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16 Aug 2004

Volume 85, Issue 7, pp. 1095-1302

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1277 (2004); http://dx.doi.org/10.1063/1.1783021 (3 pages)

Katsuhiko Nishiguchi, Hiroshi Inokawa, Yukinori Ono, Akira Fujiwara, and Yasuo Takahashi
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Band offset design with quantum-well gate insulating structures

Tatsuo Schimizu and Takeshi Yamaguchi

Appl. Phys. Lett. 85, 1167 (2004); http://dx.doi.org/10.1063/1.1783012 (2 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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The authors propose a concept, a nanoscaled quantum-well gate insulating structure. The effective conduction band offset (ΔEc) can be controlled with an appropriate combination of high-K and high-ΔEc materials. The electronic structures of SrTiO3 and Sr2TiO4 were studied by means of first-principles calculations to investigate the change in the band structures induced by SrO-layer intercalation. The ΔEc of Sr2TiO4 is raised by about +0.8 eV. A quantum-well gate insulating structure with off-resonance condition is also proposed. The ΔEc becomes as high as the barrier height of the barrier material.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Zn0.9Mg0.1O∕ZnO p–n junctions grown by pulsed-laser deposition

K. Ip, Y. W. Heo, D. P. Norton, S. J. Pearton, J. R. LaRoche, and F. Ren

Appl. Phys. Lett. 85, 1169 (2004); http://dx.doi.org/10.1063/1.1783015 (3 pages) | Cited 44 times

Online Publication Date: 10 August 2004

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The electrical characteristics of Zn0.9Mg0.1O∕ZnO p–n junctions grown by pulsed-laser deposition on bulk, single-crystal ZnO substrates are reported. The forward turn-on voltage of the junctions was in the range 3.6–4 V for Pt∕Au metallization used for the p-Ohmic contact on Zn0.9Mg0.1O.The reverse breakdown voltage is as high as 9 V, but displays a small negative temperature coefficient of −0.1–0.2 V K−1 over the range 30–200°C. The achievement of acceptable rectification in the junctions required growth of an n-type ZnO buffer on the ZnO substrate prior to growth of the p-type, phosphorus-doped Zn0.9mg0.1O.Without this buffer, the junctions showed very high leakage current.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ns Metal-nonmetal contacts
81.15.Fg Pulsed laser ablation deposition
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.S- Impurities in crystals

Influences of oligomer length on carrier-transport properties of oligofluorenes

Chung-Chih Wu, Tsung-Li Liu, Yu-Ting Lin, Wen-Yi Hung, Tung-Huei Ke, Ken-Tsung Wong, and Teng-Chih Chao

Appl. Phys. Lett. 85, 1172 (2004); http://dx.doi.org/10.1063/1.1784031 (3 pages) | Cited 14 times

Online Publication Date: 10 August 2004

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In this letter, carrier-transport properties of a homologous series of oligofluorenes with C9 diaryl substitution have been examined. These substituted oligofluorenes possess stable amorphous states, ambipolar carrier-transport properties, and processability to thin films for a range of oligomer lengths, rendering feasible investigating dependence of carrier transport on oligomer length in disordered systems. It is found that carrier mobilities of these oligofluorenes show a clear decreasing trend with the oligomer length. Such findings are in contrast with previous observations for crystalline oligomers and impose certain implications in carrier transport of conjugated polymers and oligomers.
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73.61.Ph Polymers; organic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Type-I Ge∕Ge1−x−ySixSny strained-layer heterostructures with a direct Ge bandgap

J. Menéndez and J. Kouvetakis

Appl. Phys. Lett. 85, 1175 (2004); http://dx.doi.org/10.1063/1.1784032 (3 pages) | Cited 43 times

Online Publication Date: 10 August 2004

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The electronic properties of Ge∕Ge1−x−ySixSny strained-layer heterostructures are predicted theoretically. It is found that a lattice-matched system with fully strained Ge layers and relaxed Ge1−x−ySixSny alloys can have a direct fundamental bandgap with spatial localization in the Ge layers (type I). The Si and Sn concentrations for which such a direct bandgap obtains are close to those that have already been experimentally demonstrated [M. Bauer, C. Ritter, P. A. Crozier, J. Ren, J. Menendez, G. Wolf, and J. Kouvetakis, Appl. Phys. Lett. 83, 2163 (2003)]. The required level of tensile strain in the Ge layers is compatible with Si–Ge technology. The predicted direct bandgap values are as high as 0.6 eV.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.60.Bs Mechanical and acoustical properties

Oxygen precipitate denuded zone in polycrystalline sheet silicon

Jinggang Lu, George Rozgonyi, James Rand, and Ralf Jonczyk

Appl. Phys. Lett. 85, 1178 (2004); http://dx.doi.org/10.1063/1.1781369 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2004

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The spatial variation of oxygen precipitation across the thickness of polycrystalline sheet silicon has been investigated by Fourier transform infrared (FTIR) microspectroscopy and preferential etching/optical microscopy. FTIR shows that interstitial oxygen is depleted near the top surface of the as-grown sample, thereby suppressing oxygen precipitation during subsequent annealing. Preferential etching and electron-beam-induced current imaging of polished cross sections revealed a 250-μm-wide precipitate denuded zone near the top surface. Evidently, growth-induced near-surface reduction of the oxygen profile keeps the oxygen supersaturation below a critical level for precipitate nucleation. Considering that the minority carrier diffusion length of current finished sheet silicon solar cells ranges from 50 to 100 μm, it is anticipated that optimization of the 250-μm-wide precipitate denuded zone will improve solar cell performance.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
81.30.Mh Solid-phase precipitation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
84.60.Jt Photoelectric conversion
81.65.Cf Surface cleaning, etching, patterning
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.40.Gh Other heat and thermomechanical treatments
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators

Electrical transport in amorphous semiconducting AlMgB14 films

Y. Tian, G. Li, J. Shinar, N. L. Wang, B. A. Cook, J. W. Anderegg, A. P. Constant, A. M. Russell, and J. E. Snyder

Appl. Phys. Lett. 85, 1181 (2004); http://dx.doi.org/10.1063/1.1781738 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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The electrical transport properties of semiconducting AlMgB14 films deposited at room temperature and 573 K are reported in this letter. The as-deposited films are amorphous, and they exhibit high n-type electrical conductivity, which is believed to stem from the conduction electrons donated by Al, Mg, and/or Fe impurities in these films. The film deposited at 573 K is less conductive than the room-temperature-deposited film. This is attributed to the nature of donor or trap states in the band gap related to the different deposition temperatures.
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73.61.Jc Amorphous semiconductors; glasses
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
71.55.Jv Disordered structures; amorphous and glassy solids

Optically patterned nuclear doughnuts in GaAs∕MnAs heterostructures

J. Stephens, J. Berezovsky, R. K. Kawakami, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 85, 1184 (2004); http://dx.doi.org/10.1063/1.1781743 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2004

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We demonstrate a scheme for optically patterning nuclear-spin polarization in semiconductor∕ferromagnet heterostructures. A scanning time-resolved Kerr rotation microscope is used to image the nuclear-spin polarization that results when GaAs∕MnAs epilayers are illuminated with a focused laser having a Gaussian profile. Rather than tracking the intensity profile of the laser spot, these images reveal that the nuclear polarization forms an annular lateral structure having circular symmetry with a dip rather than a peak at its center.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
78.47.-p Spectroscopy of solid state dynamics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Effect of thermal excitation on intermolecular charge transfer efficiency in conducting polyaniline

Guofeng Li, Mira Josowicz, Jiří Janata, and Steve Semancik

Appl. Phys. Lett. 85, 1187 (2004); http://dx.doi.org/10.1063/1.1779948 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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A conductometric gas-sensing platform with temperature control has been adopted to probe temperature-dependent phenomena in conducting polymers. This letter describes our recent observation of thermal effects on the intermolecular charge transfer efficiency of conducting polyaniline at both ends of the charge transfer—either as a donor or as an acceptor, upon exposure to gaseous analytes. When polyaniline is serving as a donor, the thermal excitation of electrons in polyaniline facilitates the charge transfer. However, if polyaniline assumes the role of an acceptor, the charge transfer becomes less efficient at higher temperatures. Furthermore, a simplified band structure model is employed to elucidate such discriminative behavior.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
71.20.Rv Polymers and organic compounds
82.35.Cd Conducting polymers
61.41.+e Polymers, elastomers, and plastics
73.20.At Surface states, band structure, electron density of states
71.55.Jv Disordered structures; amorphous and glassy solids

Influence of manganese contamination on high-mobility GaAs∕AlGaAs heterostructures

K. Wagenhuber, H.-P. Tranitz, M. Reinwald, and W. Wegscheider

Appl. Phys. Lett. 85, 1190 (2004); http://dx.doi.org/10.1063/1.1782262 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2004

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Photoluminescence and magnetotransport measurements have been performed to assess the quality of modulation-doped GaAs∕AlGaAs heterostructures. The temporal evolution of the low-temperature electron mobility of samples prepared in a molecular-beam-epitaxy chamber containing manganese as a source material was studied. Mn contamination was identified to be responsible for the reduction of the electron mobility to 1×106 cm2∕V s and the appearance of a distinct photoluminescence band. In contrast, structures in which this signal is absent reach mobility values of 5.4×106 cm2∕V s. This directly proves that the epitaxy of high-mobility electron systems and structures containing GaMnAs layers, in principle, can be combined in one growth chamber.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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