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30 Jun 2003

Volume 82, Issue 26, pp. 4633-4843

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4797 (2003); http://dx.doi.org/10.1063/1.1587262 (3 pages)

Ongi Englander, Dane Christensen, and Liwei Lin
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Structural and electrical characteristics of Ge nanoclusters embedded in Al2O3 gate dielectric

Q. Wan, C. L. Lin, W. L. Liu, and T. H. Wang

Appl. Phys. Lett. 82, 4708 (2003); http://dx.doi.org/10.1063/1.1588373 (3 pages) | Cited 27 times

Online Publication Date: 24 June 2003

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Structural and electrical characteristics of the metal–insulator–semiconductor (MIS) structures of Al/Al2O3/Si containing Ge nanoclusters are experimentally demonstrated. Secondary ion mass spectroscopy results indicate the out-diffusion of Ge after annealing at 800 °C in N2 ambient for 30 min. An increment of leakage current is observed due to the out-diffusion of Ge. Capacitance–voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by the hysteresis in the C–V curves in the annealed sample. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
66.30.Pa Diffusion in nanoscale solids
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Bismuth volatility effects on the perfection of SrBi2Nb2O9 and SrBi2Ta2O9 films

M. A. Zurbuchen, J. Lettieri, S. J. Fulk, Y. Jia, A. H. Carim, D. G. Schlom, and S. K. Streiffer

Appl. Phys. Lett. 82, 4711 (2003); http://dx.doi.org/10.1063/1.1574406 (3 pages) | Cited 15 times

Online Publication Date: 24 June 2003

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The volatility of bismuth and bismuth oxide species complicates the growth of phase-pure films of SrBi2Nb2O9 and SrBi2Ta2O9. Films that appear phase-pure by x-ray diffraction can have microstructural defects caused by transient bismuth nonstoichiometry which have a significant impact on properties. Such defects are resolved by transmission electron microscopy. Post-growth loss of bismuth from a slowly cooled SrBi2Ta2O9 film resulted in the generation of a high density of out-of-phase boundaries (OPBs), which are demonstrated to be ferroelectrically inactive. In another film, the difference in the rate of desorption of bismuth oxides from SrTiO3 versus that from SrBi2Nb2O9 led to bismuth enrichment at the film–substrate interface, and the formation of an epitaxial reaction layer in an otherwise stoichiometric SrBi2Nb2O9 film. This different-composition layer would be expected to alter the electrical properties of the film as a whole. These results help explain the scatter in electrical data reported for similarly oriented films. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.80.Dj Domain structure; hysteresis
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)
77.22.Ej Polarization and depolarization

Two-photon absorption and multiphoton-induced photoluminescence of bulk GaN excited below the middle of the band gap

Y. Toda, T. Matsubara, R. Morita, M. Yamashita, K. Hoshino, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 82, 4714 (2003); http://dx.doi.org/10.1063/1.1587260 (3 pages) | Cited 10 times

Online Publication Date: 24 June 2003

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Optical nonlinearity in the yellow luminescence (YL) band of GaN was investigated using thick bulk samples. Transient pump–probe measurements revealed strong transmission changes due to two-photon absorption (TPA) even at the middle of the YL band. The TPA coefficient evaluated reaches ∼ 5 cm/GW at about 1.3 eV, which was as large as the mid-gap resonance. The TPA spectrum clearly showed that the observed large nonlinearity originated from the YL band. On the basis of efficient TPA in the YL band, relaxation processes in the multiphoton-induced photoluminescence excitation spectrum were also investigated. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
42.65.-k Nonlinear optics

Optical power limiting and stabilization using a two-photon absorbing neat liquid crystal in isotropic phase

Guang S. He, Tzu-Chau Lin, Paras N. Prasad, Chih-Chien Cho, and Liang-Jye Yu

Appl. Phys. Lett. 82, 4717 (2003); http://dx.doi.org/10.1063/1.1588364 (3 pages) | Cited 22 times

Online Publication Date: 24 June 2003

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This letter reports on a neat liquid crystal that incorporates a two-photon-absorbing chromophore in its structure. The nonlinear optical properties including two-photon-induced fluorescence spectrum and decay behavior, as well as the effective two-photon absorption coefficient of this liquid crystal in its isotropic phase are presented. Fairly good optical limiting and stabilization performance with this nonlinear material have been achieved by using ∼ 815-nm and ∼ 5-ns laser pulses. © 2003 American Institute of Physics.
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42.70.Df Liquid crystals
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
33.50.Dq Fluorescence and phosphorescence spectra
78.55.Bq Liquids
61.30.-v Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
33.80.Wz Other multiphoton processes
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Temperature dependence of the energy gap and free carrier absorption in bulk InAs0.05Sb0.95 single crystals

Bhavtosh Bansal, V. K. Dixit, V. Venkataraman, and H. L. Bhat

Appl. Phys. Lett. 82, 4720 (2003); http://dx.doi.org/10.1063/1.1587002 (3 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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Temperature dependence of the energy gap and free carrier absorption in a high-quality InAs0.05Sb0.95 single crystal was studied between 90 K and 430 K through the absorption spectra. At this alloy concentration, the room-temperature energy gap was measured to be 0.15 eV. Varshni- and the Bose–Einstein-type fit parameters were obtained from the measured temperature dependence of the energy gap, and the latter gave the zero-temperature gap to be 0.214 eV. It was found that although Weider’s empirical formula for the dependence of the energy gap on temperature and the alloy concentration agrees with the value of the gap at room temperature, it is inaccurate in describing its temperature dependence. From the free carrier absorption measurements, the phonon limited cross section of 7.35×10−16 cm2 at 15 μm was deduced at room temperature. © 2003 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
63.20.-e Phonons in crystal lattices

Experimental determination of electron and hole mean drift distance: Application to chemical vapor deposition diamond

Marco Marinelli, E. Milani, G. Pucella, A. Tucciarone, G. Verona-Rinati, M. Angelone, and M. Pillon

Appl. Phys. Lett. 82, 4723 (2003); http://dx.doi.org/10.1063/1.1586475 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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A simple technique for measuring the electron and hole mean drift distance in chemical vapor deposition polycrystalline diamond in the as-grown and in the so-called pumped state obtained by 90Sr β-particle irradiation is presented. To this purpose, the efficiency η of a diamond-based particle detector was measured using a 5.5-MeV 241Am α-particle source. In particular, two different experimental setups were specifically designed and realized in order to perform a systematic study of the device efficiency as a function of the α-particle penetration depth, both in the positive and negative bias polarization. In the first setup, air is used as an absorbing layer in order to change the energy of the impinging α particles, while in the second one, the measurements were performed in vacuum and the incidence angle was varied in the 0°–80° range. The advantages of the latter setup are evidenced. The theoretical formula for the mean drift distances of carriers is derived using a properly modified Hecht model, and fitted to the data, allowing a separate evaluation of the charge collection distances of each carrier type (λe = μeτeE and λh = μhτhE). The obtained results unambiguously show that the pumping process is much more effective on hole conduction, λh being much greater than λe in the pumped state. © 2003 American Institute of Physics.
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29.40.Wk Solid-state detectors
61.82.Fk Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Cw Elemental semiconductors
61.80.Fe Electron and positron radiation effects

IrO2 Schottky contact on n-type 4H-SiC

Sang Youn Han, Ho Won Jang, and Jong-Lam Lee

Appl. Phys. Lett. 82, 4726 (2003); http://dx.doi.org/10.1063/1.1588365 (3 pages)

Online Publication Date: 24 June 2003

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A thermally stable IrO2 Schottky contact on n-type 4H-SiC was achieved by annealing an Ir contact under O2 ambient. The IrO2 contact exhibited a high Schottky barrier height of 2.22 eV and low reverse leakage current. Little degradation in Schottky barrier height was observed even after annealing at 450 °C for 24 h under atmospheric air. The oxidation annealing transformed the Ir layer into IrO2, resulting in the increase in the work function of the contact layer. Simultaneously, Si atoms diffused out, leaving the Si vacancy below the contact. These played a role in forming a thermally stable Schottky contact with a high Schottky barrier height. © 2003 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects
81.65.Mq Oxidation
68.35.Fx Diffusion; interface formation
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Self-assembly and magnetic properties of cobalt nanoparticles

H. T. Yang, C. M. Shen, Y. K. Su, T. Z. Yang, H. J. Gao, and Y. G. Wang

Appl. Phys. Lett. 82, 4729 (2003); http://dx.doi.org/10.1063/1.1586481 (3 pages) | Cited 35 times

Online Publication Date: 24 June 2003

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Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
81.16.Be Chemical synthesis methods
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Current-induced effect on the resistivity of epitaxial thin films of La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3

J. Gao, S. Q. Shen, T. K. Li, and J. R. Sun

Appl. Phys. Lett. 82, 4732 (2003); http://dx.doi.org/10.1063/1.1587001 (3 pages) | Cited 67 times

Online Publication Date: 24 June 2003

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Electric-current-dependent resistance has been studied in epitaxial thin films of La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3. Attention was focused at the influence of the applied dc current on the resistance of these epitaxial thin films in the absence of a magnetic field. A significant change in the ratio of the peak resistance at different currents or current resistance was found to be ∼23%–26% with a current density up to 8×104 Acm−2. For both La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3 compounds, the dependence of the measured resistance on the current revealed a good linear relationship. Although the nature behind such an effect has not been well understood yet, the feature that the resistance in doped manganese oxides could be easily controlled by the electric current should be of interest for various applications such as field effect devices. © 2003 American Institute of Physics.
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73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films

Electron transport properties in magnetic tunnel junctions with epitaxial NiFe (111) ferromagnetic bottom electrodes

Ji Hyung Yu, Hyuck Mo Lee, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 82, 4735 (2003); http://dx.doi.org/10.1063/1.1587271 (3 pages) | Cited 9 times

Online Publication Date: 24 June 2003

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By employing epitaxial NiFe (111) films as ferromagnetic bottom electrodes, magnetic tunnel junctions with layer sequence of Si (111)/epitaxial Ag/epitaxial Cu/epitaxial NiFe/Al-oxide/CoFe/IrMn/NiFe/Ta were prepared. High tunneling magnetoresistance (TMR) ratios were obtained and the bias dependence of TMR was remarkably reduced. The reason for the small bias dependence of TMR was explained by inelastic electron tunneling spectroscopy. It was clearly elucidated that a well-defined sharp interface formed between the tunnel barrier and the ferromagnetic electrode that is nearly free of crystalline defects. This magnetic tunnel junction has a large capability in engineering aspects if we can reduce the barrier thickness further by decreasing the interface roughness. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys

Investigation of superparamagnetism in Co–Zn ferrite thin films produced by pulsed-laser deposition

D. Ravinder and P. Shalini

Appl. Phys. Lett. 82, 4738 (2003); http://dx.doi.org/10.1063/1.1581980 (2 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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Modern communication systems use increasingly higher frequencies and smaller and lighter possible devices. This requires magnetic devices using thin-film inductors or transformers and microwave integrated nonreciprocal circuits with incorporated thin ferrite films. Due to their better high-frequency characteristics, the polycrystalline materials are preferred to the monocrystalline ones in such thin-film applications. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
81.15.Fg Pulsed laser ablation deposition

Theory of semiconductor magnetic bipolar transistors

M. E. Flatté, Z. G. Yu, E. Johnston-Halperin, and D. D. Awschalom

Appl. Phys. Lett. 82, 4740 (2003); http://dx.doi.org/10.1063/1.1586996 (3 pages) | Cited 49 times

Online Publication Date: 24 June 2003

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Bipolar transistors with a ferromagnetic base are shown theoretically to have the potential to generate almost 100% spin-polarized current injection into nonmagnetic semiconductors. Optical control of ferromagnetism and spin splitting in the base can lead to either long-lived or ultrafast switching behavior. Fringe field control of the base magnetization could be used for information transfer between metallic magnetoelectronics and conventional semiconducting electronics. © 2003 American Institute of Physics.
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85.30.Pq Bipolar transistors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Decoupling between rare-earth moment and transition metal moment in NdCo12−xVx compounds

W. F. Liu, G. H. Rao, Z. W. Ouyang, H. F. Yang, G. Y. Liu, X. M. Feng, H. Chang, and J. K. Liang

Appl. Phys. Lett. 82, 4743 (2003); http://dx.doi.org/10.1063/1.1587884 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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Single-phase compounds NdCo12−xVx (x = 2.2–2.6) crystallizing in the tetragonal ThMn12 structure with space group I4/mmm are synthesized. The lattice parameters a and c increase linearly with increasing V content. The Curie temperature of the compounds shows a linear decrease from 309 K for x = 2.2 to 147 K for x = 2.6. A domain-wall pinning phenomenon is observed in all of the compounds. It is intriguing that the Nd ions seem to make no contribution to the total moment of the compounds in an applied magnetic field up to 50 kOe. A further increase of the applied field induces a moment of a Nd sublattice that ferromagnetically couples with the moment of a Co sublattice. The instability of the Nd moment in NdCo12−xVx compounds can be well understood by the local environment effect. © 2003 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.60.Ch Domain walls and domain structure

Magnetization steps in a noncharge-ordered manganite, Pr0.5Ba0.5MnO3

C. Autret, A. Maignan, C. Martin, M. Hervieu, V. Hardy, S. Hébert, and B. Raveau

Appl. Phys. Lett. 82, 4746 (2003); http://dx.doi.org/10.1063/1.1588756 (3 pages) | Cited 8 times

Online Publication Date: 24 June 2003

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Magnetization and resisitivity steps under application of a magnetic field are evidenced in absence of charge ordering at low temperature (T = 2.5 K), in the manganite Pr0.5Ba0.5MnO3. Electron microscopy observations emphasize the important role of phase separation, suggesting that the observed antiferromagnetic to ferromagnetic metamagnetic transition originates from cation-ordered PrBaMn2O6 nanoregions. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials
64.75.-g Phase equilibria
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Observation of sphere resonance peak in ferromagnetic GaN:Mn

S. S. A. Seo, M. W. Kim, Y. S. Lee, T. W. Noh, Y. D. Park, G. T. Thaler, M. E. Overberg, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 82, 4749 (2003); http://dx.doi.org/10.1063/1.1588741 (3 pages) | Cited 28 times

Online Publication Date: 24 June 2003

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We report temperature-dependent optical spectra of ferromagnetic Mn-doped GaN in a wide photon energy region of 5 meV–4 eV. Below the GaN gap, an absorption peak around 1.25 eV whose intensity increases at lower temperatures was observed. A composite medium theory, called the Maxwell–Garnett theory, shows that the absorption peak can be assigned to a sphere resonance from metallic particles embedded in a Mn-doped GaN matrix. We also report that the far-infrared absorption of Mn-doped GaN sample was very small. This result suggests that itinerant carrier-mediated ferromagnetism does not fully explain the observed magnetic properties. © 2003 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials

Josephson effect in high-Tc La2−xSrxCuO4/La2−xSrxCuO4 ramp-edge junctions

H. Haibara and I. Iguchi

Appl. Phys. Lett. 82, 4752 (2003); http://dx.doi.org/10.1063/1.1589183 (3 pages) | Cited 1 time

Online Publication Date: 24 June 2003

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The observation of Josephson effect in high-Tc La2−xSrxCuO4/La2−xSrxCuO4 (LSCO/LSCO) ramp-edge junctions is reported. The LSCO/LSCO ramp-edge junctions are fabricated by pulsed laser deposition, Ar ion milling, and photolithography techniques adopting an interface-engineered process. The fabricated junctions have the maximum Josephson current Ic of a few hundred microamperes and clear Shapiro steps are observable under microwave irradiation. The modulation of Ic under an external magnetic field is also recognized. © 2003 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
81.15.Fg Pulsed laser ablation deposition

Enhanced carrier-mediated ferromagnetism in GaMnN by codoping of Mg

K. H. Kim, K. J. Lee, D. J. Kim, H. J. Kim, Y. E. Ihm, C. G. Kim, S. H. Yoo, and C. S. Kim

Appl. Phys. Lett. 82, 4755 (2003); http://dx.doi.org/10.1063/1.1586484 (3 pages) | Cited 23 times

Online Publication Date: 24 June 2003

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The effects of Mg codoping on the structural, electronic transport, and magnetic properties of GaMnN films are investigated. Mg was shown to compete with Mn for incorporation into the growing films at impingement, and to replace Mn. The partial replacement of Mn by Mg in GaMnN has resulted in an increase of conductivity of the region. The enhanced transport property due to the highly efficient dopant Mg resulted in a remarkable increase of the saturation magnetization, indicating an interaction between Mn and Mg for the carrier-mediated ferromagnetism. The increased carrier population by Mg codoping enabled a full mediation among the Mn atoms, and consequently, suppressed the paramagnetic rise in the temperature-dependent magnetization measurement. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Dn Low-field transport and mobility; piezoresistance
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Nucleation and interface formation mechanisms in atomic layer deposition of gate oxides

Martin M. Frank, Yves J. Chabal, and Glen D. Wilk

Appl. Phys. Lett. 82, 4758 (2003); http://dx.doi.org/10.1063/1.1585129 (3 pages) | Cited 54 times

Online Publication Date: 24 June 2003

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We present an in situ infrared spectroscopic study of the interface formation during atomic layer deposition of alternative high-permittivity (high-κ) gate dielectrics. Layer-by-layer oxide growth may be achieved by alternating pulses of a molecular metal precursor (e.g., trimethylaluminum for aluminum oxide growth) and water vapor. Contrary to common belief, we find that the metal precursor, not the oxidizing agent, is the key factor to control Al2O3 nucleation on hydrogen-terminated silicon. Metal surface species catalyze subsurface Si oxidation. These findings have direct implications on growth conditions to optimize semiconductor-dielectric interfaces. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics

Large remanent polarization of 100% polar-axis-oriented epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 thin films

Hitoshi Morioka, Gouji Asano, Takahiro Oikawa, Hiroshi Funakubo, and Keisuke Saito

Appl. Phys. Lett. 82, 4761 (2003); http://dx.doi.org/10.1063/1.1586993 (3 pages) | Cited 41 times

Online Publication Date: 24 June 2003

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100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.50.Gk Non-volatile ferroelectric memories

Influence of implantation energy on the electrical properties of ultrathin gate oxides grown on nitrogen implanted Si substrates

E. Kapetanakis, D. Skarlatos, C. Tsamis, P. Normand, and D. Tsoukalas

Appl. Phys. Lett. 82, 4764 (2003); http://dx.doi.org/10.1063/1.1585133 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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Metal–oxide–semiconductor tunnel diodes with gate oxides, in the range of 2.5–3.5 nm, grown either on 25 or 3 keV nitrogen-implanted Si substrates at (0.3 or 1) ×1015 cm−2 dose, respectively, are investigated. The dependence of N2+ ion implant energy on the electrical quality of the growing oxide layers is studied through capacitance, equivalent parallel conductance, and gate current measurements. Superior electrical characteristics in terms of interface state trap density, leakage current, and breakdown fields are found for oxides obtained through 3 keV nitrogen implants. These findings together with the full absence of any extended defect in the silicon substrate make the low-energy nitrogen implantation technique an attractive option for reproducible low-cost growth of nanometer-thick gate oxides. © 2003 American Institute of Physics.
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73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.20.At Surface states, band structure, electron density of states

Dielectric and transverse piezoelectric properties of sol-gel-derived (001) Pb[Yb1/2Nb1/2]O3–PbTiO3 epitaxial thin films

Q. F. Zhou, Q. Q. Zhang, T. Yoshimura, and S. Trolier-McKinstry

Appl. Phys. Lett. 82, 4767 (2003); http://dx.doi.org/10.1063/1.1581366 (3 pages) | Cited 14 times

Online Publication Date: 24 June 2003

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(1−x)Pb[Yb1/2Nb1/2]O3–xPbTiO3 (PYbN–PT, x = 0.5) epitaxial thin films were deposited on (001) SrRuO3/(001) MgO substrates by sol-gel processing. X-ray diffraction analysis revealed that the films were pyrochlore-free (001) epitaxial films when crystallized at 750 °C for 1 min. The dielectric permittivity and loss factor varied only slightly with frequency in the range of 100 to 10 000 Hz. At 1 kHz, the dielectric permittivity was 870 and the dielectric loss was 0.03 at room temperature. Compared with (111) PYbN–PT films, (001) PYbN–PT films exhibited better ferroelectric and piezoelectric properties. The remanent polarization (Pr) was 37 μC/cm2. The effective transverse piezoelectric e31,f coefficient of the films were −10.2 C/m2 when films were poled at room temperature. Enhanced piezoelectric properties were obtained using unique two-step method poling the PYbN–PT films at higher temperatures. © 2003 American Institute of Physics.
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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.-j Piezoelectricity and electromechanical effects
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization

Ferroelectric field-effect transistor with a SrRuxTi1−xO3 channel

A. G. Schrott, J. A. Misewich, V. Nagarajan, and R. Ramesh

Appl. Phys. Lett. 82, 4770 (2003); http://dx.doi.org/10.1063/1.1588753 (3 pages) | Cited 18 times

Online Publication Date: 24 June 2003

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A ferroelectric field-effect transistor with a SrRuxTi1−xO3 solid-solution channel layer and a lead zirconate titanate gate oxide has been fabricated. The remnant polarization of the ferroelectric yields two states at 0 V, which produce a relative change in channel resistance (ΔR/R) of 75% and a coercivity of 3 V. The channel has sufficient off-state free carrier concentration to provide sufficient balancing charge for ferroelectric stability. The device was subjected to more than 1010 read-write cycles with no degradation. This nonvolatile device offers the possibility of a nondestructive, current sense memory cell with good retention properties. © 2003 American Institute of Physics.
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85.50.Gk Non-volatile ferroelectric memories
85.30.Tv Field effect devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.30.Sk Pulse and digital circuits
77.22.Ej Polarization and depolarization

B-site disordering in Pb(Sc1/2Ta1/2)O3 by mechanical activation

X. S. Gao, J. M. Xue, J. Wang, T. Yu, and Z. X. Shen

Appl. Phys. Lett. 82, 4773 (2003); http://dx.doi.org/10.1063/1.1581384 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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B-site disorder in Pb(Sc1/2Ta1/2)O3 (PST) is traditionally tailored by thermal annealing after sintering at elevated temperatures. In this letter, we report B-site disordering in PST triggered by mechanical activation (MA), and the resulting ferroelectric behaviors thus derived. MA induces B-site order–disorder transformation in PST, and more interestingly, the structural disorder can well be retained in sintered PST, leading to a change in ferroelectric transition behavior (e.g., from a normal ferroelectric to relaxor) and a shift in Curie temperature. A designed degree of disorder in PST can therefore be obtained by the effective combination of presinter MA and subsequent sintering, giving rise to the specific ferroelectric properties that are required for certain applications. © 2003 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
64.70.K- Solid-solid transitions
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
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Light amplification in semiconductor nanocrystals: Quantum rods versus quantum dots

H. Htoon, J. A. Hollingworth, A. V. Malko, R. Dickerson, and V. I. Klimov

Appl. Phys. Lett. 82, 4776 (2003); http://dx.doi.org/10.1063/1.1586460 (3 pages) | Cited 52 times

Online Publication Date: 24 June 2003

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We perform side-by-side comparison of optical gain properties of spherical and elongated nanocrystals (quantum dots and quantum rods, respectively). This comparison indicates that elongated nanoparticles provide several features beneficial for lasing applications, such as enhanced absorption cross sections (and hence reduced lasing threshold and improved photostability), increased optical gain lifetime, and extended optical gain spectral range through the use of transitions that involve both ground and excited electronic states. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Lt Quantum wires
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
73.21.Hb Quantum wires
81.07.Vb Quantum wires
73.21.La Quantum dots
81.07.Ta Quantum dots
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Yj Optical parametric oscillators and amplifiers
78.55.-m Photoluminescence, properties and materials

Two-dimensional periodic positioning of self-assembled Ge islands on prepatterned Si (001) substrates

Zhenyang Zhong, A. Halilovic, T. Fromherz, F. Schäffler, and G. Bauer

Appl. Phys. Lett. 82, 4779 (2003); http://dx.doi.org/10.1063/1.1581986 (3 pages) | Cited 70 times

Online Publication Date: 24 June 2003

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Two-dimensional (2D) periodic arrays of Ge islands were realized on prepatterned Si (001) substrates by solid-source molecular-beam epitaxy. Atomic-force microscopy images demonstrate that the Ge islands are formed in the 2D laterally ordered pits of patterned substrates. The 2D periodicity of the substrate pattern is replicated throughout a stack of Ge island layers by strain-driven vertical ordering. Photoluminescence spectra of the ordered Ge islands show well-resolved peaks of the no-phonon signal and the transverse-optical phonon replica. These peaks are observed at nearly the same energy as those of random Ge islands deposited under the same conditions on unpatterned Si substrates. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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