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13 Aug 2007

Volume 91, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 071906 (2007); http://dx.doi.org/10.1063/1.2753092 (3 pages)

Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency

A. Evans, S. R. Darvish, S. Slivken, J. Nguyen, Y. Bai, and M. Razeghi

Appl. Phys. Lett. 91, 071101 (2007); http://dx.doi.org/10.1063/1.2770768 (3 pages) | Cited 44 times

Online Publication Date: 13 August 2007

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The authors report on the development of λ ∼ 4.7 μm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675 W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150 K, with continuous-wave output powers of more than 1 W.
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42.55.Px Semiconductor lasers; laser diodes

Pump-power-controlled luminescence switching in Yb3+/Tm3+ codoped water-free low silica calcium aluminosilicate glasses

C. Jacinto, M. V. D. Vermelho, E. A. Gouveia, M. T. de Araujo, P. T. Udo, N. G. C. Astrath, and M. L. Baesso

Appl. Phys. Lett. 91, 071102 (2007); http://dx.doi.org/10.1063/1.2771051 (3 pages) | Cited 26 times

Online Publication Date: 13 August 2007

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Intense infrared-to-visible upconversion emissions in Tm3+/Yb3+ codoped water-free low silica calcium aluminosilicate glasses have been obtained under excitation at 976 nm. The results showed that as the pump power/intensity is increased, a reduction of up to one order of magnitude at the 800/480 nm emitted intensity ratio is observed; characterizing what can be denominated as luminescent switching. The physical origin of this switching is discussed and explained in terms of the tailoring of luminescent switchers to operate in a large range of pump powers, what could be used in the development of sensors and networks for optical processing and optical communications.
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78.55.Hx Other solid inorganic materials

Low threshold 1260 nm (GaIn) (NAs) semiconductor disk laser

W. Diehl, P. Brick, B. Kunert, S. Reinhard, K. Volz, and W. Stolz

Appl. Phys. Lett. 91, 071103 (2007); http://dx.doi.org/10.1063/1.2771052 (3 pages) | Cited 6 times

Online Publication Date: 13 August 2007

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Low threshold cw laser emission from a semiconductor disk laser emitting at 1260 nm was demonstrated. Using high quality metal-organic vapor phase epitaxy (GaIn) (NAs) material, nonradiative processes could be minimized. As a consequence, threshold pump power densities have been reduced down to 5 kW/cm2. The capture efficiency of carriers into the quantum wells was found to be uncritical.
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42.55.Px Semiconductor lasers; laser diodes

Edge emitting quantum cascade microlasers on InP with deeply etched one-dimensional photonic crystals

J. Semmel, L. Nähle, S. Höfling, and A. Forchel

Appl. Phys. Lett. 91, 071104 (2007); http://dx.doi.org/10.1063/1.2771054 (3 pages) | Cited 7 times

Online Publication Date: 13 August 2007

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Edge emitting quantum cascade microlasers based on InP have been fabricated and investigated. Deeply etched Bragg mirrors have been manufactured at the end of the resonators, to reduce the mirror losses of short cavity devices. In order to achieve the required high aspect ratio, an optimized plasma dry etching process has been developed, which allows monolithic device fabrication in a single dry etching step. The short resonator length results in a large Fabry-Pérot mode spacing, which leads to a single mode operation. A side mode suppression ratio of about 20 dB at 80 K has been observed.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Compact and polarization controlled 1.55 μm vertical-cavity surface-emitting laser using single-layer photonic crystal mirror

Salim Boutami, Badhise Benbakir, Jean-Louis Leclercq, and Pierre Viktorovitch

Appl. Phys. Lett. 91, 071105 (2007); http://dx.doi.org/10.1063/1.2771085 (3 pages) | Cited 17 times

Online Publication Date: 14 August 2007

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Vertical-cavity surface-emitting lasers (VCSELs) consist of a gain medium in which feedback is generally accomplished by two distributed Bragg reflectors (DBRs), for which sufficient reflectivity has to be achieved in order to obtain laser emission. As a consequence, DBRs generally consist of very thick layer stacks. In this letter, the authors report the realization of a VCSEL, of which the top mirror consists of a single-layer one-dimensional photonic crystal mirror (PCM). This PCM enables significantly improved device compactness and total polarization control, while providing a directive and single lateral mode emission.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Bh Lenses, prisms and mirrors

Optical signal storage and switching between two wavelengths

Xiao-Li Song, Lei Wang, Zhi-Hui Kang, Rui-Zhu Lin, Xin Li, Yun Jiang, and Jin-Yue Gao

Appl. Phys. Lett. 91, 071106 (2007); http://dx.doi.org/10.1063/1.2770965 (3 pages) | Cited 3 times

Online Publication Date: 14 August 2007

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The authors report an experiment in which optical pulses are effectively stored via maximal atomic coherence in a three-level Λ-type 87Rb atomic system, and then selectively released at one of the two different wavelengths by turning on the retrieve control pulse at 794.9842 or 794.9698 nm. The storage time up to 360 ns was demonstrated.
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42.79.Vb Optical storage systems, optical disks
42.50.-p Quantum optics

Planar ZnO ultraviolet modulator

X. Y. Zhang, A. Dhawan, P. Wellenius, A. Suresh, and J. F. Muth

Appl. Phys. Lett. 91, 071107 (2007); http://dx.doi.org/10.1063/1.2770995 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2007

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A planar electroabsorption modulator suitable for spatial light modulation has been constructed. The device operates near the band edge of zinc oxide at 3.3 eV and is based on broadening and shifting of the unconfined exciton with an externally applied electric field. The ZnO active layer was deposited on an aluminum/titanium oxide dielectric on an indium tin oxide conducting layer on glass. A transparent conductive InGaZnO layer on a spin on glass insulator served as the top contact, allowing high electric fields to be applied transverse to the ZnO layer. The modulator operates at room temperature in transmission mode with +45% modulation at 373 nm and −18% modulation at 380 nm at 140 V applied bias, corresponding to ∼ 450 kV/cm electric field across the ZnO active layer.
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42.79.Hp Optical processors, correlators, and modulators

Stoichiometry, mobility, and performance in bulk heterojunction solar cells

L. Mattias Andersson, Fengling Zhang, and Olle Inganäs

Appl. Phys. Lett. 91, 071108 (2007); http://dx.doi.org/10.1063/1.2771524 (3 pages) | Cited 23 times

Online Publication Date: 14 August 2007

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Bipolar transport in blends of a copolymer of fluorene, thiophene and electron accepting groups, and the substituted fullerene [6,6]-phenyl-C61-butyric acid methylester have been studied through charge extraction by linearly increasing voltage on solar cells and with field effect transistors. Between 10% and 90% polymer has been used and the results show a clear correlation to solar cell performance. Optimal solar cells comprise 20% polymer and have a power conversion efficiency of 3.5%. The electron mobility is increasing strongly with fullerene content, but is always lower than the hole mobility, thus explaining the low amount of polymer in optimized devices.
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84.60.Jt Photoelectric conversion
85.30.-z Semiconductor devices
85.30.Tv Field effect devices

Multistage optical memory of a liquid crystal diffraction grating in a single beam rewriting scheme

Eunje Jang, Hak-Rin Kim, Yu-Jin Na, and Sin-Doo Lee

Appl. Phys. Lett. 91, 071109 (2007); http://dx.doi.org/10.1063/1.2769955 (3 pages) | Cited 8 times

Online Publication Date: 14 August 2007

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The authors report on the multistage optical memory of a liquid crystal (LC) diffraction grating fabricated using a dye-dispersed LC/polymer composite medium. Under a single pump beam, the reorientation of dye molecules, confined within spatially periodic interpolymer networks produced by a patterned exposure of ultraviolet light, allows for a pure optic-axis modulation which gives high diffraction efficiency in a planar LC configuration. The resultant multistage optical memory of the LC grating is controlled solely by the polarization state of a single rewriting beam without the use of an erasing step prior to every rewriting process.
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42.79.Vb Optical storage systems, optical disks
42.70.Df Liquid crystals
42.79.Dj Gratings
42.86.+b Optical workshop techniques

Optical manipulable polymer optical fiber Bragg gratings with azopolymer as core material

Yanhua Luo, Jingli Zhou, Qing Yan, Wei Su, Zengchang Li, Qijin Zhang, Jintang Huang, and Keyi Wang

Appl. Phys. Lett. 91, 071110 (2007); http://dx.doi.org/10.1063/1.2770657 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2007

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Polymer optical fiber (POF) with a core of azopolymer has been fabricated. Based on the photoinduced birefringence of azopolymer materials, a mechanism for writing POF gratings is presented. After writing in azopolymer optical fiber (APOF) by two beams of mutually orthogonal polarizations, a birefringence grating was formed, and then the gratings could be erased almost totally for a short time by the circularly polarized beam at the same wavelength. By manipulating the APOF gratings, the transmittance through APOF at 632.8 nm can be adjustable as revealed by the transmittance change during write-erase-write procedure.
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42.81.Wg Other fiber-optical devices
42.70.Jk Polymers and organics
42.81.Gs Birefringence, polarization
42.81.Dp Propagation, scattering, and losses; solitons

Electron and hole dynamics of InAs/GaAs quantum dot semiconductor optical amplifiers

I. O’Driscoll, T. Piwonski, C.-F. Schleussner, J. Houlihan, G. Huyet, and R. J. Manning

Appl. Phys. Lett. 91, 071111 (2007); http://dx.doi.org/10.1063/1.2771374 (3 pages) | Cited 19 times

Online Publication Date: 15 August 2007

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Single-color and two-color pump-probe measurements are used to analyze carrier dynamics in InAs/GaAs quantum dot amplifiers. The study reveals that hole recovery and intradot electron relaxation occur on a picosecond time scale, while the electron capture time is on the order of 10 ps. A longer time scale of hundreds of picoseconds is associated with carrier recovery in the wetting layer, similar to that observed in quantum well semiconductor amplifiers.
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42.55.Px Semiconductor lasers; laser diodes

High power subterahertz electromagnetic wave radiation from GaN photoconductive switch

Osamu Imafuji, Brahm Pal Singh, Yutaka Hirose, Yasuyuki Fukushima, and Shinichi Takigawa

Appl. Phys. Lett. 91, 071112 (2007); http://dx.doi.org/10.1063/1.2771528 (3 pages) | Cited 2 times

Online Publication Date: 15 August 2007

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The authors present apparently the observation of subterahertz electromagnetic wave emission from GaN based large aperture photoconductive switches (LA-PCSWs) excited by ultraviolet femtosecond laser pulses. The photoconductive layer of the GaN LA-PCSW is doped with carbon giving rise to a resistivity as high as 60 MΩ cm. The absolute energy of the emitted radiation pulses is measured to be 93.3 pJ/pulse under 500 V bias voltage. The Fourier spectrum of the measured pulse by the time-domain-spectroscopy shows the main components lie in 0.1–0.2 THz regime.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
85.60.-q Optoelectronic devices

Anisotropic nonlinear response of silicon in the near-infrared region

J. Zhang, Q. Lin, G. Piredda, R. W. Boyd, G. P. Agrawal, and P. M. Fauchet

Appl. Phys. Lett. 91, 071113 (2007); http://dx.doi.org/10.1063/1.2768632 (3 pages) | Cited 21 times

Online Publication Date: 15 August 2007

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The authors characterize experimentally the anisotropy of two-photon absorption and the Kerr nonlinearity in silicon over a broad spectral region in the near infrared using the z-scan technique. The results show that both of these parameters decrease by about 12% along the [0 1 0] direction compared with the [0 1 math] direction, and this change occurs for wavelengths in the range of 1.2–2.4 μm.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
72.40.+w Photoconduction and photovoltaic effects
42.65.-k Nonlinear optics
84.40.Az Waveguides, transmission lines, striplines

Organic thin film transistors with ink-jet printed metal nanoparticle electrodes of a reduced channel length by laser ablation

Dongjo Kim, Sunho Jeong, Jooho Moon, Sewoon Han, and Jaewon Chung

Appl. Phys. Lett. 91, 071114 (2007); http://dx.doi.org/10.1063/1.2771059 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2007

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The authors have demonstrated organic thin film transistors (OTFTs) based on the ink-jet printed electrodes in which a reduced channel length is accomplished by laser ablation. Laser ablation on the dried silver nanoparticle electrode formed by ink-jet printing effectively shortened the channel length down to 5 μm, which is difficult to achieve by ink-jet printing alone. Reducing the channel length using this hybrid technique also allows them to observe the contact resistance effect in the OTFTs, which involves the printed silver nanoparticle electrode of a lower work function with respect to the ionization energy of the organic semiconductor.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Whispering gallery resonances in semiconductor micropillars

V. N. Astratov, S. Yang, S. Lam, B. D. Jones, D. Sanvitto, D. M. Whittaker, A. M. Fox, M. S. Skolnick, A. Tahraoui, P. W. Fry, and M. Hopkinson

Appl. Phys. Lett. 91, 071115 (2007); http://dx.doi.org/10.1063/1.2771373 (3 pages) | Cited 16 times

Online Publication Date: 15 August 2007

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In this letter, the authors observe high quality (Q up to 20 000) whispering gallery modes (WGMs) with small modal volumes V ∼ 0.3 μm3 in 4–5 μm Al(Ga)As/GaAs micropillars by employing an experimental geometry in which both excitation and collection of emission are in a direction normal to the sidewalls of the pillars. They show that WGMs provide at least two times larger values of the figure of merit for strong coupling applications Q/math compared to “photonic dot” states in pillars with comparable size.
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42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Effect of nitric oxide on gain and output power of a non-self-sustained electric discharge pumped oxygen-iodine laser

A. Hicks, J. Bruzzese, W. R. Lempert, J. W. Rich, and I. V. Adamovich

Appl. Phys. Lett. 91, 071116 (2007); http://dx.doi.org/10.1063/1.2771535 (3 pages) | Cited 10 times

Online Publication Date: 15 August 2007

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This letter discusses the effect of nitric oxide on gain and output power of a pulser-sustainer discharge excited oxygen iodine laser. Adding small amounts of NO to the laser mixture (a few hundreds of ppm) considerably increases gain and output power due to (i) O atom titration and resultant slower I* atom quenching and (ii) improved stability of the dc sustainer discharge, which allows stable operation at significantly higher discharge powers. Gain on the 1315 nm iodine atom transition and laser power in the M = 3 transverse laser cavity are 0.049%/cm and 1.24 W, at a flow temperature of T = 100 K.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems

High efficient and low color-temperature white light-emitting diodes with Tb3Al5O12:Ce3+ phosphor

Yibo Chen, Menglian Gong, Gang Wang, and Qiang Su

Appl. Phys. Lett. 91, 071117 (2007); http://dx.doi.org/10.1063/1.2771538 (3 pages) | Cited 16 times

Online Publication Date: 16 August 2007

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High efficient Tb3Al5O12:Ce3+ (TAG:Ce3+) phosphors were prepared in a solid-state reaction method with various fluxes. The results show that addition of proper flux can decrease the phase-forming temperature of the TAG crystals and improve the morphology as well as enhance the photoluminescence of the phosphors greatly. High efficient and low color-temperature white light-emitting diodes (WLEDs) were fabricated with the TAG:Ce3+ phosphor. Good performances of the WLEDs indicate that a mixture of H3BO3 and LiF is an excellent flux for synthesis of TAG:0.04Ce3+ phosphor and is beneficial to the fabrication of high efficient WLEDs.
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85.60.Jb Light-emitting devices
78.55.Hx Other solid inorganic materials

Dynamic characterization of organic bulk heterojunction photodetectors

M. Punke, S. Valouch, S. W. Kettlitz, N. Christ, C. Gärtner, M. Gerken, and U. Lemmer

Appl. Phys. Lett. 91, 071118 (2007); http://dx.doi.org/10.1063/1.2772198 (3 pages) | Cited 18 times

Online Publication Date: 16 August 2007

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The authors report the dynamic properties of bulk heterojunction photodiodes based on a polymer blend system consisting of poly(3-hexylthiophene-2,5-diyl) and the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester. Devices with a high-frequency contact layout were analyzed under continuous wave and pulsed laser illumination (λ = 532 nm). The organic photodiodes exhibit a pulse response with a full width at half maximum of 11 ns to the applied 1.6-ns-long laser pulses. Rise times as small as 1.6 ns and fall times <40 ns were measured under applied reverse bias.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Investigation of the transient symmetric H state in a pi cell

Bo-Ru Yang, Steve J. Elston, Peter Raynes, and Han-Ping D. Shieh

Appl. Phys. Lett. 91, 071119 (2007); http://dx.doi.org/10.1063/1.2772670 (3 pages) | Cited 4 times

Online Publication Date: 16 August 2007

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The so-called symmetric H (Hs) state has been reported to have submillisecond response times, which results from the symmetric profile of the liquid crystal director; however, no direct evidence has been obtained to show the profile symmetry. The difficulty in proving this symmetric structure by direct observation results from the short lifetime of Hs state (typically around a few tens of milliseconds). In the work reported here, the authors utilize a burst driving method along with stroboscopic illumination from blue and red light emitting diodes to capture conoscopic images for the Hs director profile; these showed good agreement with their modeling.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
78.20.Jq Electro-optical effects

Use of ZnO thin films as sacrificial templates for metal organic vapor phase epitaxy and chemical lift-off of GaN

D. J. Rogers, F. Hosseini Teherani, A. Ougazzaden, S. Gautier, L. Divay, A. Lusson, O. Durand, F. Wyczisk, G. Garry, T. Monteiro, M. R. Correira, M. Peres, A. Neves, D. McGrouther, J. N. Chapman, et al.

Appl. Phys. Lett. 91, 071120 (2007); http://dx.doi.org/10.1063/1.2770655 (3 pages) | Cited 26 times

Online Publication Date: 16 August 2007

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Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy (MOVPE). In this work, GaN was grown on ZnO/c-Al2O3 using low temperature/pressure MOVPE with N2 as a carrier and dimethylhydrazine as a N source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the c-Al2O3 by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors

Miniaturized negative permeability materials

Kamil Boratay Alici, Filiberto Bilotti, Lucio Vegni, and Ekmel Ozbay

Appl. Phys. Lett. 91, 071121 (2007); http://dx.doi.org/10.1063/1.2772672 (3 pages) | Cited 18 times

Online Publication Date: 17 August 2007

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Experimental and numerical studies of μ-negative (MNG) materials such as multisplit ring resonators (MSRRs) and spiral resonators (SRs) are presented. The resonance frequency of the structures is determined by the transmission measurements and minimum electrical size of λ0/17 for the MSRRs and of λ0/82 for the SRs observed. These MNG materials can be easily produced by the well developed printed circuit board and optical lithography techniques. They are promising elements for the development of high resolution metamaterial lenses and electrically small antennas.
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84.40.Az Waveguides, transmission lines, striplines
85.40.Hp Lithography, masks and pattern transfer

Coupling between surface plasmons and nonresonant transmission in subwavelength holes at terahertz frequencies

Jiaguang Han, Abul K. Azad, Mufei Gong, Xinchao Lu, and Weili Zhang

Appl. Phys. Lett. 91, 071122 (2007); http://dx.doi.org/10.1063/1.2771093 (3 pages) | Cited 23 times

Online Publication Date: 17 August 2007

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Transmission spectra of terahertz pulses through periodic array of subwavelength holes exhibit a characteristic evolution with various hole widths. The peak absolute transmittance approaches a maximum value at a critical hole width, while linewidth broadening and blueshift of peak frequency are observed with increasing hole width. Such characteristic evolution is attributed to the coupling between discrete resonant excitation of surface plasmons and continuum nonresonant transmission through the holes; this agrees well with the numerical analysis based on the Fano model and the measured angle-resolved transmission band structures.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.70.Gq Microwave and radio-frequency interactions

Integrating optics and microfluidics for time-correlated single-photon counting in lab-on-a-chip devices

A. Cleary, A. Glidle, P. J. R. Laybourn, S. García-Blanco, S. Pellegrini, C. Helfter, G. S. Buller, J. S. Aitchison, and J. M. Cooper

Appl. Phys. Lett. 91, 071123 (2007); http://dx.doi.org/10.1063/1.2772175 (3 pages) | Cited 9 times

Online Publication Date: 17 August 2007

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The authors describe the integration of low-loss optical waveguides with lab-on-a-chip structures to produce an integrated optical-microfluidic platform for time-correlated single-photon counting of fluorescent molecules. Waveguides were fabricated using electron beam densification of planar silica on silicon, eliminating any requirement for depositing upper cladding silica layers. Microfluidic channels were dry etched directly through the waveguides and the device was sealed using a poly(dimethylsiloxane) gasket. Time-resolved fluorescence lifetime measurements of the fluorophore nile blue were used as a model system to demonstrate the operation of the microfluidic device, with dye concentrations as low as 1.5 nM (equivalent to <6000 molecules) being measured.
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42.82.Et Waveguides, couplers, and arrays
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.60.-q Optoelectronic devices
47.85.Np Fluidics
07.10.Cm Micromechanical devices and systems
42.50.Ar Photon statistics and coherence theory

Low-threshold surface-passivated photonic crystal nanocavity laser

Dirk Englund, Hatice Altug, and Jelena Vučković

Appl. Phys. Lett. 91, 071124 (2007); http://dx.doi.org/10.1063/1.2769957 (3 pages) | Cited 26 times

Online Publication Date: 17 August 2007

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The efficiency and operating range of a photonic crystal laser are improved by passivating the In–GaAs quantum well gain medium and GaAs membrane using a (NH4)S treatment. The passivated laser shows a fourfold reduction in nonradiative surface recombination rate, resulting in a fourfold reduction in lasing threshold. A three-level carrier dynamics model explains the results and shows that typical parameters of such lasers lead to a lasing threshold as much determined by surface recombination as by the overall impact of the cavity quality factor. Surface passivation therefore appears crucial in operating such lasers under practical conditions.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Photodetector with artificial atoms of silicon

Shu-Fen Hu, Ting-Wei Liao, and Chao-Yuan Huang

Appl. Phys. Lett. 91, 071125 (2007); http://dx.doi.org/10.1063/1.2771527 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2007

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The authors demonstrate a potential application of quantum dots for the detection of photons, showing that the Coulomb interaction resulting from the capture of photoexcited carriers by quantum dots produces a detectable change in the source-drain resistance of the transistor. This quantum effect is more pronounced with higher illumination, displaying staircase quantum steps with ΔV = 4 mV on the I-V characteristics at room temperature, implying that the photocurrent is increased as the light intensity is increased. The responsitivity of device is R ∼ 3.98×106 A/W for Vd = 0.18 V, and external quantum efficiency is more than 8.6%.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.63.Kv Quantum dots
72.40.+w Photoconduction and photovoltaic effects
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