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23 Nov 1998

Volume 73, Issue 21, pp. 3025-3166

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Artificial ferroelectricity in coupled strained quantum dots

Jacob B. Khurgin and Feng Jin

Appl. Phys. Lett. 73, 3102 (1998); http://dx.doi.org/10.1063/1.122686 (3 pages) | Cited 1 time

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A multiple quantum dot structure consisting of alternating strained and unstrained quantum dots and having nonzero net dipole moment, i.e., possessing ferroelectric properties, is proposed. Curie temperature and spontaneous polarization are estimated to be of the order of 20 K and 10−5 C/m2, respectively, for the case of InGaAs quantum dots grown on InP substrate and are shown to be insensitive to the lateral arrangement of the dots. Practical applications in information processing and storage are considered. © 1998 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
73.61.Ey III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
77.22.Ej Polarization and depolarization
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Single zero-dimensional excitons in CdSe/ZnSe nanostructures

T. Kümmell, R. Weigand, G. Bacher, A. Forchel, K. Leonardi, D. Hommel, and H. Selke

Appl. Phys. Lett. 73, 3105 (1998); http://dx.doi.org/10.1063/1.122687 (3 pages) | Cited 86 times

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Zero-dimensional excitons (0DXs) in CdSe/ZnSe nanostructures have been studied by time- and spatially resolved photoluminescence spectroscopy. The three-dimensional confinement is confirmed by an exciton lifetime up to 550 ps, independent of temperature up to 130 K. By preparing mesa structures with diameters down to 50 nm as local probes, an extremely high spatial resolution is achieved, giving experimental access to single 0DXs. A splitting of the ground state into a linearly polarized doublet with an energy spacing up to 1.5 meV is found, varying from dot to dot in sign and magnitude. This indicates a noncircular shape with no preferential orientation of the dots. The dot density is estimated to increase from 5×1010 to 1.5×1011 cm−2, when changing the nominal CdSe layer thickness from 1 to 3 ML, i.e., close to the critical thickness. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors

Excitation of intra-4f shell luminescence of Yb3+ by energy transfer from Si nanocrystals

Minoru Fujii, Shinji Hayashi, and Keiichi Yamamoto

Appl. Phys. Lett. 73, 3108 (1998); http://dx.doi.org/10.1063/1.122688 (3 pages) | Cited 12 times

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SiO2 films containing Si nanocrystals (nc-Si) and Yb were prepared and their photoluminescence (PL) properties were studied. For the sample containing nc-Si with an average diameter of 3.1 nm, a weak peak ( ∼ 1.26 eV) attributable to the intra-4f shell transition of Yb3+ could be observed at the low-energy side of a broad peak ( ∼ 1.4 eV) of nc-Si. The intensity of the 1.26 eV peak was found to depend strongly on the size of nc-Si and increase rapidly with decreasing size. The temperature dependence of the PL spectra was studied. It was found that the degree of temperature quenching of the 1.26 eV peak depends on the size of the nc-Si and becomes small as the size decreases. These results suggest that the band-gap widening of nc-Si due to the quantum size effects is essential to efficiently excite Yb3+ by nc-Si. © 1998 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Ap Elemental semiconductors
61.46.-w Structure of nanoscale materials

High minority-carrier lifetimes in GaAs grown on low-defect-density Ge/GeSi/Si substrates

R. M. Sieg, J. A. Carlin, J. J. Boeckl, S. A. Ringel, M. T. Currie, S. M. Ting, T. A. Langdo, G. Taraschi, E. A. Fitzgerald, and B. M. Keyes

Appl. Phys. Lett. 73, 3111 (1998); http://dx.doi.org/10.1063/1.122689 (3 pages) | Cited 34 times

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A high bulk minority-carrier lifetime in GaAs grown on Si-based substrates is demonstrated. This was achieved by utilizing a step-graded Ge/GeSi buffer (threading dislocation density 2×106 cm−2) grown on an offcut (001) Si wafer, coupled with monolayer-scale control of the GaAs nucleation to suppress antiphase domains. Bulk minority-carrier lifetimes (τp) were measured using room-temperature time-resolved photoluminescence applied to a series of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As double-heterojunction structures doped n = 1.1×1017 cm−3 with GaAs thicknesses of 0.5, 1.0, and 1.5 μm. A lifetime τp = 7.7 ns was determined for GaAs grown on Si. The extracted interface recombination velocity of 3.9×103 cm/s is comparable to recombination velocities found for Al0.3Ga0.7As/GaAs interfaces grown on both GaAs and Ge wafers, indicating that the crosshatch surface morphology characteristic of strain-relaxed Ge/GeSi surfaces does not impede the formation of high-electronic-quality interfaces. These results hold great promise for future integration of III–V minority-carrier devices with Si wafer technologies. © 1998 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Conducting atomic force microscopy for nanoscale electrical characterization of thin SiO2

Alexander Olbrich, Bernd Ebersberger, and Christian Boit

Appl. Phys. Lett. 73, 3114 (1998); http://dx.doi.org/10.1063/1.122690 (3 pages) | Cited 80 times

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In this work, we demonstrate the applicability of conducting atomic force microscopy (AFM) for the quantitative electrical characterization of thin (3–40 nm) SiO2 films on a nanometer scale length. Fowler–Nordheim (F–N) tunneling currents on the order of 0.02–1 pA are measured simultaneously with the oxide surface topography by applying a voltage between the AFM tip and the silicon substrate. Current variations in the F–N current images are correlated to local variations of the oxide thickness on the order of several angströms to nanometers. From the microscopic current–voltage characteristics the local oxide thickness can be obtained with an accuracy of ±0.3 nm. Local oxide thinning of up to 3.3 nm was found at the edge between gate oxide and field oxide of a metal-oxide-semiconductor capacitor with a 20-nm-thick gate oxide. © 1998 American Institute of Physics.
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73.61.Ng Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films

Millimeter wave generation by a self-sustained current oscillation in an InGaAs/InAlAs superlattice

S. Brandl, E. Schomburg, R. Scheuerer, K. Hofbeck, J. Grenzer, K. F. Renk, D. G. Pavel’ev, Yu. Koschurinov, A. Zhukov, A. Kovsch, V. Ustinov, S. Ivanov, and P. S. Kop’ev

Appl. Phys. Lett. 73, 3117 (1998); http://dx.doi.org/10.1063/1.122691 (3 pages) | Cited 10 times

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We report millimeter wave generation by a self-sustained current oscillation in a doped InGaAs/InAlAS wide miniband superlattice. The superlattice (miniband width 160 meV) showed, at room temperature, a current voltage characteristic with negative differential conductance. Coupled to a high-frequency circuit, the superlattice generated millimeter waves, at a frequency (55 GHz) which was tunable by half a percent by changing the bias voltage. The power (0.3 mW) corresponded to an efficiency (i.e., ratio of microwave power to dc power input) of 0.3%. We attribute the microwave generation to a current oscillation caused by traveling dipole domains. © 1998 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Low-temperature homoepitaxial growth on Si(111) through a Pb monolayer

P. G. Evans, O. D. Dubon, J. F. Chervinsky, F. Spaepen, and J. A. Golovchenko

Appl. Phys. Lett. 73, 3120 (1998); http://dx.doi.org/10.1063/1.122692 (3 pages) | Cited 6 times

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A monolayer of Pb mediates high-quality homoepitaxial growth on Si (111) surfaces at temperatures where growth with other overlayer elements or on bare surfaces leads to amorphous or highly defective crystalline films. Nearly defect-free epitaxy proceeds for film thicknesses up to 1000 Å with no sign that this is an upper limit. The minimum temperature for high-quality epitaxy depends on the substrate miscut. For a 0.2° miscut, the minimum temperature is 340 °C. Films grown on substrates miscut 2.3° towards [112] show good crystalline quality down to 310 °C. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Recombination processes in InxGa1−xN light-emitting diodes studied through optically detected magnetic resonance

E. R. Glaser, T. A. Kennedy, W. E. Carlos, P. P. Ruden, and S. Nakamura

Appl. Phys. Lett. 73, 3123 (1998); http://dx.doi.org/10.1063/1.122693 (3 pages) | Cited 11 times

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Optically detected magnetic resonance (ODMR) has been observed on photoluminescence from InGaN light-emitting diodes (LEDs) under low photoexcitation conditions. The samples have the usual p-i-n structure but without etching or metallizations. Distinct ODMR features from the recombining electron and hole are found with strength that indicates significant charge separation and long lifetimes (>100 ns). The electron and hole g tensors are determined for green and extra-blue LEDs. The recombination is assigned to electrons in the InGaN quantum well (QW) and holes either bound at Mg acceptors outside the well or localized at potential minima in the QW but spatially separated from the electrons. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.60.Jb Light-emitting devices
76.70.Hb Optically detected magnetic resonance (ODMR)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Laplace-transform deep-level transient spectroscopy studies of the G4 gold–hydrogen complex in silicon

P. Deixler, J. Terry, I. D. Hawkins, J. H. Evans-Freeman, A. R. Peaker, L. Rubaldo, D. K. Maude, J.-C. Portal, L. Dobaczewski, K. Bonde Nielsen, A. Nylandsted Larsen, and A. Mesli

Appl. Phys. Lett. 73, 3126 (1998); http://dx.doi.org/10.1063/1.122694 (3 pages) | Cited 13 times

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We have studied n-type silicon containing gold and gold–hydrogen complexes using high-resolution “Laplace” deep-level transient spectroscopy. This technique has enabled two quite distinct electron emission rates to be observed at temperatures between 240 and 300 K. These are associated with the gold acceptor and the level referred to as G4, which is observed when hydrogen and gold are present in silicon. The gold acceptor has a measured activation energy for electron emission of 558±8 meV, and the G4 state of 542±8 meV. The directly measured electron capture cross section for G4 is determined to be 0.6±0.1 σn(gold acceptor) at 275 K from which it is inferred that the state is acceptor-like. © 1998 American Institute of Physics.
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71.55.Cn Elemental semiconductors

Fabrication and room-temperature characterization of a silicon self-assembled quantum-dot transistor

B. H. Choi, S. W. Hwang, I. G. Kim, H. C. Shin, Yong Kim, and E. K. Kim

Appl. Phys. Lett. 73, 3129 (1998); http://dx.doi.org/10.1063/1.122695 (3 pages) | Cited 57 times

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A quantum-dot transistor based on silicon self-assembled quantum dots has been fabricated. The device shows staircases and oscillations in the drain current at room temperature. These data are interpreted as due to single electron tunneling through the dots located in the shortest current path between the source and the drain electrodes. The dot size calculated from the data is ∼7 nm, which is consistent with the size of the self-assembled dots incorporated in the transistor. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Cw Elemental semiconductors

Determination of the concentration and temperature dependence of the fundamental energy gap in AlxIn1−xSb

N. Dai, F. Brown, R. E. Doezema, S. J. Chung, K. J. Goldammer, and M. B. Santos

Appl. Phys. Lett. 73, 3132 (1998); http://dx.doi.org/10.1063/1.122696 (3 pages) | Cited 17 times

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We use transmission spectroscopy to determine the energy gap for the AlxIn1−xSb alloy system in the Al concentration range from 0% to 25% from cryogenic to room temperature. The samples are epitaxial layers grown by molecular beam epitaxy on GaAs substrates. Our room temperature results are compared to those from two earlier studies. In our Al concentration range, we find a linear change of energy gap with alloy lattice constant. © 1998 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Size-quantized CdS films in thin film CuInS2 solar cells

Dori Gal, Gary Hodes, Dimitri Hariskos, Dieter Braunger, and Hans-Werner Schock

Appl. Phys. Lett. 73, 3135 (1998); http://dx.doi.org/10.1063/1.122697 (3 pages) | Cited 8 times

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Semiconductor quantum dots and wires are the subject of great interest, mainly due to their size-dependent electronic structures, in particular increased band gap and therefore optoelectronic properties. We have electrodeposited films of size-quantized CdS (∼4 to 5 nm cross section by 15 nm height) as a buffer layer on CuInS2. The resulting CuInS2/CdS thin-film solar cells gave increased photocurrents and higher light-to-electricity conversion efficiencies (>11%) than those made with conventional nonquantized CdS films. This was due mainly to the increased band gap of the quantized CdS, allowing more light to reach the active CuInS2 layer. © 1998 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Ballistic electron emission microscopy on biased GaAs–AlGaAs superlattices

R. Heer, J. Smoliner, G. Strasser, and E. Gornik

Appl. Phys. Lett. 73, 3138 (1998); http://dx.doi.org/10.1063/1.122698 (3 pages) | Cited 6 times

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In this work, ballistic electron transport through the lowest miniband of a biased GaAs–AlGaAs superlattice is investigated by ballistic electron emission microscopy (BEEM). In the BEEM spectra the miniband manifests itself as clear peak in the second derivative of the ballistic electron current. Biasing the superlattice results in a shift of the miniband position and the corresponding peak position. It is shown that the measured total transmission of the superlattice is in excellent agreement with the calculated transmission, which makes the superlattice a promising tunable energy filter for studying the energetic distribution of ballistic electrons. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
73.50.Fq High-field and nonlinear effects
68.37.Vj Field emission and field-ion microscopy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.20.Ht High-field and nonlinear effects

Measurement of the critical thickness of ZnCdSe quantum wells in ZnSe barrier layers by the piezoelectric effect

J. S. Milnes, C. Morhain, S. A. Telfer, B. Urbaszek, I. Galbraith, K. A. Prior, and B. C. Cavenett

Appl. Phys. Lett. 73, 3141 (1998); http://dx.doi.org/10.1063/1.122699 (3 pages) | Cited 2 times

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The occurrence of the piezoelectric effect in a strained zincblende semiconductor layer grown on an (h11) plane results in an internal electric field which can be observed through the optical properties. We report a study of Zn0.85Cd0.15Se/ZnSe quantum wells grown on (211)B GaAs substrates where the quantum confined Stark effect due to the internal field shifts the luminescence to longer wavelengths provided that the quantum well layer is strained. When the well width is greater than the critical thickness the layer begins to relax and the internal field decreases. We have used these measurements to determine that the critical thickness for the onset of strain relaxation of the Zn0.85Cd0.15Se quantum wells grown on (211) oriented substrates is 20 nm. The method will be applicable to materials such as the nitride semiconductors with wurtzite symmetry. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.20.Jq Electro-optical effects
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
77.65.Ly Strain-induced piezoelectric fields
78.55.Et II-VI semiconductors

Self-organized chain of crystalline-silicon nanospheres

Hideo Kohno and Seiji Takeda

Appl. Phys. Lett. 73, 3144 (1998); http://dx.doi.org/10.1063/1.122700 (3 pages) | Cited 37 times

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We have fabricated a self-organized chain of crystalline-silicon nanospheres via an extension of the vapor-liquid-solid mechanism. Transmission electron microscopy, electron energy-loss spectroscopy, and electron-induced x-ray fluorescence analyses have proved that the crystalline silicon nanospheres, of about 10 nm in diameter and at a nearly equal spacing, are supported in amorphous silica and carbon. The novel self-organized phenomenon is attributed to the periodic instability of catalysts and spontaneous oxidization during the growth of nanowhiskers. © 1998 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
79.20.Kz Other electron-impact emission phenomena
81.05.Cy Elemental semiconductors
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.65.Mq Oxidation

High-transconductance self-aligned AlGaN/GaN modulation-doped field-effect transistors with regrown ohmic contacts

Ching-Hui Chen, Stacia Keller, Gia Parish, Ramakrishna Vetury, Peter Kozodoy, Evelyn L. Hu, Steven P. Denbaars, Umesh K. Mishra, and Yifeng Wu

Appl. Phys. Lett. 73, 3147 (1998); http://dx.doi.org/10.1063/1.122701 (3 pages) | Cited 25 times

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Self-aligned AlGaN/GaN modulation-doped field-effect transistors (MODFETs) with high transconductances have been demonstrated on a sapphire substrate. Source and drain were selectively regrown with ∼1700 Å of n-GaN adjacent to the gate electrode. Source resistance was reduced to 0.95 Ω mm from 1.4 to 1.8 Ω mm with conventional GaN-based MODFETs. These self-aligned devices show a record high value of extrinsic transconductance ∼400 mS/mm for AlGaN/GaN MODFETs with a gate length of 1.2 μm. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ey III-V semiconductors
73.40.Ns Metal-nonmetal contacts

Photoluminescence anisotropy from laterally anodized porous silicon

A. Givant, J. Shappir, and A. Sa’ar

Appl. Phys. Lett. 73, 3150 (1998); http://dx.doi.org/10.1063/1.122702 (3 pages) | Cited 11 times

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We report on a technique to fabricate planar structures of porous silicon using standard photolithography and processing steps. Uniform stripes of porous silicon with smooth interfaces with the surrounding silicon have been observed. Using now the freedom to define the crystallographic direction of the anodization process we studied the correlation between the crystallographic orientation of the porous silicon medium and the polarization selection rules of the emitted light. Our main conclusion is that the polarization selection rules are independent of the crystallographic direction of the porous silicon medium and determined solely by the anodization direction. © 1998 American Institute of Physics.
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78.55.Mb Porous materials
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.05.Rm Porous materials; granular materials

Characteristics of InGaAs quantum dot infrared photodetectors

S. J. Xu, S. J. Chua, T. Mei, X. C. Wang, X. H. Zhang, G. Karunasiri, W. J. Fan, C. H. Wang, J. Jiang, S. Wang, and X. G. Xie

Appl. Phys. Lett. 73, 3153 (1998); http://dx.doi.org/10.1063/1.122703 (3 pages) | Cited 70 times

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A quantum dot infrared photodetector (QDIP) consisting of self-assembled InGaAs quantum dots has been demonstrated. Responsivity of 3.25 mA/W at 9.2 μm was obtained for nonpolarized incident light on the detector with a 45° angle facet at 60 K. The QDIPs exhibit some unique electro-optic characteristics such as a strong negative differential photoconductance effect and blueshift of the response peak wavelength. © 1998 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
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