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6 May 2002

Volume 80, Issue 18, pp. 3247-3450

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High-sensitivity quantum Hall far-infrared photodetector integrated with log-periodic antenna

Y. Kawaguchi, K. Hirakawa, and S. Komiyama

Appl. Phys. Lett. 80, 3418 (2002); http://dx.doi.org/10.1063/1.1476061 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2002

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We have developed a high sensitivity far-infrared (FIR) photodetector by using the two-dimensional electron gas system in modulation-doped Al0.3Ga0.7As/GaAs heterojunctions. A FIR-sensitive channel was formed by applying a negative bias voltage to the split gates which were integrated with a log-periodic antenna. Although the area of sensitivity was small (850×850 μm2), the responsivity reached as high as 5.8×104 V/W. It is also demonstrated that the responsivity can be modulated by a factor of 10 by changing the split-gate voltages. The capability of ON/OFF switching of photoresponsivity suggests that this detector is suitable for realizing high sensitivity FIR imaging arrays. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.43.-f Quantum Hall effects

Charge retention in metal–oxide–semiconductor capacitors on SiC used as nonvolatile-memory elements

Sima Dimitrijev, Kuan Yew Cheong, Jisheng Han, and H. Barry Harrison

Appl. Phys. Lett. 80, 3421 (2002); http://dx.doi.org/10.1063/1.1476060 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2002

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In this letter, the possibility of using metal–oxide–semiconductor capacitors on SiC as nonvolatile random-access memory elements has been experimentally investigated. Because of the wide energy gap and the very low minority-carrier generation rate in SiC, it should be possible to achieve very long retention times. The investigations show that charge leakage through the gate oxide may prevent the use of SiC metal–oxide–semiconductor (MOS) capacitors as memory elements. Importantly, the experiments demonstrate that both the charge leakage and carrier-generation rate are low in the case of nitrided SiO2–SiC interfaces. The retention time extrapolated to room temperature is in the order of 109 years for the case of MOS capacitors on 4H–SiC, which is approximately equal to the theoretical limit. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Piezoelectric and electrostrictive strain behavior of Ce-doped BaTiO3 ceramics

Chen Ang, Zhi Yu, Zhi Jing, Ruyan Guo, A. S. Bhalla, and L. E. Cross

Appl. Phys. Lett. 80, 3424 (2002); http://dx.doi.org/10.1063/1.1473871 (3 pages) | Cited 29 times

Online Publication Date: 29 April 2002

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The ferroelectric and strain behavior of the Ba(Ti1−yCey)O3 solid solutions was studied. Three phase transition temperatures were shifted with increasing Ce concentration, and pinched at y = 0.06. The samples could be structurally indexed by x-ray diffraction in a tetragonal symmetry at y ⩽ 0.06; and in a pseudo-cubic symmetry at y>0.06. The strain levels in the range of 0.15–0.19% at ∼60 kV/cm with small hysteresis were obtained for the samples with low content Ce. With increasing Ce concentration, the tetragonality decreases, the strain level decreases, and becomes less hysteretic. The physical mechanism of the electrostrictive, piezoelectric, and ferroelectric-relaxor behavior is briefly discussed. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Ly Strain-induced piezoelectric fields
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
61.66.Fn Inorganic compounds

Tunable, monochromatic x rays using the internal beam of a betatron

V. V. Kaplin, S. R. Uglov, O. F. Bulaev, V. J. Goncharov, A. A. Voronin, M. A. Piestrup, C. K. Gary, N. N. Nasonov, and M. K. Fuller

Appl. Phys. Lett. 80, 3427 (2002); http://dx.doi.org/10.1063/1.1475360 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2002

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Tunable, monochromatic x rays from thin radiators mounted inside a betatron have been observed. Parametric x-ray radiation (PXR) was generated by 33-MeV electrons passing multiple times through three radiators: a 43-μm-thick Si crystal, a 400-μm-thick graphite crystal, or a 310-layered-pair (W and B4C, d = 14.86 Å) multilayer. The pulse-height spectrum of the radiation (5 to 30 keV) was obtained and was tuned by rocking the crystal or multilayer relative to the electron-beam direction. The experimental results appear to follow theoretical predictions for PXR emission with some modification required for the curved trajectory of the electrons. © 2002 American Institute of Physics.
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29.20.df Betatrons
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
41.75.Fr Electron and positron beams
29.27.Eg Beam handling; beam transport
41.85.-p Beam optics

Influence of temperature and drive current on degradation mechanisms in organic light-emitting diodes

Masahiko Ishii and Yasunori Taga

Appl. Phys. Lett. 80, 3430 (2002); http://dx.doi.org/10.1063/1.1476704 (3 pages) | Cited 39 times

Online Publication Date: 29 April 2002

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We measured luminance decay and half life for green organic light-emitting diodes composed of materials with high glass transition temperature. The devices were driven at dc, constant current density ranging from 3.8 to 130 mA/cm2 at 25, 85, and 120 °C. The shapes of the luminance decay curves were compared by redrawing the curves on a time scale normalized by each half life. Temperature and drive current shortened the half life. However, the normalized decay curve of the device driven at 120 °C had the same shape as that of the device driven at 25 °C. Drive current also left the shape of the decay curves unchanged. Therefore, we conclude that the temperature and drive current do not change the relative contribution of multiple degradation mechanisms. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Resonant detection of subterahertz radiation by plasma waves in a submicron field-effect transistor

W. Knap, Y. Deng, S. Rumyantsev, J.-Q. Lü, M. S. Shur, C. A. Saylor, and L. C. Brunel

Appl. Phys. Lett. 80, 3433 (2002); http://dx.doi.org/10.1063/1.1473685 (3 pages) | Cited 73 times

Online Publication Date: 29 April 2002

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The resonant detection of subterahertz radiation by two-dimensional electron plasma confined in a submicron gate GaAs/AlGaAs field-effect transistor is demonstrated. The results show that the critical parameter that governs the sensitivity of the resonant detection is ωτ, where ω is the radiation frequency and τ is the momentum scattering time. By lowering the temperature and hence increasing τ and increasing the detection frequency ω, we reached ωτ ∼ 1 and observed resonant detection of 600 GHz radiation in a 0.15 μm gate length GaAs field-effect transistor. The evolution of the observed photoresponse signal with temperature and frequency is reproduced well within the framework of a theoretical model. © 2002 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.30.Tv Field effect devices
72.40.+w Photoconduction and photovoltaic effects

Effects of wet-oxidation treatment on Al0.45Ga0.55As/GaAs graded-like superlattice-emitter bipolar transistor with low turn-on voltage

Wen-Shiung Lour, Yen-Wei Wu, Shih-Wei Tan, Ming-Kwen Tsai, and Ying-Jay Yang

Appl. Phys. Lett. 80, 3436 (2002); http://dx.doi.org/10.1063/1.1473861 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2002

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We report an AlxGa1−xAs/GaAs heterojunction bipolar transistor (HBT) with a high Al mole fraction of x = 0.45. A digital graded superlattice emitter, forming a step-wise graded composition, is used to smooth out the potential spike resulting from a large conduction-band offset. HBT’s with such a digital graded emitter as a passivation layer exhibit a small offset voltage of 55 mV, a low turn-on voltage of 0.87 V and a current gain as high as 400. Effects of wet-oxidation treatment on fabricated HBT’s are also investigated. Experimental results reveal that the studied HBT’s exhibit reduced collector currents at a fixed base current in the early stage of the wet-oxidation treatment. However, better surface passivation and higher current gain are available after an appropriate wet-oxidation treatment is used to reduce base current. We qualitatively modeled these behaviors by introducing a concept of built-in field along the graded emitter. © 2002 American Institute of Physics.
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85.30.Pq Bipolar transistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Cd Superlattices
81.65.Mq Oxidation
81.65.Rv Passivation
85.30.De Semiconductor-device characterization, design, and modeling
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electrical properties of amorphous silicon carbide films

N. Biswas, X. Wang, and S. Gangopadhyay

Appl. Phys. Lett. 80, 3439 (2002); http://dx.doi.org/10.1063/1.1476389 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2002

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The interfacial properties of silicon carbide films on silicon substrate, using capacitance–voltage (C–V) and conductance–voltage techniques have been studied. The C–V characteristics observed largely depended on processing conditions. An interface state density of 2.38×1010 eV−1 cm−2 at the midgap was calculated for this sample. When CF4 was added to the precursors, the C–V curves were observed to have a “ledge” at the end of the accumulation region, indicative of the presence of additional localized defect states that respond to the applied ac signal. An interface state density of 2.11×1011 eV−1 cm−2 at the midgap was observed for this sample. However fluorination in plasma caused the etching of the weak bond, and hence a reduction in the fixed charge density and hysteresis. © 2002 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
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