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9 Nov 2009

Volume 95, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 193101 (2009); http://dx.doi.org/10.1063/1.3258663 (3 pages)

L. Gaudreau, A. Kam, G. Granger, S. A. Studenikin, P. Zawadzki, and A. S. Sachrajda
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Dramatic excitation dependence of strong and stable blue luminescence of ZnO hollow nanoparticles

Haibo Zeng, Shikuan Yang, Xiaoxia Xu, and Weiping Cai

Appl. Phys. Lett. 95, 191904 (2009); http://dx.doi.org/10.1063/1.3263712 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2009

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Strong and stable blue luminescence was obtained from ZnO hollow nanoparticles. Significantly, dramatic excitation dependence was observed for blue emissions of ZnO: (1) band-gap energy (Eg) is the optimal excitation energy but smaller energies are still effective; (2) there exist several fixed emitting wavelengths in blue wave band, such as 412, 439, and 458 nm. These phenomena, combined with previously reported defect levels and formation thermodynamics, point out that the initial states of corresponding transitions to blue emissions could be zinc interstitials-related defect states, which were further verified by subsequent electron paramagnetic resonance examinations.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Nr Semiconductor compounds
71.55.Gs II-VI semiconductors

Photoreflectance and Fourier transform infrared spectroscopy study of intersubband transitions of a ZnxCd1−xSe/Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well structure for quantum cascade laser application

J. D. Wu, C. T. Huang, Y. S. Huang, W. O. Charles, A. Shen, and M. C. Tamargo

Appl. Phys. Lett. 95, 191905 (2009); http://dx.doi.org/10.1063/1.3263951 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2009

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Photoreflectance (PR) and Fourier transform infrared (FTIR) spectroscopy were used to study the intersubband (ISB) transitions of a ZnxCd1−xSe/Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well (ACQW) structure for quantum cascade laser (QCL) application. The PR spectrum revealed a wide range of possible optical transitions in the ACQW structure. A comprehensive analysis of the PR spectrum led to the identification of various interband transitions. The ISB transitions were estimated and confirmed by FTIR absorption measurements. The results demonstrated the use of PR as a complimentary technique to FTIR for the contactless and nondestructive characterization of ACQW structures for QCL application.
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78.30.Fs III-V and II-VI semiconductors
78.67.De Quantum wells
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Size effect on the lattice parameters of nanocrystalline anatase

Md. Imteyaz Ahmad and S. S. Bhattacharya

Appl. Phys. Lett. 95, 191906 (2009); http://dx.doi.org/10.1063/1.3261754 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2009

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Crystallite size dependence on the lattice parameters of nanocrystalline anatase was examined by x-ray diffraction pattern analysis, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The lattice parameter a increased while the parameter c decreased with reducing crystallite sizes. However, the cell volume increased with decreasing crystallite size indicating an overall expansion due to confinement effect. The observed shift in Eg Raman mode (at 144 cm−1) was in accordance with an empirical phonon confinement model while no substoichiometric titania could be detected by XPS. It was concluded that the lattice expansion was purely due to electrostatic relaxation as a result of size confinement.
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61.46.Hk Nanocrystals
63.22.Kn Clusters and nanocrystals
78.30.Hv Other nonmetallic inorganics
79.60.Jv Interfaces; heterostructures; nanostructures
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Giant changes in atomic dynamics on microalloying metallic melt

S. M. Chathoth, B. Damaschke, J. P. Embs, and K. Samwer

Appl. Phys. Lett. 95, 191907 (2009); http://dx.doi.org/10.1063/1.3263950 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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We report unexpectedly strong variations in the relaxational dynamics in a glass-forming metallic melt while microalloying. Analysis of quasielastic neutron scattering data revealed that changes in the values of stretching of the self-correlation function and the temperature dependence of self-diffusivity showed an Arrhenius to non-Arrhenius transition. The intermediate structure of the melts did not show any prepeak or indication of short range order. These observations are correlated with the enhanced glass-forming ability of metallic melts on microalloying.
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66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
64.70.pm Liquids

Study of minority carrier diffusion length in multicrystalline silicon solar cells using photoassisted Kelvin probe force microscopy

Masaki Takihara, Takuji Takahashi, and Toru Ujihara

Appl. Phys. Lett. 95, 191908 (2009); http://dx.doi.org/10.1063/1.3264081 (3 pages) | Cited 6 times

Online Publication Date: 13 November 2009

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We evaluated the minority carrier diffusion length in multicrystalline silicon solar cells by means of photoassisted Kelvin probe force microscopy to investigate the influence of the multicrystalline material grains and the grain boundaries on solar cell performance. We observed a reduction in the diffusion length in the vicinity of the grain boundary and differences in the diffusion lengths between grains even when considering the influence of lateral diffusion.
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88.40.jj Silicon solar cells
61.72.Mm Grain and twin boundaries
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Transformation pathways in the solid-solid phase transitions of iron nanowires

Luis Sandoval and Herbert M. Urbassek

Appl. Phys. Lett. 95, 191909 (2009); http://dx.doi.org/10.1063/1.3258002 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Using molecular dynamics simulations, we study the solid-solid phase transitions induced by strain in Fe nanowires. These show an intricate dependence on the crystallographic orientation of the wire. 〈001〉 oriented nanowires exhibit a bcc→fcc transition and preferably follow the Nishiyama–Wassermann path. In 〈011〉 and 〈111〉 oriented nanowires the transformation is bcc→hcp and proceeds according to the Burgers path. Additionally we show that it is possible to obtain multiple phase transitions accompanied with reorientations.
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64.70.Nd Structural transitions in nanoscale materials
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
64.70.kd Metals and alloys

Practical approach for a rod-connected diamond photonic crystal operating at optical wavelengths

Kanna Aoki

Appl. Phys. Lett. 95, 191910 (2009); http://dx.doi.org/10.1063/1.3264088 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Production of a rod-connected diamond (RCD) photonic crystal structure in a semiconductor material is proposed. Periodic shifting of only one building block can create a complicated three-dimensional network, with a RCD structure exhibiting a full bandgap as wide as 0.20 on a gap/midgap (Δω/ωM) basis. A point defect cavity in the structure sustains single-mode resonance throughout the operative range because of its low symmetry. The resonant mode’s highest quality factor (Q-factor) was calculated as 1.5×104 for a crystal of 11.5ax×4.25ay×12az for ai (i = x,y,z) representing three axes’ period lengths.
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42.70.Qs Photonic bandgap materials

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Sunil Kumar, M. Anija, N. Kamaraju, K. S. Vasu, K. S. Subrahmanyam, A. K. Sood, and C. N. R. Rao

Appl. Phys. Lett. 95, 191911 (2009); http://dx.doi.org/10.1063/1.3264964 (3 pages) | Cited 24 times

Online Publication Date: 13 November 2009

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Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pump-probe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, β of ( ∼ 2–9)×10−8 cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130–330 fs (related to carrier-carrier scattering) followed by a slower one in 3.5–4.9 ps range (associated with carrier-phonon scattering) are observed.
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78.47.J- Ultrafast spectroscopy (<1 psec)
82.70.Kj Emulsions and suspensions
63.20.-e Phonons in crystal lattices
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Water vapor interaction with silicon oxide films thermally grown on 6H-SiC and on Si

G. V. Soares, I. J. R. Baumvol, S. A. Corrêa, C. Radtke, and F. C. Stedile

Appl. Phys. Lett. 95, 191912 (2009); http://dx.doi.org/10.1063/1.3262971 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Thermally induced incorporation of isotopically labeled water vapor (D2 18O) species in 7 nm thick SiO2 films thermally grown on 6H-SiC(0001) and on Si(001) were investigated. Higher incorporation of hydrogen and higher isotopic exchange were observed in SiO2/SiC as compared to SiO2/Si, at temperatures above 600 °C, which can lead to electrical instabilities, especially in high-temperature devices. At any annealing temperature, oxygen is incorporated in the oxide films, reaching the SiO2/SiC interface, in contrast with SiO2/Si. The present observations show that strict control of water vapor contents in SiO2/SiC is mandatory in order to achieve further improvements in the SiC-based device technology.
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82.20.Tr Kinetic isotope effects including muonium
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
81.40.Gh Other heat and thermomechanical treatments
68.47.Fg Semiconductor surfaces

Robust atomic resolution imaging of light elements using scanning transmission electron microscopy

S. D. Findlay, N. Shibata, H. Sawada, E. Okunishi, Y. Kondo, T. Yamamoto, and Y. Ikuhara

Appl. Phys. Lett. 95, 191913 (2009); http://dx.doi.org/10.1063/1.3265946 (3 pages) | Cited 52 times

Online Publication Date: 13 November 2009

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We show that an annular detector placed within the bright field cone in scanning transmission electron microscopy allows direct imaging of light elements in crystals. In contrast to common high angle annular dark field imaging, both light and heavy atom columns are visible simultaneously. In contrast to common bright field imaging, the images are directly and robustly interpretable over a large range of thicknesses. We demonstrate this through systematic simulations and present a simple physical model to obtain some insight into the scattering dynamics.
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68.37.Ma Scanning transmission electron microscopy (STEM)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
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Geometry dependent current-voltage characteristics of ZnO nanostructures: A combined nonequilibrium Green’s function and density functional theory study

Zhiwen Yang, Bin Wen, Roderick Melnik, Shan Yao, and Tingju Li

Appl. Phys. Lett. 95, 192101 (2009); http://dx.doi.org/10.1063/1.3259657 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2009

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Current-voltage (I-V) characteristics of different ZnO nanostructures were studied using a combined nonequilibrium Green’s function and density functional theory techniques with the two-probe model. It was found that I-V characteristics of ZnO nanostructures depend strongly on their geometry. For wurtzite ZnO nanowires, currents decrease with increasing lengths under the same applied voltage conditions. The I-V characteristics are similar for single-walled ZnO nanotubes and triangular cross section ZnO nanowires but they are different from I-V characteristics of hexagonal cross section ZnO nanowires. Finally, our results are discussed in the context of calculated transmission spectra and densities of states.
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73.21.Hb Quantum wires
73.63.Nm Quantum wires
73.63.Fg Nanotubes
78.67.Ch Nanotubes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Plasmon-enhanced heat dissipation in GaN-based two-dimensional channels

A. Matulionis, J. Liberis, I. Matulionienė, M. Ramonas, E. Šermukšnis, J. H. Leach, M. Wu, X. Ni, X. Li, and H. Morkoç

Appl. Phys. Lett. 95, 192102 (2009); http://dx.doi.org/10.1063/1.3261748 (3 pages) | Cited 11 times

Online Publication Date: 9 November 2009

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Decay of nonequilibrium longitudinal optical (LO) phonons is investigated at room temperature in two-dimensional electron gas channels confined in nearly lattice-matched InAlN/AlN/GaN structures. A nonmonotonous dependence of the LO-phonon lifetime on the supplied electric power is reported for the first time and explained in terms of plasmon–LO-phonon resonance tuned by applied bias at a fixed sheet density (8×1012 cm−2). The shortest lifetime of 30±15 fs is found at the power of 20±10 nW/electron.
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63.20.kk Phonon interactions with other quasiparticles
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.63.-b Electronic transport in nanoscale materials and structures

Superconducting tunneling spectroscopy of a carbon nanotube quantum dot

Travis Dirks, Yung-Fu Chen, Norman O. Birge, and Nadya Mason

Appl. Phys. Lett. 95, 192103 (2009); http://dx.doi.org/10.1063/1.3253705 (3 pages) | Cited 8 times

Online Publication Date: 10 November 2009

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We report results on superconducting tunneling spectroscopy of a carbon nanotube quantum dot. Using a three-probe technique that includes a superconducting tunnel probe, we map out changes in conductance due to band structure, excited states, and end-to-end bias. The superconducting probe allows us to observe enhanced spectroscopic features, such as robust signals of both elastic and inelastic cotunneling. We also see evidence of inelastic scattering processes inside the quantum dot.
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73.40.Gk Tunneling
68.65.Hb Quantum dots (patterned in quantum wells)
71.20.Tx Fullerenes and related materials; intercalation compounds
61.46.Fg Nanotubes
74.50.+r Tunneling phenomena; Josephson effects

Highly efficient (Cs8V) superatom-based spin-polarizer

Haiying He, Ravindra Pandey, J. Ulises Reveles, Shiv N. Khanna, and Shashi P. Karna

Appl. Phys. Lett. 95, 192104 (2009); http://dx.doi.org/10.1063/1.3259646 (3 pages) | Cited 8 times

Online Publication Date: 10 November 2009

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Quantum transport through molecules and the possibility to manipulate spin has generated tremendous excitement. Here, we demonstrate unusual spin transport through a molecule of two Cs8V magnetic superatoms. Calculations based on density functional theory and nonequilibrium Green’s function methods find a much higher current for the spin-down charge carriers relative to the spin-up carriers in the model Au–(Cs8V)–(Cs8V)–Au device system with almost 100% spin polarization, indicating a highly efficient spin polarizer. The new behavior is rooted in strong coupling of the localized magnetic core on V and the itinerant electrons of the Cs shell atoms leading to nearly full spin polarization.
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73.40.Jn Metal-to-metal contacts
72.25.Ba Spin polarized transport in metals
72.25.Mk Spin transport through interfaces

Undoped vacuum annealed In2O3 thin films as a transparent conducting oxide

A. Dixit, C. Sudakar, R. Naik, V. M. Naik, and G. Lawes

Appl. Phys. Lett. 95, 192105 (2009); http://dx.doi.org/10.1063/1.3262963 (3 pages) | Cited 8 times

Online Publication Date: 10 November 2009

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We have investigated the structural, optical, and electrical properties of both as-grown and vacuum annealed In2O3 thin films. In contrast to the insulating as-prepared samples, vacuum annealed In2O3 films exhibit a metallic electrical conductivity with increased carrier concentration and mobility. We attribute the excess carriers to an oxygen deficiency introduced during vacuum annealing. Remarkably, these carrier densities seem to be stable under ambient conditions for at least two years. Optical spectroscopy measurements show a large optical transparency, greater than 80%, for both the as-prepared and vacuum annealed In2O3 films.
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68.55.A- Nucleation and growth
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.-w Optical properties of specific thin films
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Suppression of compensation from nitrogen and carbon related defects for p-type N-doped ZnO

Kun Tang, Shulin Gu, Shunming Zhu, Jiagao Liu, Hui Chen, Jiandong Ye, Rong Zhang, and Youdou Zheng

Appl. Phys. Lett. 95, 192106 (2009); http://dx.doi.org/10.1063/1.3262965 (3 pages) | Cited 13 times

Online Publication Date: 10 November 2009

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In this letter, the authors performed a comprehensive study on suppression mechanism of compensation from nitrogen and carbon related complex defects in N-doped ZnO grown by metal-organic chemical vapor deposition. The chemical bonding information of donorlike substitutional complex defects, (NN)O and (NC)O, were restrained with low N/O ratio, leading to the conduction type conversion. High epitaxial temperature has more suppressing effect on the formation of desired acceptor NO than that of (NC)O, as evident by the decreasing hole concentration. Upon utilization of such suppression effect, this study provides a promising route to realize p-type ZnO.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.uj III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ga II-VI semiconductors

Anisotropic electron spin relaxation in bulk GaN

J. H. Buß, J. Rudolph, F. Natali, F. Semond, and D. Hägele

Appl. Phys. Lett. 95, 192107 (2009); http://dx.doi.org/10.1063/1.3261755 (3 pages) | Cited 11 times

Online Publication Date: 11 November 2009

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Electron spin dynamics in n-type c-oriented wurtzite GaN epilayers is studied by time-resolved Kerr-rotation measurements at T = 80 K. The electron spin lifetime shows a sudden increase if an external magnetic field is applied in the sample plane. This enhancement is explained by anisotropic Dyakonov–Perel spin relaxation in bulk GaN as a direct consequence of the anisotropy of spin-orbit coupling in semiconductors with wurtzite structure.
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81.05.Ea III-V semiconductors
75.30.Gw Magnetic anisotropy
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.47.D- Time resolved spectroscopy (>1 psec)
68.55.ag Semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Cu–Cu diffusion bonding enhancement at low temperature by surface passivation using self-assembled monolayer of alkane-thiol

C. S. Tan, D. F. Lim, S. G. Singh, S. K. Goulet, and M. Bergkvist

Appl. Phys. Lett. 95, 192108 (2009); http://dx.doi.org/10.1063/1.3263154 (3 pages) | Cited 9 times

Online Publication Date: 11 November 2009

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Self-assembled monolayer (SAM) of 1-hexanethiol is applied on copper (Cu) surface to retard surface oxidation during exposure in the ambient. This SAM layer can be desorbed effectively with an annealing step in inert N2 ambient to provide a clean Cu surface. Using this passivation method with SAM, wafers covered with thin Cu layer are passivated, stored, desorbed, and bonded at 250 °C. The bonded Cu layer presents clear evidence of substantial interdiffusion and grain growth despite prolonged exposure in the ambient. This method of passivation is proven to be effective and can be further optimized to enable high quality Cu–Cu direct bonding at low temperature for application in three-dimensional integration.
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81.65.Rv Passivation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Fermi-level pinning at the interface between metals and nitrogen-doped Ge2Sb2Te5 examined by x-ray photoelectron spectroscopy

Lina Wei-Wei Fang, Rong Zhao, Jisheng Pan, Zheng Zhang, Luping Shi, Tow-Chong Chong, and Yee-Chia Yeo

Appl. Phys. Lett. 95, 192109 (2009); http://dx.doi.org/10.1063/1.3263953 (3 pages) | Cited 6 times

Online Publication Date: 12 November 2009

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The metal/α-Ge2Sb2Te5 interface was examined using x-ray photoelectron spectroscopy. Doping Ge2Sb2Te5 with nitrogen leads to an increase in hole barrier height at the interface between metals and nitrogen-doped Ge2Sb2Te5. Hole barrier height at metal/α-Ge2Sb2Te5 interface is reduced slightly by increasing the work function of the metal. We observed significant pinning of metal Fermi level toward the valence band energy of undoped or nitrogen-doped Ge2Sb2Te5. This leads to low hole barrier height and good Ohmic contact formed between metals and α-Ge2Sb2Te5.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.up Other materials
84.30.Sk Pulse and digital circuits
73.30.+y Surface double layers, Schottky barriers, and work functions

Multichannel carbon nanotube field-effect transistors with compound channel layer

Changxin Chen, Wei Zhang, and Yafei Zhang

Appl. Phys. Lett. 95, 192110 (2009); http://dx.doi.org/10.1063/1.3263723 (3 pages) | Cited 1 time

Online Publication Date: 13 November 2009

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A multichannel carbon nanotube field-effect transistor (MC-CNTFET) with compound channel layer has been built. In this MC-CNTFET, a dispersedly directed array of long single-walled carbon nanotubes (SWCNTs) is used as primary channel layer and a randomly aligned monolayer network of short SWCNTs acts as secondary set of “bridge” channel layer, which causes large numbers of short semiconducting percolation paths formed. The device exhibits a large on-state current of 2.01 mA and simultaneously retains a high current on/off ratio of 103–104. The function dependency of the on-state current on the density of long SWCNTs and length of short SWCNTs is also presented.
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85.35.Kt Nanotube devices
81.07.De Nanotubes

Sulfur passivation of InN surface electron accumulation

L. R. Bailey, T. D. Veal, C. E. Kendrick, S. M. Durbin, and C. F. McConville

Appl. Phys. Lett. 95, 192111 (2009); http://dx.doi.org/10.1063/1.3263725 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2009

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The effects of treatment with ammonium sulfide ((NH4)2Sx) solution on the electronic properties of InN surfaces have been investigated with high resolution x-ray photoemission spectroscopy. The valence band, In 3d, and N 1s x-ray photoemission spectra show that the surface Fermi level decreases by approximately 0.15 eV with (NH4)2Sx-treatment. This corresponds to a reduction of the downward band bending with the surface sheet charge density decreasing by 30%.
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81.65.Rv Passivation
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces

g-factor and exchange energy in a few-electron lateral InGaAs quantum dot

M. Larsson, H. A. Nilsson, H. Hardtdegen, and H. Q. Xu

Appl. Phys. Lett. 95, 192112 (2009); http://dx.doi.org/10.1063/1.3264053 (3 pages) | Cited 4 times

Online Publication Date: 13 November 2009

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We report on the measurements of the g-factor and the exchange interaction of electrons in a few-electron lateral quantum dot formed in an InGaAs/InP semiconductor heterostructure. The spin filling sequence of the electron states in the dot is determined by magnetotransport measurements and parallel spin filling configurations are identified. The measured g-factor (for a magnetic field applied parallel to the InGaAs quantum-well layer) has a value in the range of |g∗| ≈ 2 to |g∗| ≈ 4 and is strongly level-dependent. By analysis of the energies of the states which favor a parallel spin filling, the lower bound of the exchange energy of electrons in the dot in the order of ∼ 210 μeV is extracted.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.63.Kv Quantum dots
72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Gm Exchange interactions

Effects of a Gd capping layer on electrical characteristics of metal-oxide-semiconductor field effect transistors with a TaC gate electrode and a HfSiON gate dielectric

Hong Bae Park, Chang Seo Park, Chang Yong Kang, Seung-Chul Song, Byoung Hun Lee, Tae-Young Jang, Tea Wan Kim, Jae Kyeong Jeong, and Rino Choi

Appl. Phys. Lett. 95, 192113 (2009); http://dx.doi.org/10.1063/1.3264086 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2009

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Effects of Gd capping of HfSiON gate dielectric on the characteristics of n metal-oxide-semiconductor field effect transistor (nMOSFET) with TaC gate electrode were investigated. MOSFETs with an in situ deposited Gd/TaC bilayer demonstrated a reduced equivalent oxide thickness, 0.9 nm, and low VTH, 0.25 V, compared with MOSFETs without Gd capping layer. Backside secondary ion mass spectroscopy revealed that Gd atoms were diffused into the high-k gate dielectric and interfacial layer between high-k dielectric and Si substrate. The dipole moment at the high-k/SiO2 interface due to Hf–O and RE–O bonds is used to explain the VTH change.
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85.30.Tv Field effect devices

Disorder enhances thermoelectric figure of merit in armchair graphane nanoribbons

Xiaoxi Ni, Gengchiau Liang, Jian-Sheng Wang, and Baowen Li

Appl. Phys. Lett. 95, 192114 (2009); http://dx.doi.org/10.1063/1.3264087 (3 pages) | Cited 23 times

Online Publication Date: 13 November 2009

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We study the thermoelectric property of graphane strips by using density functional theory calculations combined with the nonequilibrium Green’s function method. It is found that figure of merit (ZT) can be remarkably enhanced five times by randomly introducing hydrogen vacancies to the graphene nanoribon derivatives—armchair graphane nanoribbons. For 5 nm wide ribbons under certain conditions, ZT can be as high as 5.8 and depends on temperature linearly. The high ZT, low cost, and rapid advances in the synthesis of nanoscale graphene derivatives make carbon-based materials a viable choice for thermoelectric applications.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Fg Nanotubes
61.72.jd Vacancies

Mapping out the distribution of electronic states in the mobility gap of amorphous zinc tin oxide

Peter T. Erslev, Eric S. Sundholm, Rick E. Presley, David Hong, John F. Wager, and J. David Cohen

Appl. Phys. Lett. 95, 192115 (2009); http://dx.doi.org/10.1063/1.3262962 (3 pages) | Cited 10 times

Online Publication Date: 13 November 2009

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Amorphous zinc tin oxide (ZTO) is a wide-band-gap (transparent) semiconductor which exhibits high electron mobilities irrespective of its disordered nature. Transient photocapacitance (TPC), drive level capacitance profiling (DLCP), and modulated photocurrent spectroscopy (MPC) were used to determine the electronic state distribution within the mobility gap of ZTO. Conduction band-tail and valence band-tail Urbach energies near 10 and 110 meV were obtained by MPC and TPC, respectively. DLCP indicated free carrier densities in the mid-1015 cm−3 range plus a 0.2eV wide band of defects 0.4eV from the conduction band. The MPC spectra for ZTO also disclosed a defect band near the conduction band-tail.
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71.20.Nr Semiconductor compounds
72.20.Fr Low-field transport and mobility; piezoresistance
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
61.72.-y Defects and impurities in crystals; microstructure
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.40.+w Photoconduction and photovoltaic effects
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