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19 Mar 2007

Volume 90, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages)

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg
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Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact

Q. L. Gu, C. C. Ling, X. D. Chen, C. K. Cheng, A. M. C. Ng, C. D. Beling, S. Fung, A. B. Djurišić, L. W. Lu, G. Brauer, and H. C. Ong

Appl. Phys. Lett. 90, 122101 (2007); http://dx.doi.org/10.1063/1.2715025 (3 pages) | Cited 28 times

Online Publication Date: 19 March 2007

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Conversion of the Au/n-ZnO contact from Ohmic to rectifying with H2O2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H2O2 treatment did not affect the carbon surface contamination or the EC–0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects (Zn vacancy or vacancy cluster) close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects.
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73.40.Ei Rectification
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Jv Interfaces; heterostructures; nanostructures
78.70.Bj Positron annihilation
71.55.-i Impurity and defect levels

High-pressure and high-temperature annealing as an activation method for ion-implanted dopants in diamond

K. Ueda, M. Kasu, and T. Makimoto

Appl. Phys. Lett. 90, 122102 (2007); http://dx.doi.org/10.1063/1.2715034 (3 pages) | Cited 11 times

Online Publication Date: 19 March 2007

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The authors show that high-pressure and high-temperature (HPHT) annealing is very effective for the activation of ion-implanted dopants in diamond. The HPHT annealing condition is located in the thermodynamically stable region for diamond in the phase diagram and is, therefore, much more efficient for the recovery of implantation-induced damage and for the activation of ion-implanted dopants than thermal annealing in vacuum. The B-implanted film after HPHT annealing showed a high mobility of 632 cm2/V s with a sheet hole concentration of 4.8×1010 cm−2 at 300 K and the doping efficiency of ∼ 7%. The mobility is the highest so far for ion-implanted diamond. In the entire annealing temperature range, the HPHT annealing is more efficient than the thermal annealing in vacuum.
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61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
62.50.-p High-pressure effects in solids and liquids
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Pressure-tuned colossal improvement of thermoelectric efficiency of PbTe

Sergey V. Ovsyannikov and Vladimir V. Shchennikov

Appl. Phys. Lett. 90, 122103 (2007); http://dx.doi.org/10.1063/1.2715123 (3 pages) | Cited 26 times

Online Publication Date: 19 March 2007

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The variations in thermoelectric (TE) efficiencies æ of lead chalcogenide compounds (p-PbTe, n-PbTe, p-Pb0.55Te0.45, p-Pb1−xSnxTe1−y, p-PbSe, and p-PbS) at room temperature for the pressure P range of P ∼ 0–10 GPa are reported. A colossal ( ∼ 100 times) pressure-tuned improvement of æ is found for PbTe-based crystals under application of P ∼ 2–3 GPa. The employed high-pressure cell with synthetic diamond anvils is a model of a simple and effective TE device.
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72.80.Jc Other crystalline inorganic semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
62.50.-p High-pressure effects in solids and liquids

Resistance switching of copper doped MoOx films for nonvolatile memory applications

Dongsoo Lee, Dong-jun Seong, Inhwa Jo, F. Xiang, R. Dong, Seokjoon Oh, and Hyunsang Hwang

Appl. Phys. Lett. 90, 122104 (2007); http://dx.doi.org/10.1063/1.2715002 (3 pages) | Cited 39 times

Online Publication Date: 20 March 2007

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Nonvolatile and reversible resistance switching of copper doped MoOx film was studied. Hysteretic-type resistive switching was observed under dc. Reproducible resistance switching over 106 cycles was observed under alternative voltage pulses. Two resistance states can be maintained for 25 h at 85 °C. The authors proved that resistance switching might be strongly related with the rupture and generation of multifilaments confirmed by spreading resistance images of a conducting atomic force microscope as well as filamentary conduction by double logarithmic plots. Based on the x-ray photoelectron spectroscopy analysis, local conducting filaments could be formed by thermally diffused copper into MoOx film from the bottom electrode.
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73.61.Ng Insulators
66.30.J- Diffusion of impurities
79.60.Dp Adsorbed layers and thin films
68.37.Ps Atomic force microscopy (AFM)
84.30.Sk Pulse and digital circuits

Air-stable ambipolar organic transistors

Thomas D. Anthopoulos, G. C. Anyfantis, G. C. Papavassiliou, and Dago M. de Leeuw

Appl. Phys. Lett. 90, 122105 (2007); http://dx.doi.org/10.1063/1.2715028 (3 pages) | Cited 57 times

Online Publication Date: 20 March 2007

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The authors report on ambipolar organic transistors based on the soluble dithiolene derivative (diphenylethylenedithiolato)(1,3-dithiol-2-thione-4,5-dithiolato)nickel [Ni(dpedt)(dmit)]. Due to its small band gap, efficient injection of holes and electrons from gold source/drain electrodes is possible. Both carrier mobilities are estimated to be approximately equal with maximum value on the order of 10−4 cm2/V s. The transistors exhibit excellent ambient stability with a shelve lifetime exceeding 3 months. The pronounced stability of Ni(dpedt)(dmit) as well as of several other molecules studied here is correlated to their redox potential. The present findings can be used as a general guide towards design and synthesis of air-stable ambipolar/n-channel molecules.
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85.30.Pq Bipolar transistors
85.30.Tv Field effect devices

Enhanced charge-discharge characteristics of RuO2 supercapacitors on heat-treated TiO2 nanorods

Young Rack Ahn, Chong Rae Park, Seong Mu Jo, and Dong Young Kim

Appl. Phys. Lett. 90, 122106 (2007); http://dx.doi.org/10.1063/1.2715038 (3 pages) | Cited 5 times

Online Publication Date: 20 March 2007

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Electrochemical capacitors based on RuO2 were prepared onto electrospun TiO2 nanorods. Further heat treatment of the TiO2 at 800 °C under nitrogen was found to greatly improve the electrochemical performance of the RuO2 electrodes, especially at fast charge-discharge rates. The specific capacitance was found to decrease by only 33% when the scan rate increased from 10 to 1000 mV s−1 (from 687 to 460 F g−1). The characteristic response time of the RuO2 electrode was found to be 0.15 s when a heat-treated TiO2 substrate was used, which is 20 times better than that of the pristine TiO2 used.
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82.47.Uv Electrochemical capacitors; supercapacitors
84.32.Tt Capacitors
82.45.Fk Electrodes

Zeeman splitting in ballistic GaInAs/InP split-gate quantum point contacts

Th. Schäpers, V. A. Guzenko, and H. Hardtdegen

Appl. Phys. Lett. 90, 122107 (2007); http://dx.doi.org/10.1063/1.2715106 (3 pages) | Cited 9 times

Online Publication Date: 20 March 2007

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The Zeeman splitting in ballistic GaxIn1−xAs/InP split-gate point contacts was investigated. The measurements were performed in a magnetic field perpendicular to the plane of the two-dimensional electron gas. The Zeeman energy splitting between the one-dimensional subbands was determined by measuring the differential conductance as a function of the dc source-drain voltage across the point contact. The g factor of approximately 4.0 extracted from measurements at various magnetic fields agrees well to the value obtained by other methods for this type of heterostructure.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Carrier capture dynamics of InAs/GaAs quantum dots

T. Piwonski, I. O’Driscoll, J. Houlihan, G. Huyet, R. J. Manning, and A. V. Uskov

Appl. Phys. Lett. 90, 122108 (2007); http://dx.doi.org/10.1063/1.2715115 (3 pages) | Cited 19 times

Online Publication Date: 20 March 2007

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Carrier dynamics of a 1.3 μm InAs/GaAs quantum dot amplifier is studied using heterodyne pump-probe spectroscopy. Measurements of the recovery times versus injection current reveal a power law behavior predicted by a quantum dot rate equation model. These results indicate that Auger processes dominate the carrier dynamics.
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73.63.Kv Quantum dots
79.20.Fv Electron impact: Auger emission
42.55.Px Semiconductor lasers; laser diodes

Resonant tunneling diode with spin polarized injector

A. Slobodskyy, C. Gould, T. Slobodskyy, G. Schmidt, L. W. Molenkamp, and D. Sánchez

Appl. Phys. Lett. 90, 122109 (2007); http://dx.doi.org/10.1063/1.2715120 (3 pages) | Cited 10 times

Online Publication Date: 20 March 2007

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The authors investigate the current-voltage characteristics of a II-VI semiconductor resonant tunneling diode coupled to a diluted magnetic semiconductor injector. As a result of an external magnetic field, a giant Zeeman splitting develops in the injector, which modifies the band structure of the device, strongly affecting the transport properties. They find a large increase in peak amplitude accompanied by a shift of the resonance to higher voltages with increasing fields. They discuss a model which shows that the effect arises from a combination of three-dimensional incident distribution, giant Zeeman spin splitting, and broad resonance linewidth.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.75.Mm Spin polarized resonant tunnel junctions

Impacts of a polycrystalline-silicon buffer layer on the performance and reliability of strained n-channel metal-oxide-semiconductor field-effect transistors with SiN capping

Ching-Sen Lu, Horng-Chih Lin, Jian-Ming Huang, and Yao-Jen Lee

Appl. Phys. Lett. 90, 122110 (2007); http://dx.doi.org/10.1063/1.2715122 (3 pages) | Cited 1 time

Online Publication Date: 20 March 2007

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Characteristics of n-channel metal-oxide-semiconductor field-effect transistors with SiN capping were investigated in this work. Although the SiN capping could dramatically enhance the carrier mobility and thus the device drive current, the resistance to hot-carrier degradation is compromised as well, owing to the large amount of hydrogen contained in the SiN layer which may diffuse into the channel region during the process. To eliminate this shortcoming, the insertion of an ultrathin (10 nm) polycrystalline-silicon buffer layer between the gate and the SiN capping was proposed and demonstrated to restore the hot-carrier reliability of the devices without compromising the current enhancement due to the SiN capping.
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85.30.Tv Field effect devices

Nonvolatile polycrystalline silicon thin-film-transistor memory with oxide/nitride/oxide stack gate dielectrics and nanowire channels

Shih-Ching Chen, Ting-Chang Chang, Po-Tsun Liu, Yung-Chun Wu, Ping-Hung Yeh, Chi-Feng Weng, S. M. Sze, Chun-Yen Chang, and Chen-Hsin Lien

Appl. Phys. Lett. 90, 122111 (2007); http://dx.doi.org/10.1063/1.2715443 (3 pages) | Cited 8 times

Online Publication Date: 20 March 2007

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In this work, the authors study a polycrystalline silicon thin-film transistor (poly-Si TFT) with oxide/nitride/oxide (ONO) stack gate dielectrics and multiple nanowire channels for the applications of both nonvolatile silicon-oxide-nitride-oxide-silicon (SONOS) memory and switch transistor. The proposed device named as nanowire SONOS-TFT has superior electrical characteristics of a transistor such as on/off current ratio, threshold voltage (Vth), and subthreshold slope due to the good gate control ability originated from fringing electrical field effects. Moreover, the proposed device under adequate operation scheme can exhibit high program/erase efficiency and good retention time characteristics at high temperature.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Investigations of enhanced device characteristics in pentacene-based field effect transistors with sol-gel interfacial layer

T. Cahyadi, J. N. Tey, S. G. Mhaisalkar, F. Boey, V. R. Rao, R. Lal, Z. H. Huang, G. J. Qi, Z.-K. Chen, and C. M. Ng

Appl. Phys. Lett. 90, 122112 (2007); http://dx.doi.org/10.1063/1.2715030 (3 pages) | Cited 7 times

Online Publication Date: 22 March 2007

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Pentacene films grown on sol-gel silica dielectrics showed a significant enhancement in field effect mobility, threshold voltages, and subthreshold swings. This letter investigates the contributing factors for the enhanced device characteristics. The smoother and more hydrophobic film surfaces of sol-gel silica (rms roughness of ∼ 1.9 Å and water contact angle of ∼ 75°) induced larger pentacene grains, yielding mobilities in excess of ∼ 1 cm2/V s at an operating voltage of −20 V. Different sol-gel silica film thicknesses showed similar trends in improved performances, indicating that this phenomenon is clearly a semiconductor-dielectric interface phenomenon rather than a bulk dielectric effect.
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85.30.Tv Field effect devices

Spontaneous charge transfer at organic-organic homointerfaces to establish thermodynamic equilibrium

S. Duhm, H. Glowatzki, J. P. Rabe, N. Koch, and R. L. Johnson

Appl. Phys. Lett. 90, 122113 (2007); http://dx.doi.org/10.1063/1.2715042 (3 pages) | Cited 11 times

Online Publication Date: 22 March 2007

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The energy level alignment of α,ω-dihexylsexithienyl (DH6T) mono- and multilayers on tetrafluorotetracyanoquinodimethane (F4-TCNQ) precovered Ag(111) and polycrystalline Au substrates was investigated with ultraviolet photoelectron spectroscopy. For certain F4-TCNQ precoverages molecular level pinning at DH6T monolayer-multilayer homointerfaces was observed. The pinning behavior shows that thermodynamic equilibrium can be established across hexyl chains via charge transfer, indicating the limited use of these short alkyl chains for insulation in the field of molecular electronics.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Enhanced photocatalytic activity of Ag microgrid connected TiO2 nanocrystalline films

Feng Pan, Junying Zhang, Weiwei Zhang, Tianmin Wang, and Chao Cai

Appl. Phys. Lett. 90, 122114 (2007); http://dx.doi.org/10.1063/1.2715477 (3 pages) | Cited 7 times

Online Publication Date: 22 March 2007

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One reason for the high degree of photogenerated carrier recombination was found to be the charge accumulation caused by the uneven reaction area on the photocatalyst surface. The authors connected TiO2 nanoparticles with conducting Ag microgrid. Obvious photocatalytic activity improvement (81%) over the pure TiO2 was observed, which is attributed to the electron-hole pairs separation by the metal-semiconductor contact and the large specific area of metal grid, which increased the O2 absorption and transported the electrons to the sites needed for the deoxidize reactions. This structure lowers the electron accumulation on the particles and improves the utilization ratio of the photoexcited carriers.
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82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Ns Metal-nonmetal contacts
73.63.Bd Nanocrystalline materials
73.61.Le Other inorganic semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Reduced conductivity in the terahertz skin-depth layer of metals

N. Laman and D. Grischkowsky

Appl. Phys. Lett. 90, 122115 (2007); http://dx.doi.org/10.1063/1.2716066 (3 pages) | Cited 11 times

Online Publication Date: 23 March 2007

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The terahertz conductivities of plates of Cu and Al were measured to remain the same at 295 and 77 K using waveguide terahertz time domain spectroscopy (THz-TDS). This result was true for a variety of commercial alloys and surface preparations. Consequently, carrier scattering by lattice defects within the 100 nm THz skin depth is much larger than scattering by phonons at room temperature. However, an exception was found to be the THz skin-depth layer of an evaporated 300 nm Al film in contact with a polished Si surface. For this interface Al layer, the conductivity increased by a factor of 4 when cooled to 77 K.
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72.30.+q High-frequency effects; plasma effects

Lateral epitaxial overgrowth of aluminum nitride on patterned silicon carbide substrates by hydride vapor phase epitaxy

Derrick S. Kamber, Yuan Wu, Edward Letts, Steven P. DenBaars, James S. Speck, Shuji Nakamura, and Scott A. Newman

Appl. Phys. Lett. 90, 122116 (2007); http://dx.doi.org/10.1063/1.2716068 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2007

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This letter reports on the reduction of threading dislocation densities in AlN films via lateral epitaxial overgrowth by hydride vapor phase epitaxy. A variety of different stripe patterns were used to produce fully coalesced AlN films. Transmission electron microscopy (TEM) was used to assess the structural quality of these films. TEM determined that the dislocation density in the laterally grown wing regions was less than 8.3×106 cm−2 as compared to 1.8×109 cm−2 in the seed regions. Atomic force microscopy revealed that the films have a smooth surface morphology with a rms roughness of 0.71 nm over 10×10 μm2 sampling areas.
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81.05.Dz II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
68.37.Ps Atomic force microscopy (AFM)

Current-induced asymmetric I-V behavior of La0.82Ca0.18MnO3 thin films and its tunability

Y. H. Sun, Y. G. Zhao, and C. M. Xiong

Appl. Phys. Lett. 90, 122117 (2007); http://dx.doi.org/10.1063/1.2716307 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2007

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Asymmetric I-V behaviors induced by large currents in La0.82Ca0.18MnO3 (LCMO) films are studied. The contribution of LCMO to the asymmetric I-V behaviors is demonstrated by eliminating the contribution of the LCMO/electrode interface. The asymmetric I-V behaviors of LCMO can be tuned by the negative voltage pulse and positive current excitations between two resistive states. A band bending model based on the local oxygen electromigration at the grain boundaries of LCMO is proposed to account for the results. This work is helpful for understanding the mechanism of the current effect on manganites and also its applications.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
66.30.Qa Electromigration
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Mm Grain and twin boundaries

Simultaneous measurement of potential and dopant atom distributions on wet-prepared Si(111):H surfaces by scanning tunneling microscopy

M. Nishizawa, L. Bolotov, and T. Kanayama

Appl. Phys. Lett. 90, 122118 (2007); http://dx.doi.org/10.1063/1.2716837 (3 pages) | Cited 11 times

Online Publication Date: 23 March 2007

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The authors demonstrate the ability of scanning tunneling microscopy and spectroscopy to simultaneously measure the distributions of both the surface potential and the individual dopant atoms on the atomically flat hydrogen-terminated Si(111) surfaces prepared by an aqueous NH4F etching without disturbing the original dopant distribution. At the p-n junctions, the acceptor and donor atoms were detected distinctly, and the variation in the observed height reflected the surface potential under the biasing condition. Further, a strong correlation between the dopant fluctuations and the surface potential distributions was identified.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.uf Ge and Si
61.72.S- Impurities in crystals
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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