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21 Feb 2013

Volume 113, Issue 7, Articles (07xxxx)

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J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt
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back to top Electronic Structure and Transport

Extended X-ray absorption fine structure study of mixed-ligand copper(II) complexes having analogous structures

Abhijeet Gaur, B. D. Shrivastava, Krishna Srivastava, and J. Prasad

J. Appl. Phys. 113, 073701 (2013); http://dx.doi.org/10.1063/1.4792039 (11 pages)

Online Publication Date: 15 February 2013

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X-ray absorption fine structure spectra have been studied at the Cu K-edge in five mixed-ligand copper(II) complexes, viz., [Cu(L-glu)(bipy)] 1, [Cu(L-glu)(phen) (H2O)]·3H2O 2, [Cu(L-tyro)(bipy)(ClO4)]·2H2O 3, [Cu(L-phen)(bipy)(H2O)] (ClO4) 4, and [Cu(L-tyro)(phen)(H2O)] (ClO4)·1·5H2O 5 (where L-glu = L-glutamate dianion, L-tyro = L-tyrosinate anion, bipy = 2,2′-bipyridine, and phen =1,10-phenanthroline), having essentially the same structure. The crystallographic data are available for all the complexes using which five theoretical models have been generated. Firstly, extended X-ray absorption fine structure (EXAFS) data of each complex has been analyzed using its own theoretical model and the results obtained are found to be comparable with the crystallographic results. Then, the EXAFS data of each complex has been analyzed using the theoretical models of the remaining four of these complexes. For each complex, the structural parameters obtained by fitting EXAFS data with theoretical models of the four remaining complexes have been found to be comparable with those obtained by fitting its own theoretical model. Thus, it has been found that if the crystal structure is not available for a complex, then the crystal structure of similar or analogous complex can be used satisfactorily for generating the theoretical model for the EXAFS data analysis of that complex, even if different ligands are attached to the central metal atom. On the basis of EXAFS data analysis, the coordination geometries around the central metal ions in these complexes have been depicted.
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78.70.Dm X-ray absorption spectra
61.66.Hq Organic compounds

Temperature dependent surface photovoltage spectra of type I GaAs1−xSbx/GaAs multiple quantum well structures

P. Sitarek, J. Misiewicz, Y. S. Huang, H. P. Hsu, and K. K. Tiong

J. Appl. Phys. 113, 073702 (2013); http://dx.doi.org/10.1063/1.4792065 (4 pages)

Online Publication Date: 15 February 2013

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We present temperature dependent surface photovoltage spectra of GaAs1−xSbx/GaAs multiple quantum well structures. Our previous studies [Sitarek et al., J. Appl. Phys. 105, 123523 (2009)] have identified all features present in the surface photovoltage spectra and showed weak type-I band alignment in the investigated GaAsSb/GaAs system. By analyzing the changes in the relative intensity of features near the energy of fundamental transitions caused by the temperature variations, we are able to determine the energy difference between electronic states localized in GaAsSb quantum well and conduction band edge in the GaAs barrier. In addition, the Bose-Einstein parameters that describe the temperature dependences of 1hh-1e transitions are evaluated and discussed.
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72.40.+w Photoconduction and photovoltaic effects
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
73.25.+i Surface conductivity and carrier phenomena

Electroresistance and Joule heating effects in manganite thin films

Ll. Balcells, L. Peña, R. Galceran, A. Pomar, B. Bozzo, Z. Konstantinovic, F. Sandiumenge, and B. Martinez

J. Appl. Phys. 113, 073703 (2013); http://dx.doi.org/10.1063/1.4792222 (6 pages)

Online Publication Date: 15 February 2013

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Electroresistance phenomena have been investigated in La2/3Sr1/3MnO3 (LSMO) microbridges through the analysis of I-V characteristic curves. I-V curves are nonlinear in all the range of temperatures explored, but are almost reversible and exhibit origin symmetry which suggest the existence of Joule self-heating effects. However, comparing the resistance determined from the I-V curves (R = V/I) at the actual sample temperature, measured through a Pt thermometer microfabricated on top of the LSMO microbridges, with the resistance measured in thermal equilibrium, i.e., in the low current regime, it is evident that Joule self-heating effects alone cannot account for the experimental results. We demonstrate that oxygen depletion is the cause for the observed increase of resistance and the reduction of TC.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Bb Fe and its alloys

Co-doping with antimony to control phosphorous diffusion in germanium

H. A. Tahini, A. Chroneos, R. W. Grimes, and U. Schwingenschlögl

J. Appl. Phys. 113, 073704 (2013); http://dx.doi.org/10.1063/1.4792480 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2013

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In germanium, phosphorous and antimony diffuse quickly and as such their transport must be controlled in order to design efficient n-typed doped regions. Here, density functional theory based calculations are used to predict the influence of double donor co-doping on the migration activation energies of vacancy-mediated diffusion processes. The migration energy barriers for phosphorous and antimony were found to be increased significantly when larger clusters involving two donor atoms and a vacancy were formed. These clusters are energetically stable and can lead to the formation of even larger clusters involving a number of donor atoms around a vacancy, thereby affecting the properties of devices.
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66.30.J- Diffusion of impurities
61.72.jd Vacancies
61.72.uf Ge and Si

Effects of suboxide layers on the electronic properties of Si(100)/SiO2 interfaces: Atomistic multi-scale approach

Byung-Hyun Kim, Gyubong Kim, Kihoon Park, Mincheol Shin, Yong-Chae Chung, and Kwang-Ryeol Lee

J. Appl. Phys. 113, 073705 (2013); http://dx.doi.org/10.1063/1.4791706 (6 pages)

Online Publication Date: 15 February 2013

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A multi-scale approach connecting the atomistic process simulations to the device-level simulations has been applied to the Si(100)/SiO2 interface system. The oxidation of Si(100) surface was simulated by the atomic level molecular dynamics, the electronic structure of the resultant Si/suboxide/SiO2 interface was then obtained by the first-principles calculations, and finally, the leakage currents through the SiO2 gate dielectric were evaluated, with the obtained interface model, by the non-equilibrium Green's function method. We have found that the suboxide layers play a significant role for the electronic properties of the interface system and hence the leakage currents through the gate dielectric.
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71.20.-b Electron density of states and band structure of crystalline solids
81.65.Mq Oxidation
68.35.Ct Interface structure and roughness
71.15.-m Methods of electronic structure calculations
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Understanding and resolving the discrepancy between differential and actual minority carrier lifetime

J. A. Giesecke, S. W. Glunz, and W. Warta

J. Appl. Phys. 113, 073706 (2013); http://dx.doi.org/10.1063/1.4790716 (8 pages) | Cited 1 time

Online Publication Date: 19 February 2013

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Differential light-biased dynamic measurements of charge carrier recombination properties in semiconductors have long been known to yield only differential rather than actual recombination properties. Therefore, the determination of injection-dependent recombination properties from such measurements was previously found to require integration over the entire injection range. Recent investigations of the phase shift between a time-modulated irradiation of silicon samples and excess carrier density reveal a striking analogy to the above findings: the phase shift is greater than the actual effective carrier lifetime in the case of a positive derivative of lifetime with respect to excess carrier density, and vice versa. This work attempts to rearrange the mentioned previous findings in a quantitative theoretical description of light-biased dynamic measurements of effective carrier lifetime. Both light-biased differential lifetime measurements as well as harmonically time-modulated methods without additional bias light are shown to represent a limiting case in a general treatment of light-biased dynamic lifetime measurements derived here. Finally, we sketch a way to obtain actual recombination properties from differential measurements—referred to as a differential-to-actual (d2a) lifetime analysis, which does not require integration over the entire injection range.
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81.05.Cy Elemental semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Achieving direct band gap in germanium through integration of Sn alloying and external strain

Suyog Gupta, Blanka Magyari-Köpe, Yoshio Nishi, and Krishna C. Saraswat

J. Appl. Phys. 113, 073707 (2013); http://dx.doi.org/10.1063/1.4792649 (7 pages)

Online Publication Date: 19 February 2013

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GeSn is predicted to exhibit an indirect to direct band gap transition at alloy Sn composition of 6.5% and biaxial strain effects are investigated in order to further optimize GeSn band structure for optoelectronics and high speed electronic devices. A theoretical model has been developed based on the nonlocal empirical pseudopotential method to determine the electronic band structure of germanium tin (GeSn) alloys. Modifications to the virtual crystal potential accounting for disorder induced potential fluctuations are incorporated to reproduce the large direct band gap bowing observed in GeSn alloys.
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71.20.Gj Other metals and alloys
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Lattice strain analysis of silicon fin field-effect transistor structures wrapped by Ge2Sb2Te5 liner stressor

Yinjie Ding, Ran Cheng, Anyan Du, and Yee-Chia Yeo

J. Appl. Phys. 113, 073708 (2013); http://dx.doi.org/10.1063/1.4792477 (8 pages)

Online Publication Date: 20 February 2013

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The local strain components in the source/drain (S/D) and channel regions of Si fin field-effect transistor (FinFET) structures wrapped around by a Ge2Sb2Te5 liner stressor were investigated for the first time using nano-beam diffraction. When the Ge2Sb2Te5 (GST) layer changes phase from amorphous to crystalline, it contracts and exerts a large stress on the Si fins. This results in large compressive strain in the S/D region of ⟨math10⟩-oriented Si FinFETs of up to −1.15% and −1.57% in the ⟨110⟩ (horizontal) and ⟨001⟩ (vertical) directions, respectively. In the channel region of the FinFETs under the metal gate, the GST contraction results in up to −1.47% and −0.61% compressive strain in the ⟨110⟩ and ⟨001⟩ directions, respectively. In the channel region, the ⟨110⟩ compressive strain is higher at the fin sidewalls and lower near the fin center, while the ⟨001⟩ compressive strain is lower at the sidewalls and higher near the center.
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85.30.Tv Field effect devices

Thermoelectric properties of p-type (Bi2Te3)x(Sb2Te3)1−x single crystals doped with 3 wt. % Te

Ö. Ceyda Yelgel and G. P. Srivastava

J. Appl. Phys. 113, 073709 (2013); http://dx.doi.org/10.1063/1.4792653 (8 pages)

Online Publication Date: 20 February 2013

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In the present work, thermoelectric properties of p-type (Bi2Te3)x (Sb2Te3)1−x single crystals doped with 3 wt. % Te are theoretically explored for various chemical compositions (x = 0.18, 0.19, 0.20, 0.22, 0.24, 0.26) in the temperature range of 290–500 K. The influence of the chemical composition in enhancing the thermoelectric figure of merit (ZT) is discussed in detail. Using the nearly-free electron approximation and the Fermi-Dirac statistics, the temperature dependences of Fermi level (Ef), Seebeck coefficient (S), and electrical conductivity (σ) are successfully reproduced as reported in the experimental study of Li et al. [Intermetallics 19, 2002 (2011)]. The thermal conductivity contributions from phonons (κph), acceptor holes (κh), and electron-hole pairs (κbp) are included by employing Srivastava's scheme, Wiedemann-Franz law, and Price's theory, respectively. By combining all three contributions of the thermal conductivity we successfully explain the experimental measurements of the total thermal conductivity as reported by Li et al. Furthermore, it is theoretically found that among all the compositions the p-type 20%(Bi2Te3)-80%(Sb2Te3) sample has the maximum ZT value of 1.31 at 390 K, which is also in good agreement with the experimental results obtained by Li et al.
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81.05.Hd Other semiconductors
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
71.20.Ps Other inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
72.80.Jc Other crystalline inorganic semiconductors

Directional quantum transport in graphyne p-n junction

Bumned Soodchomshom, I.-Ming Tang, and Rassmidara Hoonsawat

J. Appl. Phys. 113, 073710 (2013); http://dx.doi.org/10.1063/1.4792500 (8 pages)

Online Publication Date: 21 February 2013

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Graphyne, a newly proposed allotrope of carbon, has a structure which is topologically equivalent to that of a strongly distorted graphene [B. G. Kim and H. J. Choi, Phys. Rev. B 86, 115435 (2012)]. The energy gap between the valence and conduction bands is due to the symmetry breaking caused by there being three topologically inequivalent hoping elements. The valleyless fermionic transport properties of γ-graphyne are different from those of graphene since the two valleys are merged together in this carbon allotrope. The transmission and conductance of the electrons in γ-graphyne are found to be directionally dependent. Klein tunneling is predicted if the tunneling is in the y-direction. If the tunneling is in the x-direction, perfect back reflection (anti Klein tunneling) is predicted if the tunneling is at normal incidence. The consequences of these directional transport properties on the performances of p-n junctions fabricated with this carbon allotrope are studied. This work reveals the advantages of building p-n junctions based on γ-gaphyne.
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72.80.Vp Electronic transport in graphene
73.22.Pr Electronic structure of graphene
72.20.Ee Mobility edges; hopping transport
73.40.Gk Tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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