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1 Mar 2004

Volume 84, Issue 9, pp. 1435-1613

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages)

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber
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Anomalous charge transport behavior of Fullerene based diodes

G. J. Matt, N. S. Sariciftci, and T. Fromherz

Appl. Phys. Lett. 84, 1570 (2004); http://dx.doi.org/10.1063/1.1651642 (3 pages) | Cited 14 times

Online Publication Date: 25 February 2004

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We observed an anomalous voltage–current (V–I) characteristics of fullerene based diodes in the low temperature regime. The diodes exhibit a negative differential resistance and voltage hysteresis for opposite current sweep directions. This behavior is directly observable at temperatures below 95 K and indicates the formation of highly conductive filaments in the fullerene thin films. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
77.80.Dj Domain structure; hysteresis

Thin-film field-effect transistors based on La-doped SrTiO3 heterostructures

Feng Pan, David Olaya, John C. Price, and Charles T. Rogers

Appl. Phys. Lett. 84, 1573 (2004); http://dx.doi.org/10.1063/1.1651647 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2004

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Field-effect transistors have been fabricated from epitaxial perovskite strontium titanate heterostructures. Lanthanum-doped SrTiO3 was used as the semiconducting channel while insulating SrTiO3 was used as a gate insulator. Both depletion and accumulation effects in the channel have been studied from 300 to 4 K. Hall effect measurements indicate a temperature independent n-type carrier density around 5×1019 cm−3. At 300 K, typical mobilities are 2–3 cm2 V−1 s−1 while low temperature mobilities are as high as 15 cm2 V−1 s−1. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electron-beam-induced current observed for dislocations in diffused 4H-SiC P–N diodes

S. Maximenko, S. Soloviev, D. Cherednichenko, and T. Sudarshan

Appl. Phys. Lett. 84, 1576 (2004); http://dx.doi.org/10.1063/1.1652229 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2004

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The electron-beam-induced current (EBIC) method was employed to investigate the electrical activity of dislocations in silicon carbide Schottky and diffused p–n diodes. Dislocations in Schottky diodes appear as dark spots with the EBIC current signal at the dislocations reduced with respect to the background. However, in p–n diodes, the same dislocations exhibited characteristic bright halos, with the EBIC current higher than that of the background. These bright halos were attributed to a nonuniform impurity distribution around dislocations caused by the high-temperature (∼2000 °C) diffusion process. © 2004 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
66.30.Lw Diffusion of other defects
85.30.Kk Junction diodes

Bulk-acoustic waves radiated from low-loss surface-acoustic-wave resonators

J. V. Knuuttila, J. J. Vartiainen, J. Koskela, V. P. Plessky, C. S. Hartmann, and M. M. Salomaa

Appl. Phys. Lett. 84, 1579 (2004); http://dx.doi.org/10.1063/1.1650557 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2004

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The bulk-acoustic conductance in low-loss surface-acoustic-wave filters utilizing leaky surface-acoustic waves is significant for the device operation. Here we directly measure the bulk acoustic wave radiation pattern on the backside of the piezoelectric substrate with the help of a scanning laser-interferometer probe. For the case studied, a leaky surface-acoustic wave resonator on 36°YX–LiTaO3, a numerical calculation is carried out and the different bulk-wave modes arriving at the substrate bottom are identified by comparing the measured and computed energy-flow angles. The results are expected to lead to improved models for describing the operation of low-loss surface-acoustic-wave filters. © 2004 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics

Organic thin-film transistors fabricated by microcontact printing

M. Leufgen, A. Lebib, T. Muck, U. Bass, V. Wagner, T. Borzenko, G. Schmidt, J. Geurts, and L. W. Molenkamp

Appl. Phys. Lett. 84, 1582 (2004); http://dx.doi.org/10.1063/1.1652233 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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We have fabricated organic thin-film transistors (OTFTs) using a microcontact printing technique (μCP) that employs thin polydimethylsiloxane stamps on a rigid silicon substrate in order to reduce macroscopic distortions. Systematic variation of the printing pressure, printing time, and concentration of eicosanethiol, the “molecular ink” in the μCP process, permits the fabrication of devices with smaller channel lengths (Leff) than nominally defined by the stamp. Interdigitated Ti/Au electrode structures with Leff down to 100 nm could be fabricated which, after additional surface treatment and vacuum deposition of αα′-dihexylquaterthiophene, yield OTFTs with excellent characteristics. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Ps Polishing, grinding, surface finishing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Thermal stability of Schottky contacts on strained AlGaN/GaN heterostructures

Zhaojun Lin, Hyeongnam Kim, Jaesun Lee, and Wu Lu

Appl. Phys. Lett. 84, 1585 (2004); http://dx.doi.org/10.1063/1.1650875 (3 pages) | Cited 21 times

Online Publication Date: 25 February 2004

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The thermal stability of Ni Schottky contacts on strained Al0.3Ga0.7N/GaN heterostructures and on n-type bulk GaN was investigated after various thermal stressings using capacitance–voltage and current–voltage characterization techniques. The reverse leakage current decreases after thermal treatment at up to 800 and 600 °C for Schottky contacts on the strained Al0.3Ga0.7N/GaN heterostructures and bulk n-GaN, respectively. Ni Schottky contacts on the heterostructure with 30-min thermal stressing at 700 °C exhibit lower reverse leakage current by more than three orders of magnitude lower than the control sample. However, decrease in two-dimensional electron gas sheet carrier concentration at the Al0.3Ga0.7N and GaN interface possibly due to interactions between Ni and AlGaN surface was observed with increase of stressing temperature and time. Ni Schottky contacts on bulk n-GaN layers degrade at lower annealing temperature and their rectifying property practically disappears after 700 °C annealing, while Al0.3Ga0.7N/GaN heterostructures still exhibit nice Schottky behavior after 800 °C annealing. The better thermal stability of Ni Schottky contacts on the heterostructures than those on bulk n-GaN can be attributed to the presence of piezoelectric polarization. © 2004 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing

Thermal stability of nitrogen incorporated in HfNxOy gate dielectrics prepared by reactive sputtering

J. F. Kang, H. Y. Yu, C. Ren, M.-F. Li, D. S. H. Chan, H. Hu, H. F. Lim, W. D. Wang, D. Gui, and D.-L. Kwong

Appl. Phys. Lett. 84, 1588 (2004); http://dx.doi.org/10.1063/1.1651652 (3 pages) | Cited 31 times

Online Publication Date: 25 February 2004

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In this letter, we report the thermal stability of nitrogen incorporated in HfOxNy gate dielectrics prepared by reactive sputtering using x-ray photoelectron spectroscopy, secondary ions mass spectrometry, and electrical characterization. The results indicate that the bulk Hf–N bonds in reactive-sputtered HfOxNy are not stable during the postdeposition annealing and can be easily replaced by oxygen, resulting in significant loss of nitrogen from the bulk film. However, N at the HfOxNy/Si interface forms N–Si bonds, contributing to the excellent electrical stability of reactive sputtered HfOxNy gate dielectrics during the post deposition annealing. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
81.15.Cd Deposition by sputtering
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials
79.60.Jv Interfaces; heterostructures; nanostructures

AlGaN/GaN polarization-doped field-effect transistor for microwave power applications

Siddharth Rajan, Huili Xing, Steve DenBaars, Umesh K. Mishra, and Debdeep Jena

Appl. Phys. Lett. 84, 1591 (2004); http://dx.doi.org/10.1063/1.1652254 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2004

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We discuss an AlGaN/GaN metal–semiconductor field-effect transistor (MESFET) structure grown without any impurity doping in the channel. A high-mobility polarization-induced bulk channel charge was created by grading the channel region linearly from GaN to Al0.3Ga0.7N over 1000 Å. This polarization-doped FET (PolFET) was fabricated and tested under dc and rf conditions. Current density of 850 mA/mm and transconductance of 93 mS/mm was observed under dc conditions. The 0.7 μm gate length devices had a cutoff frequency, fτ = 19 GHz, and maximum oscillation frequency, fmax = 46 GHz. We demonstrate that the PolFETs perform better than comparable MESFETs with impurity-doped channels, and are suitable for high power microwave applications. An important advantage of these devices over AlGaN/GaN high electron mobility transistors is that the transconductance versus gate voltage profile can be tailored by compositional grading for better large-signal linearity. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
84.40.-x Radiowave and microwave (including millimeter wave) technology
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