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21 Sep 2009

Volume 95, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 95, 121104 (2009); http://dx.doi.org/10.1063/1.3231448 (3 pages)

E. H. Khoo, I. Ahmed, and E. P. Li
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Efficient black silicon solar cell with a density-graded nanoporous surface: Optical properties, performance limitations, and design rules

Hao-Chih Yuan, Vernon E. Yost, Matthew R. Page, Paul Stradins, Daniel L. Meier, and Howard M. Branz

Appl. Phys. Lett. 95, 123501 (2009); http://dx.doi.org/10.1063/1.3231438 (3 pages) | Cited 53 times

Online Publication Date: 22 September 2009

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We study optical effects and factors limiting performance of our confirmed 16.8% efficiency “black silicon” solar cells. The cells incorporate density-graded nanoporous surface layers made by a one-step nanoparticle-catalyzed etch and reflect less than 3% of the solar spectrum, with no conventional antireflection coating. The cells are limited by recombination in the nanoporous layer which decreases short-wavelength spectral response. The optimum density-graded layer depth is then a compromise between reflectance reduction and recombination loss. Finally, we propose universal design rules for high-efficiency solar cells based on density-graded surfaces.
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84.60.Jt Photoelectric conversion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

The influence of the gate dielectrics on threshold voltage instability in amorphous indium-gallium-zinc oxide thin film transistors

Jaeseob Lee, Jin-Seong Park, Young Shin Pyo, Dong Bum Lee, Eun Hyun Kim, Denis Stryakhilev, Tae Woong Kim, Dong Un Jin, and Yeon-Gon Mo

Appl. Phys. Lett. 95, 123502 (2009); http://dx.doi.org/10.1063/1.3232179 (3 pages) | Cited 46 times

Online Publication Date: 22 September 2009

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We investigated the threshold voltage (Vth) instability for various gate dielectrics (SiNx and SiOx) in amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs). The a-IGZO TFTs with SiNx 150 °C exhibited reasonable electrical performance (field-effect mobility of 8.1 cm2/V s and Ion/off ratio of >108) but showed huge Vth shift under positive gate bias. The TFTs with SiOx dielectrics exhibit smaller Vth instability than those of SiNx dielectrics. This behavior can be explained by using simple charge trapping into the gate insulators and the difference of Vth instability on various dielectrics may be originated from the hydrogen contents, providing high density of charge traps in gate dielectrics.
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85.30.Tv Field effect devices

Selective liquid crystal molecule orientation on ion beam irradiated tantalum oxide ultrathin films

Ji-Hun Lim, Byeong-Yun Oh, Won-Kyu Lee, Kang-Min Lee, Hyun-Jae Na, Byoung-Yong Kim, Dae-Shik Seo, Jeong-Min Han, and Jeong-Yeon Hwang

Appl. Phys. Lett. 95, 123503 (2009); http://dx.doi.org/10.1063/1.3232239 (3 pages) | Cited 7 times

Online Publication Date: 22 September 2009

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We recently achieved the homogeneous alignment of liquid crystal (LC) on amorphous Ta2O5 layers. This study demonstrates that LC layers could be aligned either homogeneously or vertically by increasing the growth temperature of rf magnetron sputtering device and the irradiation time of the DuoPIGatron type Ar ion beam device causing uniform and dense plasma. We attained two LC orientations by observing Ta 4f and O 1s peak shifts with x-ray photoelectron spectroscopy. Moreover, the decreased thickness of layers with high-k dielectric constants helped to decrease driving LC voltages and in turn to achieve low power consumption.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.22.Ch Permittivity (dielectric function)
61.80.Jh Ion radiation effects
81.15.Cd Deposition by sputtering
77.55.-g Dielectric thin films

Voltage-tunable two-color quantum-dot infrared photodetectors

Shih-Yen Lin, Wei-Hsun Lin, Chi-Che Tseng, Kuang-Ping Chao, and Shu-Cheng Mai

Appl. Phys. Lett. 95, 123504 (2009); http://dx.doi.org/10.1063/1.3236543 (3 pages) | Cited 9 times

Online Publication Date: 22 September 2009

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A two-terminal quantum-dot infrared photodetector with stacked five-period InAs/GaAs and InGaAs-capped InAs/GaAs quantum-dot (QD) structures is investigated. The device has exhibited distinct responses at mid-wavelength and long-wavelength infrared regions under positive and negative biases, respectively. The results suggest that the QD confinement states near the anode side are completely filled, such that selective responses at different wavelength ranges would be observed for the stacked structure under different voltage polarities. Also observed are the similar absorption ratios of the device under different incident light polarizations at the two response regions.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Impact of device configuration on the temperature instability of Al–Zn–Sn–O thin film transistors

Jae Kyeong Jeong, Shinhyuk Yang, Doo-Hee Cho, Sang-Hee Ko Park, Chi-Sun Hwang, and Kyoung Ik Cho

Appl. Phys. Lett. 95, 123505 (2009); http://dx.doi.org/10.1063/1.3236694 (3 pages) | Cited 14 times

Online Publication Date: 23 September 2009

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We compared the effect of the temperature on the device stability of Al–Zn–Sn–O (AZTO) thin film transistors (TFTs) with top gate and bottom gate architectures. While the bottom gate device without any passivation layer on the AZTO channel layer showed a large threshold voltage (Vth) shift of 1.6 V after heating it from 298 to 398 K, the naturally passivated top gate device exhibited a smaller Vth shift of 0.6 V. This different behavior is discussed based on the concept of the thermal activation energy of the subthreshold drain current. It is proposed that the suitable passivation and lower interfacial trap density for the top gate TFT are responsible for its superior temperature stability compared to the bottom gate device.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Reduction of surface acoustic wave resonator normal acceleration sensitivity using piezoelectric actuators

X. Y. Shan, Y. T. Hu, and J. S. Yang

Appl. Phys. Lett. 95, 123506 (2009); http://dx.doi.org/10.1063/1.3236750 (3 pages)

Online Publication Date: 23 September 2009

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We attach a piezoelectric actuator to a surface acoustic wave resonator under normal acceleration to reduce its acceleration sensitivity. It is shown theoretically that under a given acceleration, the acceleration induced frequency shift in the resonator can be reduced or even completely eliminated when a proper electric field is applied to the piezoelectric actuator.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

A mechanical Kerr effect in deformable photonic media

W. H. P. Pernice, Mo Li, and H. X. Tang

Appl. Phys. Lett. 95, 123507 (2009); http://dx.doi.org/10.1063/1.3236530 (3 pages) | Cited 9 times

Online Publication Date: 23 September 2009

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We theoretically introduce a mechanism for achieving the mechanical analog of optical Kerr nonlinearity. By exploiting optomechanical interactions in deformable waveguide structures, a nonlinear phase shift proportional to the optical field intensity is induced. Resulting Kerr coefficients several orders of magnitude larger than the intrinsic silicon optical Kerr coefficient are predicted.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials

Role of shallow Si/SiO2 interface states on high frequency channel noise in n-channel metal-oxide-semiconductor field effect transistors

Hao Su (苏浩), Hong Wang (汪宏), Tao Xu (徐涛), and Rong Zeng (曾嵘)

Appl. Phys. Lett. 95, 123508 (2009); http://dx.doi.org/10.1063/1.3231924 (3 pages)

Online Publication Date: 24 September 2009

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The role of shallow interface states on high frequency channel noise in n-channel metal-oxide-semiconductor field effect transistors (n-MOSFETs) has been studied. Our experimental results reveal that the excess channel noise in gigahertz range induced by hot carrier stress could be attributed to the carrier transitions associated with shallow interface states. This suggests that the shallow Si/SiO2 interface states in MOSFETs may play an important role in determining the channel noise in gigahertz frequency range.
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85.30.Tv Field effect devices

A high-Q hybrid acoustic mode in thin film ZnO solidly mounted resonators

Adam D. Wathen, Farasat Munir, and William D. Hunt

Appl. Phys. Lett. 95, 123509 (2009); http://dx.doi.org/10.1063/1.3238265 (2 pages) | Cited 3 times

Online Publication Date: 25 September 2009

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An extremely high-Q hybrid acoustic mode was observed in laterally excited c-axis ZnO solidly mounted resonators. The acoustic velocity through the thickness is approximately 3500 m/s which is inconsistent with both the thickness shear and longitudinal modes (2800 and 6400 m/s, respectively). In nearly 300 devices tested, the mode exhibits an average Q of 1957 with the highest observed being 34 000. With small device sizes relative to excitation wavelength and resonant frequency invariant with electrode geometry, we attribute this resonance to purely acoustic effects and not electromagnetic radiative effects. These devices have great potential for high frequency filters and sensing applications.
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62.65.+k Acoustical properties of solids
68.55.ag Semiconductors
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
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