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8 Aug 2011

Volume 99, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 063701 (2011); http://dx.doi.org/10.1063/1.3622631 (3 pages)

Bomi Gweon, Mina Kim, Dan Bee Kim, Daeyeon Kim, Hyeonyu Kim, Heesoo Jung, Jennifer H. Shin, and Wonho Choe
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Enhanced electroluminescence from the fluorine-plasma implanted Ni/Au-AlGaN/GaN Schottky diode

B. K. Li, M. J. Wang, K. J. Chen, and J. N. Wang

Appl. Phys. Lett. 99, 062101 (2011); http://dx.doi.org/10.1063/1.3622643 (3 pages)

Online Publication Date: 8 August 2011

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The effect of fluorine-plasma (F-plasma) implantation on the current-voltage (I-V) and electroluminescence (EL) characteristics of Ni/Au-AlGaN/GaN Schottky diodes have been investigated. The observed EL spectrum is dominated by the GaN near band edge emissions. The threshold current of the EL emission for F-plasma implanted diodes is significantly lower than that for the previously reported diodes without the F-plasma implantation. This reduction of threshold current results from the presence of negatively charged F-centers in AlGaN layer which leads to upward band bending of AlGaN layer and enhanced hole injection by multi-step tunneling process through AlGaN layer. The magnitude of the upward banding in AlGaN layer is estimated to be 0.36 eV by analyzing the forward-biased I-V characteristics.
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85.30.Kk Junction diodes
61.72.uj III-V and II-VI semiconductors
52.77.Dq Plasma-based ion implantation and deposition
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
78.60.Fi Electroluminescence

Efficiency enhancement of a-Si:H single junction solar cells by a-Ge:H incorporation at the p+ a-SiC:H/transparent conducting oxide interface

Jeehwan Kim, Ahmed I. Abou-Kandil, Augustin J. Hong, Mohamed M. Saad, Devendra K. Sadana, and Tze-Chiang Chen

Appl. Phys. Lett. 99, 062102 (2011); http://dx.doi.org/10.1063/1.3619185 (3 pages) | Cited 3 times

Online Publication Date: 8 August 2011

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Carbon (C) incorporation in the p+ hydrogenated amorphous silicon (a-SiC:H) is highly desirable for a-Si:H based solar cells because of the following reasons: (i) it increases the band gap of the p+ layer to ∼2 eV, which allows a majority of the sun light to pass through the thin p+ layer (∼15 nm) and get absorbed in the underlying intrinsic a-Si:H layer, and (ii) it enhances built-in potential of the a-Si:H p-i-n stack, resulting in enhanced short circuit current (JSC) and open circuit voltage (VOC). Hence, it is a desire to incorporate the highest possible C % in the p+ a-Si:H. However, C incorporation results in a Schottky barrier at the p+ a-SiC:H/transparent conducting oxide (TCO) interface, which degrades the fill factor (FF) of the solar cell. In this paper, we present a method that increases the C incorporation in p+ a-SiC:H but without adversely affecting the FF, by adding a thin layer of hydrogenated amorphous germanium (a-Ge:H) buffer at the p+ a-SiC:H/TCO interface. The presence of a-Ge:H can either minimize or eliminate the Schottky barrier. We demonstrate ∼25% enhanced efficiency of the a-Si:H solar cell by using the a-Ge:H interfacial buffer compared to that without an a-Ge:H interfacial layer.
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88.40.H- Solar cells (photovoltaics)

Impact of a few dopant positions controlled by deterministic single-ion doping on the transconductance of field-effect transistors

Masahiro Hori, Takahiro Shinada, Yukinori Ono, Akira Komatsubara, Kuninori Kumagai, Takashi Tanii, Tetsuo Endoh, and Iwao Ohdomari

Appl. Phys. Lett. 99, 062103 (2011); http://dx.doi.org/10.1063/1.3622141 (3 pages) | Cited 4 times

Online Publication Date: 8 August 2011

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As semiconductor device dimensions decrease, the individual impurity atom position becomes a critical factor in determining device performance. We fabricated transistors with ordered and random dopant distributions on one side of the channel and evaluated the transconductance to investigate the impact of discrete dopant positions on the electron transport properties. The largest transconductance was observed when dopants were placed on the drain side in an ordered distribution; this was attributed to the suppression of injection velocity degradation on the source side and the uniformity of the electrostatic potential. Thus, the control of discrete dopant positions could enhance the device performance.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Optical properties of high quality Cu2ZnSnSe4 thin films

F. Luckert, D. I. Hamilton, M. V. Yakushev, N. S. Beattie, G. Zoppi, M. Moynihan, I. Forbes, A. V. Karotki, A. V. Mudryi, M. Grossberg, J. Krustok, and R. W. Martin

Appl. Phys. Lett. 99, 062104 (2011); http://dx.doi.org/10.1063/1.3624827 (3 pages) | Cited 9 times

Online Publication Date: 9 August 2011

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Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.
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78.66.Li Other semiconductors
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Sensitivity improvement of silicon-on-insulator photodiode by gold nanoparticles with substrate bias control

Atsushi Ono, Yuki Matsuo, Hiroaki Satoh, and Hiroshi Inokawa

Appl. Phys. Lett. 99, 062105 (2011); http://dx.doi.org/10.1063/1.3622650 (3 pages)

Online Publication Date: 9 August 2011

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The sensitivity of silicon-on-insulator (SOI) lateral p-n junction photodiode was enhanced by attaching gold (Au) nanoparticles. This was confirmed by comparing I-V characteristics with and without Au nanoparticles at various substrate voltages. Twofold enhancement was attained in the visible wavelength region when the substrate was biased to positive. The substrate bias changed the area of depletion layer in SOI, and the light scattering by Au nanoparticles effectively enhanced the sensitivity when the area of depletion layer was small.
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85.60.Dw Photodiodes; phototransistors; photoresistors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Measurement, analysis, and modeling of 1/f noise in pentacene thin film transistors

Hongki Kang, Lakshmi Jagannathan, and Vivek Subramanian

Appl. Phys. Lett. 99, 062106 (2011); http://dx.doi.org/10.1063/1.3622651 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2011

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In order to facilitate accurate noise modeling of organic thin-film-transistors (OTFTs), we provide comprehensive experimental results and analysis of unique low frequency noise characteristics in OTFTs. We conduct drain current noise measurements for pentacene-based thin-film-transistors (TFTs) having different grain size and operating region and use the resulting data to provide detailed mechanistic understanding of the underlying noise-generation phenomena that exist in OTFTs. The results show carrier trapping by traps within the semiconductor is the dominant source of low frequency noise and can be used in conjunction with a conventional unified noise model to accurately describe the noise behavior of pentacene TFTs.
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85.30.Tv Field effect devices
05.40.Ca Noise
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Structural and semiconductor-to-metal transitions of double-perovskite cobalt oxide Sr2−xLaxCoTiO6−δ with enhanced thermoelectric capability

Tohru Sugahara and Michitaka Ohtaki

Appl. Phys. Lett. 99, 062107 (2011); http://dx.doi.org/10.1063/1.3623476 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2011

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The thermoelectric properties of double-perovskite oxide Sr2−xLaxCoTiO6−δ were revealed to vary anomalously with the La concentration, plausibly due to a structural transition found in this study. Although the temperature dependence of the resistivity and thermopower of the present oxide showed a semiconductor-to-metal transition similar to those observed for other perovskite-related Co oxides such as Sr1−xYxCoO3−δ, the transition temperature was more than 350 K higher, implying considerable stabilization of the low-spin state of Co ions in the double-perovskite oxide. Consequently, the operating temperature range of the oxide for potential thermoelectric applications was significantly expanded toward higher temperatures.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.20.Pa Thermoelectric and thermomagnetic effects
72.60.+g Mixed conductivity and conductivity transitions

Origin of threshold voltage shift by interfacial trap density in amorphous InGaZnO thin film transistor under temperature induced stress

Bosul Kim, Eugene Chong, Do Hyung Kim, Yong Woo Jeon, Dae Hwan Kim, and Sang Yeol Lee

Appl. Phys. Lett. 99, 062108 (2011); http://dx.doi.org/10.1063/1.3615304 (3 pages) | Cited 4 times

Online Publication Date: 9 August 2011

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Effect of trap-density of amorphous InGaZnO thin film transistors (a-IGZO TFTs) were studied using different analysis of x-ray photoelectron spectroscopy (XPS) depth profile and density of states (DOSs). To change trap-densities systematically, rf-power was varied to cause different effect on the initial growth stage of a-IGZO layer grown on gate insulator. The interfacial trap-density was confirmed to be dominant effect on the performance and the threshold voltage shift of a-IGZO TFT by observing the variation of O1s binding energy from XPS. The relation between temperature stress induced and trap-density in deep level was investigated by analyzing DOSs.
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85.30.Tv Field effect devices

Correlation between low-frequency current-noise enhancement and high-frequency oscillations in GaN-based planar nanodiodes: A Monte Carlo study

A. Íñiguez-de-la-Torre, I. Íñiguez-de-la-Torre, J. Mateos, and T. González

Appl. Phys. Lett. 99, 062109 (2011); http://dx.doi.org/10.1063/1.3613956 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2011

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We present a spectral analysis of time sequences of current, calculated by means of Monte Carlo simulations, in GaN-based asymmetric nanodiodes, devices that are potential candidates to exhibit Gunn oscillations. It is found that the low-frequency noise increases significantly for biases close to the threshold voltage of Gunn oscillations, taking place at much higher frequencies of hundreds of gigahertz. Due to the inherent difficulty in detecting so fast fluctuations, the measurement of the low-frequency noise can be a quite useful tool for predicting current oscillations at sub-terahertz frequencies in these devices.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

High rate dry etching of InGaZnO by BCl3/O2 plasma

Wanjae Park, Ki-Woong Whang, Young Gwang Yoon, Jeong Hwan Kim, Sang-Ho Rha, and Cheol Seong Hwang

Appl. Phys. Lett. 99, 062110 (2011); http://dx.doi.org/10.1063/1.3624594 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2011

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This paper reports the results of the high-rate dry etching of indium gallium zinc oxide (IGZO) at room temperature using BCl3/O2 plasma. We achieved an etch rate of 250 nm/min. We inferred from the x-ray photoelectron spectroscopy analysis that BOx or BOClx radicals generated from BCl3/O2 plasma cause the etching of the IGZO material. O2 initiates the etching of IGZO, and Ar removes nonvolatile byproducts from the surface during the etching process. Consequently, a smooth etched surface results when these gases are added to the etch gas.
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81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Two-dimensional deformation potential model of mobility in small molecule organic semiconductors

J. E. Northrup

Appl. Phys. Lett. 99, 062111 (2011); http://dx.doi.org/10.1063/1.3624588 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2011

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An acoustic deformation potential model appropriate for transport in two dimensions is employed to estimate upper limits on the intrinsic hole mobility of DNTT-C10 [2,9-dialkyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene] and BTBT-C12 [2,7-dialkyl[1]benzo-thieno[3,2-b][1]benzothiophene]. First-principles calculations are employed to determine the values of effective masses, deformation potentials, and elastic constants entering the model. The analysis suggests that the upper limit on room temperature mobility within a single crystalline region in DNTT-C10 or BTBT-C12 may be some tens of cm2/Vs. The width of the π-bonded molecular core in the direction perpendicular to the transport plane is identified as a structural feature affecting mobility in two-dimensional organic semiconductors.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
71.15.-m Methods of electronic structure calculations
71.20.Rv Polymers and organic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Jj Elasticity and anelasticity, stress-strain relations

Enhanced thermoelectric power factor with impurity-induced resonant level

M. Liu, X. Y. Qin, C. S. Liu, and Z. Zeng

Appl. Phys. Lett. 99, 062112 (2011); http://dx.doi.org/10.1063/1.3624467 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2011

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Based on the resonant level concept, we presented an analytic calculation for the enhancement of the thermoelectric properties of semiconductor materials with element doping. We show that the power factor can be significantly enhanced due to a resonant energy level introduced by some element lies in the host bands and near the Fermi level and band edge. Our calculations reveal that by choosing optimal parameters for the element doping, such as impurity level, and doping concentration, one can obtain an optimum power factor for improved thermoelectric performance.
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71.55.Ht Other nonmetals
72.20.Pa Thermoelectric and thermomagnetic effects
73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization
61.72.up Other materials

Link between crystal quality and electrical properties of metalorganic vapour phase epitaxy InxGa1−xN thin films

V. Gorge, Z. Djebbour, A. Migan-Dubois, C. Pareige, C. Longeaud, K. Pantzas, T. Moudakir, S. Gautier, G. Orsal, P. L. Voss, and A. Ougazzaden

Appl. Phys. Lett. 99, 062113 (2011); http://dx.doi.org/10.1063/1.3624598 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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We report on the crystal quality of metalorganic vapour phase epitaxy-grown InGaN with indium content ranging from 0% to 20%. Absorbance measurements are fit to a model including band tails and a defect represented as a Brendel oscillator (R. Brendel, Appl. Phys. A 50, 587, 1990). Band tail absorbance, corresponding to contorted bonds, increases with increased In content. Above 10% of In, the presence of another defect, the concentration of which increases with In content, has been correlated with x-ray diffraction and Raman. We suggest that this defect corresponds to nitrogen vacancies, in agreement with a reported model for GaN.
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68.55.ag Semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.jd Vacancies
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Field-effect modulation of conductance in VO2 nanobeam transistors with HfO2 as the gate dielectric

Shamashis Sengupta, Kevin Wang, Kai Liu, Ajay K. Bhat, Sajal Dhara, Junqiao Wu, and Mandar M. Deshmukh

Appl. Phys. Lett. 99, 062114 (2011); http://dx.doi.org/10.1063/1.3624896 (3 pages) | Cited 7 times

Online Publication Date: 12 August 2011

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We study field-effect transistors realized from VO2 nanobeams with HfO2 as the gate dielectric. When heated up from low to high temperatures, VO2 undergoes an insulator-to-metal transition. We observe a change in conductance (∼6%) of our devices induced by gate voltage when the system is in the insulating phase. The response is reversible and hysteretic, and the area of hysteresis loop becomes larger as the rate of gate sweep is slowed down. A phase lag exists between the response of the conductance and the gate voltage. This indicates the existence of a memory of the system and we discuss its possible origins.
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72.60.+g Mixed conductivity and conductivity transitions
77.80.Dj Domain structure; hysteresis
85.30.Tv Field effect devices
71.30.+h Metal-insulator transitions and other electronic transitions
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