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25 Nov 2002

Volume 81, Issue 22, pp. 4103-4293

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Silicon tip arrays with ultrathin amorphous diamond apexes

J. C. She, N. S. Xu, S. E. Huq, S. Z. Deng, and Jun Chen

Appl. Phys. Lett. 81, 4257 (2002); http://dx.doi.org/10.1063/1.1525061 (3 pages) | Cited 11 times

Online Publication Date: 19 November 2002

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Silicon (Si) tip emitter arrays with uniform, smooth, and ultrathin (∼2 nm) amorphous diamond (a-D) apexes were fabricated. Aqueous buffer hydrofluoric acid and H2/Ar plasma have been employed to remove the native oxide layer of Si tips, prior to the a-D film deposition. Scanning electron microscopy study showed that uniform a-D coatings were highly localized on the apex of individual Si tips. Study using high-resolution transmission electron microscopy and x-ray energy dispersive spectroscopy confirmed that the Si/a-D junction is free from the oxide interlayer. Field-emission measurements demonstrated that the removal of the native oxide layer and the a-D apex coating are important to stabilize and enhance the electron emission from Si field emitters. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials
81.15.Rs Spray coating techniques
81.65.-b Surface treatments

Organic polymeric thin-film transistors fabricated by selective dewetting

Michael L. Chabinyc, William S. Wong, Alberto Salleo, Kateri E. Paul, and Robert A. Street

Appl. Phys. Lett. 81, 4260 (2002); http://dx.doi.org/10.1063/1.1524301 (3 pages) | Cited 30 times

Online Publication Date: 19 November 2002

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Thin-film transistors (TFTs) of polymeric semiconductors were fabricated using selective dewetting in the patterning process. The process consists of: (i) patterning the wettability of the substrate using a protective layer of printed wax and a self-assembled monolayer, and (ii) patterning a polymeric semiconductor by selective dewetting from an organic solution. The method has been used to fabricate small arrays of TFTs with a regioregular poly(thiophene) and poly(9-9′-dioctyl-fluorene-co-bithiophene). The TFTs exhibited mobilities of 0.5–1.0×10−3 cm2 V−1 s−1 and on-to-off ratios on the order of 104. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
81.65.-b Surface treatments
68.08.Bc Wetting
73.50.Dn Low-field transport and mobility; piezoresistance

Planar GaN n+–p photodetectors formed by Si implantation into p-GaN

J. K. Sheu, M. L. Lee, L. S. Yeh, C. J. Kao, C. J. Tun, M. G. Chen, G. C. Chi, S. J. Chang, Y. K. Su, and C. T. Lee

Appl. Phys. Lett. 81, 4263 (2002); http://dx.doi.org/10.1063/1.1524689 (3 pages) | Cited 21 times

Online Publication Date: 19 November 2002

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GaN n+–p junction diodes were fabricated by implanting Si atoms into p-GaN. It was shown that we could use these diodes as GaN-based planar photodetectors. It was found that the dark current density of the diodes was around 1.5 μA/cm2 and 50 nA/cm2 at reverse biases of 3 and 1 V, respectively. Spectra response measurements revealed a cutoff wavelength at around 365 nm and a peak responsivity of 0.33 mA/W at 365 nm for the GaN planar n+–p photodetectors. It was also found that the visible rejection ratio was around 260. Furthermore, temporal response measurements revealed that the fall times of these GaN planar n+–p photodetectors were found to be shorter than 0.4 μs. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.uj III-V and II-VI semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Nitrogen passivation of deposited oxides on n 4H–SiC

G. Y. Chung, J. R. Williams, T. Isaacs-Smith, F. Ren, K. McDonald, and L. C. Feldman

Appl. Phys. Lett. 81, 4266 (2002); http://dx.doi.org/10.1063/1.1525058 (3 pages) | Cited 4 times

Online Publication Date: 19 November 2002

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Results for measurements of interface state density and breakdown field strength are reported for deposited oxides on n 4H–SiC following passivation with nitric oxide. Low-temperature oxides deposited by plasma-enhanced chemical vapor deposition and high-temperature oxides deposited at 950 °C were investigated. Nitrogen passivation of deposited oxides on n 4H–SiC is found to produce interface state densities of 1–2×1012 cm−2 eV−1 at Ec−E = 0.1 eV, regardless of variations in oxide deposition procedures that affect the residual interfacial carbon concentration. Breakdown field strengths were higher for passivated high-temperature oxides compared to passivated low-temperature oxides at room temperature and 290 °C. We suggest that additional oxide growth during the NO passivation is the reason for the observed interface state densities. © 2002 American Institute of Physics.
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81.65.Rv Passivation
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Jp Dielectric breakdown and space-charge effects
73.20.At Surface states, band structure, electron density of states

Polymer-based red, green, and blue emitting devices fabricated by reductive photopatterning

Gernot Trattnig, Alexander Pogantsch, Gregor Langer, Wolfgang Kern, and Egbert Zojer

Appl. Phys. Lett. 81, 4269 (2002); http://dx.doi.org/10.1063/1.1524703 (3 pages) | Cited 11 times

Online Publication Date: 19 November 2002

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Using a color tuning approach reliant on reductive photopatterning, we present red-green-blue electroluminescence from a single layer polymer light-emitting device. To be able to cover the full color range, we employ a single emissive layer consisting of a blue emitter (the host polymer), as well as green and red emitting guest polymers. The energy transfer between the host and the various guest compounds is tuned via a reductive photoinitiated process in the presence of gaseous hydrazine. This process is compatible with regular film casting techniques such as spin coating, and therefore can be regarded as a promising alternative to the more complex, traditional patterning approaches. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.Cd Conducting polymers
82.50.Hp Processes caused by visible and UV light
82.35.Jk Copolymers, phase transitions, structure

Enhanced photoconductive gain in quantum-well infrared photodetectors

M. A. Gadir, P. Harrison, and R. A. Soref

Appl. Phys. Lett. 81, 4272 (2002); http://dx.doi.org/10.1063/1.1525055 (3 pages) | Cited 4 times

Online Publication Date: 19 November 2002

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A quantum-mechanical scattering theory approach is taken to evaluate the capture probability from the continuum into the quantum wells in quantum-well infrared photodetectors. The calculations show that the capture probability is dependent on the well width, the barrier height, and bias. An additional tunnel barrier is introduced to disturb the continuum levels near the top of the quantum well. It is shown that this can be optimized to reduce the capture probability and thus increase the photoconductive gain of the device. © 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
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
73.63.Hs Quantum wells

Higher efficiency InGaN laser diodes with an improved quantum well capping configuration

M. Hansen, J. Piprek, P. M. Pattison, J. S. Speck, S. Nakamura, and S. P. DenBaars

Appl. Phys. Lett. 81, 4275 (2002); http://dx.doi.org/10.1063/1.1524690 (3 pages) | Cited 24 times

Online Publication Date: 19 November 2002

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A thin AlGaN cap is typically employed above the multiple quantum wells of InGaN-based lasers to prevent electron overflow from the active region and to protect the InGaN active region from the high temperature growth of subsequent p-type layers. The growth conditions and placement of this cap can significantly affect the efficiency and operating characteristics of laser diodes. A 200 Å Al0.2Ga0.8N:Mg cap was placed above the last barrier of a three quantum well (QW) laser diode, as well as directly above the last QW. Lasers with the cap above the last QW exhibit a lower threshold current and a higher internal quantum efficiency than lasers with the cap above the last barrier. The internal quantum efficiency nearly doubles from 16.6% for lasers with the cap above the last barrier to 34.7% for the cap above the last QW. The improvement in efficiency from moving the cap to the last QW is attributed to electrons falling into the last QW and participating in radiative recombination, instead of nonradiative recombination at dislocation sites of the last barrier, or recombining radiatively at the barrier wavelength, rather than at the laser emission wavelength. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems
73.21.Cd Superlattices

Phosphorescent light-emitting electrochemical cell

Fang-Chung Chen, Yang Yang, and Qibing Pei

Appl. Phys. Lett. 81, 4278 (2002); http://dx.doi.org/10.1063/1.1525881 (3 pages) | Cited 24 times

Online Publication Date: 19 November 2002

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Due to the harvest of singlet and triplet excitons, highly-efficient phosphorescent polymer light-emitting diodes have been demonstrated. However, the driving voltage of these devices remains high because of the carrier trapping at the dopant sites. To achieve high power efficiency, a phosphorescent light-emitting electrochemical cell, which consists of bis[2-(2′-benzothienyl)-pyridinato-N,C3′]iridium(acetylacetonate) as the dopant, poly[9,9-bis(3,6-dioxaheptyl)-fluorene-2,7-diyl] as the host polymer, and lithium trifluoromethane sulfonate has been demonstrated in this letter. The turn-on voltage for light emission was as low as the band gap of the host material (2.8 eV). Compared with the light-emitting diode with a similar device structure, a sixfold enhancement in power efficiency has been achieved. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.47.-a Applied electrochemistry
71.35.-y Excitons and related phenomena
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
78.55.Kz Solid organic materials

Heterojunction diode fabrication from polyaniline and a ferroelectric polymer

B. Xu, Y. Ovchenkov, M. Bai, A. N. Caruso, A. V. Sorokin, Stephen Ducharme, B. Doudin, and P. A. Dowben

Appl. Phys. Lett. 81, 4281 (2002); http://dx.doi.org/10.1063/1.1524695 (3 pages) | Cited 11 times

Online Publication Date: 19 November 2002

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We have fabricated a p–n heterojunction diode by vapor depositing a thin film of polyaniline on top of the crystalline copolymer: poly(vinylidene fluoride with trifluoroethylene). The formation of a diode is expected from the band offsets of the two polymers near the Fermi level. The interface between the two components was investigated, and an abrupt interface was found that is very different from the inorganic analog. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
73.61.Ph Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
71.20.Rv Polymers and organic compounds

Magnetically and electrically tunable semiconductor quantum waveguide inverter

M. J. Gilbert, R. Akis, and D. K. Ferry

Appl. Phys. Lett. 81, 4284 (2002); http://dx.doi.org/10.1063/1.1525073 (3 pages) | Cited 10 times

Online Publication Date: 19 November 2002

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In recent years, quantum computing and information theory has received a great deal of attention as a means of drastically improving the computational speed and resources traditionally associated with current binary implementations. We present an electrically tunable semiconductor quantum waveguide implementation of an inverter gate in a GaAs/AlGaAs heterostructure in which the output of the waveguide structure may be selected via the application of an appropriate magnetic field or electrical bias. The resulting behavior observed by our implementation shows a great deal of promise for an eventual semiconductor realization of this basic qubit structure. © 2002 American Institute of Physics.
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85.35.Ds Quantum interference devices
03.67.Lx Quantum computation architectures and implementations
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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