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6 Aug 2007

Volume 91, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 063118 (2007); http://dx.doi.org/10.1063/1.2768861 (3 pages)

Douglas C. Meier, Steve Semancik, Bradley Button, Evgheni Strelcov, and Andrei Kolmakov
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Incipient plasticity in metallic glass modulated nanolaminates

Y. M. Wang, A. V. Hamza, and T. W. Barbee, Jr.

Appl. Phys. Lett. 91, 061924 (2007); http://dx.doi.org/10.1063/1.2768939 (3 pages) | Cited 5 times

Online Publication Date: 10 August 2007

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The plastic deformation in copper-zirconium nanocrystalline-amorphous nanolaminates is investigated by means of stress-relaxation experiments at a range of initial stress levels. Progressive multistep relaxation cycles reveal that the onset of plastic deformation occurs at a much lower stress level in nanocrystalline-amorphous nanolaminate than in crystalline-crystalline nanolaminates or other nanostructured materials. The derived activation volumes and strain rate sensitivities imply interfacial dislocation mechanisms, consistent with the observations from postmorterm transmission electron microscopy. This indicates that the crystalline-amorphous interfaces may be the preferred source for dislocation nucleation and/or emission.
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68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Ct Interface structure and roughness

Identification of sub-band-gap absorption features at the HfO2/Si(100) interface via spectroscopic ellipsometry

J. Price, P. S. Lysaght, S. C. Song, Hong-Jyh Li, and A. C. Diebold

Appl. Phys. Lett. 91, 061925 (2007); http://dx.doi.org/10.1063/1.2769389 (3 pages) | Cited 14 times

Online Publication Date: 10 August 2007

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Spectroscopic ellipsometry is used to characterize charge trapping defect states in thin HfO2 gate dielectric films deposited by atomic layer deposition on chemically oxidized p-type Si (100) substrates. The intensity of specific absorption features detected below the band gap of HfO2 at 2.9 and 4.75 eV is clearly distinguished from the Si critical points; however, repeating this spectroscopic evaluation for identical HfO2 films deposited and annealed on fused silica substrates results in no defect features detected. The HfO2/Si(100) results, therefore, suggest these oxygen deficient defects are not intrinsic to HfO2 but reside primarily at the interface with the silicon substrate. The feasibility of utilizing spectroscopic ellipsometry to identify stoichiometric variations at the SiO2/Si(100) interface and the corresponding changes associated with the electrical performance is presented.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
71.55.Ht Other nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Confining P diffusion in Si by an As-doped barrier layer

Lugang Bai, Decai Yu, Guang-Hong Lu, Feng Liu, Q. Wang, and Hamza Yilmaz

Appl. Phys. Lett. 91, 061926 (2007); http://dx.doi.org/10.1063/1.2769392 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2007

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The miniaturization of Si-based devices requires control of doping profile, which makes the understanding of dopant interaction and diffusion in Si critical. The authors have studied the effect of As doping on P diffusion in Si using first-principles calculations. The authors found a form of As-vacancy complex is energetically favorable, allowing As to consume the vacancy so as to prohibit the vacancy-mediated P diffusion. Also, in the vicinity of As, the vacancy-mediated P diffusion barrier is increased, decreasing further the P mobility. The results provide useful guidance for designing As-doped barriers to block P diffusion in Si wafer processing and metal oxide semiconductor field-effect transistor device fabrication.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters

Strain-induced interface instability in GaN/AlN multiple quantum wells

S. Nicolay, E. Feltin, J.-F. Carlin, N. Grandjean, L. Nevou, F. H. Julien, M. Schmidbauer, T. Remmele, and M. Albrecht

Appl. Phys. Lett. 91, 061927 (2007); http://dx.doi.org/10.1063/1.2769399 (3 pages) | Cited 17 times

Online Publication Date: 10 August 2007

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It is shown that in GaN/AlN multiple quantum wells (MQWs), strain is a critical parameter for achieving short-wavelength intersubband transitions (ISBTs). This is investigated by comparing GaN/AlN MQWs grown by metal organic vapor phase epitaxy on either AlN or GaN templates. The GaN/AlN interface is found to be unstable when pseudomorphically strained onto GaN, in agreement with theory. This effect deeply affects the quantum well potential profile leading to a strong redshift of the ISBT energies.
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78.67.De Quantum wells
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Anomalous thickness and dopant effects on photochemical deposition of Ag on epitaxial TiO2(110)/Nb:TiO2(110) heterostructures

T. Abe, T. Ohsawa, M. Katayama, H. Koinuma, and Y. Matsumoto

Appl. Phys. Lett. 91, 061928 (2007); http://dx.doi.org/10.1063/1.2769937 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2007

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The authors have found anomalous thickness and dopant effects on photochemical deposition of Ag on the epitaxial heterostructures of TiO2(110) and V:TiO2(110)/Nb:TiO2(110). The photodeposition of Ag on TiO2(110)/Nb:TiO2(110) is limited to a specific film thickness region of about 5 nm and the V doping is found to enhance the photoactivity, irrespective of the film thickness, on V:TiO2(110)/Nb:TiO2(110). They have also found that the film thickness for maximum photoactivity depends on the wavelength of the irradiated light.
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81.05.Hd Other semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Development of nonaqueous polymer gels that exhibit broad temperature performance

Joseph L. Lenhart, Phillip J. Cole, Burcu Unal, and Ronald Hedden

Appl. Phys. Lett. 91, 061929 (2007); http://dx.doi.org/10.1063/1.2769938 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2007

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While significant work has focused on aqueous hydrogels for biotechnology applications, hydrogels suffer from a limited operating temperature range due to the moderate freezing point and high volatility of water. In this work, a nonaqueous, chemically cross-linked polybutadiene gel has been designed which exhibits stable properties over a temperature range of −60–70 °C. A combination of rheology, neutron scattering, and tack adhesion testing was utilized to characterize the gel properties. The methodology employed to design the polybutadiene gel can be generalized to a variety of gel materials and applications.
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82.70.Gg Gels and sols
83.80.Kn Physical gels and microgels
83.80.Rs Polymer solutions
61.25.H- Macromolecular and polymers solutions; polymer melts
81.20.-n Methods of materials synthesis and materials processing

Electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface: A first-principles investigation

Fabien Devynck, Ž. Šljivančanin, and Alfredo Pasquarello

Appl. Phys. Lett. 91, 061930 (2007); http://dx.doi.org/10.1063/1.2769949 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2007

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Using a density functional scheme, the authors investigate the electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface, as recently realized experimentally. Simulated scanning-tunneling-microscopy images of filled and empty states agree well with the experiment, lending support to the proposed atomic structure. In accord with the experiment, the local density of states indicates that the electronic band gap in the thin silicate layer at the surface is close to that of bulk SiO2. The authors show that this effect results from the surface of the epitaxial adlayer acting as a high-barrier potential for the SiC states induced in the oxide band gap.
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73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.55.-a Thin film structure and morphology
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Transport properties of microstructured ultrathin films of La0.67Ca0.33MnO3 on SrTiO3

C. Beekman, I. Komissarov, M. Hesselberth, and J. Aarts

Appl. Phys. Lett. 91, 062101 (2007); http://dx.doi.org/10.1063/1.2756166 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2007

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The authors have investigated the electrical transport properties of 8 nm thick La0.67Ca0.33MnO3 (LCMO) films, sputter deposited on SrTiO3 (STO), and etched into 5 μm wide bridges by Ar-ion etching. The authors find that even slight overetching of the film leads to conductance of the STO substrate, and asymmetric and nonlinear current-voltage (I-V) characteristics. However, a brief oxygen plasma etch allows full recovery of the insulating character of the substrate. The I-V characteristics of the bridges are then fully linear over a large range of current densities. The authors find colossal magnetoresistance properties typical for strained LCMO on STO but no signature of nonlinear effects (the so-called electroresistance) connected to electronic inhomogeneites. In the metallic state below 150 K, the highest current densities lead to heating effects and nonlinear I-V characteristics.
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75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Inter-Landau level scattering and LO-phonon emission in terahertz quantum cascade laser

N. Péré-Laperne, L. A. de Vaulchier, Y. Guldner, G. Bastard, G. Scalari, M. Giovannini, J. Faist, A. Vasanelli, S. Dhillon, and C. Sirtori

Appl. Phys. Lett. 91, 062102 (2007); http://dx.doi.org/10.1063/1.2766862 (3 pages) | Cited 10 times

Online Publication Date: 6 August 2007

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A terahertz quantum cascade laser (QCL) structure based on a bound to continuum and LO-phonon extraction stage is studied under a strong magnetic field. Two series of power oscillations as a function of magnetic field are observed. Comprehensive simulations of the lifetimes allow the first series to be assigned to interface roughness (elastic) and the second to LO-phonon scattering (inelastic) of hot carriers in an excited Landau level, previously unobserved in terahertz QCL. The authors demonstrate that for the latter, the thermal electron distribution in the upper laser state leads to a breaking of the population inversion and hence laser action.
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68.35.Ja Surface and interface dynamics and vibrations
42.55.Px Semiconductor lasers; laser diodes

Suppression of Schottky leakage current in island-in amorphous silicon thin film transistors with the Cu/CuMg as source/drain metal

M. C. Wang, T. C. Chang, Po-Tsun Liu, R. W. Xiao, L. F. Lin, Y. Y. Li, F. S. Huang, and J. R. Chen

Appl. Phys. Lett. 91, 062103 (2007); http://dx.doi.org/10.1063/1.2767147 (3 pages) | Cited 1 time

Online Publication Date: 7 August 2007

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The feasibility of using Cu/CuMg as a source/drain metal for the island-in amorphous silicon thin film transistors (a-Si:H TFTs) has been investigated. The issue of adhesion between the Cu film and n+–a-Si layer has been overcome by introducing the Cu/CuMg alloy. Furthermore, the suppression of Schottky leakage current in metal/a-Si:H structure was also observed in the island-in a-Si:H TFT. The island-in a-Si:H TFT exhibited the mobility of 0.52 cm2/V s, the subthreshold slope of 0.78 V/decade, and the Vth of 3.02 V. The experimental result also showed superior performance of the a-Si:H TFT with minimal loss of critical dimension and good thermal stability.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Observation of a uniform temperature dependence in the electrical resistance across the structural phase transition in thin film vanadium oxide (VO2)

R. G. Mani and S. Ramanathan

Appl. Phys. Lett. 91, 062104 (2007); http://dx.doi.org/10.1063/1.2767189 (3 pages) | Cited 7 times

Online Publication Date: 7 August 2007

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An electrical study of thin VO2 films in the vicinity of the structural phase transition at 68 °C shows (a) that the electrical resistance R follows log(R)∝−T over the T range, 20<T<80 °C covering both sides of the structural transition, and (b) a history dependent hysteresis loop in R upon thermal cycling. These features are attributed here to transport through a granular network.
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73.61.Ng Insulators
68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Rectifying characteristics and transport behavior of SrTiO3−δ(110)/p-Si (100) heterojunctions

Z. Luo, J. H. Hao, and J. Gao

Appl. Phys. Lett. 91, 062105 (2007); http://dx.doi.org/10.1063/1.2767999 (3 pages) | Cited 7 times

Online Publication Date: 7 August 2007

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Introducing oxygen vacancy causes the dielectric insulator SrTiO3 to evolve to a n-type semiconductor. The authors have fabricated n-SrTiO3−δ(110)/p-Si (100) heterojunctions, showing clear rectifying characteristics at different temperatures from 100 to 292 K. A forward-to-reverse bias ratio of about 1200 was found at V = ±2 V for the p-n junction operated at T = 292 K. The current-voltage characteristic follows I∝exp(eV/ηkT) for the p-n junction at relatively low forward-bias voltage, while the relation of I ∼ V1.9 describes the transport behavior of p-n junction at relatively high forward-bias voltage. The measured results have been discussed in Anderson model and space charge limited model.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification

Reduction of microtwin defects for high-electron-mobility InSb quantum wells

T. D. Mishima, M. Edirisooriya, and M. B. Santos

Appl. Phys. Lett. 91, 062106 (2007); http://dx.doi.org/10.1063/1.2768033 (3 pages) | Cited 6 times

Online Publication Date: 7 August 2007

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The effect of structural defects on electron mobilities has been investigated in InSb quantum wells (QWs) grown on GaAs (001) substrates. The usefulness of a ⟨116⟩-directional transmission electron microscopy analysis for microtwins (MTs) in a plan-view specimen is demonstrated. MTs and threading dislocations reduce the room-temperature (RT) electron mobility in InSb QWs. It is found that the use of 2° off-axis GaAs (001) substrates is effective in reducing MT densities in InSb QWs. The electron mobility in InSb QW at RT, 4.0×104 cm2/V s with an electron density of 4.6×1011/cm2, is among the highest values reported in semiconductor QWs.
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73.63.Hs Quantum wells
73.61.Ey III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries

Suppression of secondary phase formation in Fe implanted ZnO single crystals

K. Potzger, Shengqiang Zhou, H. Reuther, K. Kuepper, G. Talut, M. Helm, J. Fassbender, and J. D. Denlinger

Appl. Phys. Lett. 91, 062107 (2007); http://dx.doi.org/10.1063/1.2768196 (3 pages) | Cited 13 times

Online Publication Date: 7 August 2007

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Unwanted secondary phases are one of the major problems in diluted magnetic semiconductor creation. Here, the authors show possibilities to avoid such phases in Fe implanted and postannealed ZnO(0001) single crystals. While α-Fe nanoparticles are formed after such doping in as-polished crystals, high temperature (1273 K) annealing in O2 or high vacuum before implantation suppresses these phases. Thus, the residual saturation magnetization in the preannealed ZnO single crystals is about 20 times lower than for the as-polished ones and assigned to indirect coupling between isolated Fe ions rather than to clusters.
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75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Cc Kinetics of defect formation and annealing

Transconductance enhancement of nanowire field-effect transistors by built-up stress induced during thermal oxidation

A. Seike, T. Tange, I. Sano, Y. Sugiura, D. Kosemura, A. Ogura, and I. Ohdomari

Appl. Phys. Lett. 91, 062108 (2007); http://dx.doi.org/10.1063/1.2768637 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2007

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The authors report the enhancement of transconductance in nanowire field effect transistors due to build-up tensile stress during thermal oxidation. To evaluate the effect of stress, nanowires were thermally oxidized at (A) 900 °C/15 min, (B) 850 °C/1 h, and (C) 850 °C/1 h with a subsequent 1000 °C annealing. The transconductance of sample B is enhanced 2.6 times compared to sample A. No enhancement of transconductance is observed in sample C. The Raman spectra indicate tensile stress in sample B and compressive stress in sample C. This establishes that gm enhancement is due to the build-up tensile stress in nanowires, but is diminished by viscoelastic relaxation.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
62.20.-x Mechanical properties of solids
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.30.Jw Organic compounds, polymers
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Drift and diffusion of spins generated by the spin Hall effect

N. P. Stern, D. W. Steuerman, S. Mack, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 91, 062109 (2007); http://dx.doi.org/10.1063/1.2768633 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2007

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Electrically generated spin accumulation due to the spin Hall effect is imaged in n-GaAs channels using Kerr rotation microscopy, focusing on its spatial distribution and time-averaged behavior in a magnetic field. Spatially resolved imaging reveals that spin accumulation observed in transverse arms develops due to the longitudinal drift of spin polarization produced at the sample boundaries. One- and two-dimensional drift-diffusion modeling is used to explain these features, providing a more complete understanding of observations of spin accumulation and the spin Hall effect.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Dc Spin polarized transport in semiconductors
78.20.Ek Optical activity
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Evolution of spin coherence dynamics and g factor with electron excess energy in bulk intrinsic GaAs

Tianshu Lai, Lihua Teng, Zhongxing Jiao, Haihong Xu, Liang Lei, Jinhui Wen, and Weizhu Lin

Appl. Phys. Lett. 91, 062110 (2007); http://dx.doi.org/10.1063/1.2763978 (3 pages) | Cited 8 times

Online Publication Date: 9 August 2007

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Circularly polarized absorption quantum-beat spectroscopy is used to study excess-energy dependence of electron-spin coherence dynamics in intrinsic GaAs. Absorption quantum beats are observed. The quantum-beat oscillatory frequency is used as a high precision measure of electron g factor. Double linear energy dependence of g factor is obtained and disagrees with the prediction of k∙p theory. A theoretical calculation reveals the double linear energy dependence reflects the energy dependence of g factor of electrons measured through light-hole- and heavy-hole-electron transitions, respectively. The phase of the quantum beats provides the key information to distinguish the two transitions experimentally.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.-d Level splitting and interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.47.-p Spectroscopy of solid state dynamics
75.30.Cr Saturation moments and magnetic susceptibilities

Nonvolatile resistive switching memory utilizing gold nanocrystals embedded in zirconium oxide

Weihua Guan, Shibing Long, Rui Jia, and Ming Liu

Appl. Phys. Lett. 91, 062111 (2007); http://dx.doi.org/10.1063/1.2760156 (3 pages) | Cited 40 times

Online Publication Date: 9 August 2007

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Resistive switching characteristics of ZrO2 films containing gold nanocrystals (nc-Au) are investigated for nonvolatile memory applications. The sandwiched top electrode/ZrO2 (with nc-Au embedded)/n+ Si structure exhibits two stable resistance states (high-resistance state and low-resistance state). By applying proper voltage bias, resistive switching from one state to the other state can be achieved. This resistive switching behavior is reproducible and the ratio between the high and low resistances can be as high as two orders. The intentionally introduced nc-Au in ZrO2 films can improve the device yield greatly. ZrO2 films with gold nanocrystals embedded are promising to be used in the nonvolatile resistive switching memory devices.
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77.55.-g Dielectric thin films
61.46.-w Structure of nanoscale materials
84.32.Tt Capacitors

Annealing characteristics of electrically isolated InGaAsP devices

S. Ahmed, yR. Nawaz, W. A. Syed, R. Taiq, K. Amirov, and U. Larsson

Appl. Phys. Lett. 91, 062112 (2007); http://dx.doi.org/10.1063/1.2769390 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2007

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The authors report on the effects of fluorine implants on the sheet resistivity of n-type InGaAsP layers grown lattice matched to InP by metal organic molecular beam epitaxy. Projected range matched fluorine ions are implanted at multiple energies and single MeV energy at room temperature (RT) and 77 K in both cases. Hall and resistivity measurements are carried out for the van der Pauw samples and the evolution of sheet resistivity (Rs) as a function of annealing temperature was studied in both cases. Fluorine multienergy implantation at 77 K produces higher as-implanted resistivity layers of ∼ 107 Ω/◻ compared to RT implants. It is further observed that RT and 77 K implants recover to their preimplanted sheet resistivity values as soon as they are annealed at temperatures higher than 500 °C. Substrate temperature and collision cascade density due to multiple energy implants are found to play an important role to optimize the isolation process.
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61.72.Cc Kinetics of defect formation and annealing
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.40.Sz Deposition technology
85.30.-z Semiconductor devices

Zn vacancy induced room-temperature ferromagnetism in Mn-doped ZnO

Wensheng Yan, Zhihu Sun, Qinghua Liu, Zhongrui Li, Zhiyun Pan, Jie Wang, Shiqiang Wei, Dan Wang, Yingxue Zhou, and Xinyi Zhang

Appl. Phys. Lett. 91, 062113 (2007); http://dx.doi.org/10.1063/1.2769391 (3 pages) | Cited 58 times

Online Publication Date: 10 August 2007

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X-ray absorption fine structure (XAFS) and first-principles calculations were employed to study the structure and ferromagnetism origin of Zn0.97Mn0.03O thin film grown by metal organic chemical vapor deposition. The magnetization measurements indicate that this sample is ferromagnetic at room temperature. The Mn ions are located at the substitutional Zn sites as revealed by the Mn K-edge XAFS spectroscopy. Moreover, the O K-edge XAFS analysis indicated the existence of numerous Zn vacancies. Based on first-principles calculations, the authors propose that the Zn vacancy can induce the room-temperature ferromagnetism in Mn-doped ZnO.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Dm X-ray absorption spectra

Quasi-unipolar InGaAs/InP photodetection for enhanced optical saturation power and maximal bandwidth

P. D. Yoder and E. J. Flynn

Appl. Phys. Lett. 91, 062114 (2007); http://dx.doi.org/10.1063/1.2769395 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2007

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The potential to exploit quasi-unipolar charge transport for superior III-V photodetector performance is demonstrated by the growth, fabrication, and characterization of InGaAs/InP devices suitable for 1.3 and 1.55 μm operation. Incomplete electrical depletion of the absorber may be optimized to both balance and reduce the temporal extent of the electrical responses of both electrons and holes to an optical impulse, without penalty to quantum efficiency or necessarily even junction capacitance. The associated transit-time reduction is demonstrated to be considerable. Characterization of devices exhibiting high internal quantum efficiency demonstrates improvements in bandwidth, optical saturation power, and power dissipation.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.65.-k Nonlinear optics
85.30.De Semiconductor-device characterization, design, and modeling

Effect of Sn doping on the thermoelectric properties of ErNiSb-based p-type half-Heusler compound

Kenta Kawano, Ken Kurosaki, Takeyuki Sekimoto, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 91, 062115 (2007); http://dx.doi.org/10.1063/1.2769398 (3 pages) | Cited 12 times

Online Publication Date: 10 August 2007

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The authors characterized polycrystalline samples of Sn-doped ErNiSb “ErNiSnxSb1−x (x = 0, 0.01, 0.03, and 0.05)” to develop p-type half-Heusler thermoelectric materials. All samples prepared in this study exhibited positive Seebeck coefficients. With increasing Sn content x, the carrier concentration increased, leading to decreases in both electrical resistivity (ρ) and the Seebeck coefficient (S). Thermal conductivity (κ) values were at a similar level in all of the compositions. Sn-doping improved the thermoelectric figure of merit ZT( = S2T/ρ/κ) of ErNiSb; the maximum ZT value was 0.29 at 669 K, obtained in the composition ErNiSn0.01Sb0.99.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
61.72.up Other materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Technique to detect two-photon absorption in Si

Yan Ling and Fang Lu

Appl. Phys. Lett. 91, 062116 (2007); http://dx.doi.org/10.1063/1.2769943 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2007

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A technique to detect two-photon absorption in Si is presented. The light-induced voltage rather than the transmitted light is measured. The sample acts as the detector and the measurement is easy to be carried out. The nonlinear coefficients can be calculated conveniently from experimental data. From the experimental data measured at different light powers and different temperatures, the simultaneous two-photon absorption coefficients at 800 nm in Si are calculated to be about 230 cm/MW at 300 K and 360 cm/MW at 77 K.
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42.25.Bs Wave propagation, transmission and absorption
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators
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Band structures, magnetic properties, and enhanced magnetoresistance in the high pressure phase of Gd and Y doped two-dimensional perovskite Sr2CoO4 compounds

X. L. Wang, E. Takayama-Muromachi, S. X. Dou, and Z. X. Cheng

Appl. Phys. Lett. 91, 062501 (2007); http://dx.doi.org/10.1063/1.2759273 (3 pages) | Cited 7 times

Online Publication Date: 6 August 2007

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The authors present their studies on the band structures and on the magnetic and magnetotransport properties of the high pressure phase of Sr2−xRExCoO4 [rare earth (RE) = Gd and Y, x = 0.1–0.5] compounds which were synthesized by a high pressure and high temperature technique. The authors found that as x increases, the magnetoresistance {(ρH−ρ0)/ρ0} increases up to −17% at 5 K and 7 T, which is 2.5 times higher than that for undoped Sr2CoO4, although the ferromagnetic transition drops from 255 to 200 K for the Gd doping with x = 0.3. The saturation moments at low temperature are significantly enhanced for the Gd doped Sr2CoO4. Observation of a close correlation between resistance and field revealed a strong spin-dependent tunneling magnetoresistance. First-principles band structure calculations indicate that high spin polarization is present for both undoped and doped compounds.
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75.47.Pq Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
61.72.up Other materials

Nonreciprocal spin wave spectroscopy of thin Ni–Fe stripes

Pedram Khalili Amiri, Behzad Rejaei, Marina Vroubel, and Yan Zhuang

Appl. Phys. Lett. 91, 062502 (2007); http://dx.doi.org/10.1063/1.2766842 (3 pages) | Cited 8 times

Online Publication Date: 6 August 2007

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The authors report on the observation of nonreciprocal spin wave propagation in a thin ( ∼ 200 nm) patterned Ni–Fe stripe. The spin wave transmission spectrum is measured using a pair of microstrip lines as antennas. The nonreciprocity of surface wave dispersion brought about by an adjacent aluminum ground leads to a nonreciprocal coupling of the antennas. The effects of Ni–Fe film conductivity, thickness, and reflections caused by the lateral confinement of the magnetic stripe are discussed. The nonreciprocity observed in this structure can potentially be used to realize nonreciprocal microwave devices on silicon.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
73.61.At Metal and metallic alloys
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