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12 Sep 2005

Volume 87, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 87, 113902 (2005); http://dx.doi.org/10.1063/1.2045549 (3 pages)

M. Laroussi and X. Lu
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A mechanism for hole generation by octahedral B6 clusters in silicon

Kengo Ohmori, Noboru Esashi, Masakazu Takao, Daisuke Sato, and Yoshinori Hayafuji

Appl. Phys. Lett. 87, 112101 (2005); http://dx.doi.org/10.1063/1.2035880 (3 pages) | Cited 3 times

Online Publication Date: 6 September 2005

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The electronic structure and x-ray photoelectron spectra of silicon with octahedral B6 clusters are investigated using first-principles calculations. It is found that the B6 clusters act as double acceptors in silicon and that the simulated chemical shift of the B 1s orbital signals of the B6 clusters in x-ray photoelectron spectra coincides with the chemical shift of B 1s experimentally observed in as-implanted silicon at an extremely high dose of boron. These results reveal that the B6 clusters are the origin of hole carriers. We propose a mechanism of hole generation and a model of B6 cluster formation at implantation-induced divacancy sites.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.15.-m Methods of electronic structure calculations
71.20.Mq Elemental semiconductors
72.80.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.72.uf Ge and Si
61.72.J- Point defects and defect clusters

Thermoelectric power factor in semiconductors with buried epitaxial semimetallic nanoparticles

J. M. Zide, D. O. Klenov, S. Stemmer, A. C. Gossard, G. Zeng, J. E. Bowers, D. Vashaee, and A. Shakouri

Appl. Phys. Lett. 87, 112102 (2005); http://dx.doi.org/10.1063/1.2043241 (3 pages) | Cited 48 times

Online Publication Date: 7 September 2005

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We have grown composite epitaxial materials that consist of semimetallic ErAs nanoparticles embedded in a semiconducting In0.53Ga0.47As matrix both as superlattices and randomly distributed throughout the matrix. The presence of these particles increases the free electron concentration in the material while providing scattering centers for phonons. We measure electron concentration, mobility, and Seebeck coefficient of these materials and discuss their potential for use in thermoelectric power generators.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.61.Ey III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.63.Bd Nanocrystalline materials
61.72.uj III-V and II-VI semiconductors

Enhancement of bipolar carrier transport in oligofluorene films through alignment in the liquid-crystalline phase

Li-Yin Chen, Wen-Yi Hung, Yu-Ting Lin, Chung-Chih Wu, Teng-Chih Chao, Tsung-His Hung, and Ken-Tsung Wong

Appl. Phys. Lett. 87, 112103 (2005); http://dx.doi.org/10.1063/1.2042536 (3 pages) | Cited 16 times

Online Publication Date: 7 September 2005

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We investigate the formation of aligned liquid-crystal glasses of an oligofluorene and perform comparative studies of carrier-transport properties of the oligofluorene in both amorphous films and glassy liquid-crystal films. With mesophase-mediated molecular alignment, the bipolar carrier-transport capability of oligofluorene solid films is enhanced by more than an order of magnitude. High bipolar carrier mobilities, up to 2.0×10−2 cm2/V s for holes and up to 2.3×10−2 cm2/V s for electrons, are observed in the aligned glassy liquid-crystal films.
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61.30.-v Liquid crystals
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

Magnetoresistance in epitaxially grown degenerate ZnO thin films

F. Reuss, S. Frank, C. Kirchner, R. Kling, Th. Gruber, and A. Waag

Appl. Phys. Lett. 87, 112104 (2005); http://dx.doi.org/10.1063/1.2045553 (3 pages) | Cited 21 times

Online Publication Date: 8 September 2005

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The magnetoresistance of high-quality epitaxial doped ZnO(:Ga) thin films with various electron concentrations ranging from 3.2×1018 to 1.3×1020 cm−3 has been measured. All samples investigated exhibit a negative magnetoresistance at low magnetic fields. Its magnitude systematically depends on carrier concentration and temperature. Low-doped samples switch the sign of the magnetoresistance and the conventional positive component dominates at high fields, whereas highly doped degenerate samples only show a negative component up to fields of 14.5 T. Therefore, the data are analyzed as the sum of a positive and negative contribution to the magnetoresistance applying a semiempirical expression to describe the observed behavior. The model takes into account third-order s–d exchange Hamiltonians describing the negative part and a two-band model for the positive contribution. Least-squares fits to the data are presented. Theory and experiment are in excellent agreement.
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73.61.Ga II-VI semiconductors

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

Jinsong Huang, Gang Li, and Yang Yang

Appl. Phys. Lett. 87, 112105 (2005); http://dx.doi.org/10.1063/1.2045554 (3 pages) | Cited 50 times

Online Publication Date: 8 September 2005

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Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends have been demonstrated to form highly efficient polymer photovoltaic devices. In this letter, the time-of-flight technique is used to investigate the influence of composition and heat treatment on charge transport properties of P3HT and PCBM blends. The transport of electrons and holes both display a transition from dispersive to nondispersive and return to dispersive again as the percentage of PCBM increases. A balanced mobility of both electron and hole is obtained at a composition of 1:1 weight ratio, and it is nearly independent of the electrical field in the range of our test. The increase in carrier mobility is attributed to the formation of a more-ordered structure in the blend. This structural ordering is further enhanced by slowly evaporating the solvent during film formation which results in additional increase in carrier mobility. However, no such effect is observed in thick films ( ∼ 200 nm), indicating the presence of such high-degree ordering due to heat treatment.
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73.61.Ph Polymers; organic compounds
81.40.Gh Other heat and thermomechanical treatments
72.40.+w Photoconduction and photovoltaic effects
61.41.+e Polymers, elastomers, and plastics

Characteristics of a Zn0.7Mg0.3O/ZnO heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy

Kazuto Koike, Ippei Nakashima, Kazuyuki Hashimoto, Shigehiko Sasa, Masataka Inoue, and Mitsuaki Yano

Appl. Phys. Lett. 87, 112106 (2005); http://dx.doi.org/10.1063/1.2045558 (3 pages) | Cited 33 times

Online Publication Date: 8 September 2005

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Characterization of a Zn0.7Mg0.3O/ZnO heterostructure field-effect transistor (HFET) is reported. The HFET was based on a Zn0.7Mg0.3O/ZnO/Zn0.7Mg0.3O single quantum well (SQW) grown on an a-plane sapphire substrate by molecular-beam epitaxy, and was fabricated by a conventional photolithography technique combined with dry etching. Room-temperature characteristic of the HFET was a n-channel depletion type with a transconductance of 0.70 mS/mm and a field-effect mobility of 140 cm2/V s, in good agreement with the electron Hall mobility in SQW of 130 cm2/V s. The on∕off ratio at VDS = 3 V was ∼ 800, which was limited by an insufficiently suppressed leakage current through the bottom Zn0.7Mg0.3O barrier.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Hp Lithography, masks and pattern transfer

Selectively excited photoluminescence from Eu-implanted GaN

K. Wang, R. W. Martin, K. P. O’Donnell, V. Katchkanov, E. Nogales, K. Lorenz, E. Alves, S. Ruffenach, and O. Briot

Appl. Phys. Lett. 87, 112107 (2005); http://dx.doi.org/10.1063/1.2045551 (3 pages) | Cited 46 times

Online Publication Date: 8 September 2005

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The intensity of Eu-related luminescence from ion-implanted GaN with a 10 nm thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at 1300 °C. Photoluminescence (PL) and PL excitation (PLE) studies reveal a variety of Eu centers with different excitation mechanisms. High-resolution PL spectra at low temperature clearly show that emission lines ascribed to math-math ( ∼ 622 nm), math-math ( ∼ 664 nm), and math-math ( ∼ 602 nm) transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the math-math multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at 356 nm, and a broad subedge absorption band centred at ∼ 385 nm. Marked differences in the shape of the math-math PL multiplet are demonstrated by selective excitation via the continuum/exciton states and the below gap absorption band. The four strongest lines of the multiplet are shown to consist of two pairs due to different Eu3+ centers with different excitation mechanisms.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Cc Kinetics of defect formation and annealing
71.35.-y Excitons and related phenomena
78.40.Fy Semiconductors
61.72.uj III-V and II-VI semiconductors

High electron mobility W-doped In2O3 thin films by pulsed laser deposition

P. F. Newhouse, C.-H. Park, D. A. Keszler, J. Tate, and P. S. Nyholm

Appl. Phys. Lett. 87, 112108 (2005); http://dx.doi.org/10.1063/1.2048829 (3 pages) | Cited 20 times

Online Publication Date: 9 September 2005

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High electron mobility thin films of In2−xWxO3+y(0 ⩽ x ⩽ 0.075) were prepared on amorphous SiO2 and single-crystal yttria-stablized zirconia (001) substrates by pulsed laser deposition. Mobilities ranged between 66 and 112 cm2/Vs depending on the substrate type and deposition conditions, and the highest mobility was observed at a W-dopant concentration of x ∼ 0.03. A small band gap shift was detected from films with increasing electron carrier density; the electron effective mass calculated from Burstein-Moss theory was 0.3me. In2−xWxO3+y films have high visible transmittance of ∼ 80%.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.S- Impurities in crystals
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Le Other inorganic semiconductors
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