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16 Jul 2001

Volume 79, Issue 3, pp. 281-445

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Thermoelectric properties of Pb- and Ca-doped (Bi2Sr2O4)xCoO2 whiskers

Ryoji Funahashi and Ichiro Matsubara

Appl. Phys. Lett. 79, 362 (2001); http://dx.doi.org/10.1063/1.1385187 (3 pages) | Cited 56 times

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An oxide single crystalline whisker has been prepared which displays superior thermoelectric properties at high temperature in air. The whisker has an average composition of (Bi, Pb)2.2(Sr, Ca)2.8Co2Oy (abbreviated to BC-232 whisker) and a layered structure in which two different sublattices, CoO2 and rocksalt (Bi, Pb)2(Sr, Ca)2O4, alternate in the c-axis direction. Edge-sharing CoO2 layers act as conducting and thermoelectric units. Although a plateau is observed at around 500 K, the Seebeck coefficient of the whiskers is about 100 μV K−1 at 100 K, basically increases with temperature up to 773 K, and is saturated at temperatures higher than 773 K. Temperature dependence of electric resistivity shows semiconducting-like behavior but its value is very low compared with general semiconductors. These electrical phenomena would indicate pseudogap formation with its width of a few meV at the Fermi level. The power factor of the BC-232 whiskers is estimated at over 0.5 mWm−1 K−2 at temperatures higher than 650 K and reaches 0.9 mWm−1 K−2 at 973 K. © 2001 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators

Optical characterization of excess carrier lifetime and surface recombination in 4H/6H–SiC

A. Galeckas, J. Linnros, M. Frischholz, and V. Grivickas

Appl. Phys. Lett. 79, 365 (2001); http://dx.doi.org/10.1063/1.1385588 (3 pages) | Cited 19 times

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The high-injection lifetime and surface recombination parameters have been investigated in as-grown 4H and 6H–SiC epilayers subjected to various process treatments. A depth-resolved optical transient absorption technique was utilized to evaluate the influence of film thickness and surface treatment on carrier lifetime. We demonstrate that besides polishing and ion implantation, both natural and thermal oxidation may also result in lifetime reduction due to enhanced surface losses. Moreover, a long-term stability test has revealed a substantial degradation of lifetime characteristics, consistent with a spontaneous surface oxidation and slow relaxation of SiO2/SiC interface states. We show that for common film thickness <100 μm, the effective lifetime is dominated by surface leakage, which is found, generally, to be higher in 4H compared to 6H–SiC. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
81.65.Ps Polishing, grinding, surface finishing
81.65.Mq Oxidation
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

Computational band-structure engineering of III–V semiconductor alloys

Clint B. Geller, Walter Wolf, Silvia Picozzi, Alessandra Continenza, Ryoji Asahi, Wolfgang Mannstadt, Arthur J. Freeman, and Erich Wimmer

Appl. Phys. Lett. 79, 368 (2001); http://dx.doi.org/10.1063/1.1383282 (3 pages) | Cited 40 times

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Accurate band structures of binary semiconductors AB (A=Al, Ga, In and B=P, As, Sb) and selected ternary III–V semiconductors were calculated using an all-electron screened exchange approach within the full potential linearized augmented plane-wave method. Fundamental band gaps and Γ–L and Γ–X separations in higher-lying conduction bands are predicted with an accuracy of a few tenths of 1 eV. Screened exchange also performs better than the local density approximation for calculating conduction-band effective masses. Highly n-doped InPAs materials with compositions near InP0.2As0.8 offer lower effective masses, greater optical band-gap shifts, and potentially higher electron mobility than n-doped InGaAs materials with comparable band gaps. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Quasi-one-dimensional transport characteristics of ridge-type InGaAs quantum-wire field-effect transistors

Takeyoshi Sugaya, Mutsuo Ogura, Yoshinobu Sugiyama, Toshiyuki Shimizu, Kenji Yonei, Kee Youn Jang, Jonathan P. Bird, and David K. Ferry

Appl. Phys. Lett. 79, 371 (2001); http://dx.doi.org/10.1063/1.1385344 (3 pages) | Cited 6 times

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Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties. © 2001 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Tv Field effect devices
73.63.Nm Quantum wires
73.21.Hb Quantum wires
81.07.Vb Quantum wires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Subband electron properties of modulation-doped AlxGa1−xN/GaN heterostructures with different barrier thicknesses

C. P. Jiang, S. L. Guo, Z. M. Huang, J. Yu, Y. S. Gui, G. Z. Zheng, J. H. Chu, Z. W. Zheng, B. Shen, and Y. D. Zheng

Appl. Phys. Lett. 79, 374 (2001); http://dx.doi.org/10.1063/1.1386620 (3 pages) | Cited 17 times

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Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostructures with different barrier thicknesses of 25–100 nm have been investigated in magnetic fields up to 9 T at 1.4 K. Fast Fourier transform has been applied to obtain the subband density and mobility of the two-dimensional electron gas in these heterostructures. High electron density of 1.18×1013 cm−2 and quantum mobility of ∼8200 cm2 V−1 s−1 are obtained when the barrier thickness is 75 nm, which indicates that there exists a critical barrier thickness between 50 and 100 nm in the modulation-doped Al0.22Ga0.78N/GaN heterostructures. We also find that the elastic strain relaxation of the barrier does not significantly enhance the quantum mobilities of the ground subbands, however, it has strong effect on the mobilities of the excited states. The experimental values obtained in this work are useful for the design and optimization AlxGa1−xN/GaN device. © 2001 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Increased thermal budget for selectively doped heterostructures by employing AlAs/GaAs superlattices

D. Reuter, C. Meier, M. A. Serrano Álvarez, and A. D. Wieck

Appl. Phys. Lett. 79, 377 (2001); http://dx.doi.org/10.1063/1.1386618 (3 pages) | Cited 7 times

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The degradation of selectivity doped Al0.35Ga0.65As/GaAs heterostructures caused by rapid thermal annealing (RTA) was studied. The samples were annealed for 30 s at temperatures between 600 °C and 850 °C. Thereafter, the samples were characterized by Hall measurements at room temperature. Conventional heterostructures with a random alloy Al0.35Ga0.65As spacer and donor layer show a strong degradation for annealing temperatures of 650 °C or higher. For heterostructures employing a stoichiometric equivalent short period superlattice (SPS) in spacer and donor region only a slight degradation was found for annealing temperatures up to 850 °C. As reason for the increased thermal stability, the suppression of As loss during the annealing by the SPS was identified. © 2001 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects
73.63.-b Electronic transport in nanoscale materials and structures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

High current gains obtained by InGaN/GaN double heterojunction bipolar transistors with p-InGaN base

Toshiki Makimoto, Kazuhide Kumakura, and Naoki Kobayashi

Appl. Phys. Lett. 79, 380 (2001); http://dx.doi.org/10.1063/1.1387261 (2 pages) | Cited 33 times

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InGaN/GaN double heterojunction bipolar transistors have been fabricated using p-type InGaN as a base layer. The structures were grown on SiC substrates by metalorganic vapor phase expitaxy and defined by electron cyclotron resonance plasma etching. The In mole fraction in the base layer and its thickness were 0.06 and 100 nm, respectively. The Mg doping concentration in the base layer was 1×1019 cm−3 corresponding to a hole concentration of 5×1018 cm−3 at room temperature. From their common-emitter current–voltage characteristics, the maximum current gain of 20 was obtained at room temperature. © 2001 American Institute of Physics.
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85.30.Pq Bipolar transistors
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Enhanced oxidation of silicon using a collimated hyperthermal ozone beam

T. Nishiguchi, Y. Morikawa, M. Miyamoto, H. Nonaka, and S. Ichimura

Appl. Phys. Lett. 79, 382 (2001); http://dx.doi.org/10.1063/1.1380242 (3 pages) | Cited 4 times

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Silicon was oxidized by a collimated hyperthermal ozone beam produced by pulsed-laser ablation of solid ozone to increase the controllability of the silicon dioxide film thickness and to achieve low-temperature oxidation. The oxidation rate could be accurately controlled by the number of laser shots to which the number of supplied ozone molecules was proportional. Ozone molecules with a translational energy of around 1 eV obtained by laser ablation produced an initially rapid oxidized region with no temperature dependence in which a 0.6 nm silicon dioxide film could be synthesized at room temperature with only 200 laser shots. Higher-efficiency oxidation was also achieved in comparison with that by using a spray of ozone with thermal energy. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
37.20.+j Atomic and molecular beam sources and techniques
34.35.+a Interactions of atoms and molecules with surfaces
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