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4 Jul 2005

Volume 87, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 87, 013110 (2005); http://dx.doi.org/10.1063/1.1977187 (3 pages)

R. C. Wang, C. P. Liu, J. L. Huang, S.-J. Chen, Y.-K. Tseng, and S.-C. Kung
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Influence of plasmons on terahertz conductivity measurements

Han-Kwang Nienhuys and Villy Sundström

Appl. Phys. Lett. 87, 012101 (2005); http://dx.doi.org/10.1063/1.1977213 (3 pages) | Cited 15 times

Online Publication Date: 27 June 2005

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Time-domain terahertz spectroscopy allows measuring the complex conductivity spectrum of materials at frequencies on the order of 1 THz. Typically, terahertz (THz) studies produce conductivity spectra that are different from those predicted by the classical Drude model, especially in nanostructured materials. We claim that plasmon resonances in particles that are small compared to the THz wavelength cause these deviations. This is supported by measurements on photoexcited silicon, in bulk as well as in micron-sized particles. In the latter, the behavior is vastly different and strongly dependent on charge carrier concentration.
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72.30.+q High-frequency effects; plasma effects
72.80.Cw Elemental semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Role of near-surface states in ohmic-Schottky conversion of Au contacts to ZnO

H. L. Mosbacker, Y. M. Strzhemechny, B. D. White, P. E. Smith, D. C. Look, D. C. Reynolds, C. W. Litton, and L. J. Brillson

Appl. Phys. Lett. 87, 012102 (2005); http://dx.doi.org/10.1063/1.1984089 (3 pages) | Cited 70 times

Online Publication Date: 27 June 2005

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A conversion from ohmic to rectifying behavior is observed for Au contacts on atomically ordered polar ZnO surfaces following remote, room-temperature oxygen plasma treatment. This transition is accompanied by reduction of the “green” deep level cathodoluminescence emission, suppression of the hydrogen donor-bound exciton photoluminescence and a ∼ 0.75 eV increase in n-type band bending observed via x-ray photoemission. These results demonstrate that the contact type conversion involves more than one mechanism, specifically, removal of the adsorbate-induced accumulation layer plus lowered tunneling due to reduction of near-surface donor density and defect-assisted hopping transport.
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81.05.Dz II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.30.+y Surface double layers, Schottky barriers, and work functions
71.55.Gs II-VI semiconductors
73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
72.20.Ee Mobility edges; hopping transport
71.35.-y Excitons and related phenomena
52.77.-j Plasma applications
81.65.-b Surface treatments
78.55.Et II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.60.Hk Cathodoluminescence, ionoluminescence

Direct experimental evidence of hybridization of Pb states with O 2p states in ferroelectric perovskite oxides

J. C. Jan, H. M. Tsai, C. W. Pao, J. W. Chiou, K. Asokan, K. P. Krishna Kumar, W. F. Pong, Y. H. Tang, M.-H. Tsai, S. Y. Kuo, and W. F. Hsieh

Appl. Phys. Lett. 87, 012103 (2005); http://dx.doi.org/10.1063/1.1988984 (3 pages) | Cited 9 times

Online Publication Date: 28 June 2005

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This work presents the O K- and Ti L3,2-edge x-ray absorption near-edge structure (XANES) spectra of PbxSr1−xTiO3 (PxSTO) and BaxSr1−xTiO3 (BxSTO) compounds with various Pb and Ba concentrations. The result provides direct evidence that the Pb–O bonding strongly affects O 2p–Ti 3d hybridization in the TiO6 octahedron of PxSTO. In contrast, the Ba–O bonding does not substantially affect O 2p–Ti 3d hybridization in BxSTO. The Ti L3-edge XANES spectra show the splitting of the eg band for PxSTO with x≳0.5, which provides an evidence of Pb-induced tetragonal distortion in the TiO6 octahedron. In contrast, eg band splitting is absent in BxSTO.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra
77.80.-e Ferroelectricity and antiferroelectricity

Surface roughness and dislocation distribution in compositionally graded relaxed SiGe buffer layer with inserted-strained Si layers

Tae-Sik Yoon, Jian Liu, Atif M. Noori, Mark S. Goorsky, and Ya-Hong Xie

Appl. Phys. Lett. 87, 012104 (2005); http://dx.doi.org/10.1063/1.1988986 (3 pages) | Cited 5 times

Online Publication Date: 28 June 2005

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We investigate the surface roughness and dislocation distribution of compositionally graded relaxed SiGe buffer layers by inserting two tensile-strained Si layers. The 20 nm thick strained Si layers, less than the critical thickness for dislocation formation, are inserted at 10 and 20% Ge content regions of the 1 μm thick graded SiGe layer with a final Ge content of 30%. The surface immediately after growing the second strained Si layer on SiGe with 20% Ge content is found to be flat with about 1.1 nm root-mean-square roughness. However, the crosshatched surface with the 7.8 nm roughness develops during subsequent SiGe growths, which is slightly less than the 10.3 nm value for SiGe without inserted Si layers. Another important issue of consideration is that inserting the strained Si layers leads to increased interaction among dislocations as shown by cross-sectional transmission electron microscopy. This study explores the possibility of using strained layers for achieving flat surfaces and illustrates the need for optimization when using this approach.
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81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Tunneling magnetoresistance in GaMnAs/AlAs/InGaAs/AlAs/GaMnAs double-barrier magnetic tunnel junctions

Shinobu Ohya, Pham Nam Hai, and Masaaki Tanaka

Appl. Phys. Lett. 87, 012105 (2005); http://dx.doi.org/10.1063/1.1978976 (3 pages) | Cited 18 times

Online Publication Date: 29 June 2005

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We have studied the tunneling magnetoresistance (TMR) of Ga0.94Mn0.06As/AlAs(d nm)/In0.4Ga0.6As(0.42 nm)/AlAs(d nm)/Ga0.94Mn0.06As double-barrier magnetic tunnel junctions with various AlAs thicknesses (d = 0.8–2.7 nm) grown on p+GaAs (001) substrates by low-temperature molecular-beam epitaxy. In some junctions, unusual inverse TMR, in which the tunnel resistance in antiparallel magnetization is lower than that in parallel magnetization, was observed. The TMR ratio oscillated between positive and negative values with increasing the AlAs thickness, suggesting the existence of the resonant tunneling effect in the InGaAs quantum well.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.63.Hs Quantum wells
75.47.Pq Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
73.61.Ey III-V semiconductors
73.23.-b Electronic transport in mesoscopic systems
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Organic-inorganic hybrid photopolymer with reduced volume shrinkage

Won Sun Kim, Yong-Cheol Jeong, and Jung-Ki Park

Appl. Phys. Lett. 87, 012106 (2005); http://dx.doi.org/10.1063/1.1954884 (3 pages) | Cited 12 times

Online Publication Date: 30 June 2005

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An organic-inorganic hybrid photopolymer containing surface-photoreactive nanoparticles, which exhibits a significant enhancement in optical properties is reported. The photopolymer containing surface-photoreactive nanoparticles showed high diffraction efficiency near 90% and reduced volume shrinkage without affecting the energetic sensitivity and optical quality of the photopolymer.
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42.70.Jk Polymers and organics
78.40.Me Organic compounds and polymers
61.41.+e Polymers, elastomers, and plastics
82.35.-x Polymers: properties; reactions; polymerization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Carrier dynamics in Ga0.53In0.47As/InP near-surface quantum wells

Clémentine Symonds, Juliette Mangeney, Guillaume Saint-Girons, and Isabelle Sagnes

Appl. Phys. Lett. 87, 012107 (2005); http://dx.doi.org/10.1063/1.1993763 (3 pages) | Cited 2 times

Online Publication Date: 30 June 2005

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Ga0.53In0.47As/InP single-quantum wells with thin top barrier layers of InP and InAlAs have been studied by pump-probe experiments and temperature-dependent photoluminescence spectroscopy. The carrier lifetimes are shorter in samples with an InAlAs surface barrier than with an InP surface barrier. The decays consist in an early stage decay of typically 30 ps and an extended stage decay of several hundreds of picoseconds. This nonexponential relaxation is the result of thermally activated carrier escape, trapping, and recombination on the surface states. Two nonradiative surface states, at 11 and 68 meV from the ground state of the quantum well, were identified.
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73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
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