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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Branched SnO2 nanowires on metallic nanowire backbones for ethanol sensors application

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu

Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages) | Cited 36 times

Online Publication Date: 10 March 2008

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We report the synthesis of hierarchically branched semiconducting SnO2 nanowire on metallic Sb-doped SnO2 nanowires by the sequential seeding of multiple nanowire generations with Au nanoparticles as catalysts. Such semiconducting nanowire/metallic backbone complex structures increase the potential functionality of SnO2 nanowires. Branched SnO2 nanowire films are used as sensing materials for high-performance ethanol sensor fabrication. The nanowire sensors show sub-ppm sensitivity and fast response and recovery times at 300 °C. A linear equation relationship between sensitivity and the ethanol vapor concentration was observed.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Hd Other semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
68.65.La Quantum wires (patterned in quantum wells)
82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Single crystalline highly epitaxial Pt thin films on (001) SrTiO3

X. M. Xu, J. Liu, Z. Yuan, J. Weaver, C. L. Chen, Y. R. Li, Hongjun Gao, and N. Shi

Appl. Phys. Lett. 92, 102102 (2008); http://dx.doi.org/10.1063/1.2890844 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2008

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(001) oriented Pt thin films with excellent single crystal quality were epitaxially grown on (001) SrTiO3. The interface relationship was determined and shown to be (001)Pt∥(001)STO and [100]Pt∥[100]STO. Two unexpected “transitions” were found at 138 and 34 K in the evolution of resistivity with temperature as the samples were heated up, which can probably be attributed to phase transitions of the single crystalline SrTiO3. The fact that epitaxial (001) Pt film growth is observed under oxygen plasma is believed to be a result of oxygen ashing of S-containing impurities in the Pt target.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.J- Morphology of films
73.61.At Metal and metallic alloys

Intense terahertz emission from a-plane InN surface

H. Ahn, Y.-P. Ku, C.-H. Chuang, C.-L. Pan, H.-W. Lin, Y.-L. Hong, and S. Gwo

Appl. Phys. Lett. 92, 102103 (2008); http://dx.doi.org/10.1063/1.2892655 (3 pages) | Cited 19 times

Online Publication Date: 10 March 2008

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We report a significant enhancement in terahertz emission from the indium nitride (InN) films grown along the a axis (a-plane InN), relative to the InN films grown along the c axis. The primary radiation mechanism of the a-plane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor. In addition, azimuthal angle dependence measurement shows that the p-polarized terahertz output consists of a large angularly independent component and a weak component with a distinctive fourfold rotation symmetry.
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78.66.Fd III-V semiconductors

Multiple critical layer thicknesses in retro-graded heterostructures

J. E. Ayers

Appl. Phys. Lett. 92, 102104 (2008); http://dx.doi.org/10.1063/1.2883962 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2008

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We determined the critical layer thicknesses for the glide of strain-relaxing dislocations in retrograded semiconductor layers using force balance. For a retro-graded layer, the lattice mismatch varies with distance from the interface y as f = f0+Cfy with sgn(Cf) = −sgn(f0). For a particular combination of f0 and Cf, there may be three different critical thicknesses for which the line tension and glide force of the dislocation are equal. Lattice relaxation by positive glide of grown-in dislocations is favorable for thicknesses in the range hc1<h<hc2 but lattice relaxation by negative glide can occur if h>hc3. If the grading is sufficiently steep, lattice relaxation will only proceed if h>hc3.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.65.Ac Multilayers

Probing nanoscale potential modulation by defect-induced gap states on GaAs(110) with light-modulated scanning tunneling spectroscopy

Shoji Yoshida, Yuya Kanitani, Osamu Takeuchi, and Hidemi Shigekawa

Appl. Phys. Lett. 92, 102105 (2008); http://dx.doi.org/10.1063/1.2888733 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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We investigated charged defects on an n-GaAs(110) surface using light-modulated scanning tunneling spectroscopy. Tunneling via a single defect-induced gap state under photoillumination was observed for the isolated atomic defects. Screened Coulomb potentials induced around a charged Ga vacancy and a step edge were visualized, for the first time, with a nanometer spatial resolution. Furthermore, the charge states of the individual defects were determined on the atomic level.
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71.55.Eq III-V semiconductors
73.40.Gk Tunneling
73.61.Ey III-V semiconductors

Electron beam induced current profiling of ZnO p-n homojunctions

L. Chernyak, C. Schwarz, E. S. Flitsiyan, S. Chu, J. L. Liu, and K. Gartsman

Appl. Phys. Lett. 92, 102106 (2008); http://dx.doi.org/10.1063/1.2896613 (3 pages) | Cited 5 times

Online Publication Date: 13 March 2008

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Variable temperature electron beam induced current technique was employed for the profiling of ZnO p-n homojunctions and the extraction of minority electron diffusion length values in the Sb-doped p-type ZnO region. A thermally induced increase for diffusion length of minority electrons was determined to have an activation energy of ∼ 145 meV. The latter parameter likely represents carrier delocalization energy and determines the increase of the diffusion length due to the reduction in recombination efficiency.
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73.61.Ga II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Narrow-band radiation sensing in the terahertz and microwave bands using the radiation-induced magnetoresistance oscillations

R. G. Mani

Appl. Phys. Lett. 92, 102107 (2008); http://dx.doi.org/10.1063/1.2896614 (3 pages) | Cited 16 times

Online Publication Date: 13 March 2008

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Tuned narrow-band sensing of microwave and terahertz radiation can be realized by subjecting an irradiated two-dimensional electron system to both a static and a time varying magnetic field, and detecting at the harmonics of the modulation. A third harmonic sensor is considered here in conjunction with periodic-in-the-inverse-magnetic-field radiation-induced magnetoresistance oscillations.
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29.40.Wk Solid-state detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Electrical properties of Be-implanted polycrystalline cubic boron nitride films

B. He, W. J. Zhang, Y. S. Zou, Y. M. Chong, Q. Ye, A. L. Ji, Y. Yang, I. Bello, S. T. Lee, and G. H. Chen

Appl. Phys. Lett. 92, 102108 (2008); http://dx.doi.org/10.1063/1.2896643 (3 pages) | Cited 11 times

Online Publication Date: 13 March 2008

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P-type conductivity of polycrystalline cubic boron nitride (cBN) films was achieved by implantation of beryllium ions. The effects of implantation doses and annealing on the phase composition and electrical properties of cBN films were studied. A reduction in resistivity by seven orders of magnitude was observed. Hall measurement revealed a corresponding hole concentration of 6.1×1018 cm−3 and mobility of 3 cm2/V s. The activation energy was estimated to be 0.20±0.02 eV from the temperature dependence of resistance. The electrical properties of Be-implanted films are comparable to that of Be-doped cBN single crystals synthesized by high-pressure and high-temperature method.
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73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Fluorine plasma ion implantation in AlGaN/GaN heterostructures: A molecular dynamics simulation study

L. Yuan, M. J. Wang, and K. J. Chen

Appl. Phys. Lett. 92, 102109 (2008); http://dx.doi.org/10.1063/1.2896646 (3 pages) | Cited 7 times

Online Publication Date: 13 March 2008

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Fluoride-based plasma treatment is a robust technique that enables shallow implantation of fluorine ions into group III-nitride epitaxial structures. This technique has been used to achieve robust threshold voltage control of the AlGaN/GaN high electron mobility transistors and led to the realization of self-aligned enhancement-mode devices. To reveal the atomic scale interactions and provide a modeling tool for process design and optimization, a molecular dynamics (MD) simulation is conducted for fluorine plasma ion implantation. Specific potential functions are applied to calculate the interactions among atoms and simulate the dynamic process of fluorine ions’ penetration and stopping in III-nitride materials. The MD simulation provides accurate information on dopant profiles that are verified by secondary-ion-mass-spectrum measurements. Defect formation and distributions, that are critical in process development, are also investigated.
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61.72.uj III-V and II-VI semiconductors
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Multilevel nonvolatile memory effects in hybrid devices containing CdSe/ZnS nanoparticle double arrays embedded in the C60 matrices

Fushan Li, Sung Hwan Cho, Dong Ick Son, Kyu Ha Park, and Tae Whan Kim

Appl. Phys. Lett. 92, 102110 (2008); http://dx.doi.org/10.1063/1.2898163 (3 pages) | Cited 10 times

Online Publication Date: 13 March 2008

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Electrical properties of nonvolatile memory devices containing core/shell CdSe/ZnS nanoparticle double arrays embedded in the C60 layers formed by using a spin-coating technique were investigated. Transmission electron microscopy images showed that CdSe/ZnS nanoparticles were randomly distributed in the C60 layers. Capacitance-voltage (C-V) measurements on Al/C60/double-stacked CdSe/ZnS nanoparticle arrays/C60/p-Si devices showed that the flat-band voltage shift of the C-V curve related to the charge storage density was enhanced due to a stack of the CdSe/ZnS nanoparticle layers and that the flat-band voltage shift increased with the magnitude of applied bias voltage due to the variations of the charged electron density in the stacked CdSe/ZnS nanoparticle double arrays.
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84.30.Sk Pulse and digital circuits
85.65.+h Molecular electronic devices

Spin current diode based on an electron waveguide with spin-orbit interaction

Feng Zhai, Kai Chang, and H. Q. Xu

Appl. Phys. Lett. 92, 102111 (2008); http://dx.doi.org/10.1063/1.2894582 (3 pages) | Cited 12 times

Online Publication Date: 13 March 2008

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We propose a spin current diode which can work even in a small applied bias condition (the linear-response regime). The prototypal device consists of a hornlike electron waveguide with Rashba spin-orbit interaction, which is connected to two leads with different widths. It is demonstrated that when electrons are incident from the narrow lead, the generated spin conductance fluctuates around a constant value in a wide range of incident energy. When the transport direction is reversed, the spin conductance is suppressed strongly. Such a remarkable difference arises from spin-flipped transitions caused by the spin-orbit interaction.
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72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Ultrashallow defect states at SiO2/4H–SiC interfaces

S. Dhar, X. D. Chen, P. M. Mooney, J. R. Williams, and L. C. Feldman

Appl. Phys. Lett. 92, 102112 (2008); http://dx.doi.org/10.1063/1.2898502 (3 pages) | Cited 8 times

Online Publication Date: 13 March 2008

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Interface state density (Dit) at SiO2/4H–SiC interfaces are reported for states lying energetically within ∼ 0.05–0.2 eV of the conduction band edge (EC) of 4H–SiC using capacitance-voltage characterization as a function of temperature. Comparison of as-grown dry oxidized and nitrided interfaces confirms the significant reduction of Dit associated with nitridation. In the as-oxidized case (no nitridation), the Dit in the energy range ∼ 0.05–0.2 eV below EC is found to consist of a broad Dit peak at about ∼ 0.1 eV below EC with an energy width of about ∼ 0.2 eV and a peak magnitude of ∼ 2×1013 cm−2 eV−1 superimposed on an exponentially decaying background distribution. Interfacial nitridation completely eliminates the broad peak but does not strongly affect the background.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation

Rectifying current-voltage characteristics of BiFeO3/Nb-doped SrTiO3 heterojunction

H. Yang, H. M. Luo, H. Wang, I. O. Usov, N. A. Suvorova, M. Jain, D. M. Feldmann, P. C. Dowden, R. F. DePaula, and Q. X. Jia

Appl. Phys. Lett. 92, 102113 (2008); http://dx.doi.org/10.1063/1.2896302 (3 pages) | Cited 39 times

Online Publication Date: 14 March 2008

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Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1/C2 versus V plot, from which a built-in potential of 0.6 V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.
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68.55.ag Semiconductors
81.15.Fg Pulsed laser ablation deposition
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.jd Vacancies
73.40.Ei Rectification
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