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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Thermionic emission perpendicular to bulk and multiquantum AlxGa1−xInP barriers

J. Ní Chróinín and A. P. Morrison

Appl. Phys. Lett. 88, 142110 (2006); http://dx.doi.org/10.1063/1.2181648 (3 pages)

Online Publication Date: 7 April 2006

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A study on thermally activated currents across the bulk and multiquantum barrier (MQB) AlxGa1−xInP/GaInP has been carried out and compared to experimental results from a series of n-i-n diodes over a range of temperatures. By considering the true quantum mechanical nature of the barriers, in contrast to the classical Richardson formalism, it is found that the alloy crossover strongly affects the transport properties of the material. The measured prefactor is found to decrease as Al content is increased. When applied to the MQB structures, the existing model fails to capture the experimental results.
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79.40.+z Thermionic emission
85.30.Kk Junction diodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Rectifying NdNiO3/Nb:SrTiO3 junctions as a probe of the surface electronic structure of NdNiO3

Y. Kozuka, T. Susaki, and H. Y. Hwang

Appl. Phys. Lett. 88, 142111 (2006); http://dx.doi.org/10.1063/1.2193800 (3 pages) | Cited 12 times

Online Publication Date: 7 April 2006

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We have studied the electronic properties of junctions formed between Nb-doped SrTiO3 substrates, an n-type semiconductor, and NdNiO3 films, which exhibit a strong first-order phase transition from a high temperature paramagnetic metal to a low temperature antiferromagnetic insulator. Although the junctions are rectifying at all temperatures, the current-voltage and capacitance characteristics show no indication of the metal-insulator transition clearly observed in the films. This suggests that the surface electronic structure of NdNiO3 is distinct from the interior of the film and does not undergo the bulk transition.
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73.40.Ei Rectification
73.20.At Surface states, band structure, electron density of states
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Hydrogen self-trapping near silicon atoms in Ge-rich SiGe alloys

R. N. Pereira, B. Bech Nielsen, J. Coutinho, V. J. B. Torres, and P. R. Briddon

Appl. Phys. Lett. 88, 142112 (2006); http://dx.doi.org/10.1063/1.2193802 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2006

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Infrared absorption spectroscopy and ab initio density functional modeling are used to investigate hydrogen defects that are stable at and above room temperature in proton-implanted Ge-rich SiGe alloys. We find that Si atoms are effective nucleation sites for hydrogen, leading to the formation of a dominant defect closely related to the H2* dimer in pure Si and Ge. The minority Si species in the alloys stabilizes the new complex, and strongly reduces the trapping efficiency of hydrogen by vacancies and self-interstitials.
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71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
78.30.Hv Other nonmetallic inorganics

Evaluation of titanium silicon nitride as gate electrodes for complementary metal-oxide semiconductor

H. Luan, H. N. Alshareef, H. R. Harris, H. C. Wen, K. Choi, Y. Senzaki, P. Majhi, and B.- H. Lee

Appl. Phys. Lett. 88, 142113 (2006); http://dx.doi.org/10.1063/1.2188380 (3 pages) | Cited 4 times

Online Publication Date: 7 April 2006

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The effect of deposition temperature and film thickness on the work function of TiSiN gate electrodes has been studied. It is shown that the work function of TiSiN can be tuned from 4.28–4.74 eV on SiO2, 4.40–4.79 eV on HfO2, and 4.44–4.83 eV on HfSiOx. For high-k dielectrics, the work function can be tuned by 200 meV on each side of the band gap, making it a suitable electrode for fully depleted silicon-on-insulator devices. Furthermore, TiSiN deposition at high temperature increases the work function to 4.87 eV while Si implantation increases it to 4.93 eV, making TiSiN a good p-type metal candidate.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
71.20.-b Electron density of states and band structure of crystalline solids
77.55.-g Dielectric thin films
85.30.Tv Field effect devices

Robust, scalable self-aligned platinum silicide process

Z. Zhang, S.-L. Zhang, M. Östling, and J. Lu

Appl. Phys. Lett. 88, 142114 (2006); http://dx.doi.org/10.1063/1.2194313 (3 pages) | Cited 5 times

Online Publication Date: 7 April 2006

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A robust, scalable PtSix process is developed. The process consists of two consecutive annealing steps in a single run; the first is silicidation of Pt films on Si substrates carried out in N2, whereas the second is surface oxidation of the resultant PtSix in O2. By adequately adjusting the temperature during the oxidation step, a protective SiOx hard mask forms on PtSix of different thicknesses and compositions. Such a surface oxidation is absent for Pt on SiO2 isolation, which is crucial for the subsequent selective wet etch for a self-aligned process. Ultralong PtSix nanowires are fabricated using this robust self-aligned process.
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68.65.La Quantum wires (patterned in quantum wells)
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Band offsets in the Sc2O3/GaN heterojunction system

J.-J. Chen, B. P. Gila, M. Hlad, A. Gerger, F. Ren, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 88, 142115 (2006); http://dx.doi.org/10.1063/1.2194314 (3 pages) | Cited 9 times

Online Publication Date: 7 April 2006

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The Sc2O3/GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN/GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3/GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv = 0.42±0.07 eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0 eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14 eV in this system.
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71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
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Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions

Myung-Ho Bae and Hu-Jong Lee

Appl. Phys. Lett. 88, 142501 (2006); http://dx.doi.org/10.1063/1.2191415 (3 pages) | Cited 6 times

Online Publication Date: 3 April 2006

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We confirmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi2Sr2CaCu2O8+x by observing the multiple subbranches in the Josephson-vortex-flow current-voltage characteristics. We also observed the symptom of the microwave emission from the resonance between the Josephson vortex lattice and the collective transverse plasma modes, which provides the possibility of developing Josephson-vortex-flow electromagnetic oscillators.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.25.F- Transport properties

Ferromagnetism in 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films

Basavaraj Angadi, Y. S. Jung, Won-Kook Choi, Ravi Kumar, K. Jeong, S. W. Shin, J. H. Lee, J. H. Song, M. Wasi Khan, and J. P. Srivastava

Appl. Phys. Lett. 88, 142502 (2006); http://dx.doi.org/10.1063/1.2192577 (3 pages) | Cited 20 times

Online Publication Date: 4 April 2006

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Structural, electrical resistivity, and magnetization properties of 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films are presented. The structural studies show the presence of Co clusters whose size is found to increase with increase of Co implantation. The implanted films were irradiated with 200-MeV Ag+15 ions to fluence of 1×1012 ions/cm2. The Co clusters on irradiation dissolve in the ZnO matrix. The electrical resistivity of the irradiated samples is lowered to half. The magnetization hysteresis measurements show ferromagnetic behavior at 300 K, and the coercive field increases with the Co implantation. The ferromagnetism at room temperature is confirmed by magnetic force microscopy measurements. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors

Multiferroic BiFeO3 thin films prepared via a simple sol-gel method

Yao Wang, Qing-hui Jiang, Hong-cai He, and Ce-Wen Nan

Appl. Phys. Lett. 88, 142503 (2006); http://dx.doi.org/10.1063/1.2191947 (3 pages) | Cited 53 times

Online Publication Date: 4 April 2006

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Single-phase multiferroic BiFeO3 thin films were grown on (111) Pt/Ti/SiO2/Si substrates via a simple sol-gel spin-coating technique, as evidenced by x-ray diffraction. The thickness of the films can be controlled by the number of layers spin coated. Scanning electron microscope confirmed good surface and cross-section morphology of the films. Obvious multiferroic behavior with small saturation polarization but high saturation magnetization was observed in the films. X-ray photoelectron spectroscopy was used to examine the combination state of Fe 2p electron in the BiFeO3 films.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Magnetoelectric effect in laminate composite of magnets/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

Yanmin Jia, Xiangyong Zhao, Haosu Luo, Siu Wing Or, and Helen Lai Wa Chan

Appl. Phys. Lett. 88, 142504 (2006); http://dx.doi.org/10.1063/1.2191948 (3 pages) | Cited 9 times

Online Publication Date: 4 April 2006

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A magnetoelectric (ME) laminate composite was fabricated by sandwiching one 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) piezoelectric single crystal layer between two NdFeB magnet layers along the thickness direction. The high ME effect was obtained by the product of the magnetic attractive-repellent effect in the magnet layers and the piezoelectric effect in the piezoelectric layer. The magnetoelectric voltage coefficient of the composite was measured to be ∼ 12.5 mV/cm Oe with a flat frequency response in the range of 0.1–20 kHz. The induced ME voltage showed an excellent linear relationship to the applied ac magnetic field with field amplitude varying from 10−3 to 10 Oe. Other advantages included low heat generation, no bias magnetic field required, and high scale-down capability. These made the composite to be a promising ME material for realizing high-performance, small-size, and low-cost magnetic sensors.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.80.+q Magnetomechanical effects, magnetostriction
77.65.-j Piezoelectricity and electromechanical effects

Search for ferromagnetism in undoped and cobalt-doped HfO2−δ

M. S. Ramachandra Rao, Darshan C. Kundaliya, S. B. Ogale, L. F. Fu, S. J. Welz, N. D. Browning, V. Zaitsev, B. Varughese, C. A. Cardoso, A. Curtin, S. Dhar, S. R. Shinde, T. Venkatesan, S. E. Lofland, and S. A. Schwarz

Appl. Phys. Lett. 88, 142505 (2006); http://dx.doi.org/10.1063/1.2190909 (3 pages) | Cited 22 times

Online Publication Date: 5 April 2006

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We report on the search for ferromagnetism in undoped and cobalt-doped high-k dielectric HfO2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped HfO2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped HfO2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements

L. D. Cooley, Y. F. Hu, and A. R. Moodenbaugh

Appl. Phys. Lett. 88, 142506 (2006); http://dx.doi.org/10.1063/1.2193047 (3 pages) | Cited 6 times

Online Publication Date: 5 April 2006

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Nb3Sn was prepared by milling Nb and Sn powder mixtures followed by limited reactions to restrict disorder recovery. Although disorder reduced the superconducting critical temperature Tc, the concomitant electron scattering increased the upper critical field μ0Hc2 to as high as 35 T at 0 K, as determined by the Werthamer-Helfand-Hohenberg equation. Hc2 was higher for longer milling times and lower annealing temperatures. Substitution of 2% Ti for Nb did not appreciably enhance Hc2, suggesting that alloying mitigates the benefits of disorder. Since alloyed Nb3Sn wires have μ0Hc2(0) ≈ 29 T, wires based on heavily milled powders could extend the field range for applications if they can be made with high current density.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Op Mixed states, critical fields, and surface sheaths

Current-assisted magnetization switching in a mesoscopic NiFe ring with nanoconstrictions of a wire

Zhengqi Lu, Yun Zhou, Yuqing Du, Roy Moate, David Wilton, Genhua Pan, Yifang Chen, and Zheng Cui

Appl. Phys. Lett. 88, 142507 (2006); http://dx.doi.org/10.1063/1.2195007 (3 pages) | Cited 8 times

Online Publication Date: 6 April 2006

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A mesoscopic NiFe ring with nanoconstrictions of a wire was fabricated by electron beam lithography and lift-off techniques. Magnetic switching and reversal process have been measured by magnetoresistance as a function of the applied current. It is shown that the applied current has an effect on the switching fields and finally affects the reversal process. The decrease or increase in the switching field from the vortex state to the onion state depends on the electron flow with respect to the direction of domain propagation. The spin in the ring switches from an onion state to the opposite onion state in the low applied current via the double switching process. However, the spin in the ring switches directly from an onion state to the opposite due to the spin torque effect when the applied current is higher than the critical current density (of 107 A/cm2).
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75.60.Jk Magnetization reversal mechanisms
72.15.Gd Galvanomagnetic and other magnetotransport effects

Electric-field-induced resistance switching universally observed in transition-metal-oxide thin films

M. Hamaguchi, K. Aoyama, S. Asanuma, Y. Uesu, and T. Katsufuji

Appl. Phys. Lett. 88, 142508 (2006); http://dx.doi.org/10.1063/1.2193328 (3 pages) | Cited 34 times

Online Publication Date: 6 April 2006

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We show that polarity-dependent, nonvolatile resistance switching by electric field occurs in the thin film of various transition-metal oxides in almost the same manner. This result indicates that, contrary to the general acceptance, perovskite manganite is by no means a special compound for this phenomenon. It is also suggested that the resistance switching is not dominated by a detailed electronic structure of each sample, but dominated by a more general origin, e.g., crystalline defect.
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73.61.Ng Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films

J. F. Bi, J. H. Zhao, J. J. Deng, Y. H. Zheng, S. S. Li, X. G. Wu, and Q. J. Jia

Appl. Phys. Lett. 88, 142509 (2006); http://dx.doi.org/10.1063/1.2193430 (3 pages) | Cited 16 times

Online Publication Date: 6 April 2006

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We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films

G. Cifariello, M. Aurino, E. Di Gennaro, G. Lamura, A. Andreone, P. Orgiani, X. X. Xi, and J.-C. Villégier

Appl. Phys. Lett. 88, 142510 (2006); http://dx.doi.org/10.1063/1.2193053 (3 pages) | Cited 5 times

Online Publication Date: 6 April 2006

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The two-tone intermodulation distortion arising in MgB2 thin films synthesized by hybrid physical-chemical vapor deposition is studied in order to probe the influence of the two bands on the nonlinear response of this superconductor. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10 are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, the signal arising from distortion versus temperature shows the intrinsic s-wave behavior expected for this compound. Data are compared with measurements performed on Nb and YBa2Cu3O7−δ thin films using the same technique.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
74.10.+v Occurrence, potential candidates
74.62.Yb Other effects
74.78.-w Superconducting films and low-dimensional structures

Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature

Ashutosh Tiwari, V. M. Bhosle, S. Ramachandran, N. Sudhakar, J. Narayan, S. Budak, and A. Gupta

Appl. Phys. Lett. 88, 142511 (2006); http://dx.doi.org/10.1063/1.2193431 (3 pages) | Cited 71 times

Online Publication Date: 7 April 2006

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We report room temperature ferromagnetism in single crystal Ce1−xCoxO2−δ (x ⩽ 0.05) films deposited on a LaAlO3(001) substrate. Films were grown by a pulsed laser deposition technique and were thoroughly characterized using x-ray diffraction, high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy and scanning transmission electron microscopy-Z contrast, x-ray photoelectron spectroscopy, optical transmission spectroscopy, and magnetic measurements. These films are transparent in the visible regime and exhibit a very high Curie temperature ∼ 740–875 K with a giant magnetic moment. Our results indicate that the ferromagnetic property is intrinsic to the CeO2 system and is not a result of any secondary magnetic phase or cluster formation.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.20.Uv Electron energy loss spectroscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Comparison of free surface polarization of NiMnSb and Co2MnSi

Y. Miyoshi, Y. Bugoslavsky, M. H. Syed, T. Robinson, L. F. Cohen, L. J. Singh, Z. H. Barber, C. E. A. Grigorescu, S. Gardelis, J. Giapintzakis, and W. Van Roy

Appl. Phys. Lett. 88, 142512 (2006); http://dx.doi.org/10.1063/1.2193787 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2006

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We present a systematic study of the polarization of the transport current from a variety of NiMnSb and Co2MnSi thin films and bulk material using point contact Andreev reflection spectroscopy. The simple analysis suggests that the free surface polarization of NiMnSb is within error 10% lower than that of Co2MnSi. In either material the measured polarization is rather insensitive to key physical and material properties. We use a two channel model to rule out the influence that stray magnetic field from the ferromagnet might have on the measurements presented.
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73.61.At Metal and metallic alloys
72.25.Ba Spin polarized transport in metals

Identification of unidirectional anisotropy in exchange-biased MnO/GaMnAs bilayers using ferromagnetic resonance

K. Dziatkowski, Z. Ge, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 88, 142513 (2006); http://dx.doi.org/10.1063/1.2190767 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2006

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We report ferromagnetic resonance (FMR) studies of epitaxial MnO/GaMnAs bilayers. The FMR data have revealed a distinct unidirectional anisotropy about the [1math0] axis, which we attribute to exchange biasing of ferromagnetic GaMnAs by the adjacent antiferromagnetic MnO layer. The observed unidirectional anisotropy is surprisingly robust with respect to temperature and changing magnetic field.
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75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
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Magnesium oxide as a candidate high-κ gate dielectric

L. Yan, C. M. Lopez, R. P. Shrestha, E. A. Irene, A. A. Suvorova, and M. Saunders

Appl. Phys. Lett. 88, 142901 (2006); http://dx.doi.org/10.1063/1.2191419 (3 pages) | Cited 22 times

Online Publication Date: 3 April 2006

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Magnesium oxide (MgO) thin films with sharp interfaces were deposited by sputtering of a Mg target on Si. The film stack was characterized using spectroscopic ellipsometry and transmission electron microscopy and the film static dielectric constant (κ) and interface traps were determined. An amorphous SiO2 layer was found at the MgO/Si interface as a result of subcutaneous Si oxidation. κ for the MgO films was found to be about twice that of SiO2, and the interface trap densities of MgO/Si were found to be comparable with SiO2/Si, rendering MgO competitive with all presently considered high-κ dielectrics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Study on vacancy formation in ferroelectric PbTiO3 from ab initio

Zhen Zhang, Ping Wu, Li Lu, and Chang Shu

Appl. Phys. Lett. 88, 142902 (2006); http://dx.doi.org/10.1063/1.2192623 (3 pages) | Cited 21 times

Online Publication Date: 3 April 2006

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Formation energies of possible vacancies under different oxygen partial pressures were studied using an ab initio density functional theory and supercell approach. Under oxygen-rich conditions, lead vacancies are the stable ones throughout the band gap, and their ionization level locates at 0.56 eV from the top of valence band, which may contribute to p-type conduction. Under oxygen-poor conditions, oxygen vacancies are the stable ones at the top of the valence band. It is a deep donor that may not only dilute the acceptor carriers to weaken the p-type conduction but hardly contribute to n-type conduction.
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61.72.J- Point defects and defect clusters
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals

Substrate-induced strain effects on the transport properties of pulsed laser-deposited Nb-doped SrTiO3 films

W. Ramadan, S. B. Ogale, S. Dhar, S. X. Zhang, D. C. Kundaliya, I. Satoh, and T. Venkatesan

Appl. Phys. Lett. 88, 142903 (2006); http://dx.doi.org/10.1063/1.2187439 (3 pages) | Cited 7 times

Online Publication Date: 4 April 2006

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Thin films of Nb-doped SrTiO3 (NSTO) are grown via pulsed laser deposition (PLD) on LaAlO3 (LAO,001), MgAl2O4 (MAO,001), SrTiO3 (STO,001), and Y-stabilized ZrO2 (YSZ,001) substrates. The effects of the film-substrate lattice mismatch, film thickness, and substrate temperature during growth on the film properties are investigated. The electrical transport in NSTO films is shown to exhibit a strong sensitivity to strain, which is suggested to arise from the dependence of carrier mobility on bond distortions/stretching and related changes in phonon modes.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
73.61.Ng Insulators
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Fg Pulsed laser ablation deposition

Thickness dependence of structural and piezoelectric properties of epitaxial Pb(Zr0.52Ti0.48)O3 films on Si and SrTiO3 substrates

D. M. Kim, C. B. Eom, V. Nagarajan, J. Ouyang, R. Ramesh, V. Vaithyanathan, and D. G. Schlom

Appl. Phys. Lett. 88, 142904 (2006); http://dx.doi.org/10.1063/1.2185614 (3 pages) | Cited 24 times

Online Publication Date: 7 April 2006

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We report the structural and longitudinal piezoelectric responses (d33) of epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) films on (001) SrTiO3 and Si substrates in the thickness range of 40 nm–4 μm. With increasing film thickness the tetragonality of PZT was reduced. The increase in d33 value with increasing film thicknesses was attributed to the reduction of substrate constraints and softening of PZT due to reduced tetragonality. The d33 values of PZT films on Si substrates ( ∼ 330 pm/V) are higher than those on SrTiO3 substrates ( ∼ 200 pm/V). The epitaxial PZT films on silicon will lead to the fabrication of high performance piezoelectric microelectromechanical devices.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
68.55.-a Thin film structure and morphology

Fabrication and characterizations of proton-exchanged LiNbO3 waveguides fabricated by inductively coupled plasma technique

Z. Ren, P. J. Heard, K. R. Hallam, Alex Wotherspoon, Q. Jiang, R. Varrazza, and S. Yu

Appl. Phys. Lett. 88, 142905 (2006); http://dx.doi.org/10.1063/1.2191704 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2006

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This Letter reports the use of an inductively coupled plasma technique for fabrication of proton-exchanged (PE) LiNbO3 (LN) waveguides. Planar and stripe waveguides have been formed in Y-cut LN which are difficult to obtain with the conventional molten acid method due to the occurrence of surface damage. Secondary ion mass spectrometry, scanning electron microscopy, and infrared absorption spectrum characterization results revealed that a uniform vertical PE profile with a single low order crystal phase has been directly obtained as a result of this unique process. X-ray photoelectron spectroscopy characterization of the treated surface revealed the existence of NbO as the cause for a sometimes darkened surface and confirms the ability to completely restore the surface to LN by oxygen plasma treatment. Atomic force microscopy measurement confirms that good surface quality has been maintained after regeneration of the surface to LN.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
84.40.Az Waveguides, transmission lines, striplines
52.77.-j Plasma applications
68.37.Ps Atomic force microscopy (AFM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
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Room temperature demonstration of GaN/AlN quantum dot intraband infrared photodetector at fiber-optics communication wavelength

A. Vardi, N. Akopian, G. Bahir, L. Doyennette, M. Tchernycheva, L. Nevou, F. H. Julien, F. Guillot, and E. Monroy

Appl. Phys. Lett. 88, 143101 (2006); http://dx.doi.org/10.1063/1.2186108 (3 pages) | Cited 31 times

Online Publication Date: 3 April 2006

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We fabricated a communication wavelength photodetector based on intraband transition in GaN/AlN self-assembled quantum dot heterostructures. The quantum dot photodetector is based on in-plane transport and has a room temperature spectral peak responsivity of 8 mA/W at wavelength of 1.41 μm. We use multipass waveguide geometry to show that the polarization sensitive optical absorption spectrum of the heterostructure is nearly the same as its photocurrent spectral response. This establishes that the detector’s response is due to the presence of quantum dots in its active layer. We use photoluminescence, transmission, and intraband photocurrent spectroscopy to consistently describe the alignment between the energy levels of the quantum dots and that of the wetting layer.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
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