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1 Mar 2009

Volume 105, Issue 5, Articles (05xxxx)

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J. Appl. Phys. 105, 051101 (2009); http://dx.doi.org/10.1063/1.3081635 (17 pages)

Kraig E. Sheetz and Jeff Squier
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Modeling two-dimensional solid-phase epitaxial regrowth using level set methods

S. Morarka, N. G. Rudawski, M. E. Law, K. S. Jones, and R. G. Elliman

J. Appl. Phys. 105, 053701 (2009); http://dx.doi.org/10.1063/1.3082086 (5 pages) | Cited 7 times

Online Publication Date: 3 March 2009

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Modeling the two-dimensional (2D) solid-phase epitaxial regrowth (SPER) of amorphized Si (variously referred to as solid-phase epitaxial growth, solid-phase epitaxy, solid-phase epitaxial crystallization, and solid-phase epitaxial recrystallization) has become important in light of recent studies which have indicated that relative differences in the velocities of regrowth fronts with different crystallographic orientations can lead to the formation of device degrading mask edge defects. Here, a 2D SPER model that uses level set techniques as implemented in the Florida object oriented process simulator to propagate regrowth fronts with variable crystallographic orientation (patterned material) is presented. Apart from the inherent orientation dependence of the SPER velocity, it is established that regrowth interface curvature significantly affects the regrowth velocity. Specifically, by modeling the local SPER velocity as being linearly dependent on the local regrowth interface curvature, data acquired from transmission electron microscopy experiments matches reasonably well with simulations, thus providing a stable model for simulating 2D regrowth and mask edge defect formation in Si.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.ag Semiconductors
61.80.Jh Ion radiation effects

Theory of the motion at the band crossing points in bulk semiconductor crystals and in inversion layers

David Esseni and Pierpaolo Palestri

J. Appl. Phys. 105, 053702 (2009); http://dx.doi.org/10.1063/1.3078039 (11 pages) | Cited 1 time

Online Publication Date: 3 March 2009

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This paper presents an original investigation of the motion at the band crossing points in the energy dispersion of either bulk crystals or inversion layers. In particular, by using a formalism based on the time dependent Schrödinger equation, we address the quite elusive topic of the belonging of the carriers to the bands that are degenerate at the crossing point. This problem is relevant and delicate for the semiclassical transport modeling in numerically calculated band structures; however, its clarification demands a full-quantum transport treatment. We here propose analytical derivations and numerical calculations clearly demonstrating that, in a given band structure, the motion of the carriers at the band crossing points is entirely governed by the overlap integrals between the eigenfunctions of the Hamiltonian that has produced the same band structure. Our formulation of the problem is quite general and we apply it to the silicon conduction band calculated by means of the nonlocal pseudopotential method, to the hole inversion layers described by a quantized k⋅p approach, and to the electron inversion layers described by the effective mass approximation method. In all the physical systems, our results underline the crucial role played by the abovementioned overlap integrals.
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71.20.Mq Elemental semiconductors
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Thermoelectric performance of NiyMo3Sb7−xTex (y ≤ 0.1, 1.5 ≤ x ≤ 1.7)

H. Xu, K. M. Kleinke, T. Holgate, H. Zhang, Z. Su, T. M. Tritt, and H. Kleinke

J. Appl. Phys. 105, 053703 (2009); http://dx.doi.org/10.1063/1.3086641 (5 pages) | Cited 8 times

Online Publication Date: 3 March 2009

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Mo3Sb7−xTex is a high temperature thermoelectric material, reported to reach figure of merit (ZT) = 0.8 at 1023 K. Various p-type samples of NiyMo3Sb7−xTex were prepared with y ≤ 0.1 and 1.5 ≤ x ≤ 1.7 via high temperature reactions at 993 K. Adding transition metal atoms into the empty cube formed by Sb atoms significantly alters the band structure and thus the thermoelectric properties. Electronic band structure calculations indicate that adding Ni slightly increases the charge carrier concentration, while higher Te content causes a decrease. Thermoelectric properties were determined on pellets densified via hot pressing at 993 K. Seebeck as well as electrical and thermal conductivity measurements were performed up to 1023 K. The highest ZT value thus far was obtained from a sample of nominal composition Ni0.06Mo3Sb5.4Te1.6, which amounts to 0.93 at 1023 K.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.20.Nr Semiconductor compounds

MoOx modified ZnGaO based transparent conducting oxides

Titas Dutta, P. Gupta, V. Bhosle, and J. Narayan

J. Appl. Phys. 105, 053704 (2009); http://dx.doi.org/10.1063/1.3078812 (8 pages) | Cited 3 times

Online Publication Date: 4 March 2009

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We report here the growth of high work function bilayered structures of thin MoOx (2.0<x<2.75) layer (few nanometers) on Zn0.95Ga0.05O films by pulsed laser deposition (PLD) on glass and sapphire substrates for transparent electrode applications. It was found that the films were highly textured along [0001] direction. The crystalline quality of the films deposited at different substrate temperatures was investigated by x-ray diffraction, transmission electron microscopy (TEM) imaging, and selected area diffraction pattern (SAED). In the MoOx layer, molybdenum exists in Mo4+, Mo5+, and Mo6+ oxidation states, and the ratio of (Mo4++Mo5+) to Mo6+ was determined to be ∼ 2:1. The bilayer films showed good optical transparency ( ≥ 80%) and low resistivity of ∼ 10−4 Ω cm. Different transport behavior of the MoOx/ZnGa0.05O films grown at different Ts (substrate temperature) was observed in temperature-dependent resistivity measurements. The bilayer film at higher Ts showed metallic conductivity behavior down to 113 K. Moreover, a blueshift of the absorption edge in the transmission spectrum was observed with the increase in Ts, indicating an increase in the carrier concentration. It was observed that the ZnGa0.05O films with ultrathin MoOx ( ∼ 1–2 nanometers) overlayer showed a higher work function (varying from 4.7 to 5.1 eV) as compared to the single layer ZnGa0.05O film work function ( ∼ 4.4 eV). A correlation between the surface work function and MoOx layer thickness is observed. The higher work function of the MoOx overlayer is envisaged to improve the transport of the carriers across the heterojunction in a solid state device, thus resulting an increase in device efficiency.
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81.15.Fg Pulsed laser ablation deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.30.+y Surface double layers, Schottky barriers, and work functions
68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors

Time dependent dc resistance degradation in lead-based perovskites: 0.7 Pb(Mg1/3Nb2/3)O3−0.3 PbTiO3

S. Zhao, S. J. Zhang, W. Liu, N. J. Donnelly, Z. Xu, and C. A. Randall

J. Appl. Phys. 105, 053705 (2009); http://dx.doi.org/10.1063/1.3082484 (7 pages) | Cited 8 times

Online Publication Date: 5 March 2009

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Highly accelerated lifetime tests (HALTs), thermally stimulated depolarization current (TSDC), and impedance spectroscopy (IS) measurements were performed on 0.7 Pb(Mg1/3Nb2/3)O3−0.3 PbTiO3 (PMN-PT) single crystal to investigate time dependent dc resistance degradation under a dc bias. A low activation energy of 0.61±0.04 eV which controls the degradation process in PMN-PT single crystal is determined from the characteristic degradation time tC in HALT. Meanwhile, in a complementary TSDC investigation, a broad depolarization peak with an activation energy of 0.6±0.03 eV is observed in virgin PMN-PT single crystal having the characteristics of ionic space charge. Finally, impedance spectra of degraded PMN-PT single crystal exhibited three relaxations in contrast to two relaxations in virgin PMN-PT single crystal. In terms of equivalent circuit, an element combination R-ZCPE corresponding to ionic conduction is common to both virgin and degraded single crystals, and an activation energy about 0.64 eV, attributed to the ionic transport, is also obtained. This value is low compared to similar studies on alkaline-earth titanate perovskites, such as Fe-doped SrTiO3, however, here we suggest the activation energy about 0.6 eV from three independent measurements is attributed to the migration of oxygen vacancies in this particular lead-based single crystal, and besides this apparent ionic conduction, band electronic conduction is also discussed in both virgin and degraded single crystals in this paper.
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77.22.Ej Polarization and depolarization
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
66.30.H- Self-diffusion and ionic conduction in nonmetals
77.22.Jp Dielectric breakdown and space-charge effects
66.30.Lw Diffusion of other defects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.jd Vacancies

Physics of thermoelectric cooling: Alternative approach

Igor Lashkevych, Carlos Cortes, and Yuri G. Gurevich

J. Appl. Phys. 105, 053706 (2009); http://dx.doi.org/10.1063/1.3086629 (5 pages) | Cited 2 times

Online Publication Date: 5 March 2009

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The paper is devoted to the analysis of thermoelectric cooling phenomena in semiconductors containing potential barriers (p-n-junction). The formulation of an adequate self-consistent theoretical model describing the effect is presented. The role of the recombination rate as a new source of heat in linear approximation of the electric current was discussed, leading to a reformulation of the heat balance equations. The importance of redistribution of nonequilibrium charge carriers, which has been ignored in most publications on this subject, is also shown. The conventional theory of thermoelectric cooling, not taking into account the influence of the nonequilibrium charge carriers, is shown to be inadequate. Besides, when the recombination rate decreases, cooling changes to heating.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Three-dimensional Monte Carlo study of three-terminal junctions based on InGaAs/InAlAs heterostructures

Toufik Sadi, François Dessenne, and Jean-Luc Thobel

J. Appl. Phys. 105, 053707 (2009); http://dx.doi.org/10.1063/1.3087703 (9 pages) | Cited 10 times

Online Publication Date: 5 March 2009

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We apply a three-dimensional (3D) semiclassical ensemble Monte Carlo simulation method to study T-branch junctions based on InGaAs/InAlAs heterostructures and obtain an accurate insight into the physics behind the operation of such structures. Electron transport in these devices is investigated and their rectifying behavior is demonstrated at 77 and 300 K and for different branch sizes. Detailed device analysis is performed to establish the relationship between the extent of ballistic transport and the rectifying behavior of the junctions and show the influence of surface charge effects, which are carefully included in the model. Results from the simulation of a T-branch junction with a Schottky gate terminal are presented, demonstrating the necessity of using 3D simulation models to study the physics of semiconductor junctions.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects
73.40.Ei Rectification
72.80.Ey III-V and II-VI semiconductors

Microstructure and transport properties of ZnO:Mn diluted magnetic semiconductor thin films

Z. Yang, W. P. Beyermann, M. B. Katz, O. K. Ezekoye, Z. Zuo, Y. Pu, J. Shi, X. Q. Pan, and J. L. Liu

J. Appl. Phys. 105, 053708 (2009); http://dx.doi.org/10.1063/1.3087473 (6 pages) | Cited 7 times

Online Publication Date: 9 March 2009

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Microstructural studies using transmission electron microscopy were performed on a ZnO:Mn diluted magnetic semiconductor thin film. The high-resolution imaging and electron diffraction reveal that the ZnO:Mn thin film has a high structural quality and is free of clustering/segregated phases. High-angle annular dark field imaging and x-ray diffraction patterns further support the absence of phase segregation in the film. Magnetotransport was studied on the ZnO:Mn samples, and from these measurements, the temperature dependence of the resistivity and magnetoresistance, electron carrier concentration, and anomalous Hall coefficient of the sample is discussed. The anomalous Hall coefficient depends on the resistivity, and from this relation, the presence of the quadratic dependence term supports the intrinsic spin-obit origin of the anomalous Hall effect in the ZnO:Mn thin film.
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73.61.Ga II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Pq Other materials
68.55.-a Thin film structure and morphology
75.50.Pp Magnetic semiconductors

Deep levels in GaTe and GaTe:In crystals investigated by deep-level transient spectroscopy and photoluminescence

Yunlong Cui, David D. Caudel, Pijush Bhattacharya, Arnold Burger, Krishna C. Mandal, D. Johnstone, and S. A. Payne

J. Appl. Phys. 105, 053709 (2009); http://dx.doi.org/10.1063/1.3080157 (4 pages) | Cited 1 time

Online Publication Date: 9 March 2009

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Deep levels of undoped GaTe and indium-doped GaTe crystals are reported for samples grown by the vertical Bridgman technique. Schottky diodes of GaTe and GaTe:In have been fabricated and characterized using current-voltage, capacitance-voltage, and deep-level transient spectroscopy (DLTS). Three deep levels at 0.40, 0.59, and 0.67 eV above the valence band were found in undoped GaTe crystals. The level at 0.40 eV is associated with the complex consisting of gallium vacancy and gallium interstitial (VGa-Gai), the level at 0.59 eV is identified as the tellurium-on-gallium antisite (TeGa), and the last one is tentatively assigned to be the doubly ionized gallium vacancy (VGa∗). Indium isoelectronic doping is found to have noticeable impacts on reducing the Schottky saturation current and suppressing the densities of TeGa and VGa∗ defects. The peak which dominated the DLTS spectrum of GaTe:In is assigned to be the defect complex consisting of VGa and indium interstitial (Ini). Low-temperature photoluminescence (PL) spectroscopy measurements were performed on GaTe and GaTe:In crystals. A shallow acceptor level at 140 meV corresponding to VGa was measured in undoped GaTe. Two shallow acceptor levels at 123 and 74 meV corresponding to VGa and indium-on-gallium antisite InGa were observed in GaTe:In samples. The PL results suggested that the indium atoms could occupy gallium vacant sites during GaTe crystal growth period and thereby change the electrical and optical properties of GaTe crystal.
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71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials
85.30.Kk Junction diodes
61.72.up Other materials
61.72.jj Interstitials
81.10.Fq Growth from melts; zone melting and refining
72.80.Jc Other crystalline inorganic semiconductors
81.05.Hd Other semiconductors

External electric field effect on the hydrogenic donor impurity in zinc-blende GaN/AlGaN cylindrical quantum dot

Liming Jiang, Hailong Wang, Huiting Wu, Qian Gong, and Songlin Feng

J. Appl. Phys. 105, 053710 (2009); http://dx.doi.org/10.1063/1.3080175 (5 pages) | Cited 13 times

Online Publication Date: 9 March 2009

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The binding energy of a hydrogenic donor impurity in a zinc-blende GaN/AlGaN cylindrical quantum dot (QD) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position and QD size. The external electric field induces an asymmetrical distribution of the donor binding energy with respect to the center of the QD. The maximum of the donor binding energy is shifted from the center of the QD. The degenerating energy levels for symmetrical positions with respect to the center of QD are also split. The splitting increases with the increase in QD height while the splitting increases up to a maximum and then decreases with the increase in QD radius. In the presence of the external electric field, the donor binding energy is insensitive to dot height when the impurity is located at the left side of the QD with large dot height. In addition, Stark shift dependence on hydrogenic impurity position is calculated.
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73.21.La Quantum dots
71.55.Eq III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Exciton diffusion lengths of organic semiconductor thin films measured by spectrally resolved photoluminescence quenching

Richard R. Lunt, Noel C. Giebink, Anna A. Belak, Jay B. Benziger, and Stephen R. Forrest

J. Appl. Phys. 105, 053711 (2009); http://dx.doi.org/10.1063/1.3079797 (7 pages) | Cited 64 times

Online Publication Date: 11 March 2009

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We demonstrate spectrally resolved photoluminescence quenching as a means to determine the exciton diffusion length of several archetype organic semiconductors used in thin film devices. We show that aggregation and crystal orientation influence the anisotropy of the diffusion length for vacuum-deposited polycrystalline films. The measurement of the singlet diffusion lengths is found to be in agreement with diffusion by Förster transfer, whereas triplet diffusion occurs primarily via Dexter transfer.
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71.35.-y Excitons and related phenomena
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
81.05.Hd Other semiconductors
68.55.J- Morphology of films

Thermal and electronic transport properties of CeTe2−xSnx compounds

Jong-Soo Rhyee, Eunseog Cho, Kyu Hyoung Lee, Sang Il Kim, Eun Sung Lee, Sang Mock Lee, and Yong Seung Kwon

J. Appl. Phys. 105, 053712 (2009); http://dx.doi.org/10.1063/1.3080143 (5 pages) | Cited 6 times

Online Publication Date: 11 March 2009

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The thermal and electronic transport properties on rare-earth dichalcogenide compounds of CeTe2−xSnx (x ≤ 0.1) were investigated by measuring electrical resistivity ρ, thermal conductivity κ, and Seebeck coefficient S. Compound of CeTe2 exhibited very low κ (1.25 W m−1 K−1) at 300 K, which was understood by the charge density wave lattice distortion. From the ρ(T) measurements, the metallic property of CeTe2 was significantly enhanced by Sn substitution. The temperature-dependent behavior of S(T) for CeTe2−xSnx (x = 0.05 and 0.1) was well described by the inelastic Umklapp process and the phonon drag. The low Seebeck coefficient of CeTe2 (S ≈ 2.5 μV/K at T ≈ 300 K) was increased by Sn doping. From the band structure calculation, the semimetallic band character of CeTe2 was revealed with symmetric electron-hole band dispersion near the Fermi level. The symmetric electron-hole band dispersion of CeTe2 is responsible for the low Seebeck coefficient. The enhancement of the metallic property and Seebeck coefficient because of Sn substitution could be understood by the charge imbalance between electrons and holes caused by hole doping in the Te monolayer.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
71.45.Lr Charge-density-wave systems
63.20.kd Phonon-electron interactions
71.20.Gj Other metals and alloys

Theoretical prediction on the structural, electronic, and polarization properties of tetragonal Bi2ZnTiO6

Hai Wang, Haitao Huang, Wei Lu, Helen L. W. Chan, Biao Wang, and C. H. Woo

J. Appl. Phys. 105, 053713 (2009); http://dx.doi.org/10.1063/1.3086628 (8 pages) | Cited 6 times

Online Publication Date: 12 March 2009

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We present first-principles investigations on the structural, electronic, and polarization properties of Bi2ZnTiO6 using density-functional theory within the generalized gradient approximation. The theoretical structure we obtained confirms the extra large tetragonality observed by experiment. The materials exhibit a semiconductor behavior with an indirect band gap determined by the occupied O 2p and unoccupied Bi 6p states. There are strong hybridization effects between Bi–O ions, as well as Ti–O and Zn–O ones. The resulting covalent bondings, having a PbTiO3-type two-dimensional character, strengthen each other and favor the coupling between the tetragonal distortion of unit cell and the off-center displacement of A and B-site cations and O anions due to the existence of Zn, and result in the large tetragonality of this compound. Berry-phase calculation gives the polarization as high as 122 μC/cm2.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.50.Lt Crystal binding; cohesive energy
77.22.Ej Polarization and depolarization
71.20.Ps Other inorganic compounds

Determining the excess carrier lifetime in crystalline silicon thin-films by photoluminescence measurements

Philipp Rosenits, Thomas Roth, Wilhelm Warta, Stefan Reber, and Stefan W. Glunz

J. Appl. Phys. 105, 053714 (2009); http://dx.doi.org/10.1063/1.3080174 (5 pages) | Cited 2 times

Online Publication Date: 12 March 2009

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A valuable nondestructive measurement and analysis method for determining individual excess carrier lifetimes in multilayer systems is presented. This is particularly interesting for the characterization of crystalline silicon thin-film samples consisting of an electrically active epitaxial layer on top of a highly doped crystalline substrate. The analysis principle is based on a comparison between a measured photoluminescence intensity ratio and associated simulated radiative recombination ratios for samples with different epitaxial layer thicknesses. It benefits from the fact that for low excess carrier lifetimes within the epitaxial layer the carrier concentration in the said layer is limited by bulk recombination, while for high carrier lifetimes surface and interface recombination is dominating. In order to verify this measurement and analysis principle, results of a set of crystalline silicon thin-film samples with varying epitaxial layer thickness on a highly doped Czochralski substrate are presented.
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73.61.Cw Elemental semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
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