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23 May 2005

Volume 86, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 86, 213111 (2005); http://dx.doi.org/10.1063/1.1931027 (3 pages)

R. H. Miwa, W. Orellana, and A. Fazzio
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Temperature dependence of electrical conductance in single-crystalline boron nanobelts

K. Kirihara, Z. Wang, K. Kawaguchi, Y. Shimizu, T. Sasaki, N. Koshizaki, K. Soga, and K. Kimura

Appl. Phys. Lett. 86, 212101 (2005); http://dx.doi.org/10.1063/1.1935036 (3 pages) | Cited 16 times

Online Publication Date: 16 May 2005

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We studied electrical transport in single-crystalline boron nanobelts with α-tetragonal crystalline structure. We obtained ohmic contacts to the boron nanobelts by metal electrodes of Ni/Au bilayer. From the temperature dependence of electrical conductance, we found that the boron nanobelt is a semiconductor. The electrical conductivity was of the order of 10−3 (Ω cm)−1 at 295 K. Fitting the results to variable-range-hopping conduction revealed a high density of localized states at the Fermi level compared with bulk β-rhombohedral boron.
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72.20.Ee Mobility edges; hopping transport
73.63.Bd Nanocrystalline materials
73.40.Ns Metal-nonmetal contacts
61.46.-w Structure of nanoscale materials
61.66.Bi Elemental solids

Where does photocurrent flow in polycrystalline CdS?

D. Azulay, O. Millo, S. Silbert, I. Balberg, and N. Naghavi

Appl. Phys. Lett. 86, 212102 (2005); http://dx.doi.org/10.1063/1.1923157 (3 pages) | Cited 10 times

Online Publication Date: 16 May 2005

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We have studied the local photoconductance in polycrystalline CdS films using conductance atomic force microscopy under illumination, and found that photoconductivity along the grain boundaries is excited at photon energies significantly smaller than the CdS band gap, Eg, whereas phototransport through the grains is detected only above Eg. In addition, we observed a rather strong persistent photoconductivity effect at both conduction channels. The implications of these findings regarding the band tails in CdS films and photovoltaic applications are discussed.
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72.40.+w Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
71.20.Nr Semiconductor compounds
61.72.Mm Grain and twin boundaries
68.37.Ps Atomic force microscopy (AFM)

Operation and high-frequency performance of nanoscale unipolar rectifying diodes

J. Mateos, B. G. Vasallo, D. Pardo, and T. González

Appl. Phys. Lett. 86, 212103 (2005); http://dx.doi.org/10.1063/1.1931051 (3 pages) | Cited 20 times

Online Publication Date: 16 May 2005

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By means of the microscopic transport description supplied by a semiclassical two-dimensional Monte Carlo simulator, we provide an in depth explanation of the operation (based on electrostatic effects) of the nanoscale unipolar rectifying diode, so called self-switching diode, recently proposed in A. M. Song, M. Missous, P. Omling, A. R. Peaker, L. Samuelson, and W. Seifert, Appl. Phys. Lett. 83, 1881 (2003) . The simple downscaling of this device and the intrinsically high electron velocity of InGaAs channels allows one to envisaging the fabrication of structures working in the THz range. We analyze the high-frequency performance of the diodes and provide design considerations for the optimization of the downscaling process.
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85.30.Kk Junction diodes
73.40.Ei Rectification

Odd filling factor quantum Hall sequence in magnetic type-III quantum wells

H. Buhmann, E. G. Novik, V. Daumer, J. Liu, Y. S. Gui, C. R. Becker, and L. W. Molenkamp

Appl. Phys. Lett. 86, 212104 (2005); http://dx.doi.org/10.1063/1.1935753 (3 pages)

Online Publication Date: 17 May 2005

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The magnetotransport properties of a series of Hg1−yMnyTe quantum wells (y = 2%) reveal anomalous sequences of quantum Hall plateaus and corresponding minima in the longitudinal magnetoresistance which correspond solely to odd filling factors. This anomaly originates from the very large spin splitting in this material, which exceeds the cyclotron energy even at moderate magnetic fields (B>2T). An 8×8 band k∙p approach has been used to calculate the magnetic field dependence of the Landau levels. Finite temperature and Landau level broadening considerations confirm that subband crossings in the vicinity of the Fermi energy are responsible for the suppression of even filling factor quantum Hall states.
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81.07.St Quantum wells
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
73.63.Hs Quantum wells
73.43.Qt Magnetoresistance
73.21.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
75.75.-c Magnetic properties of nanostructures
71.70.Di Landau levels
71.15.-m Methods of electronic structure calculations
75.47.Pq Other materials

Study on anomalous n-type conduction of P-doped ZnO using P2O5 dopant source

Zhi Gen Yu, Hao Gong, and Ping Wu

Appl. Phys. Lett. 86, 212105 (2005); http://dx.doi.org/10.1063/1.1938249 (3 pages) | Cited 12 times

Online Publication Date: 17 May 2005

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The unexpected n-type conduction observed in P-doped ZnO thin films fabricated from rf magnetron sputtering, was studied systematically through a combined approach of experiment and computer modeling. The carrier stability was predicted from first-principles density functional theory and chemical thermodynamic calculations. It demonstrated that, under oxygen-poor growth condition and low temperature, the stable doping defect PO−1 may have negative effect on n-type conduction and, under oxygen-poor growth condition and high temperature, the stable doping defect may contribute significantly to the n-type conduction. Furthermore, under oxygen-rich growth condition, the stable doping defect PZn1 may help to maintain the n-type conduction at high oxygen partial pressures. Our model predictions are in good agreement with experimental observations in anomalous conduction of P2O5-doped ZnO thin films and provide scientific explanation. This research not only revealed increased fundamental understanding on electronic behaviors but also provided a fabrication strategy for P-doped n-type ZnO.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
65.40.G- Other thermodynamical quantities

Arsenic activation in molecular beam epitaxy grown, in situ doped HgCdTe(211)

P. Boieriu, C. H. Grein, H. S. Jung, J. Garland, and V. Nathan

Appl. Phys. Lett. 86, 212106 (2005); http://dx.doi.org/10.1063/1.1940119 (3 pages) | Cited 13 times

Online Publication Date: 19 May 2005

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Photovoltaic p-n junctions are the most significant active components of both current infrared photodetectors and advanced ones being developed. It is of the utmost importance to control both p- and n-type extrinsic doping. This letter addresses the issue of activating arsenic as a p-type dopant of Hg1−xCdxTe at temperatures sufficiently low that the integrity of p-n junctions and the intrinsic advantages of molecular beam epitaxy as a growth technique will not be compromised. The p-type activation of arsenic in (211)B Hg1−xCdxTe is reported after a two-stage anneal at temperatures below 300 °C for Cd compositions suitable for the sensing of long wavelength infrared radiation.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Gz Photodetectors (including infrared and CCD detectors)

Spin photovoltaic effect in quantum wires with Rashba interaction

Yuriy V. Pershin and Carlo Piermarocchi

Appl. Phys. Lett. 86, 212107 (2005); http://dx.doi.org/10.1063/1.1935747 (3 pages) | Cited 14 times

Online Publication Date: 19 May 2005

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We propose a mechanism for spin-polarized photocurrent generation in quantum wires. The effect is due to the combined effect of Rashba spin-orbit interaction, external magnetic field, and microwave radiation. The time-independent interactions in the wire give rise to a spectrum asymmetry in k space. The microwave radiation induces transitions between spin-splitted subbands, and, due to the peculiar energy dispersion relation, charge and spin currents are generated at zero-bias voltage. We demonstrate that the generation of pure spin currents is possible under an appropriate choice of external control parameters.
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73.21.Hb Quantum wires
72.25.Dc Spin polarized transport in semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.40.+w Photoconduction and photovoltaic effects
72.30.+q High-frequency effects; plasma effects

Magnetite Schottky barriers on GaAs substrates

Steven M. Watts, Catherine Boothman, Sebastiaan van Dijken, and J. M. D. Coey

Appl. Phys. Lett. 86, 212108 (2005); http://dx.doi.org/10.1063/1.1925758 (3 pages) | Cited 19 times

Online Publication Date: 20 May 2005

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Carrier transport across Fe3O4/GaAs interfaces has been studied for n- and p-type GaAs(001) substrates with medium (7.7×1017 cm−3) to high (3.5×1018 cm−3) carrier concentrations. Current–voltage (I-V) measurements on medium-doped substrates show a rectifying behavior that is characteristic for thermionic emission/diffusion across a Schottky barrier. The n-type structure exhibits a low ideality factor of 1.3 and a Schottky barrier height of 0.58–0.63 eV. The Schottky barrier height of the p-type sample is 0.51 eV. For Fe3O4/GaAs structures with higher doping levels the I–V dependence is nearly symmetric. In this case, tunneling of electrons and holes through the Schottky barrier dominates transport between the Fe3O4 layer and the GaAs substrate.
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81.05.Ea III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
61.72.uj III-V and II-VI semiconductors
73.40.Ei Rectification
72.20.-i Conductivity phenomena in semiconductors and insulators
66.30.-h Diffusion in solids
79.40.+z Thermionic emission
73.40.Gk Tunneling

Dipole-radiation model for terahertz radiation from semiconductors

H. J. Peng and D. E. Aspnes

Appl. Phys. Lett. 86, 212109 (2005); http://dx.doi.org/10.1063/1.1937992 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2005

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We present a simple dipole-radiation model for the generation of terahertz radiation from semiconductors under short-pulse excitation. Using a one-dimensional force model applied to bond charges and free carriers, we evaluate both current-surge and frequency-mixing contributions to obtain analytic expressions that provide an integrated description of previous results.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
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