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1 Jul 2007

Volume 102, Issue 1, Articles (01xxxx)

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J. Appl. Phys. 102, 011301 (2007); http://dx.doi.org/10.1063/1.2750414 (22 pages)

S. N. Piramanayagam
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Niobium doped TiO2: Intrinsic transparent metallic anatase versus highly resistive rutile phase

S. X. Zhang, D. C. Kundaliya, W. Yu, S. Dhar, S. Y. Young, L. G. Salamanca-Riba, S. B. Ogale, R. D. Vispute, and T. Venkatesan

J. Appl. Phys. 102, 013701 (2007); http://dx.doi.org/10.1063/1.2750407 (4 pages) | Cited 42 times

Online Publication Date: 2 July 2007

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We report on the structural, electrical, and optical properties of 5% niobium doped TiO2 thin films grown on various substrates by pulsed laser deposition. The epitaxial anatase Nb:TiO2 film on LaAlO3 is shown to be an intrinsic transparent metal and its metallic property arises from Nb substitution into Ti site as evidenced by the Rutherford backscattering channeling result. In contrast, the rutile Nb:TiO2 thin films show insulating behaviors with 2–3 orders higher room temperature electrical resistivity and ∼ 30 times lower mobility. A blueshift in the optical absorption edge is observed in both phases, though of differing magnitude.
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73.61.-r Electrical properties of specific thin films
78.66.-w Optical properties of specific thin films
72.20.Fr Low-field transport and mobility; piezoresistance

Theoretical study of the electrical transport of nickel nanowires and a single atomic chain

H. Li, X. Q. Zhang, F. W. Sun, Y. F. Li, K. M. Liew, and X. Q. He

J. Appl. Phys. 102, 013702 (2007); http://dx.doi.org/10.1063/1.2750413 (4 pages) | Cited 5 times

Online Publication Date: 2 July 2007

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Five kinds of nanowires and a nanochain that is embedded in a carbon nanotube have been optimized by density function theory, and the electronic transport properties through these nanowires and nanochain are studied. Our results indicate that the transmission spectra exhibit size-dependent oscillations. We observe and study the nonlinear contribution to the I-V characteristic (current-voltage) curves that is due to the quantum size effect. The I-V curve of the single chain is different from that when the chain is embedded in a carbon nanotube. The results provide valuable information on the correlation between the transport properties of nanowires and their microstructures.
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73.63.-b Electronic transport in nanoscale materials and structures
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials

Ballistic electron and photocurrent transport in Au-molecular layer-GaAs diodes

W.-J. Li, K. L. Kavanagh, A. A. Talin, W. M. Clift, C. M. Matzke, and J. W. P. Hsu

J. Appl. Phys. 102, 013703 (2007); http://dx.doi.org/10.1063/1.2748865 (8 pages) | Cited 6 times

Online Publication Date: 2 July 2007

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We present a study on hot electron transport through Au/molecule/n-GaAs(001) diodes via ballistic electron emission microcopy (BEEM). The molecules in the structure form a monolayer of either octanedithiol [HS–(CH2)8–SH] or hexadecanethiol [HS–(CH2)15–CH3]. For the dithiol case, the presence of the molecular interlayer leads to undetectable BEEM transmission. Whereas a small photoinduced collector current is detected at random locations at a forward (reverse) scanning tunneling microscopy (STM) tip voltage of −1.43±0.01 V (+1.50±0.02 V). In comparison, with monothiol diodes, or diodes where the molecules are sandwiched between two Au films (Au/molecule/Au/GaAs), the BEEM transmission remains a significant fraction of the reference diode signal (30%–80%) with a slight increase in the ballistic transport threshold voltage (−1.0 to −1.1 V) from that of the reference Au/GaAs diodes (−0.89 V). Auger depth profiling and cross-sectional transmission electron microscopy show that Au-molecule intermixing occurs in Au/hexadecanethiol/GaAs but not in Au/octanedithiol/GaAs diodes. The suppression of BEEM signal and the detection of STM-induced photocurrent in the Au/octanedithiol/GaAs case are consistent with an insulating monolayer containing pinholes or recombination centers with densities of 1 every 25×25 nm2 or ∼ 2000 μm−2.
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73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects
72.40.+w Photoconduction and photovoltaic effects
73.40.Ns Metal-nonmetal contacts
68.37.Vj Field emission and field-ion microscopy
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Microwave photoconductivity decay characterization of high-purity 4H-SiC substrates

R. J. Kumar, J. M. Borrego, R. J. Gutmann, J. R. Jenny, D. P. Malta, H. McD. Hobgood, and C. H. Carter, Jr.

J. Appl. Phys. 102, 013704 (2007); http://dx.doi.org/10.1063/1.2751086 (8 pages) | Cited 1 time

Online Publication Date: 3 July 2007

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A microwave photoconductivity decay (MPCD) technique, which probes conductivity change in wafers in response to either an above-band-gap or below-band-gap laser pulse, has been used to characterize recombination lifetime in high-purity 4H-SiC substrates produced with three different anneal processes. The above-band-gap (266 nm) decay times vary from ∼ 10 ns to tens of microseconds in the 4H-SiC substrates depending on the wafer growth parameters. Wafers produced using the three processes A (as-grown), B (annealed at 2000 °C), and C (annealed at 2600 °C) have decay times of 10–20 ns, 50–500 ns, and tens of microseconds, respectively. The differences in decay times are attributed to low, medium, and high densities of recombination centers in process C, B, and A wafers, respectively. The MPCD results correlate with other characterization results such as deep level transient spectroscopy, which also showed that the 2600 °C anneal process significantly reduces defect densities, resulting in the enhanced recombination lifetimes. Modeling and one-dimensional simulations indicate a trapping center closer to the conduction band results in a longer MPCD decay transient, but such a trapping based model for the enhanced lifetimes is not compatible with the wide range of experimental characterization results described in this work, which indicate an annealing out of recombination centers at 2600 °C.
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73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
61.72.Cc Kinetics of defect formation and annealing
71.55.Ht Other nonmetals

Semiclassical electronic transport calculations in multilayered granular alloys

J. Milano and A. M. Llois

J. Appl. Phys. 102, 013705 (2007); http://dx.doi.org/10.1063/1.2751083 (6 pages)

Online Publication Date: 6 July 2007

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We have calculated the electrical conductivity in the current-in-plane geometry of multilayered granular alloys composed of Co clusters embedded in Ag alternating with pure Ag layers. In particular, we have paid attention to the conductivity behavior as a function of Ag layer thickness, Co clusters’ size, and degree of percolation. The electronic structure is self-consistently calculated within the unrestricted Hartree–Fock approximation using a parametrized tight binding Hamiltonian which includes a Hubbard-like term. The conductivity tensor is obtained by using the semiclassical Boltzmann equation in the anisotropic relaxation time approximation. We have used a s−d Mott-like scattering model for the electronic mean free path taking into account the Sondheimer’s picture for electronic transport in thin films. We find that the experimental conductivity behavior at coalescence can be explained through the electronic band contribution. The conductivity behavior of continuous multilayers is already attained in the very early stage of percolation, as in the experiments.
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73.63.-b Electronic transport in nanoscale materials and structures
72.15.Lh Relaxation times and mean free paths
73.21.Ac Multilayers
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Importance of aspect ratio over shape in determining the quantization potential of self-assembled zinc-blende III-V quantum dots

S. I. Rybchenko, G. Yeap, R. Gupta, I. E. Itskevich, and S. K. Haywood

J. Appl. Phys. 102, 013706 (2007); http://dx.doi.org/10.1063/1.2752127 (14 pages) | Cited 7 times

Online Publication Date: 9 July 2007

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We have studied the effect of shape on the strain-modified electron∕hole confinement potential in zinc-blende quantum dots (QDs), using standard deformation potential theory and an anisotropic continuum-elasticity approximation. Calculations were performed for a variety of shapes of InAs/GaAs (001) QDs. Our results show that the essential features of the confinement potential are determined primarily by one geometric parameter, i.e., the aspect ratio, being insensitive to other details of the QD shape. The underlying trends in strain distribution are also revealed. Our results suggest that a simple analytical model, based on the oblate-ellipsoid shape and isotropic elasticity approximation, adequately describes the major features of the strain-modified confinement potential for a wide range of self-assembled III-V (zinc-blende) QDs.
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73.21.La Quantum dots
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Transport through small world networks

S. Çalışkan, M. A. Novotny, and J. I. Cerdá

J. Appl. Phys. 102, 013707 (2007); http://dx.doi.org/10.1063/1.2752142 (7 pages) | Cited 4 times

Online Publication Date: 9 July 2007

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We numerically investigate the transport properties through a system where small world networks are added to a one-dimensional chain. One-electron Green’s function method is applied to standard tight-binding Hamiltonians on networks, modeled as (i) adding connections between any two nonadjacent random sites in the chain, (ii) introducing finite one-dimensional chains between any pair of such connected sites, and (iii) attaching finite dangling chains at random sites in the chain. Due to the small world bonds and dangling conduction paths, the systems have irregular geometrical shapes, leading to quenched disordered systems. We consider the qualitative influence of the small world bonds and dangling bonds on the transmittance and find that the systems exhibit a strong energy dependence on the transmittance, with strong sample-to-sample fluctuations.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.60.-k Transport processes
02.30.-f Function theory, analysis
02.50.Ey Stochastic processes
02.40.-k Geometry, differential geometry, and topology

A theoretical interpretation of magnetoresistance mobility in silicon inversion layers

L. Donetti, F. Gámiz, and S. Cristoloveanu

J. Appl. Phys. 102, 013708 (2007); http://dx.doi.org/10.1063/1.2752103 (6 pages) | Cited 3 times

Online Publication Date: 10 July 2007

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The magnetoresistance technique has been introduced recently as a means of determining experimentally the mobility in bulk metal-oxide-semiconductor transistor and silicon-on-insulator devices. This technique does not require a precise determination of the channel length, and it also has the advantage of allowing mobility extraction when the application of other methods is problematic, notably with weak inversion and short device length. The magnetoresistance mobility extracted in this way is related but not identical to the normal effective drift mobility. In this work we simulate electron transport in the presence of a magnetic field for different device structures. The simulations allow us to study the conditions under which magnetoresistance mobility and effective mobility coincide, and to measure the difference, where it exists. We find that at low temperatures the two quantities coincide, while at room temperature a difference of more than 20% may appear. We take this to be a consequence of the energy difference between subbands and the resulting distribution of electrons among them. We then explain the fact that the two mobility measures coincide at low temperatures when only the ground subband is occupied by analyzing the energy dependence of the momentum relaxation time.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

First-principles study of contact between Ti surface and semiconducting carbon nanotube

Tiezhu Meng, Chong-Yu Wang, and Shan-Ying Wang

J. Appl. Phys. 102, 013709 (2007); http://dx.doi.org/10.1063/1.2748716 (4 pages) | Cited 15 times

Online Publication Date: 11 July 2007

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The electronic structure of contact between Ti surface and a semiconducting carbon nanotube is investigated by using first-principles method. The nanotube placed on the Ti surface exhibits obvious cross section distortion and strong chemical bonds form between C and Ti. Our results suggest that the nanotube may become metallic and the electrons can be transferred from the nanotube to the Ti electrode without any electrostatic potential barrier. The results are quite different from those of semiconducting carbon nanotube on Al surface, given that Al and Ti have similar work functions. This difference can explain the unexpected experimental difference between Al-nanotube contact and Ti-nanotube contact.
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73.22.-f Electronic structure of nanoscale materials and related systems
71.15.-m Methods of electronic structure calculations
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

First-principles analysis of interfacial nanoscaled oxide layers of bonded N- and P-type GaAs wafers

Hao Ouyang, Hsiao-Hao Chiou, YewChung Sermon Wu, Ji-Hao Cheng, and Wen Ouyang

J. Appl. Phys. 102, 013710 (2007); http://dx.doi.org/10.1063/1.2748335 (4 pages) | Cited 4 times

Online Publication Date: 12 July 2007

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First-principles analysis is applied in relating microstructures with properties of interfacial nanoscaled oxide layers of bonded N- and P-type GaAs wafers. Using high-resolution transmission electron microscope results, the detailed atomic arrangements of materials specimen can be obtained and fed into the first-principles calculations. Therefore, the corresponding electronic structure and associated property can be reliably derived to identify responsible microstructural features. The electrical performance is found to be closely related to the variation of nanosized interface morphology and types of wafers.
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73.20.At Surface states, band structure, electron density of states
73.40.Jn Metal-to-metal contacts
68.35.Ct Interface structure and roughness
61.46.-w Structure of nanoscale materials
73.63.-b Electronic transport in nanoscale materials and structures

Electronic structure and linear optical properties of YAl3(BO3)4

Yuhua Wang, Lingli Wang, and Handong Li

J. Appl. Phys. 102, 013711 (2007); http://dx.doi.org/10.1063/1.2752109 (5 pages) | Cited 7 times

Online Publication Date: 12 July 2007

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The electronic structure and linear optical properties of YAl3(BO3)4 (YAB) crystal are calculated by density functional method with the local-density approximation. An indirect band gap of 6.54 eV and a direct gap of 6.91 eV at M are obtained for YAB. The calculated total and partial densities of states indicate that the top valence band is constructed from O 2p, B 2s, and B 2p states and the low conduction band mostly consists of Y 4d and B 2p states. The calculated linear optical properties, such as refractive index and absorption spectrum, are in good agreement with experimental values.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Mp Nonlinear optical crystals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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