (FWHM) ≈ 10°. In addition, the phase sector can be individually biased to provide a mechanism of frequency tuning through gain-induced optical index change, without significantly affecting the output power levels. A tuning range of 1.5 GHz around 3.9 THz was achieved. This fine tunability could be utilized to frequency- or phase-lock the DFB array to an external reference.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

High performance tunnel injection quantum dot comb laser

Chi-Sen Lee, Wei Guo, Debashish Basu, and Pallab Bhattacharya

Appl. Phys. Lett. 96, 101107 (2010); http://dx.doi.org/10.1063/1.3358142 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2010

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A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (Δ−15 dB) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231–1252 nm and 1274–1311 nm, respectively, for a laser with 1040 μm cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300–323 K. The small signal modulation bandwidth is 7.5 GHz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Dielectrophoretically tuneable optical waveguides using nanoparticles in microfluidics

K. Kalantar-zadeh, K. Khoshmanesh, A. A. Kayani, S. Nahavandi, and A. Mitchell

Appl. Phys. Lett. 96, 101108 (2010); http://dx.doi.org/10.1063/1.3358384 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2010

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We present a tuneable optical waveguide using dielectrophoretically controlled nanoparticles in microfluidics. Silicon dioxide nanoparticles of different sizes in de-ionized water are channelled through a microfluidic system. An array of microelectrodes generates the dielectrophoretic force to funnel nanoparticles, forming narrowbands at the center of the microfluidics at different applied voltages and frequencies. It is observed that these narrowbands either scatter or guide the coupled light under selected conditions. The realization of such a system offers exciting possibilities for the development of a new class of optofluidics, which are tuned by the positioning of nanoparticles on demand.
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42.79.Gn Optical waveguides and couplers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Super-reflection and cloaking based on zero index metamaterial

Jiaming Hao, Wei Yan, and Min Qiu

Appl. Phys. Lett. 96, 101109 (2010); http://dx.doi.org/10.1063/1.3359428 (3 pages) | Cited 25 times

Online Publication Date: 10 March 2010

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A zero index metamaterial (ZIM) can be utilized to block wave (super-reflection) or conceal objects completely (cloaking). The “super-reflection” device can be realized by a Mu zero (Epsilon zero) metamaterial with a perfect electric (magnetic) conductor inclusion of arbitrary shape and size for a transverse electric (magnetic) incident wave. In contrast, a Mu zero (Epsilon zero) metamaterial with a perfect magnetic (electric) conductor inclusion for a transverse electric (magnetic) incident wave can be used to conceal objects of arbitrary shape. The underlying physics here is determined by the intrinsic properties of the ZIM.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.70.-a Optical materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Efficient low-power terahertz generation via on-chip triply-resonant nonlinear frequency mixing

J. Bravo-Abad, A. W. Rodriguez, J. D. Joannopoulos, P. T. Rakich, S. G. Johnson, and M. Soljačić

Appl. Phys. Lett. 96, 101110 (2010); http://dx.doi.org/10.1063/1.3359429 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2010

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In this letter, we show theoretically how the light-confining properties of triply-resonant photonic resonators can be tailored to enable dramatic enhancements of the conversion efficiency of terahertz (THz) generation via nonlinear frequency down-conversion processes. Using detailed numerical calculations, we predict that this approach can be used to reduce up to three orders of magnitude the pump powers required to reach quantum-limited conversion efficiency of THz generation in conventional nonlinear optical material systems. Furthermore, we propose a realistic design readily accessible experimentally, both for fabrication and demonstration of optimal THz conversion efficiency at sub-W power levels.
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84.40.Az Waveguides, transmission lines, striplines
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Doping tunable resonance: Toward electrically tunable mid-infrared metamaterials

Xiaoyu Miao, Brandon Passmore, Aaron Gin, William Langston, Shivashankar Vangala, William Goodhue, Eric Shaner, and Igal Brener

Appl. Phys. Lett. 96, 101111 (2010); http://dx.doi.org/10.1063/1.3309707 (3 pages) | Cited 8 times

Online Publication Date: 10 March 2010

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We demonstrate metamaterials at the mid-infrared (mid-IR) wavelengths (8–12 μm) that can be widely tuned by doping in adjacent semiconductor epilayers. The metamaterials are based on metallic split ring resonators (SRRs) fabricated on doped indium antimonide (InSb). Finite integral time-domain simulation results and measured transmission data show that the resonance blueshifts when the semiconductor electron carrier concentration is increased while keeping the split ring geometry constant. A resonant wavelength shift of 1.15 μm is achieved by varying the carrier concentration of underlying InSb epilayer from 1×1016 to 2×1018 cm−3. This work represents the first step toward active tunable metamaterials in the mid-IR where the resonance can be tuned in real time by applying an electric bias voltage to control the effective carrier density.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
61.72.U- Doping and impurity implantation

High responsivity and internal gain mechanisms in Au-ZnMgO Schottky photodiodes

G. Tabares, A. Hierro, J. M. Ulloa, A. Guzman, E. Muñoz, A. Nakamura, T. Hayashi, and J. Temmyo

Appl. Phys. Lett. 96, 101112 (2010); http://dx.doi.org/10.1063/1.3340945 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2010

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Schottky photodiodes based on Au-ZnMgO/sapphire are demonstrated covering the spectral region from 3.35 to 3.48 eV, with UV/VIS rejection ratios up to ∼ 105 and responsivities as high as 185 A/W. Both the rejection ratio and the responsivity are shown to be largely enhanced by the presence of an internal gain mechanism, by which the compensated films become highly conductive as a result of illumination. This causes a large increase in the tunnel current through the Schottky barrier, yielding internal gains that are a function of the incident photon flux.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.30.+y Surface double layers, Schottky barriers, and work functions

Electronic and optical properties of CdZnO quantum well structures with electric field and polarization effects

H. C. Jeon, S. H. Park, S. J. Lee, T. W. Kang, and T. F. George

Appl. Phys. Lett. 96, 101113 (2010); http://dx.doi.org/10.1063/1.3340946 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2010

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Electronic, optical, and electrical properties of CdZnO/MgZnO quantum well (QW) structures, considering internal field and polarization effect, are investigated by using many-body theory. The CdZnO/MgZnO QW structure with higher Cd composition, which has deeper and stronger confinement, is found to have smaller optical gain because the strain-induced piezoelectric polarization and spontaneous polarization in the well increase with the inclusion of Cd. The internal field and polarization is reduced effectively by using the ferroelectric dipole moment of the Li addition in the well region of the Li-doped CdZnO/ZnMgO QW structure. These results demonstrate that a high-performance optical devices operation can be realized in CdZnO/MgZnO QW structures by eliminating the droop phenomenon.
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78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
68.65.Fg Quantum wells

Photogated transistor of III-nitride nanorods

H. W. Seo, L. W. Tu, Q. Y. Chen, C. Y. Ho, Y. T. Lin, K. L. Wu, D. J. Jang, D. P. Norman, and N. J. Ho

Appl. Phys. Lett. 96, 101114 (2010); http://dx.doi.org/10.1063/1.3330876 (3 pages) | Cited 3 times

Online Publication Date: 11 March 2010

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A III-nitride-based photogated transistor using photons to control the channel width of an otherwise gateless field effect transistor (FET) is investigated. This is accomplished by stacking sequential layers of p-GaN/InGaN/n-GaN on a Si substrate in an array of nanorods. The nitride p-i-n diode can be activated by light, whereupon the nanorod device shows phototransistor characteristics in forward bias but behaves like a photoconductor when in reverse bias. An optically pumped FET model, as justified by the low-dimensional nanogeometry, is used in analysis of the device. The resulting photogate efficiency and photocarrier mobilities are estimated to be ∼ 0.04 V/(W/cm2) and, ∼ 2000–3000 cm2/V s, respectively.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.63.Bd Nanocrystalline materials

Near-ultraviolet light emitting diodes using strained ultrathin InN/GaN quantum well grown by metal organic vapor phase epitaxy

Wei Lin, Shuping Li, and Junyong Kang

Appl. Phys. Lett. 96, 101115 (2010); http://dx.doi.org/10.1063/1.3360199 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2010

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The near-ultraviolet (UV) light emitting diodes (LED) using ultrathin InN/GaN quantum well (QW) are fabricated by metal organic vapor phase epitaxy. The x-ray diffraction measurement shows well-defined satellite peaks, which implies abrupt interfaces and good layer periodicity of the QWs. The electroluminescence only exhibits a near-UV emission centered at approximately 3.14–3.18 eV without other emission peaks even the common yellow luminescence, which further confirms the advantages of the near-UV LED especially the minimization of phase separation, interdiffusion, and defects in the QWs. The near-UV emission is found to be stable even under high pulsed injection-current in contrast to the conventional InGaN based LED. This behavior indicates effective avoidance of the redshift related to the many body effect as well as the blueshift induced by band filling effect, localized states in the barrier, and the quantum confined stark effect. The realization of the near-UV LED using the ultrathin InN/GaN QW would facilitate the application of near-UV solid-state lighting source.
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85.60.Jb Light-emitting devices

Directional and controllable edge-emitting ZnO ultraviolet random laser diodes

H. K. Liang, S. F. Yu, and H. Y. Yang

Appl. Phys. Lett. 96, 101116 (2010); http://dx.doi.org/10.1063/1.3356221 (3 pages) | Cited 14 times

Online Publication Date: 12 March 2010

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Room-temperature ultraviolet random lasing action is demonstrated from a p-GaN/annealed i-ZnO:Al(3%)/n-ZnO:Al(5%) buried heterojunction diode with a 2 μm rib waveguide. Excellent electrical-to-optical conversion efficiency is achieved by strong electrical and optical confinement of a buried heterojunction rib waveguide structure. Hence, emission intensity (threshold current) can be enhanced (reduced) by ∼ 9 times ( ∼ 40%). Directional emission as well as controllability on the number of the random lasing modes can also be achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Vertical electric field tuning of the exciton fine structure splitting and photon correlation measurements of GaAs quantum dot

S. Marcet, K. Ohtani, and H. Ohno

Appl. Phys. Lett. 96, 101117 (2010); http://dx.doi.org/10.1063/1.3360212 (3 pages) | Cited 5 times

Online Publication Date: 12 March 2010

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The effects of a vertical electric field on the fine structure splitting of neutral exciton of monolayer fluctuation GaAs quantum dots were investigated. Using the gate voltage between the top gate electrode and the bottom n-GaAs substrate, the fine structure splitting of the neutral exciton was tuned to 15–30 μeV. Photon correlation measurements demonstrate neutral exciton single photon emission and neutral exciton—biexciton cascaded emission.
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71.35.-y Excitons and related phenomena
73.21.La Quantum dots

Nanogap quantum dot photodetectors with high sensitivity and bandwidth

Michael C. Hegg, Matthew P. Horning, Tom Baehr-Jones, Michael Hochberg, and Lih Y. Lin

Appl. Phys. Lett. 96, 101118 (2010); http://dx.doi.org/10.1063/1.3356224 (3 pages) | Cited 5 times

Online Publication Date: 12 March 2010

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We report high-performance nanoscale photodetectors utilizing annealed nanocrystal quantum dots (QDs) within a nanoscale metal electrode gap. By optimizing the nanogap size and fabrication process, the device demonstrates a significantly better sensitivity (noise equivalent power = 7.76×10−14 W/Hz1/2) and bandwidth ( ≥ 125 kHz) than previously reported nanoscale photodetectors. Furthermore, by utilizing a lateral photoconduction structure and a self-assembled layer of QDs, the detector fabrication is highly compatible with many substrates and device architectures.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.07.Ta Quantum dots
81.16.Dn Self-assembly
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