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14 Jun 2010

Volume 96, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 96, 241101 (2010); http://dx.doi.org/10.1063/1.3449576 (3 pages)

Rui Chen, H. D. Sun, T. Wang, K. N. Hui, and H. W. Choi
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Solution-processed zinc–tin oxide thin-film transistors with low interfacial trap density and improved performance

Chen-Guan Lee and Ananth Dodabalapur

Appl. Phys. Lett. 96, 243501 (2010); http://dx.doi.org/10.1063/1.3454241 (3 pages) | Cited 21 times

Online Publication Date: 14 June 2010

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Solution-processed amorphous oxide semiconductors are attractive channel materials in thin-film transistors (TFTs) for low-cost electronics. We demonstrate improved performance and uniformity of solution-processed zinc–tin oxide (ZTO) TFTs by optimizing the prebake process for the ZTO precursor film. ZTO prebake process prearranges the dielectric/semiconductor interface and minimizes the performance variation caused by the uneven thermal distribution during annealing process. Prearranging the interface also reduces interfacial trap density and results in improved performance. A mobility of 27.3 cm2/V s, an on/off ratio of ∼ 107, and a subthreshold swing of 122 mV/decade have been obtained. Significant improvement in operational stability has also been observed.
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85.30.Tv Field effect devices

TiO2 nanotubes as a cold cathode for x-ray generation

Yahya Alivov, Michael Klopfer, and Sabee Molloi

Appl. Phys. Lett. 96, 243502 (2010); http://dx.doi.org/10.1063/1.3454244 (3 pages) | Cited 11 times

Online Publication Date: 14 June 2010

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Here we report on an x-ray source based on titanium dioxide (TiO2) nanotubes grown by electrochemical oxidation. From the analysis of current-voltage characteristics of TiO2 electron emitter field emission nature of the current was confirmed. The threshold voltage and field enhancement factors were derived to be ∼ 1.8 V/μm and ∼8363, respectively. The current density was ∼ 4.0 mA/cm2 at ∼ 2.4 V/μm. The stability tests showed that the current stayed stable within 6% for more than 720 h. TiO2 nanotubes were used as a cold cathode in x-ray tube and it was demonstrated that TiO2 nanotubes could be a good candidate for such applications.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
82.45.Yz Nanostructured materials in electrochemistry
73.63.Fg Nanotubes
81.16.Be Chemical synthesis methods
79.70.+q Field emission, ionization, evaporation, and desorption
82.45.Fk Electrodes

Photocurrent characteristics of two-dimensional-electron-gas-based AlGaN/GaN metal-semiconductor-metal photodetectors

Y. Huang, D. J. Chen, H. Lu, H. B. Shi, P. Han, R. Zhang, and Y. D. Zheng

Appl. Phys. Lett. 96, 243503 (2010); http://dx.doi.org/10.1063/1.3453871 (3 pages) | Cited 2 times

Online Publication Date: 15 June 2010

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Photocurrent response characteristics of two-dimensional-electron-gas-based AlGaN/GaN metal-semiconductor-metal (MSM) photodetectors were investigated by changing the frequency of incident light signals. At low chopper frequencies, the contribution to the photocurrent is mainly from the GaN bulk layer at 5 V bias, as expected. With increasing chopper frequency, a peak response at 361 nm wavelength becomes more and more pronounced and dominates gradually the photocurrent spectrum, indicating that this peak response has a much less frequency dependence and a faster response rate than the spectral response from the GaN bulk layer. This peak response is attributed to the contribution of photoelectrons generated in the two-dimensional electron gas (2DEG) channel according to simulation results of electrical field distribution and analysis of carrier transport in the 2DEG-based AlGaN/GaN heterostructure. This characteristic makes the 2DEG-based MSM photodetectors a large potential to develop high-speed ultraviolet optoelectronic integrated devices with AlGaN/GaN high electron mobility transistors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Sx Metal-semiconductor-metal structures
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects

Scaling down of amorphous indium gallium zinc oxide thin film transistors on the polyethersulfone substrate employing the protection layer of parylene-C for the large-scale integration

Seongpil Chang, Ki-Young Dong, Jung-Ho Park, Tae-Yeon Oh, Jong-Woo Kim, Sang Yeol Lee, and Byeong-Kwon Ju

Appl. Phys. Lett. 96, 243504 (2010); http://dx.doi.org/10.1063/1.3454775 (3 pages)

Online Publication Date: 16 June 2010

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We have investigated the parylene-groups for the device scaling-down as the protection layer of polyethersulfone (PES) substrate. In general, photolithography process on the PES substrate could not be allowed due to its poor chemical resistance. In this work, parylene-C is used as the protection layer. However, adhesion problem is observed caused by the hydrophobic property of parylene-groups. Thereby we additionally used SiO2 as the adhesion layer. Finally, we demonstrated the scaling-down of amorphous indium gallium zinc oxide thin film transistor on a plastic substrate by using lithography technique. Field-effect mobility, threshold voltage, current on-to-off ratio are measured to be 0.84 cm2/V s, 19.7 V, and 7.62×104, respectively.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Tube-based geometries for organic photovoltaics

Yuan Li, Eric D. Peterson, Huihui Huang, Mingjun Wang, Dan Xue, Wanyi Nie, Wei Zhou, and David L. Carroll

Appl. Phys. Lett. 96, 243505 (2010); http://dx.doi.org/10.1063/1.3453757 (3 pages)

Online Publication Date: 17 June 2010

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We demonstrate a waveguiding tube-based optical geometry that provides a general approach to improving organic photovoltaic performance. By fabricating bulk-heterojunction photovoltaics onto thin tubular light pipes, the optical energy can be effectively captured within the absorbing layer without associated reflective losses at the front and rear surfaces of the devices as is typical in planar structures. We have used a common absorber system: poly-3-hexyl-thiophene:phenyl-C61-butyric-acid-methyl-ester to demonstrate these tubular optical geometries result in very little overall radiative loss. Surprisingly, this also leads to an overall broadening of the absorption window for the device as indicated by the external quantum efficiency.
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88.40.H- Solar cells (photovoltaics)

Threshold voltage control of InAlN/GaN heterostructure field-effect transistors for depletion- and enhancement-mode operation

Suk Choi, Hee Jin Kim, Zachary Lochner, Yun Zhang, Yi-Che Lee, Shyh-Chiang Shen, Jae-Hyun Ryou, and Russell D. Dupuis

Appl. Phys. Lett. 96, 243506 (2010); http://dx.doi.org/10.1063/1.3446891 (3 pages) | Cited 4 times

Online Publication Date: 18 June 2010

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We describe a method to change the threshold voltage of heterostructure field-effect transistors (HFETs) using InxAl1−xN/GaN heterostructures by using polarization and strain modification in the InAlN barrier layer to realize enhancement-mode operation. The threshold voltage and electronic band structure of the heterostructures were calculated for different indium compositions in the InAlN layer. Band structure calculations predict the enhancement-mode operation of compressively strained InAlN/GaN HFETs with an indium composition higher than 0.25. Studies of InAlN/GaN HFETs with different In alloy compositions show that the sheet resistance increases and the carrier concentration decreases for the heterostructures with increasing indium composition due to changes in the compressive strain and polarization in the InAlN barrier layer. Fabricated HFETs show threshold voltages of −2.5, −0.75, and +0.2 V for In ∼ 0.18Al ∼ 0.82N/GaN, In ∼ 0.22Al ∼ 0.78N/GaN, and In ∼ 0.25Al ∼ 0.75N/GaN HFETs, respectively, corresponding to a shift from depletion-mode to enhancement-mode operation.
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85.30.Tv Field effect devices

Influence of gas inertia and edge effect on squeeze film in near field acoustic levitation

Jin Li, Wenwu Cao, Pinkuan Liu, and Han Ding

Appl. Phys. Lett. 96, 243507 (2010); http://dx.doi.org/10.1063/1.3455896 (3 pages) | Cited 4 times

Online Publication Date: 18 June 2010

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Detailed analysis showed that the existing theoretical models for near field acoustic levitation are not good enough to interpret the experimental data. The best existing models can only work in a small range of the squeeze numbers even with a fitting parameter. We report here a comprehensive nonlinear model, which takes into account the nonuniform surface vibration profile, gas inertia as well as entrance pressure drop at the film edge. Our model has no empirical parameters and the predicted results agree exceptionally well with our experimental measurements over a wide range of squeeze numbers.
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43.25.Uv Acoustic levitation
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