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16 May 2011

Volume 98, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 98, 201101 (2011); http://dx.doi.org/10.1063/1.3590716 (3 pages)

Martynas Beresna, Mindaugas Gecevičius, Peter G. Kazansky, and Titas Gertus
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Strain in Si doped GaN and the Fermi level effect

Jinqiao Xie, Seiji Mita, Anthony Rice, James Tweedie, Lindsay Hussey, Ramón Collazo, and Zlatko Sitar

Appl. Phys. Lett. 98, 202101 (2011); http://dx.doi.org/10.1063/1.3589978 (3 pages) | Cited 5 times

Online Publication Date: 16 May 2011

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Using high resolution x-ray diffraction and Hall effect measurements, we found that the tensile strain caused by dislocation inclination in Si doped GaN became immeasurable when carbon codoping was used to compensate the free carriers. This result suggested that the tensile strain is related to free carrier concentration instead of Si concentration. Such an effect could be explained by the Fermi level effect on the surface-mediated dislocation climb governed by Ga vacancies, whose concentration is strongly influenced by the Fermi level position. This phenomenon is possibly similar to the well-known Fermi level effect in GaAs and GaP systems.
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71.20.Nr Semiconductor compounds
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.jd Vacancies

Solution processed Ni-doped TiO2 p-type channel in field effect transistor assembly with <10 nm thin Ba0.5Sr0.5TiO3 dielectric layer

Soumen Das, Jin-Hwan Kim, Yong-Kyu Park, and Yoon-Bong Hahn

Appl. Phys. Lett. 98, 202102 (2011); http://dx.doi.org/10.1063/1.3592736 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2011

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Solution processed field effect transistor structures were fabricated by inserting a Ba0.5Sr0.5TiO3 layer to form Ag/ZnO/Ba0.5Sr0.5TiO3/Ni2+:TiO2/n-Si assembly. Such assembly registered an on-to-off current ratio as large as 103 with very low off-state current ∼ 10−12 A. The low leakage current is attributed to the appreciably higher values of valence/conduction band off-set of Ba0.5Sr0.5TiO3/semiconductor heterojunction. The device response was studied as a function of temperature in the range of 25–175 °C. The hole diffusion coefficient and mobility of p-TiO2 was calculated ∼ 10−3 cm2/s and ∼ 0.13–0.15 cm−2 V−1 s−1, respectively.
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85.30.Tv Field effect devices

Sub-Poissonian shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions

Tomonori Arakawa, Koji Sekiguchi, Shuji Nakamura, Kensaku Chida, Yoshitaka Nishihara, Daichi Chiba, Kensuke Kobayashi, Akio Fukushima, Shinji Yuasa, and Teruo Ono

Appl. Phys. Lett. 98, 202103 (2011); http://dx.doi.org/10.1063/1.3590921 (3 pages)

Online Publication Date: 18 May 2011

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We measured the shot noise in the CoFeB/MgO/CoFeB-based magnetic tunneling junctions with a high tunneling magnetoresistance ratio (over 200% at 3 K). Although the Fano factor in the antiparallel configuration is close to unity, it is observed to be typically 0.91±0.01 in the parallel configuration. It indicates the sub-Poissonian process of the electron tunneling in the parallel configuration due to the relevance of the spin-dependent coherent transport in the low bias regime.
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72.70.+m Noise processes and phenomena
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.-b Spin polarized transport
79.60.Jv Interfaces; heterostructures; nanostructures

Fast electrical switching of spin injection in nonlocal spin transport devices

A. Fuhrer, S. F. Alvarado, G. Salis, and R. Allenspach

Appl. Phys. Lett. 98, 202104 (2011); http://dx.doi.org/10.1063/1.3590726 (3 pages) | Cited 2 times

Online Publication Date: 19 May 2011

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We present spin-injection experiments in a nonlocal spin transport device where spin is injected from a ferromagnetic FeCo electrode into a GaAs epilayer. The magnetization of the injection contact is switched by Oersted fields generated by alternating current pulses. This enables fast and offset-free measurements of nonlocal spin signals. Due to a negligible time-averaged electron spin polarization, dynamic nuclear polarization effects are small and Hanle curves measured down to T = 3 K can be fit very accurately by drift-diffusion theory if a small constant Overhauser field BN = 0.4 mT is accounted for.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport

Diffusion-limited nonradiative recombination at extended defects in hydride vapor phase epitaxy GaN layers

Patrik Ščajev, Alexander Usikov, Vitali Soukhoveev, Ramūnas Aleksiejūnas, and Kęstutis Jarašiūnas

Appl. Phys. Lett. 98, 202105 (2011); http://dx.doi.org/10.1063/1.3591173 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2011

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Time-resolved free-carrier absorption and transient grating techniques were applied to determine carrier lifetimes and diffusion coefficients in a set of hydride vapor phase epitaxy GaN layers of various thickness (from 10 to 145 μm). A linear increase in nonradiative carrier lifetime in 80–800 K range found to be in a correlation with decrease of the bipolar carrier diffusion coefficient. This correlation confirmed that recombination rate is governed by carrier diffusive flow to the grain boundaries of columnar defects. A model of diffusion-governed nonradiative lifetime was proposed for fitting the measured lifetime values in the layers of different thickness as well as lifetime dependence on temperature or threading dislocation density.
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61.72.Nn Stacking faults and other planar or extended defects
66.30.-h Diffusion in solids
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
73.61.Ey III-V semiconductors

Charge transport in solution processable polycrystalline dual-gate organic field effect transistors

A. K. Tripathi, E. C. P. Smits, M. Loth, J. E. Anthony, and G. H. Gelinck

Appl. Phys. Lett. 98, 202106 (2011); http://dx.doi.org/10.1063/1.3591969 (3 pages)

Online Publication Date: 19 May 2011

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Dual gate organic thin film transistors based on solution processable fluorinated 5,11 bis(triethylsilylethynyl) anthradithiophene semiconductor were fabricated. Top (Teflon™, εr = 2.1) and bottom (SiO2, εr = 3.9) gate dielectrics with different dielectric constants were chosen. Top gate mobilities >1 cm2/Vs and bottom gate mobilities >0.1 cm2/V s were achieved. Temperature dependent mobility measurements show thermally activated charge transport and a comparative analysis is performed in the framework of two models representing polaron hopping as well as hopping in Gaussian density of states (DOS), respectively.
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85.30.Tv Field effect devices

Band gap of InxGa1−xN: A first principles analysis

Mathieu César, Youqi Ke, Wei Ji, Hong Guo, and Zetian Mi

Appl. Phys. Lett. 98, 202107 (2011); http://dx.doi.org/10.1063/1.3592573 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2011

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We report first principles analysis of the band gap Eg of ternary group-III nitride InxGa1−xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method. We have implemented the semilocal modified Becke–Johnson (MBJ) exchange potential to accurately determine the band gap. The doping of In atoms into the GaN crystal is handled by the InxGa1−xN alloy model within the coherent potential approximation (CPA). The LMTO-CPA-MBJ approach allows us to predict Eg as a function of arbitrary In concentration x. Quantitative comparison to the experimental data is made.
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71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Discerning passivation mechanisms at a-Si:H/c-Si interfaces by means of photoconductance measurements

C. Leendertz, N. Mingirulli, T. F. Schulze, J. P. Kleider, B. Rech, and L. Korte

Appl. Phys. Lett. 98, 202108 (2011); http://dx.doi.org/10.1063/1.3590254 (3 pages) | Cited 7 times

Online Publication Date: 20 May 2011

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The photoconductance decay (PCD) measurement is a fast and simple method to characterize amorphous/crystalline (a-Si:H/c-Si) silicon interfaces for high-efficiency solar cells. However, PCD only yields information concerning the overall recombination rate in the structure. To overcome this limitation, we have developed and validated a computer-aided PCD (CA-PCD) analysis method to determine the defect density of recombination-active dangling bonds at the interface and the potential drop in the crystalline absorber adjacent to the interface. As a practical example, we investigate a-Si:H(p)/a-Si:H(i)/c-Si(n) layer stacks and show that the CA-PCD method is capable of discerning the influence of field-effect and defect passivation.
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81.65.Rv Passivation
71.55.Cn Elemental semiconductors
88.40.H- Solar cells (photovoltaics)
68.35.Ct Interface structure and roughness
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

Anisotropic thermopower and magnetothermopower in a misfit-layered calcium cobaltite

G. D. Tang, H. H. Guo, T. Yang, D. W. Zhang, X. N. Xu, L. Y. Wang, Z. H. Wang, H. H. Wen, Z. D. Zhang, and Y. W. Du

Appl. Phys. Lett. 98, 202109 (2011); http://dx.doi.org/10.1063/1.3592831 (3 pages)

Online Publication Date: 20 May 2011

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An unusual anisotropy of thermopower and magnetothermopower has been observed in the powerful thermoelectric Ca3Co4O9+δ single crystal. The in-plane thermopower is about twice as big as the out-of-plane thermopower. Combining ab initio band structure calculation with semiclassical model analysis, we understand this anisotropy with band structure effects and especially with anisotropic Fermi surface. We find that a strong anisotropy in the topology of Fermi surface leads to the anisotropy of (magneto)thermopower. This study may also shed light on anisotropic properties of other layered cobalt oxides.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.15.-m Methods of electronic structure calculations
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Ps Other inorganic compounds

Structural and vibrational properties of amorphous GeO2 from first-principles

E. Scalise, M. Houssa, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 98, 202110 (2011); http://dx.doi.org/10.1063/1.3593036 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2011

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The structural and vibrational properties of amorphous germanium oxide (a-GeO2) are investigated using first-principles calculations based on density functional theory. We first generate an a-GeO2 structure by first-principles molecular dynamics and analyze its structural properties. The vibrational spectra is then calculated within a density-functional approach. Both static and dynamic properties are in good agreement with experimental data. We next generate defects in our structure (oxygen vacancies with several density and charge states) and consider the most stable atomic configurations, focusing on the vibrational features of threefold coordinated O and divalent Ge centers.
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63.50.Lm Glasses and amorphous solids
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.23.-k Electronic structure of disordered solids
61.43.Bn Structural modeling: serial-addition models, computer simulation
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