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15 Jul 2009

Volume 106, Issue 2, Articles (02xxxx)

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Soft x-ray appearance potential spectroscopy study of NiO and CoO single crystal surfaces

Y. Fukuda, S. Mochizuki, and N. Sanada

J. Appl. Phys. 106, 023701 (2009); http://dx.doi.org/10.1063/1.3160308 (5 pages) | Cited 1 time

Online Publication Date: 16 July 2009

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Soft x-ray appearance potential spectroscopy (SXAPS) spectra of Ni 2p, Co 2p, and O 1s for NiO and CoO single crystal surfaces have been measured. Two peaks and a shoulder along with two core lines due to 2p3/2 and 2p1/2 are found for a Ni 2p raw spectrum. A Ni 2p metallic edge was observed for the NiO surface sputtered by Ar ions. An O 1s spectrum of NiO exhibits a broad peak between about 522 and 550 eV and the self-deconvoluted spectrum shows five peaks. For the Co 2p spectrum, two core lines due to 2p3/2 and 2p1/2 along with a shoulder are found and the self-deconvoluted spectrum exhibits four peaks. The broad peak is also seen between about 525 and 555 eV for the O 1s spectrum of CoO and the self-deconvoluted spectrum shows four peaks. The features of the self-deconvoluted SXAPS spectra of Ni 2p, Co 2p, and O 1s for NiO and CoO are found to resemble those of the corresponding near edge x-ray absorption fine structure (NEXAFS). The origin of the peaks is discussed to compare the present work with the previous theoretical calculations for the NEXAFS spectra.
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78.70.En X-ray emission spectra and fluorescence
78.70.Dm X-ray absorption spectra
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.68.+m Optical properties of surfaces

Effects of Cu5Zn3 addition on the thermoelectric properties of Zn4Sb3

J. L. Cui, H. Fu, L. D. Mao, D. Y. Chen, and X. L. Liu

J. Appl. Phys. 106, 023702 (2009); http://dx.doi.org/10.1063/1.3171924 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2009

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The structures and thermoelectric properties of mCu5Zn3⋅nZn4Sb3 with multiphase coexistence are reported. Rietveld analysis reveals that at least 92.3% wt % β-Zn4Sb3 phase can be obtained with only small quantities of ZnSb and Cu5Zn8 phases precipitated after proper Cu5Zn3 addition. Measurements indicate that although the β-Zn4Sb3 phase plays a determining role in controlling the transport properties involving the Seebeck coefficient, electrical conductivity, and thermal conductivity, the impurity phases Cu5Zn8 and ZnSb with a crooked riverlike and intertwined tree stump morphologies, respectively, are still of great significance to tune the thermoelectric performance. The highest ZT value of 0.84 can be obtained for the alloy mCu5Zn3⋅nZn4Sb3 (m/n = 1/200) at 631 K, approximately 1.8 times that of undoped β-Zn4Sb3, proving that a good combination between the transports of carriers and phonons can be achieved if a proper dopant is introduced in the Zn4Sb3 matrix.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors
61.66.Fn Inorganic compounds

Electrical behavior of AlGaN/GaN heterostuctures upon high-temperature selective oxidation

F. Roccaforte, F. Giannazzo, F. Iucolano, C. Bongiorno, and V Raineri

J. Appl. Phys. 106, 023703 (2009); http://dx.doi.org/10.1063/1.3174438 (6 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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In this paper, the influence of a high-temperature (900 °C) selective oxidation process on the electrical properties of AlGaN/GaN heterostructures was investigated. In particular, electrical measurements performed on appropriate devices and test patterns demonstrated that the current flow through the two-dimensional electron gas (2DEG) was suppressed, even if the thickness of the local oxide did not reach the AlGaN/GaN interface. The combination of macroscopic current-voltage and capacitance-voltage measurements with depth-resolved scanning capacitance microscopy elucidated the doping dependence and the compositional stability of the material during high-temperature oxidation. The reduction in the 2DEG sheet carrier density and the variation of the threshold voltage of simple high electron mobility transistor structures upon high-temperature annealing were also discussed.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
85.30.Tv Field effect devices
72.20.Ht High-field and nonlinear effects

Pitfalls in Kelvin probe measurements

Oliver M. Ottinger, Christian Melzer, and Heinz von Seggern

J. Appl. Phys. 106, 023704 (2009); http://dx.doi.org/10.1063/1.3174443 (5 pages) | Cited 2 times

Online Publication Date: 20 July 2009

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We report on the interpretation of thickness-dependent surface potential profiles in insulators on metal substrates measured by Kelvin probe method. The electrical potentials are calculated within a self-consistent model taking both the conductive substrate and the insulator into account. It is shown that interpreting the Kelvin potentials for different layer thicknesses as the prevailing potential profile of a thick insulator film is generally wrong. Even more controversially, the reconstruction of the potential profile in a thick insulator layer on the basis of layer-thickness-dependent Kelvin measurements alone is per se impossible. This will be demonstrated exemplarily on the basis of doped and undoped organic films on conductive substrates.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.30.Ka Basic electromagnetic quantities
73.40.Ns Metal-nonmetal contacts

The effect of surface roughness scattering on hole mobility in double gate silicon-on-insulator devices

Luca Donetti, Francisco Gámiz, Noel Rodriguez, Andres Godoy, and Carlos Sampedro

J. Appl. Phys. 106, 023705 (2009); http://dx.doi.org/10.1063/1.3176498 (7 pages) | Cited 1 time

Online Publication Date: 20 July 2009

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The effect of surface roughness of the Si/SiO2 interfaces on hole mobility in double gate silicon-on-insulator p-channel devices is studied. Wave functions and dispersion relationships of the hole subbands were computed self-consistently with the potential profile, employing a 6×6 k⋅p model. The roughness of both silicon-oxide interfaces was thoroughly taken into account as a scattering mechanism by extending a model previously developed for n-channel double gate devices and adapting it to the requirements of the k⋅p calculation. Hole mobility was computed using the Kubo–Greenwood formula and the impact of surface roughness was discussed. Volume inversion (mobility increase with regard to conventional bulk channel mobility in a range of silicon layer thicknesses) was observed to have a significant effect, as in n-channel devices.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.15.-m Methods of electronic structure calculations
72.20.Fr Low-field transport and mobility; piezoresistance
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Energy-gap dependence on the Mn mole fraction and temperature in CdMnTe crystal

K. H. Kim, A. E. Bolotnikov, G. S. Camarda, G. Yang, A. Hossain, Y. Cui, R. B. James, J. Hong, and S. U. Kim

J. Appl. Phys. 106, 023706 (2009); http://dx.doi.org/10.1063/1.3176955 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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We measured the dependence of the energy gap in Bridgman-grown Cd1−xMnxTe crystals, 0 ≤ x ≤ 0.25, on the Mn mole fraction and temperatures from 40 to 300 K. We determined the Mn mole fraction and energy gap, respectively, from electron probe microanalysis and near-infrared Fourier-transform infrared transmission spectra. The energy gap increased linearly with an increase in the Mn content in the crystal and with a decrease in temperature. We formulated new equations from these experimental results, wherein we expressed the energy gap as a function of Mn mole fraction and temperature. Also, we compare our findings with published results.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
81.10.Fq Growth from melts; zone melting and refining
78.30.Fs III-V and II-VI semiconductors

Magnetoelectric behavior of sodium doped lanthanum manganites

Y. Kalyana Lakshmi, G. Venkataiah, and P. Venugopal Reddy

J. Appl. Phys. 106, 023707 (2009); http://dx.doi.org/10.1063/1.3173285 (10 pages) | Cited 3 times

Online Publication Date: 21 July 2009

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Nanocrystalline samples of sodium doped manganites with compositional formula La1−xNaxMnO3 (0.025 ⩽ x ⩽ 0.25) were prepared by polyvinyl alcohol assisted precursor method. After characterizing the samples by x-ray diffraction and transmission electron microscopy a systematic investigation of electrical, magnetic, and thermopower properties has been undertaken. The resistivity data were analyzed using effective medium approximation. From the analysis it has been found that the metallic fraction is increasing up to x = 0.10 and remains constant with further doping. A close examination of the resistivity data clearly indicates that the sodium doped samples are slowly transformed from colossal magnetoresistance behavior to charge ordering behavior. Thermoelectric power data at low temperatures were analyzed by considering the magnon drag concept, while the high temperature data were explained by small polaron conduction mechanism.
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75.80.+q Magnetomechanical effects, magnetostriction
61.72.up Other materials
75.47.Gk Colossal magnetoresistance
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
71.38.-k Polarons and electron-phonon interactions
75.30.Ds Spin waves

Resistance and superconductivity switching caused by carrier injection: Evidences of self-trapping carriers in oxide electronics

Yuansha Chen, Liping Chen, Guijun Lian, and Guangcheng Xiong

J. Appl. Phys. 106, 023708 (2009); http://dx.doi.org/10.1063/1.3176491 (7 pages) | Cited 12 times

Online Publication Date: 21 July 2009

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Carrier injection performed in doped-manganite junction exhibits stable resistance switching effect and variety of interface barrier adjusted by electric fields, which demonstrates roles of the carrier movement across interface and suggests the importance of injected carriers’ staying. All observations suggest that the staying of injected carriers in the functional oxides leads to a carrier self-trapping mechanism to understand resistance switching phenomenon. More results in other oxide junctions and epitaxial doped manganite films support carrier self-trapping model and exhibit the importance of heterointerface on stabilizing the self-trapping carriers. Superconductivity achieved and adjusted by carrier injection can be distinct evidence that the self-trapping carriers as minority played important roles in operating of oxides’ intrinsic property. This phenomenon could relate to a novel area of researches and applications in oxide electronics.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.60.+g Mixed conductivity and conductivity transitions
74.25.F- Transport properties

Characteristics of SiC pillar-shaped nanostructure Schottky diode

Sang Youn Han and Jong-Lam Lee

J. Appl. Phys. 106, 023709 (2009); http://dx.doi.org/10.1063/1.3176898 (4 pages)

Online Publication Date: 21 July 2009

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The effect of geometrical shape on the electrical transport was analyzed in SiC nanostructure Schottky diode. Two different contacts, the pillar-shaped nanostructure contact and nanoscale contact, were fabricated separately from top down method. Compared with nanoscale contact, the nanostructure contact showed the low current level, but similar Schottky barrier property. This is attributed by the fact that pillar-shaped nanostructure has smaller base areas which prevent the electrons from efficient transport into the nanostructure. This led to the decrease in electron mobility, resulting in the higher resistance in the I-V curves. From Fowler–Nordheim plot, it was almost linear for higher voltage region, but the linear behavior disappeared in the lower one. This implied that the electron tunneling was the main transport mechanism at higher electric field in this structure.
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85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors

Bound exciton luminescence in shock compressed GaP:S and GaP:N

P. Grivickas, M. D. McCluskey, Y. M. Gupta, Y. Zhang, and J. F. Geisz

J. Appl. Phys. 106, 023710 (2009); http://dx.doi.org/10.1063/1.3159641 (7 pages) | Cited 1 time

Online Publication Date: 22 July 2009

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Photoluminescence (PL) spectra of bound excitons were measured in uniaxially strained GaP by performing shock-wave experiments at liquid nitrogen temperatures. GaP samples doped with sulfur or nitrogen were compressed up to 3 GPa when subjected to uniaxial strains along the [100] crystallographic orientation. PL lines from shallow sulfur donors redshifted upon compression, tracking the reduction in the indirect band gap. PL lines related to the isoelectronic NN1 pairs, in contrast, exhibited splitting and nonlinear blueshift. An empirical approach was used to model the NN1 behavior. It was shown that the splitting pattern is consistent with the previously proposed symmetry of NN1 defects and nonlinearities resulting from the reduction in the exciton binding energy. At high stresses, the NN1 lines disappeared due to the ionization of bound excitons.
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78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
62.50.Ef Shock wave effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
71.55.Eq III-V semiconductors
61.50.Lt Crystal binding; cohesive energy

Tuning of electrical charging effects for ferromagnetic Mn-doped ZnO nanocrystals embedded into a SiO2 layer fabricated by KrF excimer laser irradiation

Sejoon Lee, Deuk Young Kim, Tae Won Kang, and Hyung Koun Cho

J. Appl. Phys. 106, 023711 (2009); http://dx.doi.org/10.1063/1.3176933 (6 pages) | Cited 3 times

Online Publication Date: 22 July 2009

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The ZnMnO nanocrystals were formed by the laser irradiation of the sputter-deposited ZnMnO ultrathin layer using a 248 nm KrF excimer laser, and the size and density of the nanocrystals were observed to be controllable by modulations of either the energy density or the frequency of the irradiated pulsed-laser beam. Metal-oxide-semiconductor capacitors fabricated using ZnMnO nanocrystals clearly showed the electrical charging effect, and it was observed that the memory window depends on the size and density of nanocrystals. For measurements of the spontaneous magnetization, ZnMnO nanocrystals showed to have room-temperature ferromagnetism with Mr of ∼ 1.5 emu/cm3 and Hc 167 Oe. By using ferromagnetism in ZnMnO nanocrystals, tuning of the memory window was demonstrated. Namely, it was clearly observed that the flat-band voltage shift of ∼ 1.25 V can be modulated to be ∼ 0.8 V by applying the magnetic field. This is attributed to the modulation of probabilities for tunneling events due to the increased magnetoelectrical repulsion between spin-polarized carriers in ZnMnO dilute magnetic semiconductor nanocrystals and unpolarized carriers in p-Si under the magnetic field. These results suggest that ZnMnO nanocrystals can be used for spin-functional memory devices.
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81.16.-c Methods of micro- and nanofabrication and processing
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
81.15.Cd Deposition by sputtering
81.05.Dz II-VI semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
75.30.Cr Saturation moments and magnetic susceptibilities

Effects of boron and arsenic doping in β-FeSi2

K. H. Tan, K. L. Pey, and D. Z. Chi

J. Appl. Phys. 106, 023712 (2009); http://dx.doi.org/10.1063/1.3176944 (8 pages) | Cited 5 times

Online Publication Date: 22 July 2009

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The effects of boron and arsenic doping in β-FeSi2 have been studied by theoretical simulations and electrical characterization. First-principles calculations revealed that B and As were energetically favorable to occupy the SiII and SiI sites, respectively. The impurity doping was found to induce structural relaxation via lattice distortion, with As doping causing elongation of the As­Si bonds and contraction of the As–Fe bonds while B doping resulting in both inward and outward relaxations of the neighboring Si and Fe host atoms. p-type and n-type conductivities were suggested for the B- and As-doped β-FeSi2, respectively, and confirmed experimentally by Hall effect measurements. B and As were shown to introduce shallow impurity levels in the forbidden gap of β-FeSi2 and therefore could be effective dopants for β-FeSi2. A carrier concentration in a tunable range of 1017 cm−3 and a mobility in the order of 100 cm2/V s were consistently obtained.
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61.72.up Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ga Transition-metal compounds
71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals

Half-metallic properties of perovskite BaCrO3 and BaCr0.5Ti0.5O3 superlattice: LSDA+U calculations

Z. H. Zhu and X. H. Yan

J. Appl. Phys. 106, 023713 (2009); http://dx.doi.org/10.1063/1.3182721 (5 pages) | Cited 2 times

Online Publication Date: 23 July 2009

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Under the local-spin density approximation method plus on-site coulomb interaction U correction (LSDA+U), the BaCrO3 in the perovskite structure is found to be half-metallic ferromagnet with an integral magnet moment of 2.000 Bohr magnetons (μB) per unit. The feasibility of constructing the BaCr0.5Ti0.5O3 superlattice to stabilize the perovskite phase for the BaCrO3 is theoretically explored. Additionally, the influence of screened parameters U on the electronic structures and magnet moments of the perovskite BaCrO3 and BaCr0.5Ti0.5O3 superlattice is expounded.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials

Modification of the valence band structures of polar and nonpolar plane wurtzite-GaN by anisotropic strain

Deyi Fu, Rong Zhang, Baigeng Wang, Zeng Zhang, Bin Liu, Zili Xie, Xiangqian Xiu, Hai Lu, Youdou Zheng, and Gerard Edwards

J. Appl. Phys. 106, 023714 (2009); http://dx.doi.org/10.1063/1.3174436 (8 pages) | Cited 10 times

Online Publication Date: 23 July 2009

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The influence of anisotropic strain on the valence band structure and related properties, including excitonic transition energies, transition polarization selection rules, band-edge hole effective masses, and exciton reduced effective masses, of polar and nonpolar plane GaN are systematically investigated using the well-known k⋅p Hamiltonian approach. We re-examine the band deformation potentials D3 and D4, and interband hydrostatic deformation potentials a1 and a2, and find that they take the values 9.4, −4.7, −3.0, and −12.4 eV, respectively. In order to correctly interpret the optical properties of GaN, the spin-orbit coupling effect cannot be neglected. Our numerical calculations show that pure linear polarization light emissions and absorptions can be obtained. In addition, the two topmost valence subbands can be effectively separated to reduce the band-edge density of state by manipulating the strain states in GaN epilayers, which is favorable for laser diode design. Furthermore, the band-edge hole effective masses exhibit significant in-plane anisotropy and are sensitive to the residual strain, while the influence of the residual strain on the exciton reduced effective masses is relatively weak.
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71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Intrinsically limited mobility of the two-dimensional electron gas in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures

V. M. Polyakov, F. Schwierz, I. Cimalla, M. Kittler, B. Lübbers, and A. Schober

J. Appl. Phys. 106, 023715 (2009); http://dx.doi.org/10.1063/1.3174441 (5 pages) | Cited 7 times

Online Publication Date: 23 July 2009

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We report on the intrinsically limited low-field mobility of the two-dimensional electron gas (2DEG) in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures. Monte Carlo transport simulations are carried out to calculate the room-temperature 2DEG mobilities in dependence on the electron sheet density. The simulated 2DEG mobilities are compared to the phonon-limited mobility of bulk GaN. We estimate a maximum 2DEG mobility of about 2700 cm2 V−1 s−1 for an electron sheet density of ∼ 5×1012 cm−2, which remarkably exceeds the phonon-limited bulk mobility of 1520 cm2 V−1 s−1. By reducing the electron sheet density below 5×1012 cm−2, i.e., in a weak electron quantum confinement regime, the room-temperature 2DEG mobility gradually decreases and approaches the phonon-limited bulk value for vanishing quantum confinement. The insertion of a thin AlN barrier interlayer improves transport properties of the 2DEG and the mobility substantially increases due to a suppression of the alloy scattering.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Monte Carlo study of device characteristics of GaN-based avalanche photodiode devices

Zhiyuan Zheng, Yuxiang Mai, and Gang Wang

J. Appl. Phys. 106, 023716 (2009); http://dx.doi.org/10.1063/1.3176935 (6 pages) | Cited 1 time

Online Publication Date: 24 July 2009

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In this article, Monte Carlo method is used to study the characteristics of gallium nitride (GaN). Impact ionization is treated as an additional scattering mechanism, which is described by the Keldysh formula with the parameters determined by fitting the simulated results to the numerical calculation results. Based on simplified model, results of velocity overshoot and impact ionization rate of both carriers are calculated and analyzed. In addition, we get the device characteristics associated with impact ionization, i.e., gain, noise, and bandwidth (both electron- and hole-injected cases), which is compared to the reported experimental data and conventional theories. Moreover, we contrast the simulated device characteristics of GaN and the performance of several conventional materials.
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85.60.Dw Photodiodes; phototransistors; photoresistors

X-ray photoemission analysis of chemically treated GaTe semiconductor surfaces for radiation detector applications

A. J. Nelson, A. M. Conway, B. W. Sturm, E. M. Behymer, C. E. Reinhardt, R. J. Nikolic, S. A. Payne, G. Pabst, and K. C. Mandal

J. Appl. Phys. 106, 023717 (2009); http://dx.doi.org/10.1063/1.3176478 (5 pages) | Cited 3 times

Online Publication Date: 27 July 2009

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The surface of the layered III-VI chalcogenide semiconductor GaTe was subjected to various chemical treatments commonly used in device fabrication to determine the effect of the resulting microscopic surface composition on transport properties. Various mixtures of H3PO4:H2O2:H2O were accessed and the treated surfaces were allowed to oxidize in air at ambient temperature. High-resolution core-level photoemission measurements were used to evaluate the subsequent chemistry of the chemically treated surfaces. Metal electrodes were created on laminar (cleaved) and nonlaminar (cut and polished) GaTe surfaces followed by chemical surface treatment and the current versus voltage characteristics were measured. The measurements were correlated to understand the effect of surface chemistry on the electronic structure at these surfaces with the goal of minimizing the surface leakage currents for radiation detector devices.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.35.Dv Composition, segregation; defects and impurities
81.65.Rv Passivation
71.20.Nr Semiconductor compounds
29.40.Wk Solid-state detectors
72.80.Jc Other crystalline inorganic semiconductors

Seebeck effect in PbTe films and EuTe/PbTe superlattices

Akihiro Ishida, Tomohiro Yamada, Daoshe Cao, Yoku Inoue, Martin Veis, and Takuji Kita

J. Appl. Phys. 106, 023718 (2009); http://dx.doi.org/10.1063/1.3182804 (5 pages) | Cited 6 times

Online Publication Date: 28 July 2009

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Theoretical calculations of the Seebeck coefficients of bulk PbTe and PbTe based superlattices were described in the framework of Boltzmann equation, taking into account temperature dependent band gaps, nonparabolicity, and anisotropy of effective masses. It is shown that the temperature gradient along the superlattice layer works more effectively on the enhancement of the thermoelectric figure of merit than the temperature gradient normal to the superlattice layer. Calculated Seebeck coefficients were compared to the experimental values for n-type PbTe, p-type PbTe, and EuTe/PbTe superlattices. The Seebeck coefficient of p-type PbTe was higher than that of n-type PbTe. The relatively high Seebeck coefficient is explained by the contribution from other extrema in the valence band. The EuTe/PbTe [001] superlattice shows higher Seebeck coefficients than PbTe bulk owing to the large density of states.
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73.61.Le Other inorganic semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
73.21.Cd Superlattices
73.20.At Surface states, band structure, electron density of states

Effects of charged impurities and lattice defects on transport properties of nanoscale graphene structures

V. Nam Do and P. Dollfus

J. Appl. Phys. 106, 023719 (2009); http://dx.doi.org/10.1063/1.3176956 (5 pages) | Cited 6 times

Online Publication Date: 29 July 2009

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Using the nonequilibrium Green’s function theory, transport properties of nanoscale graphene structures deposited on a SiO2/Si substrate have been investigated taking into account the influence of both lattice defects and charged impurities. The calculation argues the metallic lead-graphene coupling responsible for the asymmetric transport of electrons and holes, and shows that the conductivity is generally suppressed by these scattering processes. However, at the charge neutrality point, the screening seems to weaken such a suppression, leading to the minimum conductivity value of 4e2/πh even for the impurity density higher than 1012 cm−2, while it is strongly diminished to zero for the vacancy density of 1011 cm−2. Obtained results for the conductivity and the charge mobility are also discussed to highlight available experimental data.
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73.63.-b Electronic transport in nanoscale materials and structures
61.72.jd Vacancies
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Fr Low-field transport and mobility; piezoresistance

Electronic and optical properties of mixed anion layered oxychalcogenide semiconductors: An ab initio study

S. Ramasubramanian, M. Rajagopalan, J. Kumar, and R. Thangavel

J. Appl. Phys. 106, 023720 (2009); http://dx.doi.org/10.1063/1.3184345 (6 pages) | Cited 1 time

Online Publication Date: 31 July 2009

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A full potential linear augmented plane wave method within the density functional theory is used to calculate the electronic and optical properties of layered compounds of LaCuOCh (Ch = S, Se, Te) and their alloys LaCuOCh0.5Ch0.5′(Ch, Ch′ = S, Se, Te). These compounds are found to be direct band gap semiconductors and may have a high p-type electrical conductivity, which can be tuned by proper alloying. The dielectric functions and optical constants—refractive index, absorption coefficient, and real part of optical conductivity of these materials—are calculated. The present study shows by changing the chalcogenides in the alternate covalent Cu–Ch layers that one can control the electrical conductivity and optical emission in these oxychalcogenide semiconductors.
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78.66.Jg Amorphous semiconductors; glasses
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
73.61.Jc Amorphous semiconductors; glasses
72.80.Ng Disordered solids
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