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17 Jul 2006

Volume 89, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 031107 (2006); http://dx.doi.org/10.1063/1.2222329 (3 pages)

Jiaguang Han, Zhiyuan Zhu, Sanith Ray, Abul K. Azad, Weili Zhang, Mingxia He, Shihong Li, and Yiping Zhao
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Interdigital transducers with control gates on AlGaN/GaN heterostructures

Naoteru Shigekawa, Kazumi Nishimura, Tetsuya Suemitsu, Haruki Yokoyama, and Kohji Hohkawa

Appl. Phys. Lett. 89, 033501 (2006); http://dx.doi.org/10.1063/1.2221899 (3 pages) | Cited 4 times

Online Publication Date: 17 July 2006

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We investigated surface acoustic wave (SAW) filters composed of interdigital transducers with control gates formed on AlGaN/GaN heterostructures. The contribution of SAWs appeared in the rf characteristics of the SAW filters when reverse-bias voltages were applied to the control gates and the GaN channels were depleted. We also observed higher-frequency signals due to SAWs in transducers with positively-biased control gates. These results suggest that SAW-based functional devices are achievable by employing transducers in which rf signals for exciting SAWs and control signals for modulating SAW properties are applied to different terminals.
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Effective modification of indium tin oxide for improved hole injection in organic light-emitting devices

Chong-an Di, Gui Yu, Yunqi Liu, Xinjun Xu, Yabin Song, and Daoben Zhu

Appl. Phys. Lett. 89, 033502 (2006); http://dx.doi.org/10.1063/1.2222240 (3 pages) | Cited 17 times

Online Publication Date: 18 July 2006

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We demonstrate modification of the indium tin oxide (ITO) surface with an ultrathin layer of hexadecafluorocopper phthalocyanine (F16CuPc) can significantly enhance hole injection as a result of the formation of an interfacial dipole layer. The dipole layer produces a surface potential shift, which reduces the hole injection energy barriers and thus improves the hole injection efficiency. The devices with anode modification exhibit significantly enhanced luminance efficiencies and dramatically decreased operation voltages, compared to devices with the bare ITO anode. The minimum turn-on voltage of 2.6 V and the maximum efficiency of 5.1 cd/A are achieved.
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85.60.Jb Light-emitting devices

Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts

R. X. Wang, S. J. Xu, A. B. Djurišić, C. D. Beling, C. K. Cheung, C. H. Cheung, S. Fung, D. G. Zhao, H. Yang, and X. M. Tao

Appl. Phys. Lett. 89, 033503 (2006); http://dx.doi.org/10.1063/1.2227627 (3 pages) | Cited 6 times

Online Publication Date: 19 July 2006

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Indium-tin-oxide (ITO)/n-GaN Schottky contacts were prepared by e-beam evaporation at 200 °C under various partial pressures of oxygen. X-ray photoemission spectroscopy and positron beam measurements were employed to obtain chemical and structural information of the deposited ITO films. The results indicated that the observed variation in the reverse leakage current of the Schottky contact and the optical transmittance of the ITO films were strongly dependent on the quality of the ITO film. The high concentration of point defects at the ITO-GaN interface is suggested to be responsible for the large observed leakage current of the ITO/n-GaN Schottky contacts.
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73.40.-c Electronic transport in interface structures
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.J- Point defects and defect clusters

Molecular orientation dependence of hole-injection barrier in pentacene thin film on the Au surface in organic thin film transistor

Kyuwook Ihm, Bongsoo Kim, Tai-Hee Kang, Ki-Jeong Kim, Min Ho Joo, Tae Hyeong Kim, Sang Soo Yoon, and Sukmin Chung

Appl. Phys. Lett. 89, 033504 (2006); http://dx.doi.org/10.1063/1.2227712 (3 pages) | Cited 33 times

Online Publication Date: 20 July 2006

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We have investigated the effects of a buffer layer insertion on the performance of the pentacene based thin film transistor with a bottom contact structure. When the pentacene molecules have a standing up coordination on the Au surface that is modified by the benzenethiol or methanethiol, the transition region in the pentacene thin film is removed along the boundary between the Au and silicon oxide region, and the hole-injection barrier decreases by 0.4 eV. Pentacene on various surfaces showed that the highly occupied molecular level is 0.2–0.4 eV lower in the standing up coordination than in the lying down coordination.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices

Electrospun hybrid organic/inorganic semiconductor Schottky nanodiode

Nicholas J. Pinto, Rosana González, Alan T. Johnson, and Alan G. MacDiarmid

Appl. Phys. Lett. 89, 033505 (2006); http://dx.doi.org/10.1063/1.2227758 (3 pages) | Cited 13 times

Online Publication Date: 20 July 2006

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We report on a simple method to fabricate, under ambient conditions and within seconds, Schottky nanodiodes using electrospun polyaniline nanofibers and an inorganic n-doped semiconductor. In addition to being a rectifier, the advantage of our design is the complete exposure of the rectifying nanojunction to the surrounding environment, making them attractive candidates in the potential fabrication of low power, supersensitive, and rapid response sensors as well. The diode parameters were calculated assuming the standard thermionic emission model of a Schottky junction, and the use of this junction as a gas sensor was examined.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
85.35.-p Nanoelectronic devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Microstructured silicon photodetector

Zhihong Huang, James E. Carey, Mingguo Liu, Xiangyi Guo, Eric Mazur, and Joe C. Campbell

Appl. Phys. Lett. 89, 033506 (2006); http://dx.doi.org/10.1063/1.2227629 (3 pages) | Cited 48 times

Online Publication Date: 20 July 2006

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Photodetectors fabricated on microstructured silicon are reported. The photodetectors exhibited high photoresponse; at 3 V bias, the responsivities were 92 A/W at 850 nm and 119 A/W at 960 nm. At wavelengths longer than 1.1 μm, the photodetectors still showed strong photoresponse. A generation-recombination gain mechanism has been proposed to explain the photoresponse of these photodiodes. From measurements of the noise current density, the calculated gain was approximately 1200 at 3 V bias.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Localized and distributed mass detectors with high sensitivity based on thin-film bulk acoustic resonators

Humberto Campanella, Jaume Esteve, Josep Montserrat, Arantxa Uranga, Gabriel Abadal, Nuria Barniol, and Albert Romano-Rodríguez

Appl. Phys. Lett. 89, 033507 (2006); http://dx.doi.org/10.1063/1.2234305 (3 pages) | Cited 10 times

Online Publication Date: 21 July 2006

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A mass sensor based on thin-film bulk acoustic resonator, intended for biomolecular applications, is presented. The thin film is a (002) AlN membrane, sputtered over Ti/Pt on a (001) Si wafer, and released by surface micromachining of silicon. Two experiments are proposed to test the mass sensing performance of the resonators: (a) distributed loading with a MgF2 film by means of physical vapor deposition and (b) localized mass growing of a C/Pt/Ga composite using focused-ion-beam-assisted deposition, both on the top electrode. For the distributed and localized cases, the minimum detectable mass changes are 1.58×10−8 g/cm2 and 7×10−15 g, respectively.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Dr Mass and density

Magnetic field driving custom assembly in (FeCo) nanocrystals

P. Marín, M. López, A. Vlad, A. Hernando, M. L. Ruiz-González, and J. M. González-Calbet

Appl. Phys. Lett. 89, 033508 (2006); http://dx.doi.org/10.1063/1.2222254 (3 pages) | Cited 5 times

Online Publication Date: 21 July 2006

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We present the possibility of tuning the nanocrystalline microstructure of Co-rich samples by magnetic field annealing. Custom assembly of nucleated grains, aligned in the field direction, has been observed by means of high resolution transmission microscopy. The organized microstructure was obtained on the basis of the appropriate choice of composition, annealing temperature, related to the initial stages of nanocrystallization process, and magnetic field intensity. The linear pattern of the grains has been explained as a consequence of the counterbalance between magnetic, magnetostatic, and magnetocrystalline couplings, only relevant when the nucleation temperature is well below the Curie temperature of the nucleated phase.
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81.07.Bc Nanocrystalline materials
75.60.Nt Magnetic annealing and temperature-hysteresis effects
61.46.Hk Nanocrystals
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments

Gate-metal formation-related kink effect and gate current on In0.5Al0.5As/In0.5Ga0.5As metamorphic high electron mobility transistor performance

M. K. Hsu, H. R. Chen, S. Y. Chiou, W. T. Chen, G. H. Chen, Y. C. Chang, and W. S. Lour

Appl. Phys. Lett. 89, 033509 (2006); http://dx.doi.org/10.1063/1.2222259 (3 pages) | Cited 9 times

Online Publication Date: 21 July 2006

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In0.5Ga0.5As/In0.5Al0.5As metamorphic high electron mobility transistos were fabricated with different gate-metal formations: mesa type or air type and without or with a buried gate. Only air-type devices with a buried gate show no kink effect. Experimental results indicate that gate-feeder metal and annealing process give effects on gate current and noise figure. The peak gate current of 12 (120)μA/mm for air-type (mesa-type) devices before annealing is improved to 8 (55)μA/mm after annealing. At 1.8 GHz, associated gain of 25 dB is obtained at Fmin = 1.24 dB for air-type devices after annealing, while 23 dB is obtained at Fmin = 1.25 dB before annealing.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

III-nitride transistors with capacitively coupled contacts

G. Simin, Z.-J. Yang, A. Koudymov, V. Adivarahan, J. Yang, and M. Asif Khan

Appl. Phys. Lett. 89, 033510 (2006); http://dx.doi.org/10.1063/1.2234725 (3 pages) | Cited 6 times

Online Publication Date: 21 July 2006

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AlGaN/GaN heterostructure field-effect transistor design using capacitively coupled contacts (C3HFET) is presented. Insulated-gate [C3 metal-oxide-semiconductor HFET (C3MOSHFET)] has also been realized. The capacitively coupled source, gate, and drain of C3 device do not require annealed Ohmic contacts and can be fabricated using gate alignment-free technology. For typical AlGaN/GaN heterostructures, the equivalent contact resistance of C3 transistors is below 0.6 Ω mm. In rf-control applications, the C3HFET and especially the C3MOSHFET have much higher operating rf powers as compared to HFETs. C3 design is instrumental for studying the two-dimensional electron gas transport in other wide band gap heterostructures such as AlN/GaN, diamond, etc., where Ohmic contact fabrication is difficult.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Low-voltage and high-gain pentacene inverters with plasma-enhanced atomic-layer-deposited gate dielectrics

Jae Bon Koo, Sun Jin Yun, Jung Wook Lim, Seong Hyun Kim, Chan Hoe Ku, Sang Chul Lim, Jung Hun Lee, and Taehyoung Zyung

Appl. Phys. Lett. 89, 033511 (2006); http://dx.doi.org/10.1063/1.2234835 (3 pages) | Cited 14 times

Online Publication Date: 21 July 2006

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The pentacene thin-film transistors with the plasma-enhanced atomic-layer-deposited 150 nm thick Al2O3 or 120 nm thick ZrO2 have been operated at gate voltages between −3 and 3 V. The inverter with a ZrO2 gate dielectric shows a gain of 49 and a full swing from supply voltage (Vdd) to 0 V, operating at input voltages (Vin) from 0 to −1 V and at Vdd of −1 V. The hysteresis observed in the voltage transfer characteristic of the inverter depends on the scan range of Vin applied to the driver transistor, regardless of the Vdd applied to the load transistor.
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85.30.Tv Field effect devices

Organic inverter circuits employing ambipolar pentacene field-effect transistors

Th. B. Singh, P. Senkarabacak, N. S. Sariciftci, A. Tanda, C. Lackner, R. Hagelauer, and Gilles Horowitz

Appl. Phys. Lett. 89, 033512 (2006); http://dx.doi.org/10.1063/1.2235947 (3 pages) | Cited 43 times

Online Publication Date: 21 July 2006

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Ambipolar transport has been observed in pentacene films grown on polyvinyl alcohol gate dielectric with hole and electron mobilities of 0.3 and 0.04 cm2/V s, respectively. A simple device structure with Au as source-drain electrode can be used to operate a transistor in both p-channel and n-channel modes without employing low work function metal electrodes for ambipolar charge injection. Using ambipolar pentacene field-effect transistors, we construct a complementarylike inverter with voltage inversion gain of ∼ 10. These inverters are able to operate both in first and third quadrants of the voltage output to voltage input characteristics which is a unique feature of employing ambipolar transistors.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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