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13 Sep 2004

Volume 85, Issue 11, pp. 1871-2145

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1895 (2004); http://dx.doi.org/10.1063/1.1792802 (3 pages)

Markus Deubel, Martin Wegener, Artan Kaso, and Sajeev John
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Minority carrier diffusion length and lifetime for electrons in a type-II InAs∕GaSb superlattice photodiode

Jian V. Li, Shun Lien Chuang, Eric M. Jackson, and Edward Aifer

Appl. Phys. Lett. 85, 1984 (2004); http://dx.doi.org/10.1063/1.1787598 (3 pages) | Cited 8 times

Online Publication Date: 17 September 2004

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We use the electron-beam-induced current (EBIC) technique to investigate carrier transport characteristics in a type-II InAs∕GaSb superlattice photodiode with cutoff wavelength at 7.7 μm. We use a theoretical model that includes an extended generation source and depletion region to simulate the EBIC current on both sides of the p–n junction. The electron minority diffusion length in the p-superlattice, Le, is extracted from the simulation, from which the electron lifetime τe is obtained. Le increases from 0.275 μm at 5.3 K to 0.355 μm at 100 K. τe drops from 1.5 ns at 5.3 K to 0.13 ns at 100 K.
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85.30.De Semiconductor-device characterization, design, and modeling
85.60.Dw Photodiodes; phototransistors; photoresistors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Variable range hopping in a C60 field-effect transistor

Kazunaga Horiuchi, Shin Uchino, Shinobu Hashii, Akira Hashimoto, Tomohiro Kato, Takahiko Sasaki, Nobuyuki Aoki, and Yuichi Ochiai

Appl. Phys. Lett. 85, 1987 (2004); http://dx.doi.org/10.1063/1.1790036 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2004

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A variable range hopping (VRH) has been observed in the low-temperature conductance of a C60 field-effect transistor. We have investigated a thermal annealing (TA) effect at 453 and 498 K, on the conductance in various gate voltages and several source-drain separations. VRH analysis shows that density of states in the pseudogap clearly decreases as TA temperature increases. However, there might exist the other charge trapping states at interfaces with electrodes and gate dielectric, which could be modulated also by TA.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Wp Fullerenes and related materials
73.20.At Surface states, band structure, electron density of states

Ballistic electron emission luminescence spectroscopy of an InAs quantum dot heterostructure

Wei Yi, Ian Appelbaum, K. J. Russell, V. Narayanamurti, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 85, 1990 (2004); http://dx.doi.org/10.1063/1.1790595 (3 pages) | Cited 7 times

Online Publication Date: 17 September 2004

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We present ballistic electron emission luminescence (BEEL) spectroscopy measurements of an InAs quantum dot (QD) heterostructure based on three-terminal hot electron injection using a scanning tunneling microscope (STM) and a planar tunnel-junction transistor. Due to higher injected current, the planar transistors allow us to perform wavelength spectroscopy of the emitted luminescence, which resolves both quantum-confined Stark-shifted QD luminescence near 1.34 eV and bulk GaAs luminescence at 1.48 eV. This facilitates interpretation of STM BEEL spectra as a function of collector voltage bias. By freezing out the collector leakage current at low temperatures, consistent collector-current spectra are acquired with both STM and planar transistors.
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73.63.Kv Quantum dots
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.67.Hc Quantum dots
78.60.Fi Electroluminescence
68.37.Vj Field emission and field-ion microscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.23.Ad Ballistic transport
79.70.+q Field emission, ionization, evaporation, and desorption

Carrier transport in transparent oxide semiconductor with intrinsic structural randomness probed using single-crystalline InGaO3(ZnO)5 films

Kenji Nomura, Toshio Kamiya, Hiromichi Ohta, Kazushige Ueda, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 85, 1993 (2004); http://dx.doi.org/10.1063/1.1788897 (3 pages) | Cited 68 times

Online Publication Date: 17 September 2004

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We have investigated carrier transport in a crystalline oxide semiconductor InGaO3(ZnO)5 using single-crystalline thin films. When carrier concentration is less than 2×1018 cm−3, logarithm of electrical conductivity decreases in proportion to T −1∕4 and room-temperature Hall mobility was as low as ∼1 cm2(V s)−1. When carrier concentration was increased to 4×1018 cm−3, the conduction mechanism changed to degenerate conduction and room-temperature Hall mobility was steeply increased to >10 cm2(Vs)−1, showing metal–insulator transition behavior. These results are explained by percolation conduction over distribution of potential barriers formed around conduction band edge. The potential distribution is a consequence of potential modulation originating from random distribution of Ga3+ and Zn2+ ions in the crystal structure of InGaO3(ZnO)5.
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73.61.Le Other inorganic semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.-a Thin film structure and morphology
71.30.+h Metal-insulator transitions and other electronic transitions
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Tunnel magnetoresistance in GaMnAs: Going beyond Jullière formula

L. Brey, C. Tejedor, and J. Fernández-Rossier

Appl. Phys. Lett. 85, 1996 (2004); http://dx.doi.org/10.1063/1.1789241 (3 pages) | Cited 36 times

Online Publication Date: 17 September 2004

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The relation between tunnel magnetoresistance (TMR) and spin polarization is explored for GaMnAs∕GaAlAs∕GaMnAs structures where the carriers experience strong spin–orbit interactions. TMR is calculated using the Landauer approach. The materials are described in the 6 band k⋅p model which includes spin–orbit interaction. Ferromagnetism is described in the virtual crystal mean field approximations. Our results indicate that TMR is a function of spin polarization and barrier thickness. As a result of the stong spin–orbit interactions, TMR also depends on the the angle between current flow direction and the electrode magnetization. These results compromise the validity of Julliere formula.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects
71.15.-m Methods of electronic structure calculations

Visualization of buried SiGe quantum dots at cleavages by cross-sectional atomic force microscopy

M. S. Dunaevskii, A. N. Titkov, Z. F. Krasilnik, A. V. Novikov, D. N. Lobanov, and R. Laiho

Appl. Phys. Lett. 85, 1999 (2004); http://dx.doi.org/10.1063/1.1791744 (3 pages)

Online Publication Date: 17 September 2004

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Cross-sectional atomic force microscopy (XAFM) is used to visualize in ambient atmosphere SiGe quantum dots (QDs) embedded in Si. Buried QDs are revealed as nanometer high topographic features on cross-sectional cleavages of the samples. Details of the images are used to get information about strain relaxation of the QDs and its relationship with the shape of the surface relief. We propose XAFM as a simple method to check the presence of QDs and to estimate their sizes and surface density. This method also allows detailed investigation of effects related to vertical alignment of the dots in different layers of multilayer QD structures.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Ps Atomic force microscopy (AFM)

Electrical transport properties of single ZnO nanorods

Y. W. Heo, L. C. Tien, D. P. Norton, B. S. Kang, F. Ren, B. P. Gila, and S. J. Pearton

Appl. Phys. Lett. 85, 2002 (2004); http://dx.doi.org/10.1063/1.1792373 (3 pages) | Cited 82 times

Online Publication Date: 17 September 2004

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Single ZnO nanorods with diameters of ∼130 nm were grown on Au-coated Al2O3 substrates by catalyst-driven molecular beam epitaxy. Individual nanorods were removed from the substrate and placed between Ohmic contact pads and the current–voltage characteristics measured as a function of temperature and gas ambient. In the temperature range from 25 to 150 °C, the resistivity of nanorods treated in H2 at 400 °C prior to measurement showed an activation energy of 0.089±0.02 eV and was insensitive to the ambient used (C2H4,N2O,O2 or 10% H2 in N2). By sharp contrast, the conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
73.40.Ns Metal-nonmetal contacts
73.63.Bd Nanocrystalline materials
61.46.-w Structure of nanoscale materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Time-resolved detection of individual electrons in a quantum dot

R. Schleser, E. Ruh, T. Ihn, K. Ensslin, D. C. Driscoll, and A. C. Gossard

Appl. Phys. Lett. 85, 2005 (2004); http://dx.doi.org/10.1063/1.1784875 (3 pages) | Cited 15 times

Online Publication Date: 17 September 2004

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We present measurements on a quantum dot and a nearby, capacitively coupled, quantum point contact used as a charge detector. With the dot being weakly coupled to only a single reservoir, the transfer of individual electrons onto and off the dot can be observed in real time in the current signal from the quantum point contact. From these time-dependent traces, the quantum mechanical coupling between dot and reservoir can be extracted quantitatively. A similar analysis allows the determination of the occupation probability of the dot states.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.37.Ps Atomic force microscopy (AFM)
73.61.Ey III-V semiconductors

Confinement in silicon nanowires: Optical properties

S. Bhattacharya, D. Banerjee, K. W. Adu, S. Samui, and Somnath Bhattacharyya

Appl. Phys. Lett. 85, 2008 (2004); http://dx.doi.org/10.1063/1.1787164 (3 pages) | Cited 17 times

Online Publication Date: 17 September 2004

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The blueshift of the optical absorption edge along with the intense red photoluminescence (PL) peak has been observed from micron-long crystalline silicon nanowires prepared by pulsed-laser vaporization of heated Si (mixed with metal catalyst) targets. Previous studies on the confinement in silicon nanostructures resulted in a dispute regarding the application of theoretical models to explain their optical properties. Based on the microstructure a phenomenological confinement model, incorporating the nanowire diameter distribution is used, which is found to describe the optical properties including the shape of absorption spectra, the band gap, and the PL peak position of the Si nanowires very well.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.46.-w Structure of nanoscale materials
81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
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