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1 Jul 2010

Volume 108, Issue 1, Articles (01xxxx)

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J. Appl. Phys. 108, 011101 (2010); http://dx.doi.org/10.1063/1.3457141 (19 pages)

Xunlin Qiu
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back to top Electronic Structure and Transport

Polarization screening and induced carrier density at the interface of LaAlO3 overlayer on SrTiO3 (001)

Yun Li and Jaejun Yu

J. Appl. Phys. 108, 013701 (2010); http://dx.doi.org/10.1063/1.3455877 (5 pages) | Cited 3 times

Online Publication Date: 1 July 2010

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We investigate the role of lattice polarization in determination of induced carrier density at the n-type interface of LaAlO3 overlayer on SrTiO3 (001) by carrying out density-functional-theory calculations. When no oxygen vacancy or defect is present, the magnitude of polarization screening in the LaAlO3 layers is found to be correlated with the carrier charge induced at the interface. For the interfaces with less than seven LaAlO3 layers, the density of induced carrier is smaller than 0.1 electrons per unit-cell and the electrostatic screening can be covered by the interface state consisting of Ti dxy state. When the overlayer becomes thicker, the extended bound state in the SrTiO3 side contributes to the charge screening.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
73.20.-r Electron states at surfaces and interfaces

Effects of single-layer Shockley stacking faults on the transport properties of high-purity semi-insulating 4H–SiC

F. Fabbri and A. Cavallini

J. Appl. Phys. 108, 013702 (2010); http://dx.doi.org/10.1063/1.3456160 (4 pages)

Online Publication Date: 2 July 2010

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The electrical properties of high-purity 4H–SiC epitaxial layers are investigated. The current density versus applied voltage curves shows that some specimens have space charge limited transport behavior. Lampert–Mark model for trap-controlled electron transport in semi-insulating materials demonstrated the presence of an intragap state at 0.26 eV below the conduction band. Photodeep level transient spectroscopy has confirmed the presence of a deep level at about 0.3 eV below the conduction band only in samples with non-Ohmic behavior. Cathodoluminescence imaging has revealed the presence of high luminescent areas related to stacking faults (SFs) under the devices showing non-Ohmic behavior. The presence of single-layer SFs was detected by cathodoluminescence spectroscopy due to the typical emission at 2.95 eV. Thus, we demonstrated that the SFs modified the charge transport from Ohmic conduction to space charge limited conduction of the affected samples.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
73.50.Fq High-field and nonlinear effects
71.55.Ht Other nonmetals
78.60.Hk Cathodoluminescence, ionoluminescence

First-principles calculation and transmission electron microscopy observation for hydrogen adsorption on carbon nanowalls

Y. Kita, S. Hayashi, I. Kinoshita, M. Tachibana, M. Tachikawa, K. Kobayashi, and M. Tanimura

J. Appl. Phys. 108, 013703 (2010); http://dx.doi.org/10.1063/1.3446830 (4 pages) | Cited 2 times

Online Publication Date: 2 July 2010

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Transmission electron microscopy (TEM) technique was used to investigate the structure of carbon nanowalls (CNWs). The TEM observation clearly indicated the existence of the bended graphene structure in boundary regions between the crystallites of CNWs. According to this TEM result, the first-principles calculation was employed for the bended coronene molecule as the model of the boundary region between the crystallites of CNWs, to elucidate the mechanism of the hydrogen adsorption to CNWs. The hydrogen adsorption energies onto both on-top and hollow sites become greater as the bending angle increases, because the electronic structure of the carbon atom at the adsorption site changes from sp2 to sp3 hybridization character by natural bond orbital analysis. Our computational result is reasonably consistent with the specific feature of hydrogen adsorption to CNWs, which had been reported in our previous work by ultraviolet photoelectron spectroscopy and temperature program desorption measurements by Kinoshita et al.[Chem. Phys. Lett. 450, 360 (2008)] .
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.65.Pq Graphene films

Comparative NMR study of copper-based intermetallics with ZrCuSiAs-type structure

C. S. Lue, W. J. ChangJen, and T. H. Su

J. Appl. Phys. 108, 013704 (2010); http://dx.doi.org/10.1063/1.3457222 (4 pages)

Online Publication Date: 6 July 2010

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The electronic characteristics of ZrCuGe2, ZrCuSi2, and HfCuSi2 are systematically investigated using 63Cu NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on each individual compound have been identified. We found that the observed electric field gradient is consistent with the covalent bonding nature within the Cu atomic layers. The Knight shifts together with relaxation rates provide a measure of Cu d partial Fermi-level density of states, Nd(EF). Universally small Nd(EF) was found in all studied materials, suggests that the Cu d states are well below the Fermi energy and therefore the characteristic electronic structure near EF is primarily of sp type. We further pointed out that the low Nd(EF) value is an important factor for the lack of superconductivity in these Cu-based intermetallics within the ZrCuSiAs-type structure.
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76.60.Cq Chemical and Knight shifts
76.60.Gv Quadrupole resonance
76.60.Es Relaxation effects
71.20.Gj Other metals and alloys

Advanced analytical model for the effective recombination velocity of locally contacted surfaces

Pierre Saint-Cast, Marc Rüdiger, Andreas Wolf, Marc Hofmann, Jochen Rentsch, and Ralf Preu

J. Appl. Phys. 108, 013705 (2010); http://dx.doi.org/10.1063/1.3437126 (7 pages) | Cited 4 times

Online Publication Date: 6 July 2010

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In this paper an analytical model of the effective recombination (Seff) on the back surface of locally contacted solar cell is developed. We justify this approach by first showing that the three-dimensional (3D) problem can be reduced to a one-dimensional (1D) problem by calculating Seff. The values of Seff calculated with our model and two existing models are compared to finite element simulations. A large range of cases from high to low scale structures, including variation in the surface recombination velocity at the passivated area are investigated. The model presented in this paper is in good agreement with finite element simulations. Existing models from literature are also compared to finite element simulations, showing some of their limitations. In addition, we propose a method, not restricted to dark conditions, that simulates the 3D locally contacted structures by means of two 1D simulations.
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88.40.H- Solar cells (photovoltaics)
81.65.Rv Passivation

Electron and hole mobility reduction and Hall factor in phosphorus-compensated p-type silicon

F. E. Rougieux, D. Macdonald, A. Cuevas, S. Ruffell, J. Schmidt, B. Lim, and A. P. Knights

J. Appl. Phys. 108, 013706 (2010); http://dx.doi.org/10.1063/1.3456076 (5 pages) | Cited 13 times

Online Publication Date: 7 July 2010

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The conductivity mobility for majority carrier holes in compensated p-type silicon is determined by combined measurement of the resistivity and the net doping, the latter via electrochemical capacitance-voltage measurements. The minority electron mobility was also measured with a technique based on measurements of surface-limited effective carrier lifetimes. While both minority and majority carrier mobilities are found to be significantly reduced by compensation, the impact is greater on the minority electron mobility. The Hall factor, which relates the Hall mobility to the conductivity mobility, has also been determined using the Hall method combined with the capacitance-voltage measurements. Our results indicate a similar Hall factor in both compensated and noncompensated samples.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

Synthesis and thermoelectric properties of RuO2 nanorods

Denis Music, Felix H.-U. Basse, Ralf Haßdorf, and Jochen M. Schneider

J. Appl. Phys. 108, 013707 (2010); http://dx.doi.org/10.1063/1.3452380 (5 pages) | Cited 5 times

Online Publication Date: 7 July 2010

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We have explored the effect of the O/Ru ratio on the morphology and the Seebeck coefficient of RuO2 nanorods (space group P42/mnm) synthesized by reactive sputtering. At an O/Ru ratio of 1.69, a faceted surface is observed, while nanorod formation occurs at O/Ru ratios of 2.03 and 2.24. Using classical molecular dynamics with the potential parameters derived in this work, we show that volatile species enable nanorod formation. Based on ab initio calculations, two effects of the nanorod formation on the Seebeck coefficient are observed: (i) increase due to additional states in the vicinity of the Fermi level and (ii) decrease due to oxygen point defects (volatile species). These two competing effects give rise to a moderate increase in the Seebeck coefficient upon nanorod formation.
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81.07.Bc Nanocrystalline materials
72.20.Pa Thermoelectric and thermomagnetic effects
81.15.Cd Deposition by sputtering

Effect of threading screw and edge dislocations on transport properties of 4H–SiC homoepitaxial layers

S. I. Maximenko, J. A. Freitas, Jr., R. L. Myers-Ward, K.-K. Lew, B. L. VanMil, C. R. Eddy, Jr., D. K. Gaskill, P. G. Muzykov, and T. S. Sudarshan

J. Appl. Phys. 108, 013708 (2010); http://dx.doi.org/10.1063/1.3448230 (6 pages) | Cited 5 times

Online Publication Date: 8 July 2010

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Local recombination properties of threading screw and edge dislocations in 4H–SiC epitaxial layers have been studied using electron beam induced current (EBIC). The minority carrier diffusion length in the vicinity of dislocations was found to vary with dislocation type. Screw dislocations had a more pronounced impact on diffusion length than the edge dislocations, evidencing stronger recombination activity. Temperature dependence of EBIC contrast of dislocations suggests that their recombination activity is controlled by deep energy levels in the vicinity of dislocation cores. This paper shows that the type of dislocation (screw or edge) can be identified from analysis of EBIC contrast.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Le Other inorganic semiconductors
71.55.Ht Other nonmetals
68.60.-p Physical properties of thin films, nonelectronic
81.05.Hd Other semiconductors

Energy exchange between electrons and phonons in quantum dot connected between pyramidal and abrupt transport nanojunctions

Jack Yang and Sean Li

J. Appl. Phys. 108, 013709 (2010); http://dx.doi.org/10.1063/1.3437650 (5 pages)

Online Publication Date: 8 July 2010

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Electron–phonon scattering induced intensive heat generation is one of the major bottlenecks for high performance nanoelectronic circuits in miniaturizing their line widths beyond submicron scales. The existence of quantum confinement effects in nanoscaled conduction channels results in which the behaviors of electrons and phonons will become drastically different from those in bulk materials. This is especially true in the junction regions where the nanochannel is linked with the electronic and thermal reservoirs. The present study investigated the structural effect of pyramidal and abrupt junctions in heat exchange between electron and phonon subsystems in the transport through a quantum dot (QD). The numerical results indicated that by confining the electronic and phononic wave functions in the pyramidal junctions, a higher saturation heat exchange would be reached at a lower bias, compared to that of the abrupt junction. The pyramidal junction also becomes more subjected to size effects, where the saturation heat exchange decreases as the size of the junction increases. Such an effect is less significant in the abrupt junctions. Surface reconstruction induced bond stiffening in the pyramidal junctions plays a dominant role in modulating the junction heat exchange by blockading the phonon transportation between the reservoirs through the QD, which effectively reducing the amount of heat being generated. The results may provide new insights on the fundamental science and relationship between contact atomic structures and thermal dissipations in nanoelectronics.
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73.63.Kv Quantum dots
73.21.La Quantum dots
63.20.kd Phonon-electron interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
47.27.te Turbulent convective heat transfer

Electronic band structure calculations for biaxially strained Si, Ge, and III–V semiconductors

Jiseok Kim and Massimo V. Fischetti

J. Appl. Phys. 108, 013710 (2010); http://dx.doi.org/10.1063/1.3437655 (15 pages) | Cited 12 times

Online Publication Date: 9 July 2010

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Electronic band structure and effective masses for relaxed and biaxially strained Si, Ge, III–V compound semiconductors (GaAs, GaSb, InAs, InSb, InP) and their alloys (InxGa1−xAs, InxGa1−xSb) on different interface orientations, (001), (110), and (111), are calculated using nonlocal empirical pseudopotential with spin-orbit interaction. Local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and to obtain correct workfunctions. The nonlocal and spin-orbit terms are linearly interpolated between anions and cations for III–V semiconductors. The virtual crystal approximation is employed for the InxGa1−xAs and InxGa1−xSb alloys and deformation potentials are determined using linear deformation-potential theory. Band gap bowing parameters are extracted using least-square fitting for relaxed alloys and for strained InxGa1−xAs on (001), (110), and (111) InP. The dependence on biaxial strain of the electron and hole effective masses at the symmetry points Γ, X, and L exhibits a continuous variation at Γ and L but sudden changes appear at Δ minima caused by the flatness of the dispersion along the Δ line near the minimum.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.-b Electron density of states and band structure of crystalline solids
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
02.60.Ed Interpolation; curve fitting
02.10.De Algebraic structures and number theory

Characterization of gate recessed GaN/AlGaN/GaN high electron mobility transistors fabricated using a SiCl4/SF6 dry etch recipe

R. T. Green, I. J. Luxmoore, K. B. Lee, P. A. Houston, F. Ranalli, T. Wang, P. J. Parbrook, M. J. Uren, D. J. Wallis, and T. Martin

J. Appl. Phys. 108, 013711 (2010); http://dx.doi.org/10.1063/1.3457356 (7 pages)

Online Publication Date: 12 July 2010

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Incorporating GaN capping layers in conjunction with recessing has been identified as a means to maximize the high frequency performance of AlGaN/GaN high electron mobility transistors (HEMTs). Doping the cap heavily n-type is required in order to ensure minimal loss of carriers from the channel. Using a SiCl4/SF6 dry etch plasma recipe, 250 nm gate length HEMTs with recess lengths varying from 300 nm to 5 μm are fabricated. Heavily doped n+GaN caps enabled contact resistances of 0.3 Ω mm to be achieved. Recessing using a SiCl4/SF6 recipe does not introduce significant numbers of bulk traps. Gate recessing in conjunction with Si3N4 passivation reduces rf dispersion to negligible levels.
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85.30.Tv Field effect devices

Scattering analysis of two-dimensional electrons in AlGaN/GaN with bulk related parameters extracted by simple parallel conduction extraction method

S. B. Lisesivdin, A. Yildiz, N. Balkan, M. Kasap, S. Ozcelik, and E. Ozbay

J. Appl. Phys. 108, 013712 (2010); http://dx.doi.org/10.1063/1.3456008 (7 pages) | Cited 5 times

Online Publication Date: 15 July 2010

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We carried out the temperature (22–350 K) and magnetic field (0.05 and 1.4 T) dependent Hall mobility and carrier density measurements on Al0.22Ga0.78N/GaN heterostructures with AlN interlayer grown by metal-organic chemical-vapor deposition. Hall data is analyzed with a simple parallel conduction extraction method and temperature dependent mobility and carrier densities of the bulk and two-dimensional (2D) electrons are extracted successfully. The results for the bulk carriers are discussed using a theoretical model that includes the most important scattering mechanisms that contribute to the mobility. In order to investigate the mobility of two-dimensional electron gas, we used a theoretical model that takes into account the polar optical phonon scattering, acoustic phonon scattering, background impurity scattering, and interface roughness scattering in 2D. In these calculations, the values are used for the deformation potential and ionized impurity density values were obtained from the bulk scattering analysis. Therefore, the number of fitting parameters was reduced from four to two.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Ey III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
68.35.Ct Interface structure and roughness
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