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17 Aug 2009

Volume 95, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 073703 (2009); http://dx.doi.org/10.1063/1.3152768 (3 pages)

Mohammud R. Noor, Swati Goyal, Shawn M. Christensen, and Samir M. Iqbal
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Strong nonlinear optical response of graphene in the terahertz regime

A. R. Wright, X. G. Xu, J. C. Cao, and C. Zhang

Appl. Phys. Lett. 95, 072101 (2009); http://dx.doi.org/10.1063/1.3205115 (3 pages) | Cited 24 times

Online Publication Date: 17 August 2009

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We demonstrate that within the model of massless Dirac fermions, graphene has a strong nonlinear optical response in the terahertz regime. It is found that the nonlinear contribution significantly alters both the single frequency and frequency tripled optical response at experimentally relevant field strengths. The optical activity of single layer graphene is significantly enhanced by nonlinear effects, and the frequency tripled response opens the gateway to photonic and optoelectronic device applications.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Observation of negative differential transconductance in tunneling emitter bipolar transistors

Marc J. van Veenhuizen, Nicolas Locatelli, Jagadeesh Moodera, and Joonyeon Chang

Appl. Phys. Lett. 95, 072102 (2009); http://dx.doi.org/10.1063/1.3205104 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2009

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We report on measurement of negative differential transconductance (NDTC) of iron (Fe)/magnesium-oxide (MgO)/silicon tunneling emitter NPN bipolar transistors. Device simulations reveal that the NDTC is a consequence of an inversion layer at the tunneling-oxide/P-silicon interface for low base voltages. Electrons travel laterally through the inversion layer into the base and give rise to an increase in collector current. The NDTC results from the recombination of those electrons at the interface between emitter and base contact which is dependent on the base voltage. For larger base voltages, the inversion layer disappears marking the onset of normal bipolar transistor behavior.
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85.30.Pq Bipolar transistors

Experimental validation of a higher dimensional theory of electrical contact resistance

Matthew R. Gomez, David M. French, Wilkin Tang, Peng Zhang, Y. Y. Lau, and R. M. Gilgenbach

Appl. Phys. Lett. 95, 072103 (2009); http://dx.doi.org/10.1063/1.3205116 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2009

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The increased resistance of a cylindrical conducting channel due to constrictions of various radii and axial lengths was measured experimentally. The experimental data corroborate the higher dimensional contact resistance theory that was recently developed.
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73.40.Cg Contact resistance, contact potential

High performance thin film transistor with cosputtered amorphous Zn–In–Sn–O channel: Combinatorial approach

Min Ki Ryu, Shinhyuk Yang, Sang-Hee Ko Park, Chi-Sun Hwang, and Jae Kyeong Jeong

Appl. Phys. Lett. 95, 072104 (2009); http://dx.doi.org/10.1063/1.3206948 (3 pages) | Cited 26 times

Online Publication Date: 18 August 2009

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Thin film transistors with a channel of Zn–In–Sn–O were fabricated via a combinatorial rf sputtering method. It was found that the role of the In atoms is to enhance the mobility and to shift the threshold voltage (Vth) negatively. On the other hand, the Sn fraction is critical for improving the overall trap density including the density-of-states of the bulk channel layer and the interfacial trap density at the ZnInSnO interface. The optimized transistor was obtained at a compositional ratio of Zn:In:Sn = 40:20:40, which exhibited an excellent subthreshold gate swing of 0.12 V/decade, Vth of −0.4 V, and high Ion/off ratio of >109 as well as a high field-effect mobility of 24.6 cm2/V s.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

The polarity origin of the bipolar resistance switching behaviors in metal/La0.7Ca0.3MnO3/Pt junctions

R. Yang, X. M. Li, W. D. Yu, X. D. Gao, D. S. Shang, X. J. Liu, X. Cao, Q. Wang, and L. D. Chen

Appl. Phys. Lett. 95, 072105 (2009); http://dx.doi.org/10.1063/1.3203999 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2009

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Bipolar resistance switching behaviors in the M/La0.7Ca0.3MnO3/Pt (M = Pt, Ag, Cu, Al, Ti, and W) junctions were investigated. We found that the switching polarities of the junctions for M = Pt, Ag, and Cu were opposite to those for M = Al, Ti, and W. This phenomenon was attributed to the different Gibbs free energy of the metal oxide formation. Based on Auger electron spectroscopy measurement of the M/La0.7Ca0.3MnO3 interfaces, the switching mechanisms were further discussed in terms of metal electrode redox reaction for M = Al, Ti, and W and oxygen vacancy generation/annihilation in the La0.7Ca0.3MnO3 film for M = Pt, Ag, and Cu, respectively.
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73.40.Rw Metal-insulator-metal structures
79.20.Fv Electron impact: Auger emission
82.45.Fk Electrodes
61.72.jd Vacancies

Terahertz radiation detection by field effect transistor in magnetic field

S. Boubanga-Tombet, M. Sakowicz, D. Coquillat, F. Teppe, W. Knap, M. I. Dyakonov, K. Karpierz, J. Łusakowski, and M. Grynberg

Appl. Phys. Lett. 95, 072106 (2009); http://dx.doi.org/10.1063/1.3207886 (3 pages) | Cited 5 times

Online Publication Date: 19 August 2009

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We report on terahertz radiation detection with InGaAs/InAlAs field effect transistors in quantizing magnetic field. The photovoltaic detection signal was investigated as a function of the gate voltage and magnetic field. Oscillations analogous to Shubnikov–de Haas oscillations as well as their strong enhancement at the cyclotron resonance were observed. The results are quantitatively described by a recent theory, showing that the detection is due to rectification of the terahertz radiation by plasma waves related nonlinearities in the gated part of the channel.
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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)
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.Tv Field effect devices

Origin of nanoscale potential fluctuations in two-dimensional semiconductors

S. Landrock, Y. Jiang, K. H. Wu, E. G. Wang, K. Urban, and Ph. Ebert

Appl. Phys. Lett. 95, 072107 (2009); http://dx.doi.org/10.1063/1.3177329 (3 pages) | Cited 9 times

Online Publication Date: 19 August 2009

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We demonstrate a direct atomically resolved visualization and quantification of the impact of inhomogeneities in the dopant distribution on the nanoscale potential fluctuations in a two-dimensional semiconducting math×math Ga overlayer on Si(111) using scanning tunneling microscopy. By a quantitative analysis, two regimes of the potential at nanometer scale are found, which arise from the local distribution of charge carriers in the bands and from electron-electron interactions.
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81.05.Cy Elemental semiconductors
72.20.Dp General theory, scattering mechanisms
73.61.Cw Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.A- Nucleation and growth
68.55.ag Semiconductors

Nanoscale doping of InAs via sulfur monolayers

Johnny C. Ho, Alexandra C. Ford, Yu-Lun Chueh, Paul W. Leu, Onur Ergen, Kuniharu Takei, Gregory Smith, Prashant Majhi, Joseph Bennett, and Ali Javey

Appl. Phys. Lett. 95, 072108 (2009); http://dx.doi.org/10.1063/1.3205113 (3 pages) | Cited 14 times

Online Publication Date: 20 August 2009

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One of the challenges for the nanoscale device fabrication of III-V semiconductors is controllable postdeposition doping techniques to create ultrashallow junctions. Here, we demonstrate nanoscale, sulfur doping of InAs planar substrates with high dopant areal dose and uniformity by using a self-limiting monolayer doping approach. From transmission electron microscopy and secondary ion mass spectrometry, a dopant profile abruptness of ∼ 3.5 nm/decade is observed without significant defect density. The n+/p+ junctions fabricated by using this doping scheme exhibit negative differential resistance characteristics, further demonstrating the utility of this approach for device fabrication with high electrically active sulfur concentrations of ∼ 8×1018 cm−3.
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61.72.uj III-V and II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Compensation of interfacial states located inside the “buffer-free” GaSb/GaAs (001) heterojunction via δ-doping

A. Jallipalli, K. Nunna, M. N. Kutty, G. Balakrishnan, G. B. Lush, L. R. Dawson, and D. L. Huffaker

Appl. Phys. Lett. 95, 072109 (2009); http://dx.doi.org/10.1063/1.3210783 (3 pages) | Cited 1 time

Online Publication Date: 20 August 2009

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We report the compensation of interfacial states formed by interfacial misfit dislocation (IMF) arrays via δ-doping. The IMF arrays are located inside the “buffer-free” heterojunction of GaSb/GaAs (001). The interfacial states are measured using surface photovoltage measurements and are positioned at 0.41, 0.49, and 0.61 eV. A higher reverse bias leakage current (IRB) was observed in the heterogeneous GaSb/GaAs IMF sample (73 μA at −5 V) compared to the homogeneous GaAs control sample (3.9 μA), which does not contain IMF. This increase in IRB is attributed to the interfacial states. Hence, the interfacial states are compensated by δ-doping the GaSb/GaAs interface using Te atoms. A low turn-on voltage of 0.85 V and a very low IRB of 0.1 nA were achieved for the δ-doped sample compared to the control and IMF samples. Hence, for optoelectronic applications, such as lasers, solar cells, and detectors, this compensated IMF technology is useful for integration of buffer-free III-Sb devices on an inexpensive GaAs platform.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors

Current-induced spin polarization in gallium nitride

W. F. Koehl, M. H. Wong, C. Poblenz, B. Swenson, U. K. Mishra, J. S. Speck, and D. D. Awschalom

Appl. Phys. Lett. 95, 072110 (2009); http://dx.doi.org/10.1063/1.3194781 (3 pages) | Cited 5 times

Online Publication Date: 20 August 2009

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Electrically generated spin polarization is probed directly in bulk GaN using Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the wurtzite phase both by molecular beam epitaxy and metalorganic chemical vapor deposition with a variety of doping densities chosen to broadly modulate the transverse spin lifetime, T2∗. The spin polarization is characterized as a function of electrical excitation energy over a range of temperatures. Despite weak spin-orbit interactions in GaN, a current-induced spin polarization is observed in the material at temperatures of up to 200 K.
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73.61.Ey III-V semiconductors
72.25.Dc Spin polarized transport in semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ek Optical activity

Correlation between a threshold failure time and void nucleation for describing the bimodal electromigration behavior of copper interconnects

R. G. Filippi, P.-C. Wang, A. Brendler, and J. R. Lloyd

Appl. Phys. Lett. 95, 072111 (2009); http://dx.doi.org/10.1063/1.3200233 (3 pages) | Cited 3 times

Online Publication Date: 21 August 2009

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Electromigration testing of an interconnect system comprised of copper metallization and a low-k dielectric material gives rise to bimodal lognormal statistics with early and late fails. When separated from one another, we observed failure modes characterized by a three-parameter lognormal distribution and the same threshold failure time. It is shown that the threshold failure time corresponds to damage (presumably voids) nucleation of the electromigration process. The dependence of the threshold failure time and the median time to failure on current density suggests that both void nucleation and void growth need to be considered for accurate modeling of the electromigration lifetime.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
02.50.Ng Distribution theory and Monte Carlo studies

High performance ZnO-thin-film transistor with Ta2O5 dielectrics fabricated at room temperature

L. Zhang, J. Li, X. W. Zhang, X. Y. Jiang, and Z. L. Zhang

Appl. Phys. Lett. 95, 072112 (2009); http://dx.doi.org/10.1063/1.3206917 (3 pages) | Cited 20 times

Online Publication Date: 21 August 2009

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The authors report on the fabrication of low-driven-voltage and high mobility ZnO thin-film transistor with sputtering Ta2O5 film as the dielectric. The device shows a field effect mobility of 60.4 cm2/V s, a threshold voltage of 1.1 V, an on/off ratio of 1.22×107, and a subthreshold swing of 0.23 V/decade. The high mobility partially resulted from the fringing-electric-field effect due to the undefined active layer. Therefore, considering our device geometry, the actual mobility is about 40.5 cm2/V s. We contribute the high performance to the proper dielectric thickness, smooth insulator surface, and relatively low trap state densities in the insulator/channel interface.
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85.30.Tv Field effect devices
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Room temperature ferromagnetism of ZnO nanocrystals in amorphous ZnO–Al2O3 matrix

Y. W. Ma, J. Ding, D. C. Qi, J. B. Yi, H. M. Fan, H. Gong, A. T. S. Wee, and A. Rusydi

Appl. Phys. Lett. 95, 072501 (2009); http://dx.doi.org/10.1063/1.3206654 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2009

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In this work, we demonstrate room temperature ferromagnetism of ZnO nanocrystals (NCs) embedded in alumina-based amorphous matrix. Our study has shown that solid solution occurred for lower Al concentration [ ≤ x = 0.09 for (Zn1−x,Alx)O]. No ferromagnetism appears in Al-doped ZnO with x ≤ 0.09. With higher Al concentration, alumina-based amorphous structure appeared and fully amorphous was found in the composition of (Zn0.30,Al0.70)O. Ferromagnetism was found in (Zn1−x,Alx)O with a threshold of 16 mol % of Al. The room temperature ferromagnetism was found to be attributed to ZnO NCs in an alumina-based amorphous ZnO–Al2O3 matrix. Ferromagnetism reached a maximum with a volume percentage of ZnO NCs to be ∼ 27 vol %. The detailed investigations (transmission electron microscopy, x-ray photoelectron spectroscopy, and superconducting quantum interference device) show that the optimized size of these NCs is in the range of 4–5 nm. No ferromagnetism appears if the sample contains a fully amorphous structure.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Abnormal frequency dependence of ac susceptibility in melt texture Gd–Ba–Cu–O single domain

Ke-Xi Xu, Xing-Da Wu, and Peng-Jun Pan

Appl. Phys. Lett. 95, 072502 (2009); http://dx.doi.org/10.1063/1.3206657 (3 pages)

Online Publication Date: 17 August 2009

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In this paper, the pinning property of the melt texture Gd–Ba–Cu–O single domain has been examined by ac susceptibility measurements. An unexpected frequency dependence behavior of the irreversibility line Birr(T) has been found, in which the power n for Birr(T)∝(1−t)n is affected by frequencies of the ac fields, no longer kept as a constant as in the Yeshurun and Malozemoff theory. We present the abnormal frequency dependent behavior and interpret it in framework of the flux diffusion model.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Subtle interplay between native point defects and magnetism in ZnO:Co

M. H. N. Assadi, Y. B. Zhang, and S. Li

Appl. Phys. Lett. 95, 072503 (2009); http://dx.doi.org/10.1063/1.3210793 (3 pages) | Cited 10 times

Online Publication Date: 18 August 2009

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Distribution of Co ions and its effect on magnetic properties of ZnO:Co in the presence of native point defects, oxygen vacancy, and interstitial hydrogen, have been investigated using first-principles density functional calculations. The study provides a fundamental theoretical understanding on the correlation between magnetism and the distribution of magnetic ions and the native point defects in the semiconducting host. Results show that Co ions have a strong tendency toward aggregation via oxygen within ab plane in the presence of point defects. The room temperature ferromagnetism observed experimentally in ZnO:Co is mainly dominated by the interstitial hydrogen rather than oxygen vacancy.
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61.72.jd Vacancies
61.72.jj Interstitials
75.50.Pp Magnetic semiconductors

Modelling the quasistatic and dynamical sensing response of Galfenol-based magnetostrictive devices

Philip Weetman and George Akhras

Appl. Phys. Lett. 95, 072504 (2009); http://dx.doi.org/10.1063/1.3210789 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2009

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A computational model for the quasistatic and dynamical response of Galfenol based magnetostrictive devices in the sensing configuration is presented. The model calculates the fraction of magnetic moments oriented along the preferred orientations within the crystal as a function of time using a self-consistent rate equation technique. These magnetic moment fractions are then used to determine the total magnetization as a function of time. The model is compared to experiments for uniaxial, compressive, and quasistatic loading. Predictive calculations are presented for dynamical loading. Eddy currents and finite transition times lead to increasing hysteresis as the frequency increases.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetically tuned mechanical resonances in magnetoelectric multilayer capacitors

C. Israel, V. M. Petrov, G. Srinivasan, and N. D. Mathur

Appl. Phys. Lett. 95, 072505 (2009); http://dx.doi.org/10.1063/1.3205477 (3 pages) | Cited 9 times

Online Publication Date: 19 August 2009

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Poled multilayer capacitors based on barium titanate represent model magnetoelectric systems because the interdigitated planar electrodes are nowadays based on a magnetostrictive material, namely nickel. Here we demonstrate electrically excited mechanical resonances that can be magnetically tuned. Nonmonotonic variations in resonant frequency with applied magnetic field are interpreted in terms of the influence of magnetostriction on the Young’s modulus of the electrodes, i.e., the ΔEY effect.
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75.80.+q Magnetomechanical effects, magnetostriction
77.65.Fs Electromechanical resonance; quartz resonators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors

100 ps precessional spin-transfer switching of a planar magnetic random access memory cell with perpendicular spin polarizer

C. Papusoi, B. Delaët, B. Rodmacq, D. Houssameddine, J.-P. Michel, U. Ebels, R. C. Sousa, L. Buda-Prejbeanu, and B. Dieny

Appl. Phys. Lett. 95, 072506 (2009); http://dx.doi.org/10.1063/1.3206919 (3 pages) | Cited 16 times

Online Publication Date: 20 August 2009

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Ultrafast spin-transfer precessional switching between two stable states of a magnetic random access memory device is demonstrated in structures comprising a perpendicularly magnetized polarizing layer (PL⊥), an in-plane magnetized free layer (FL), and an in-plane magnetized analyzing layer (AL) in a PL⊥/spacer/FL/spacer/AL stack. Back and forth switching can be achieved with sub-ns current pulses of the same polarity. The spin-torque influence from the analyzer leads to an asymmetric dependence of the switching properties as a function of the current sign and initial state.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Effects of thickness on the cation segregation in epitaxial (001) and (110) La2/3Ca1/3MnO3 thin films

S. Estradé, J. M. Rebled, J. Arbiol, F. Peiró, I. C. Infante, G. Herranz, F. Sánchez, J. Fontcuberta, R. Córdoba, B. G. Mendis, and A. L. Bleloch

Appl. Phys. Lett. 95, 072507 (2009); http://dx.doi.org/10.1063/1.3211130 (3 pages) | Cited 8 times

Online Publication Date: 21 August 2009

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Electron-energy-loss spectroscopy is used to map composition and electronic states in epitaxial La2/3Ca1/3MnO3 (LCMO) films of various thicknesses grown on SrTiO3 (001) and (110) substrates. For relatively thick films ( ≥ 20 nm), epitaxial tensile strain in (001) films promotes a compositional La/Ca gradient across the film thickness, being the interface La rich, while the relaxed (110) films are chemically homogeneous. In contrast, much thinner (001) and (110) LCMO films display a different La/Ca distribution, being La rich at the free surface. The observed distinct thickness-dependent composition gradient behavior reflects a balance between strain-induced elastic energy minimization and kinetic effects during growth.
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75.50.Dd Nonmetallic ferromagnetic materials
68.55.jd Thickness
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Bs Mechanical and acoustical properties
79.20.Uv Electron energy loss spectroscopy
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Microscopic evidence of a strain-enhanced ferromagnetic state in LaCoO3 thin films

S. Park, P. Ryan, E. Karapetrova, J. W. Kim, J. X. Ma, J. Shi, J. W. Freeland, and Weida Wu

Appl. Phys. Lett. 95, 072508 (2009); http://dx.doi.org/10.1063/1.3206667 (3 pages) | Cited 7 times

Online Publication Date: 21 August 2009

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Strain-induced modification of magnetic properties of lightly hole doped epitaxial LaCoO3 thin films on different substrates were studied with variable temperature magnetic force microscopy (MFM). Real space observation at 10 K reveals the formation of the local magnetic clusters on a relaxed film grown on LaAlO3 (001). In contrast, a ferromagnetic ground state has been confirmed for tensile-strained film on SrTiO3 (001), indicating that strain is an important factor in creating the ferromagnetic state. Simultaneous atomic force microscopy and MFM measurements reveal nanoscale defect lines for the tensile-strained films, where the structural defects have a large impact on the local magnetic properties.
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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
75.30.Cr Saturation moments and magnetic susceptibilities

The “colossal” magnetocaloric effect in Mn1−xFexAs: What are we really measuring?

Mohamed Balli, Daniel Fruchart, Damien Gignoux, and Ryszard Zach

Appl. Phys. Lett. 95, 072509 (2009); http://dx.doi.org/10.1063/1.3194144 (3 pages) | Cited 34 times

Online Publication Date: 21 August 2009

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Recently, a so-called “colossal” magnetocaloric effect (MCE) was reported in Mn1−xFexAs [ A. de Campos et al., Nat. Mater. 5, 802 (2006) ]. However, the value of ΔS that was determined appears markedly overestimated since it results from the inadequate use of the Maxwell relation. Here, we report on recent measurements of ΔS in Mn1−xFexAs from which a correct MCE value is deduced by using the Clausius–Clapeyron equation. This result is asserted by careful use of the Maxwell relation.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Dd Nonmetallic ferromagnetic materials
65.40.gd Entropy

Effect of hydrostatic pressure in degenerate Ge1−xMnxTe

S. T. Lim, J. F. Bi, K. L. Teo, Feng Y. P, T. Liew, and T. C. Chong

Appl. Phys. Lett. 95, 072510 (2009); http://dx.doi.org/10.1063/1.3211990 (3 pages) | Cited 5 times

Online Publication Date: 21 August 2009

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We utilize the effect of hydrostatic pressure to investigate the magnetotransport properties of degenerate p-Ge1−xMnxTe (x = 0.10) ferromagnetic semiconductor. The Curie temperature was found to increase with pressure as 0.27 K/kbar, which can be understood on the basis of the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction mechanism. For sufficiently high carrier concentration of po ∼ 1021 cm−3, both the light holes from the L valence band and the heavy holes from the Σ valence band contribute to the RKKY interaction. Additionally, a negative magnetoresistance is observed at low temperature and is found to decrease with pressure.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Jc Other crystalline inorganic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
62.50.-p High-pressure effects in solids and liquids
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Suppression of the current leakage in charge ordered Lu2Fe2Fe1−xMnxO7 (0<x ≤ 0.86)

Y. B. Qin, H. X. Yang, Y. Zhang, H. F. Tian, C. Ma, L. J. Zeng, and J. Q. Li

Appl. Phys. Lett. 95, 072901 (2009); http://dx.doi.org/10.1063/1.3207751 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2009

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The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1−xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization–electric field switching curves. The charge ordering states in Lu2Fe2Fe1−xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.Dj Domain structure; hysteresis
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

dc field effect on stability of piezoelectric PZN-0.06PT single crystals under compressive stress

Chiaki Okawara and Ahmed Amin

Appl. Phys. Lett. 95, 072902 (2009); http://dx.doi.org/10.1063/1.3193547 (3 pages) | Cited 10 times

Online Publication Date: 19 August 2009

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A reversible elastic instability was observed in PZN-0.06PT high coupling single crystals when subjected to uniaxial compressions similar to those used in sound projectors. The strain magnitude at the onset of the instability supported a free energy prediction of a ferroelectric rhombohedral (FR)-ferroelectric orthorhombic (FO) phase transition. The thermal response of the normalized phase transition strain is in a good agreement with model calculation. A dc bias field drastically enhanced the crystal stability under compression. dc bias and compressive stress levels that are required for their stable operation in sound projectors have been deduced and will be presented.
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77.80.B- Phase transitions and Curie point
77.65.-j Piezoelectricity and electromechanical effects
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
65.40.G- Other thermodynamical quantities
81.40.Jj Elasticity and anelasticity, stress-strain relations

High resolution photoemission study of SiOx/Si(111) interface disruption following in situ HfO2 deposition

Stephen McDonnell, Barry Brennan, and Greg Hughes

Appl. Phys. Lett. 95, 072903 (2009); http://dx.doi.org/10.1063/1.3210794 (3 pages) | Cited 4 times

Online Publication Date: 20 August 2009

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We report on an in situ high resolution core level photoemission study of the early stages of interface formation between an ultrathin SiOx layer ( ∼ 0.3 nm) grown on the atomically clean Si(111) surface and a HfO2 dielectric layer. Si 2p core level spectra acquired at 130 eV photon energy reveal evidence of a chemically shifted component on the lower binding energy side of the substrate peak which is attributed to interface defect states resulting from the incorporation of silicon atoms from the substrate into the interfacial oxide at room temperature. This evidence of Si/SiOx interface disruption would be expected to increase charge carrier scattering mechanisms in the silicon and contribute to the generally observed mobility degradation in high-k stacks with ultrathin silicon oxide interface layers.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films
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