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5 Nov 2007

Volume 91, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages)

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle
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High performance n-channel thin-film transistors with an amorphous phase C60 film on plastic substrate

Jong H. Na, M. Kitamura, and Y. Arakawa

Appl. Phys. Lett. 91, 193501 (2007); http://dx.doi.org/10.1063/1.2807843 (3 pages) | Cited 11 times

Online Publication Date: 5 November 2007

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We fabricated high mobility, low voltage n-channel transistors on plastic substrates by combining an amorphous phase C60 film and a high dielectric constant gate insulator titanium silicon oxide (TiSiO2). The transistors exhibited high performance with a threshold voltage of 1.13 V, an inverse subthreshold swing of 252 mV/decade, and a field-effect mobility up to 1 cm2/V s at an operating voltage as low as 5 V. The amorphous phase C60 films can be formed at room temperature, implying that this transistor is suitable for corresponding n-channel transistors in flexible organic logic devices.
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85.30.Tv Field effect devices

Detection of low energy single ion impacts in micron scale transistors at room temperature

A. Batra, C. D. Weis, J. Reijonen, A. Persaud, T. Schenkel, S. Cabrini, C. C. Lo, and J. Bokor

Appl. Phys. Lett. 91, 193502 (2007); http://dx.doi.org/10.1063/1.2805634 (3 pages) | Cited 19 times

Online Publication Date: 5 November 2007

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We report the detection of single ion impacts through monitoring of changes in the source-drain currents of field effect transistors at room temperature. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, microscale transistors by electron beam assisted etching. Device currents increase due to the generation of positively charged defects in gate oxides when ions (121Sb12+,14+ and Xe6+; 50–70 keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization for the development of single atom devices and studies of dopant fluctuation effects.
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85.30.Tv Field effect devices

GaAs metal-oxide-semiconductor capacitors using atomic layer deposition of HfO2 gate dielectric: Fabrication and characterization

D. Shahrjerdi, D. I. Garcia-Gutierrez, T. Akyol, S. R. Bank, E. Tutuc, J. C. Lee, and S. K. Banerjee

Appl. Phys. Lett. 91, 193503 (2007); http://dx.doi.org/10.1063/1.2806190 (3 pages) | Cited 23 times

Online Publication Date: 5 November 2007

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In this letter, we have investigated the physical and electrical characteristics of atomic layer deposition of HfO2 on GaAs substrates. X-ray photoelectron spectroscopy (XPS) analysis revealed no significant reduction of arsenic oxides upon deposition of HfO2 on GaAs using tetrakis(dimethyl-amino)hafnium [Hf(NMe2)4] as the metallic precursor. However, XPS confirmed the absence of arsenic oxides at the interface of HfO2 and sulfide-treated GaAs. High-resolution transmission electron microcopy analysis verified a smooth interface between HfO2 and sulfur-passivated GaAs. In addition, frequency dispersion behavior of capacitors on p-type GaAs substrates was remarkably improved by employing an appropriate surface chemical treatment.
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68.37.Lp Transmission electron microscopy (TEM)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors
81.65.-b Surface treatments
79.60.Bm Clean metal, semiconductor, and insulator surfaces

The influence of visible light on transparent zinc tin oxide thin film transistors

P. Görrn, M. Lehnhardt, T. Riedl, and W. Kowalsky

Appl. Phys. Lett. 91, 193504 (2007); http://dx.doi.org/10.1063/1.2806934 (3 pages) | Cited 43 times

Online Publication Date: 6 November 2007

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The characteristics of transparent zinc tin oxide thin film transistors (TTFTs) upon illumination with visible light are reported. Generally, a reversible decrease of threshold voltage Vth, saturation field effect mobility μsat, and an increase of the off current are found. The time scale of the recovery in the dark is governed by the persistent photoconductivity in the semiconductor. Devices with tuned [Zn]:[Sn] ratio show a shift of Vth of less 2 V upon illumination at 5 mW/cm2 (brightness >30 000 cd/m2) throughout the visible spectrum. These results demonstrate TTFTs which are candidates as pixel drivers in transparent active-matrix organic light emitting diode displays.
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85.30.Tv Field effect devices

Growth front nucleation of rubrene thin films for high mobility organic transistors

C. H. Hsu, J. Deng, C. R. Staddon, and P. H. Beton

Appl. Phys. Lett. 91, 193505 (2007); http://dx.doi.org/10.1063/1.2805030 (3 pages) | Cited 20 times

Online Publication Date: 7 November 2007

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We demonstrate a mode of thin film growth in which amorphous islands crystallize into highly oriented platelets. A cascade of crystallization is observed, in which platelets growing outward from a central nucleation point impinge on neighboring amorphous islands and provide a seed for further nucleation. Through control of growth parameters, it is possible to produce high quality thin films which are well suited to the formation of organic transistors. We demonstrate this through the fabrication of rubrene thin film transistors with high carrier mobility.
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68.55.A- Nucleation and growth
85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.15.Aa Theory and models of film growth

Flexible programmable logic gate using organic ferroelectric multilayer

Satoshi Horie, Kei Noda, Hirofumi Yamada, Kazumi Matsushige, Kenji Ishida, and Shuichiro Kuwajima

Appl. Phys. Lett. 91, 193506 (2007); http://dx.doi.org/10.1063/1.2805219 (3 pages) | Cited 3 times

Online Publication Date: 7 November 2007

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In order to simplify the design and to further improve the integration, programmable, three-dimensional circuits are required alongside the development of fine process technology. We demonstrate the operation of programmable logic gates using organic ferroelectrics. Three-dimensionally stacked organic ferroelectric capacitors were assembled, which form logic elements with two inputs and one output. By controlling the directions of the electric dipoles, we have demonstrated the logical “and” and “or” operations using our device.
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84.30.Sk Pulse and digital circuits
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Electrical characteristics of palladium Schottky contacts to hydrogen peroxide treated hydrothermally grown ZnO

R. Schifano, E. V. Monakhov, U. Grossner, and B. G. Svensson

Appl. Phys. Lett. 91, 193507 (2007); http://dx.doi.org/10.1063/1.2806194 (3 pages) | Cited 23 times

Online Publication Date: 7 November 2007

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The formation of Schottky barrier contacts to hydrogen peroxide treated ZnO has been investigated. Low resistivity hydrothermally grown single crystal ZnO wafers of n-type were used. Pd contacts deposited on organic solvent cleaned O face (000math) showed Ohmic behavior, while on the H2O2 treated O face up to nine orders of magnitude in rectification of the current was obtained for biases of −2 and +2 V. Concurrently, the surface roughness increases from 1.0±0.5 up to 2.0±0.5 nm due to the H2O2 treatment. A majority of the contacs deposited were stable or improved their performance by annealing in air at 200 °C for 30 min. However, the contacts both before and after the annealing exhibited ideality factors of at least ∼ 1.8 at +0.5 V suggesting that the current transport cannot be described as purely thermionic. Finally, results of capacitance versus voltage and capacitance versus temperature measurements are discussed and show a dominant electron state at ∼ 0.32 eV below the conduction band edge.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.10.Dn Growth from solutions

Numerical modeling study of the unipolar accumulation transistor

Stephen J. Fonash, Md Mash-hud Iqbal, Florin Udrea, and Piero Migliorato

Appl. Phys. Lett. 91, 193508 (2007); http://dx.doi.org/10.1063/1.2805630 (3 pages) | Cited 1 time

Online Publication Date: 8 November 2007

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A unipolar accumulation transistor configuration has recently been proposed and experimentally demonstrated. This transistor has a simple structure with Ohmic contacts and only one doping type. The device, termed the accumulation metal oxide semiconductor field effect transistor (AMOSFET), relies on having a nanoscale depth dimension, which forces the current through an accumulated (on state) or depleted (off state) region. Detailed numerical modeling presented here elucidates the previously proposed and experimentally observed AMOSFET features. These include linear and saturation currents which depend on doping rather than gate capacitance, good subthreshold swing behavior, and low threshold voltages. This modeling predicts on-off ratios exceeding 109.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.35.-p Nanoelectronic devices

Pentacene-based low voltage organic field-effect transistors with anodized Ta2O5 gate dielectric

Yeon Taek Jeong and Ananth Dodabalapur

Appl. Phys. Lett. 91, 193509 (2007); http://dx.doi.org/10.1063/1.2806914 (3 pages) | Cited 11 times

Online Publication Date: 8 November 2007

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Pentacene-based low voltage organic field-effect transistors were realized using an anodized Ta2O5 gate dielectric. The Ta2O5 gate dielectric layer with a surface roughness of 1.3 Å was obtained by anodizing an e-beam evaporated Ta film. The device exhibited values of saturation mobility, threshold voltage, and Ion/Ioff ratio of 0.45 cm2/V s, 0.56 V, and 7.5×101, respectively. The gate leakage current was reduced by more than 70% with a hexamethyldisilazane (HMDS) treatment on the Ta2O5 layer. The HMDS treatment also resulted in enhanced mobility values and a larger pentacene grain size.
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85.30.Tv Field effect devices

Interface effects on the external quantum efficiency of organic bulk heterojunction photodetectors

Y. Kim, M. Ballarotto, D. Park, M. Du, W. Cao, C. H. Lee, W. N. Herman, and D. B. Romero

Appl. Phys. Lett. 91, 193510 (2007); http://dx.doi.org/10.1063/1.2809410 (3 pages) | Cited 5 times

Online Publication Date: 9 November 2007

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We investigate the effects of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and LiF interfacial layers on the efficiency of organic bulk heterojunction photodetectors fabricated with blends of regioregular poly(3-hexylthiophene-2,5-diyl) as electron donor and {6}-1-[3-(methoxycarbonyl)propyl]-{5}-1-phenyl-[5,6]-C61 as electron acceptor. At high reverse bias voltage, we find that the efficiency of these devices is limited only by the rate of creating excitons in the organic layer. Upon correction for the optical loss at the interfacial layers, the internal quantum efficiency can approach 100% in this highly disordered network of donor-acceptor molecular heterojunctions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Direct ultraviolet excitation of an amorphous AlN:praseodymium phosphor by codoped Gd3+ cathodoluminescence

Muhammad Maqbool, I. Ahmad, H. H. Richardson, and M. E. Kordesch

Appl. Phys. Lett. 91, 193511 (2007); http://dx.doi.org/10.1063/1.2809607 (3 pages) | Cited 21 times

Online Publication Date: 9 November 2007

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Sputter deposited thin film amorphous AlN:Pr (1 at. %) emits in the blue-green (490–530 nm) and red ( ∼ 650 nm) regions of the visible spectrum under electron excitation. The addition of Gd 1 at. % in the film enhances the blue emission by an order of magnitude. The enhancement in the blue region is a result of cathodoluminescence from Gd3+ at 313 nm. The optical bandgap of amorphous AlN is about 210 nm, so that the film is transparent in the ultraviolet, allowing the Gd emission to excite the Pr3+ ions. No significant quenching of the Gd emission is observed when the Gd and Pr ions are mixed. The blue enhancement is observed even with the two films containing each of the ions that are separated by a 500 μm thick quartz spacer, showing that the enhancement is due entirely to UV radiation.
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78.55.-m Photoluminescence, properties and materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.60.Hk Cathodoluminescence, ionoluminescence

Soldering to a single atomic layer

Çağlar Ö. Girit and A. Zettl

Appl. Phys. Lett. 91, 193512 (2007); http://dx.doi.org/10.1063/1.2812571 (3 pages) | Cited 18 times

Online Publication Date: 9 November 2007

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The standard technique to make electrical contact to nanostructures is electron beam lithography. This method has several drawbacks including complexity, cost, and sample contamination. We present a simple technique to cleanly solder submicron sized, Ohmic contacts to nanostructures. To demonstrate, we contact graphene, a single atomic layer of carbon, and investigate low- and high-bias electronic transport. We set lower bounds on the current carrying capacity of graphene. A simple model allows us to obtain device characteristics such as mobility, minimum conductance, and contact resistance.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
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