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14 Oct 2002

Volume 81, Issue 16, pp. 2917-3103

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Comparative study of drain-current collapse in AlGaN/GaN high-electron-mobility transistors on sapphire and semi-insulating SiC

S. Arulkumaran, T. Egawa, H. Ishikawa, and T. Jimbo

Appl. Phys. Lett. 81, 3073 (2002); http://dx.doi.org/10.1063/1.1512820 (3 pages) | Cited 27 times

Online Publication Date: 7 October 2002

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The drain-current collapse at high drain voltage has been studied in AlGaN/GaN high-electron-mobility transistors (HEMTs) on both semi-insulating (SI)–SiC and sapphire substrates using small frequency (120 Hz) sinusoidal wave superimposed dc IDS–VDS characteristics. Low drain-current collapses were observed in AlGaN/GaN HEMTs on SI–SiC substrate when compared with the HEMTs on sapphire substrates. Two and three thermally activated deep traps were observed on SiC-based and sapphire-based HEMTs, respectively. The existence of an additional deep trap (ΔE = 0.61 eV) could be associated with the material defects/ dislocations responsible for the severe drain current collapse in sapphire-based HEMTs. The white-light illuminated IDS–VDS characteristics support the existence of more number of deep traps in the sapphire-based HEMTs. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
71.55.Eq III-V semiconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Electron emission from GaN n–p junctions

Jonathan L. Shaw, Randolph E. Treece, Dinesh Patel, Carmen S. Menoni, Jim R. Smith, and J. I. Pankove

Appl. Phys. Lett. 81, 3076 (2002); http://dx.doi.org/10.1063/1.1514824 (3 pages) | Cited 2 times

Online Publication Date: 7 October 2002

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We report on electron emission from cesiated GaN n–p junctions in forward bias. Surface electric fields ∼ 3 V/μm caused a fivefold increase in emission current. Initial maximum currents in excess of 200 nA degrade to 50 nA due to charge trapping but are quickly recovered at zero bias. Energy spectra confirm negative electron affinity 80 h after cesiation, indicate resistive losses limit the emission current, and reveal significant emission at energies above the Fermi level of the injecting contact. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Cg Contact resistance, contact potential
73.25.+i Surface conductivity and carrier phenomena
73.20.-r Electron states at surfaces and interfaces

Vapor sensing with α,ω-dihexylquarterthiophene field-effect transistors: The role of grain boundaries

Takao Someya, Howard E. Katz, Alan Gelperin, Andrew J. Lovinger, and Ananth Dodabalapur

Appl. Phys. Lett. 81, 3079 (2002); http://dx.doi.org/10.1063/1.1514826 (3 pages) | Cited 53 times

Online Publication Date: 7 October 2002

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We have investigated the channel-length dependence of responses to a vapor analyte with a series of α,ω-dihexylquarterthiophene (DHα4T) field-effect transistors (FETs). Single-crystalline DHα4T devices deposited by vacuum sublimation at substrate temperatures of 70 °C are compared with polycrystalline DHα4T films deposited at room temperature. By changing the length of FET channels and/or the size of polymer grains, the number of grain boundaries per device is changed systematically. A larger response to vapor analyte is obtained by increasing the number of grain boundaries per device, showing that vapor sensing occurs mainly at grain boundaries. © 2002 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
61.72.Mm Grain and twin boundaries
85.65.+h Molecular electronic devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Impact of the channel thickness on the performance of Schottky barrier metal–oxide–semiconductor field-effect transistors

J. Knoch and J. Appenzeller

Appl. Phys. Lett. 81, 3082 (2002); http://dx.doi.org/10.1063/1.1513657 (3 pages) | Cited 38 times

Online Publication Date: 7 October 2002

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We present quantum simulations of single-gated Schottky barrier metal–oxide–semiconductor field-effect transistors on ultrathin silicon on insulator. The electrostatics of such devices is investigated and the influence of the silicon thickness on the Schottky barriers at the source and drain and, thus, the influence on the current–voltage characteristics are elaborated. We show that decreasing the channel layer thickness leads to a strong reduction of the Schottky barrier thickness and thus to an increased gate control of the drain current. The use of ultrathin channel layers improves the off- as well as the on state of such transistors and results in electrical characteristics comparable with conventional metal–oxide–semiconductor field-effect transistors. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Polymer—perylene diimide heterojunction solar cells

A. J. Breeze, A. Salomon, D. S. Ginley, B. A. Gregg, H. Tillmann, and H.-H. Hörhold

Appl. Phys. Lett. 81, 3085 (2002); http://dx.doi.org/10.1063/1.1515362 (3 pages) | Cited 55 times

Online Publication Date: 7 October 2002

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Thin-film small molecule/polymer hybrid bilayer photovoltaic cells have been constructed, exhibiting power conversion efficiencies of 0.71% under 80 mW/cm2 white light illumination. The parameters influencing the photovoltage of these devices are explored by reversing the order of the photoactive layers while maintaining the same electrode configuration. It has been found that the properties of the organic photoactive layers play an important role in determining the direction of current flow and the photovoltage of the device. Comparison is made to analogous pure small molecule bilayer devices, and conclusions about some of the factors influencing device efficiency are drawn. It has been shown that ordering of the band offsets of the two organic materials plays an important role in determining the polarity of the photocurrent and the photovoltage of the device. © 2002 American Institute of Physics.
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84.60.Jt Photoelectric conversion
78.66.Qn Polymers; organic compounds

Near-infrared electroluminescence in polymer composites based on organic nanocrystals

Eugene I. Maltsev, Dmitry A. Lypenko, Vladimir V. Bobinkin, Alek R. Tameev, Sergey V. Kirillov, Boris I. Shapiro, Herman F. M. Schoo, and Anatoly V. Vannikov

Appl. Phys. Lett. 81, 3088 (2002); http://dx.doi.org/10.1063/1.1515880 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2002

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IR electroluminescence was revealed in single-layer light-emitting diodes based on a type of electroactive polymer nanocomposites-electron-hole conducting aromatic polyimide and organic nanocrystalline particles of cyanine molecules, known as J-aggregates. These materials exhibit a very narrow emission band with a maximum at 815 nm. Dramatic increase of charge-carrier mobility was observed for these layers containing the J-aggregate nanocrystalline phase. © 2002 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
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