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23 Jun 2003

Volume 82, Issue 25, pp. 4411-4611

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages)

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin
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Variable coupling in n-type silicon–germanium double quantum dots

Andrew J. Ferguson, David G. Hasko, H. Ahmed, and David A. Williams

Appl. Phys. Lett. 82, 4492 (2003); http://dx.doi.org/10.1063/1.1577826 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2003

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We report low-temperature electron transport behavior of trench-isolated silicon–germanium (SiGe) double quantum dots. By sweeping the potentials on side gates, we find a hexagonal charging diagram in the conductance measurements. It is also found that the gates allow the parameters of individual tunnel barriers to be changed over a wide range. Charging effects may therefore be observed in different coupling regimes, for example, the two dots that comprise the double dot can be induced to merge together yielding a large single dot. © 2003 American Institute of Physics.
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73.63.Kv Quantum dots

Pyronin B as a donor for n-type doping of organic thin films

A. G. Werner, F. Li, K. Harada, M. Pfeiffer, T. Fritz, and K. Leo

Appl. Phys. Lett. 82, 4495 (2003); http://dx.doi.org/10.1063/1.1583872 (3 pages) | Cited 57 times

Online Publication Date: 16 June 2003

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We present an approach to stable n-type doping of organic matrices using organic dopands. To circumvent stability limitations inherent in strong organic donors, we produce the donor from a stable precursor compound in situ. As an example, pyronin B chloride is studied as a dopant in a 1,4,5,8-naphthalene tetracarboxylic dianhydride matrix. Conductivities up to 2×10−4 S/cm are obtained, which is two orders of magnitude higher than obtained previously using bis(ethylenedithio)-tetrathiafulvalene as a dopant [A. Nollau, M. Pfeiffer, T. Fritz, and K. Leo, J. Appl. Phys. 87, 4340 (2000)]. Field-effect measurements are used to prove n-type conduction. Other matrices which can be doped are N,N′-dimethyl-perylene-3,4,9,10-tetracarboxylic diimide and fullerene C60, frequently used in organic solar cells. Visible light and Fourier-transform infrared spectroscopy confirm the donor properties of pyronin B. © 2003 American Institute of Physics.
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61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.40.Me Organic compounds and polymers
78.30.Jw Organic compounds, polymers

Ballistic electron emission luminescence

Ian Appelbaum, K. J. Russell, V. Narayanamurti, D. J. Monsma, C. M. Marcus, M. P. Hanson, A. C. Gossard, H. Temkin, and C. H. Perry

Appl. Phys. Lett. 82, 4498 (2003); http://dx.doi.org/10.1063/1.1584524 (3 pages) | Cited 14 times

Online Publication Date: 16 June 2003

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We describe the design, fabrication, and operation of a GaAs-based heterostructure device which emits band gap luminescence from solid-state tunnel-junction ballistic injection of electrons with sub-bandgap energy. We find that, due to energy conservation requirements, a collector bias exceeding a threshold determined by the Schottky barrier height and sample band gap energy must be applied for luminescence emission. The consequences of these results for a hybrid scanning-probe microscopy and spectroscopy combining both ballistic electron emission microscopy and scanning tunneling luminescence are emphasized. © 2003 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
73.30.+y Surface double layers, Schottky barriers, and work functions
78.60.Fi Electroluminescence
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Exciton and carrier motion in quaternary AlInGaN

K. Kazlauskas, G. Tamulaitis, A. Žukauskas, M. A. Khan, J. W. Yang, J. Zhang, E. Kuokstis, G. Simin, M. S. Shur, and R. Gaska

Appl. Phys. Lett. 82, 4501 (2003); http://dx.doi.org/10.1063/1.1586782 (3 pages) | Cited 15 times

Online Publication Date: 16 June 2003

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Temperature and excitation power dependences of the photoluminescence Stokes shift and bandwidth were studied in quaternary AlInGaN epilayers as a function of indium content. At low excitation power, gradual incorporation of indium into AlGaN is shown to result in S- and W-shaped temperature dependences of the band peak position and bandwidth, respectively. At high excitation power, the S- and W-behavior disappears; however, increased indium molar fraction boosts the redshift of the luminescence band at high temperatures. Our results indicate that the incorporation of indium into AlGaN has a noticeable impact on the alloy transport properties. At low temperatures and low excitation power, the indium incorporation facilitates hopping of localized excitons, whereas at high temperatures and high excitation power, it sustains free motion of delocalized carriers that results in the band-gap renormalization via screening. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
73.50.Dn Low-field transport and mobility; piezoresistance

Effect of surface treatment on leakage current of GaAs/AlGaAs laser microcavities

Jun-Youn Kim, Jawoong Lee, Jungyeon Kim, Bongkoo Kang, and O’Dae Kwon

Appl. Phys. Lett. 82, 4504 (2003); http://dx.doi.org/10.1063/1.1584784 (3 pages) | Cited 6 times

Online Publication Date: 16 June 2003

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The effect of surface treatment on leakage current is investigated for two structures of the electropumped GaAs/AlGaAs laser microcavities, one with mesa and the other with hyperboloid-drum structures. Using surface sheet resistivity as a figure-of-merit parameter, the results of different surface treatment methods are compared. The best result is obtained when the sample has been polished in a H2SO4:H2O2:H2O = 1:8:1000 solution for 5 s, and treated subsequently in a 6% excess sulfur-containing (NH4)2Sx solution at 60 °C for 8 mins. The treatment in (NH4)2Sx solution increases the surface sheet resistivity by a factor of ∼14. The cross-sectional shape of the cavity and the vertical profile of distributed Bragg reflector mirrors have little correlation with the leakage current. © 2003 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
81.05.Ea III-V semiconductors
81.65.Ps Polishing, grinding, surface finishing
73.25.+i Surface conductivity and carrier phenomena
68.47.Fg Semiconductor surfaces
42.86.+b Optical workshop techniques
68.35.B- Structure of clean surfaces (and surface reconstruction)
42.79.Bh Lenses, prisms and mirrors

High tunnel magnetoresistance in epitaxial Fe/MgO/Fe tunnel junctions

J. Faure-Vincent, C. Tiusan, E. Jouguelet, F. Canet, M. Sajieddine, C. Bellouard, E. Popova, M. Hehn, F. Montaigne, and A. Schuhl

Appl. Phys. Lett. 82, 4507 (2003); http://dx.doi.org/10.1063/1.1586785 (3 pages) | Cited 85 times

Online Publication Date: 16 June 2003

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We report on spin-polarized tunneling in fully epitaxial Fe/MgO/Fe/Co tunnel junctions. By increasing the thickness of the insulating layer (tMgO), we have strongly enhanced the tunnel magnetoresistance. Values up to ∼100% at 80 K (∼67% at room temperature) have been observed with tMgO = 2.5 nm. This tunnel magnetoresistance ratio, which is much larger than the one predicted by the Jullière’s model, can be understood in the framework of ab initio calculations. © 2003 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Bb Fe and its alloys

Physical explanation of the barrier height temperature dependence in metal-oxide-semiconductor leakage current models

Dietmar Schroeder and Alejandro Avellán

Appl. Phys. Lett. 82, 4510 (2003); http://dx.doi.org/10.1063/1.1587256 (3 pages) | Cited 2 times

Online Publication Date: 16 June 2003

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A temperature dependence of the barrier height between silicon and oxide has been proposed by many authors in order to reflect experimental metal-oxide-semiconductor leakage current results. However, no satisfactory physical explanation of this dependence has yet been given. In this letter, the temperature dependence of the observed macroscopic barrier height is explained by thermal fluctuations of the microscopic local barrier height. Because of the exponential relationship between current and barrier height, the decrease of the barrier during the fluctuation has a dominating effect when compared to the increase, leading on the average to a raised leakage current and correspondingly to a lowered average barrier height. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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