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11 Apr 2011

Volume 98, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 98, 153103 (2011); http://dx.doi.org/10.1063/1.3555342 (3 pages)

Hsin-Yu Wu and Brian T. Cunningham
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Charge transport by modulating spin-orbit gauge fields for quasi-one-dimensional holes

T. Kernreiter, M. Governale, A. R. Hamilton, and U. Zülicke

Appl. Phys. Lett. 98, 152101 (2011); http://dx.doi.org/10.1063/1.3579197 (3 pages)

Online Publication Date: 11 April 2011

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We present a theoretical study of ac charge transport arising from adiabatic temporal variation of zero-field spin splitting in a quasi-one-dimensional hole system (realized, e.g., in a quantum wire or point contact). As in conduction-electron systems, part of the current results from spin-dependent electromotive forces. We find that the magnitude of this current contribution is two orders of magnitude larger for holes and exhibits parametric dependences that make it more easily accessible experimentally. Our results suggest hole structures to be good candidates for realizing devices where spin currents are pumped by time-varying electric fields.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

A transparent ultraviolet triggered amorphous selenium p-n junction

Ichitaro Saito, Wataru Miyazaki, Masanori Onishi, Yuki Kudo, Tomoaki Masuzawa, Takatoshi Yamada, Angel Koh, Daniel Chua, Kenichi Soga, Mauro Overend, Masami Aono, Gehan A. J. Amaratunga, and Ken Okano

Appl. Phys. Lett. 98, 152102 (2011); http://dx.doi.org/10.1063/1.3579262 (3 pages) | Cited 2 times

Online Publication Date: 11 April 2011

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This paper will introduce a semitransparent amorphous selenium (a-Se) film exhibiting photovoltaic effects under ultraviolet light created through a simple and inexpensive method. We found that chlorine can be doped into a-Se through electrolysis of saturated salt water, and converts the weak p-type material into an n-type material. Furthermore, we found that a p-n diode fabricated through this process has shown an open circuit voltage of 0.35 V toward ultraviolet illumination. Our results suggest the possibility of doping control depending on the electric current during electrolysis and the possibility of developing a simple doping method for amorphous photoconductors.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
82.45.Hk Electrolysis
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Transport and strain relaxation in wurtzite InAs–GaAs core-shell heterowires

Karen L. Kavanagh, Joe Salfi, Igor Savelyev, Marina Blumin, and Harry E. Ruda

Appl. Phys. Lett. 98, 152103 (2011); http://dx.doi.org/10.1063/1.3579251 (3 pages) | Cited 8 times

Online Publication Date: 12 April 2011

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Indium-arsenide–gallium-arsenide (InAs–GaAs) core-shell, wurtzite nanowires have been grown on GaAs (001) substrates. The core-shell geometries (core radii 11 to 26 nm, shell thickness >2.5 nm) exceeded equilibrium critical values for strain relaxation via dislocations, apparent from transmission electron microscopy. Partial axial relaxation is detected in all nanowires increasing exponentially with size, while radial strain relaxation is >90%, but undetected in nanowires with both smaller core radii <16 nm and shell thicknesses <5 nm. Electrical measurements on individual core-shell nanowires show that the resulting dislocations are correlated with reduced electron field-effect mobility compared to bare InAs nanowires.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Gy Mechanical properties; surface strains
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Deep levels in tungsten doped n-type 3C–SiC

F. C. Beyer, C. G. Hemmingsson, A. Gällström, S. Leone, H. Pedersen, A. Henry, and E. Janzén

Appl. Phys. Lett. 98, 152104 (2011); http://dx.doi.org/10.1063/1.3579527 (3 pages) | Cited 3 times

Online Publication Date: 13 April 2011

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Tungsten was incorporated in SiC and W related defects were investigated using deep level transient spectroscopy. In agreement with literature, two levels related to W were detected in 4H–SiC, whereas only the deeper level was observed in 6H–SiC. The predicted energy level for W in 3C–SiC was observed (EC−0.47 eV). Tungsten serves as a common reference level in SiC. The detected intrinsic levels align as well: E1 (EC−0.57 eV) in 3C–SiC is proposed to have the same origin, likely VC, as EH6/7 in 4H–SiC and E7 in 6H–SiC, respectively.
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71.55.Ht Other nonmetals
61.72.-y Defects and impurities in crystals; microstructure
71.20.Lp Intermetallic compounds

Increased metal-insulator transition temperatures in epitaxial thin films of V2O3 prepared in reduced oxygen environments

J. Brockman, N. P. Aetukuri, T. Topuria, M. G. Samant, K. P. Roche, and S. S. P. Parkin

Appl. Phys. Lett. 98, 152105 (2011); http://dx.doi.org/10.1063/1.3574910 (3 pages) | Cited 2 times

Online Publication Date: 13 April 2011

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Thin films of V2O3 were grown epitaxially on c-plane sapphire substrates by oxygen plasma-assisted thermal evaporation. Reducing the amount of oxygen supplied during growth led to a nearly 50 K increase in V2O3’s metal-insulator transition temperature to a temperature as high as 184 K. By systematically varying the oxygen pressure the transition temperature monotonically increased, which was accompanied by a concomitant increase in the room-temperature resistivity. These trends are consistent with a continuous change in the stoichiometry of V2O3.
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73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth
81.15.Dj E-beam and hot filament evaporation deposition

Near band-edge electron diffusion in electrospun Nb-doped anatase TiO2 nanofibers probed by electrochemical impedance spectroscopy

P. S. Archana, R. Jose, M. M. Yusoff, and S. Ramakrishna

Appl. Phys. Lett. 98, 152106 (2011); http://dx.doi.org/10.1063/1.3579194 (3 pages) | Cited 5 times

Online Publication Date: 14 April 2011

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Charge transport through Nb-doped anatase TiO2 nanofibers (diameter ∼ 100 nm) developed by electrospinning is studied under the framework of hopping transport using electrochemical impedance spectroscopy measurements. It is observed that the Fermi level of TiO2 rise close to its conduction band and result in a band-edge type diffusion mechanism even at low bias voltages when 2 at % Nb atoms replaces the Ti atoms in the anatase lattice. The Nb-doped anatase electrospun nanofibers showed high chemical capacitance, high effective diffusion coefficient, and lower transport resistance compared to the undoped samples and conventional nanoparticles (25 nm).
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73.63.Bd Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.80.Fk Electrochemical methods
82.45.Rr Electroanalytical chemistry
72.20.Ee Mobility edges; hopping transport
73.22.-f Electronic structure of nanoscale materials and related systems

Nonlinear current-voltage behavior of the isolated resistive switching filamentary channels in CuC nanolayer

Doo-In Kim, Jaesik Yoon, Ju-Bong Park, Hyunsang Hwang, Young Moon Kim, Se Hun Kwon, and Kwang Ho Kim

Appl. Phys. Lett. 98, 152107 (2011); http://dx.doi.org/10.1063/1.3570653 (3 pages) | Cited 1 time

Online Publication Date: 14 April 2011

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Copper-doped amorphous carbon film was prepared by radio frequency reactive magnetron sputtering and their resistive switching behaviors were studied under a conductive atomic force microscope (cAFM). The repetitive scanning over the same area using cAFM with various bias voltages revealed that most of the isolated conductive paths were involved in resistive switching with asymmetric nonlinear I-V characteristics. The observed I-V behavior of nanoscale filamentary channels indicates that electron transfer mechanism of resistive switching filamentary channel in Pt/CuC/Pt is a tunneling between Cu filamentary channel and electrode through the solid electrolyte rather than conduction through fully connected Cu filamentary channel.
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73.40.Rw Metal-insulator-metal structures
73.40.Gk Tunneling
81.15.Cd Deposition by sputtering
72.60.+g Mixed conductivity and conductivity transitions

Nonlinear variations in the electronic structure of II–VI and III–V wurtzite semiconductors with biaxial strain

Shenyuan Yang, David Prendergast, and Jeffrey B. Neaton

Appl. Phys. Lett. 98, 152108 (2011); http://dx.doi.org/10.1063/1.3578193 (3 pages) | Cited 2 times

Online Publication Date: 14 April 2011

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Using first-principles calculations within many-body perturbation theory, we predict effects of biaxial strain on electronic band gaps and band edges of wurtzite III–V and II–VI semiconductor compounds. We find strain-induced changes in band gaps are large and highly nonlinear. Under both compressive and tensile biaxial strains, II–VI chalcogenide band gaps are predicted to decrease by as much as 0.6 eV for 10% strain; in contrast, III–V nitrides attain maximum gaps for compressive strains near 4%. Whereas nitrides tend to preserve covalent bond angle, more ionic chalcogenides tend to preserve bond length and volume, leading to qualitatively different trends in electronic structure.
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71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
61.50.Lt Crystal binding; cohesive energy

Environment-dependent thermal instability of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors

Wan-Fang Chung, Ting-Chang Chang, Hung-Wei Li, Shih-Ching Chen, Yu-Chun Chen, Tseung-Yuen Tseng, and Ya-Hsiang Tai

Appl. Phys. Lett. 98, 152109 (2011); http://dx.doi.org/10.1063/1.3580614 (3 pages) | Cited 13 times

Online Publication Date: 14 April 2011

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The environment-dependent electrical performances as a function of temperature for sol-gel derived amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors are investigated in this letter. In the ambients without oxygen, thermal activation dominates and enhances device performance. In oxygen-containing environments, mobility and drain current degrades and the threshold slightly increase as temperature increases. We develop a porous model for a-IGZO film relating to the drain current and mobility lowering due to film porosity and oxygen adsorption/penetration. It also relates to the threshold voltage recovery at high temperature owing to the varying form of adsorbed oxygen and the combination of oxygen and vacancies.
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85.30.Tv Field effect devices

Electron field emission enhanced by geometric and quantum effects from nanostructured AlGaN/GaN quantum wells

Wei Zhao, Ru-Zhi Wang, Xue-Mei Song, Hao Wang, Bo Wang, Hui Yan, and Paul K. Chu

Appl. Phys. Lett. 98, 152110 (2011); http://dx.doi.org/10.1063/1.3581043 (3 pages) | Cited 1 time

Online Publication Date: 14 April 2011

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Electron field emitters that provide intense and stable currents are important to vacuum microelectronic devices. In this work, we demonstrate high-performance electron field emission (FE) from nanostructured AlGaN/GaN quantum wells by coupling the quantum and geometric effects. Pulsed laser deposition is utilized to fabricate the FE cathode. The field emitter exhibits a low threshold field of only 1.1 V/μm and yields a stable emission current of 5 mA/cm2 at 1.8 V/μm, making it suitable for FE-based applications.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Fg Pulsed laser ablation deposition
81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
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