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12 Nov 2007

Volume 91, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 203501 (2007); http://dx.doi.org/10.1063/1.2806922 (3 pages)

Michael N. Feiginov and Dibakar Roy Chowdhury
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An optically controlled phase shifter employing the organic semiconductor poly(3-hexylthiophene)

Hongyan Tang, R. S. Donnan, and T. Kreouzis

Appl. Phys. Lett. 91, 202101 (2007); http://dx.doi.org/10.1063/1.2806936 (3 pages)

Online Publication Date: 12 November 2007

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The transmission characteristics of optically controlled phase shifters employing the organic semiconductor poly(3-hexylthiophene) (P3HT) are reported. Two microstrip structures were fabricated onto a P3HT coated indium tin oxide substrate supported by glass. Experimental results on these unoptimized prototype structures yield reversible differential phase shifts >10° at 2.0 GHz under tens of milliwatt optical power illumination. These devices demonstrate great potential as linear analog phase shifters.
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42.79.-e Optical elements, devices, and systems

A comparative study of the electronic structures of oxygen- and chlorine-treated nitrogenated carbon nanotubes by x-ray absorption and scanning photoelectron microscopy

S. C. Ray, C. W. Pao, H. M. Tsai, J. W. Chiou, W. F. Pong, C. W. Chen, M.-H. Tsai, P. Papakonstantinou, L. C. Chen, and K. H. Chen

Appl. Phys. Lett. 91, 202102 (2007); http://dx.doi.org/10.1063/1.2807275 (3 pages) | Cited 4 times

Online Publication Date: 13 November 2007

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The electronic structures and bonding properties of oxygen- and chlorine-treated nitrogenated carbon nanotubes (N-CNTs) were studied using x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy. Features in the C K-edge XANES spectra are shifted by ∼ 0.3 eV toward higher energies and by ∼ 1.1 eV toward lower energies relatively to those of the more symmetrical pyridinelike and graphitelike structured N-CNTs upon chlorination and oxidation, respectively. Increases in N K-edge XANES intensities for both chlorination and oxidation reveal substitution of C–C bonds by C–N bonds consistent with the observed valence-band photoemission spectra of the decrease of the C 2s bond and the increase of the N 2s bond.
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71.20.Tx Fullerenes and related materials; intercalation compounds
78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures

Migration volume for polaron dielectric relaxation in disordered materials

A. N. Papathanassiou, I. Sakellis, and J. Grammatikakis

Appl. Phys. Lett. 91, 202103 (2007); http://dx.doi.org/10.1063/1.2812538 (3 pages) | Cited 10 times

Online Publication Date: 13 November 2007

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A theoretical study of the influence of pressure on the dielectric relaxation related with polaron tunneling and phonon-assisted hopping in disordered solids is developed. The sign and absolute value of the migration volume, which is obtained by employing the present formulation, evidence the nature of the relaxation. As a paradigm, positive and negative values of migration volume are evaluated by analyzing recently published dielectric loss measurements under pressure in semiconducting polypyrrole. A straightforward relation between the value of the migration volume and the nature of short-range polaron flow and the size of polaron distortion is revealed.
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77.84.Jd Polymers; organic compounds
77.22.Gm Dielectric loss and relaxation
71.38.-k Polarons and electron-phonon interactions

Acceptor, compensation, and mobility profiles in multiple Al implanted 4H‐SiC

F. Giannazzo, F. Roccaforte, and V. Raineri

Appl. Phys. Lett. 91, 202104 (2007); http://dx.doi.org/10.1063/1.2813022 (3 pages) | Cited 15 times

Online Publication Date: 13 November 2007

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In this letter, we studied the effect of the annealing temperature (from 1400 to 1650 °C) on the acceptor, compensation, and mobility depth profiles in 4H‐SiC implanted with multiple energy (40–550 keV) and medium dose (1×1013 cm−2) Al ions. Scanning capacitance microscopy and scanning spreading resistance microscopy were jointly used to determine those depth profiles with nanometric resolution. It was demonstrated that the electrical activation in the Al implanted layer at increasing annealing temperatures was the result of a counterbalance between the increase in the acceptor concentration and the decrease in the percentage compensation.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing
07.79.-v Scanning probe microscopes and components

Strained SiGeSn formed by Sn implant into SiGe and pulsed laser annealing

Grace Huiqi Wang, Eng-Huat Toh, Xincai Wang, Sudhiranjan Tripathy, Thomas Osipowicz, Taw Kuei Chan, Keat-Mun Hoe, Subramaniam Balakumar, Guo-Qiang Lo, Ganesh Samudra, and Yee-Chia Yeo

Appl. Phys. Lett. 91, 202105 (2007); http://dx.doi.org/10.1063/1.2803853 (3 pages) | Cited 7 times

Online Publication Date: 13 November 2007

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Incorporation of tin (Sn) in substitutional sites in strained Si0.75Ge0.25 was demonstrated by Sn implant and pulsed laser annealing. The surface of Si0.75Ge0.25 was amorphized by Sn implant but was recrystallized after pulsed laser annealing. The crystalline Si1−x−yGexSny layer formed was studied by Rutherford backscattering spectrometry and Raman spectroscopy. A substitutionality up to 62% Sn and 80% Ge was obtained at an optimal laser power of 400 mJ cm−2 for five laser pulses. A compressive strain of −1.15% was also obtained due to Sn incorporation. The presence of Sn also increased the active B dopant concentration in activating Si1−x−yGexSny to give low sheet resistance. The implantation of Sn and B followed by pulsed laser annealing could be useful for application in strain engineering of high mobility metal-oxide-semiconductor field-effect transistors.
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61.72.Cc Kinetics of defect formation and annealing
81.15.Fg Pulsed laser ablation deposition
61.72.uf Ge and Si

Large surface-state conductivity in ultrathin Bi films

T. Hirahara, I. Matsuda, S. Yamazaki, N. Miyata, S. Hasegawa, and T. Nagao

Appl. Phys. Lett. 91, 202106 (2007); http://dx.doi.org/10.1063/1.2813613 (3 pages) | Cited 26 times

Online Publication Date: 14 November 2007

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In situ microscopic-four-point probe conductivity measurements were performed for ultrathin Bi films on Si(111)-7×7. From the extrapolation of thickness-dependent conductivity and decrease in conductivity through surface oxidization, we found clear evidence of large surface-state conductivity (σSS ∼ 1.5×10−3 Ω−1/◻ at room temperature) in Bi(001) films. For the thinnest films ( ∼ 25 Å), the transport properties are dominated by the highly inert surface states that are Rashba spin-split, and this suggests the possibility of using these Bi surface states for spintronics device application.
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73.61.At Metal and metallic alloys
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
68.47.Fg Semiconductor surfaces
81.65.Mq Oxidation

Large negative magnetoresistance in Ge films at ultralow temperatures and low magnetic fields

V. F. Mitin, V. K. Dugaev, and G. G. Ihas

Appl. Phys. Lett. 91, 202107 (2007); http://dx.doi.org/10.1063/1.2813615 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2007

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Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resistance thermometers, at temperatures below 0.2 K and magnetic fields below 1 T. This effect is very sensitive to temperature. At T<0.3 K, the magnetoresistance is negative, and its magnitude increases with decreasing temperature. At 0.03 K, the resistance strongly decreases (up to 100 times) when the magnetic field is increased from 0 to 1 T and then saturates in higher fields. We discuss the mechanisms of this phenomenon and present results of calculations involving the hopping theory of conductivity with localization corrections.
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73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Influence of the electrode work function on the energy level alignment at organic-organic interfaces

Slawomir Braun, Michel P. de Jong, Wojciech Osikowicz, and William R. Salaneck

Appl. Phys. Lett. 91, 202108 (2007); http://dx.doi.org/10.1063/1.2806938 (3 pages) | Cited 22 times

Online Publication Date: 15 November 2007

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The energy level alignment at interfaces, in stacks comprising of (4,4′-N,N′-dicarbazolyl-biphenyl) (CBP), (4,4,4″-tris[3-methyl-phenyl(phenyl)amino]-triphenylamine) (m-MTDATA), and a conductive substrate, has been studied. We show that the alignment of energy levels depends on the equilibration of the chemical potential throughout the layer stack, while any electronic coupling between the individual layers is of lesser importance. This behavior is expected to occur for a broad class of weakly interacting interfaces and can have profound consequences for the design of organic electronic devices.
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73.30.+y Surface double layers, Schottky barriers, and work functions

InN-based anion selective sensors in aqueous solutions

Yen-Sheng Lu, Chi-Cheng Huang, J. Andrew Yeh, Chi-Fan Chen, and Shangjr Gwo

Appl. Phys. Lett. 91, 202109 (2007); http://dx.doi.org/10.1063/1.2814035 (3 pages) | Cited 12 times

Online Publication Date: 15 November 2007

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We demonstrate that indium nitride (InN) can be used as ion selective electrode (ISE) for anion concentration measurements. The InN ISE reveals remarkable selectivity, response time, signal stability, and repeatability for chlorine and hydroxyl ions. The selective interaction of Lewis bases in solutions with the N-polarity InN epitaxial layer grown on silicon is confirmed by potentiometric responses. The Helmholtz potential of the InN ISE, generated at the InN/solution interface, satisfies the Nernst equation. The observation of anion attraction to the InN surface further demonstrates the existence of donor-type surface states on InN.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Charge storage characteristics of Au nanocrystals embedded in high-k gate dielectrics on Si

Chen-Chan Wang, Jyun-Yi Wu, Yan-Kai Chiou, Che-Hao Chang, and Tai-Bor Wu

Appl. Phys. Lett. 91, 202110 (2007); http://dx.doi.org/10.1063/1.2804567 (3 pages) | Cited 16 times

Online Publication Date: 15 November 2007

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The charge storage characteristics of metal-oxide-semiconductor structures containing Au nanocrystals in atomic-layer-deposited high-k gate dielectrics were studied. Cross-sectional high-resolution transmission electron microscopy reveals that the Au nanocrystals are self-assembled in the high-k dielectric matrix after high temperature annealing in N2 ambient. The memory effect was observed from capacitance-voltage (C-V) relations and a satisfactory charge retention characteristic was obtained in the sample using Al2O3 as the gate dielectric than in the one using Hf2AlOx. Moreover, a saturation of electron storage in the metal-oxide-semiconductor capacitors was also observed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
81.16.Dn Self-assembly
61.46.Hk Nanocrystals
81.05.Bx Metals, semimetals, and alloys

Deep levels and carrier compensation in V-doped semi-insulating 4H-SiC

N. T. Son, P. Carlsson, A. Gällström, B. Magnusson, and E. Janzén

Appl. Phys. Lett. 91, 202111 (2007); http://dx.doi.org/10.1063/1.2814058 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2007

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Electron paramagnetic resonance was used to study semi-insulating (SI) 4H-SiC substrates doped with vanadium (V) in the range of 5.5×1015–1.1×1017 cm−3. Our results show that the electrical activation of V is low and hence only in heavily V-doped 4H-SiC, vanadium is responsible for the SI behavior, whereas in moderately V-doped substrates, the SI properties are thermally unstable and determined by intrinsic defects. We show that the commonly observed thermal activation energy Ea ∼ 1.1 eV in V-doped 4H–SiC may be related to deep levels of the carbon vacancy.
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76.30.Lh Other ions and impurities
71.55.-i Impurity and defect levels

Effect of Yb concentration on the resistivity and lifetime of CdTe:Ge:Yb codoped crystals

N. V. Sochinskii, M. Abellán, J. Rodríguez-Fernández, E. Saucedo, C. M. Ruiz, and V. Bermúdez

Appl. Phys. Lett. 91, 202112 (2007); http://dx.doi.org/10.1063/1.2815644 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2007

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The resistivity and electron lifetime of CdTe:Ge:Yb crystals are reported, demonstrating that the effect of Yb concentration is crucial for accurate electrical compensation. It is also demonstrated that the codoping of CdTe with Ge as deep donor and with Yb as rare-earth element could be a promising way to obtain semiinsulating CdTe crystals with good transport properties. High resistivity (5×109 Ω cm) and lifetime (9 μs) were obtained, thus confirming the beneficial effect of rare-earth doping.
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72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Water passivation effect on polycrystalline silicon nanowires

Horng-Chih Lin, Chun-Jung Su, Cheng-Yun Hsiao, Yuh-Shyong Yang, and Tiao-Yuan Huang

Appl. Phys. Lett. 91, 202113 (2007); http://dx.doi.org/10.1063/1.2814033 (3 pages) | Cited 6 times

Online Publication Date: 16 November 2007

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Defects present in the grain boundaries of polycrystalline materials are known to impede carrier transport inside the materials, and the electronic device performance having such materials as active channels will be adversely affected. In this work, dramatic improvement in device performance was observed as field-effect transistors with polycrystalline silicon nanowire (poly-SiNW) channels were exposed to a wet environment. Passivation of defects in the poly-SiNW by H+ and/or OH− contained in the aqueous solution is proposed to explain the phenomenon.
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85.30.Tv Field effect devices

Imaging spatial distributions of laser-induced charge and spin in GaAs/AlGaAs two-dimensional electron gas by pump-probe second harmonic generation

Yibo Han, Si Xiao, Hongming Zhao, Hanchao Gao, G. G. Xiong, and Q. Q. Wang

Appl. Phys. Lett. 91, 202114 (2007); http://dx.doi.org/10.1063/1.2815651 (3 pages)

Online Publication Date: 16 November 2007

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We report the spatial intensity distributions of the laser-induced charge and spin polarizations in GaAs/AlGaAs two-dimensional electron gas (2DEG) detected by using second harmonic generation (SHG) imaging technique. The spin polarized electrons in the 2DEG are pumped by a single linear polarized laser beam and probed by another beam which produces reflective SHG. By comparing the images of SHG probed with left- and right-circular polarized laser beams, the spatial distributions of the effective charge and spin polarizations in the 2DEG sample are mapped out.
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72.25.Dc Spin polarized transport in semiconductors

Resistive memory switching in epitaxially grown NiO

S. R. Lee, K. Char, D. C. Kim, R. Jung, S. Seo, X. S. Li, G.-S. Park, and I. K. Yoo

Appl. Phys. Lett. 91, 202115 (2007); http://dx.doi.org/10.1063/1.2815658 (3 pages) | Cited 26 times

Online Publication Date: 16 November 2007

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Epitaxial NiO films have been fabricated on SrRuO3 films prepared on SrTiO3 single-crystal substrates. The x-ray diffraction spectra and transmission electron microscopy confirm the epitaxial growth of NiO with atomically flat surfaces on the SRO electrode. The I-V measurements of epitaxial NiO show the resistive memory switching behavior with a change in the polarity of the voltage bias, in contrast with the switching behavior of polycrystalline NiO by a single polarity. The I-V characteristics of epitaxial NiO prepared under various synthesis conditions and electrodes are presented, which suggests an important role of interfaces between NiO and electrodes on the resistive switching behavior.
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73.61.-r Electrical properties of specific thin films

Structural investigation of nitrided c-sapphire substrate by grazing incidence x-ray diffraction and transmission electron microscopy

Hyo-Jong Lee, Jun-Seok Ha, S. W. Lee, H. J. Lee, H. Goto, S. H. Lee, M. W. Cho, T. Yao, T. Minegishi, T. Hanada, Soon-Ku Hong, Osami Sakata, Jae Wook Lee, and Jeong Yong Lee

Appl. Phys. Lett. 91, 202116 (2007); http://dx.doi.org/10.1063/1.2815919 (3 pages) | Cited 1 time

Online Publication Date: 16 November 2007

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A grazing incidence x-ray diffraction with a synchrotron radiation and a cross-sectional high-resolution transmission electron microscopy were performed on the sapphire surface nitrided at 1080 °C for 30 min. The thickness of the nitrided layer was about 2 nm. It was found out that the wurtzite, zinc-blende, and 30° rotated zinc-blende aluminum nitrides were formed on the sapphire surface. The 30° rotated zb-AlN formed the incoherent interface and has higher activation energy of formation, while the nonrotated zb-AlN formed the coherent interface.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
61.66.Fn Inorganic compounds

Strain-induced transconductance enhancement by pattern dependent oxidation in silicon nanowire field-effect transistors

A. Seike, T. Tange, Y. Sugiura, I. Tsuchida, H. Ohta, T. Watanabe, D. Kosemura, A. Ogura, and I. Ohdomari

Appl. Phys. Lett. 91, 202117 (2007); http://dx.doi.org/10.1063/1.2812577 (3 pages) | Cited 7 times

Online Publication Date: 16 November 2007

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Transconductance (gm) enhancement in n-type and p-type nanowire field-effect-transistors (nwFETs) is demonstrated by introducing controlled tensile strain into channel regions by pattern dependent oxidation (PADOX). Values of gm are enhanced relative to control devices by a factor of 1.5 in p-nwFETs and 3.0 in n-nwFETs. Strain distributions calculated by a three-dimensional molecular dynamics simulation reveal predominantly horizontal tensile stress in the nwFET channels. The Raman lines in the strain controlled devices display an increase in the full width at half maximum and a shift to lower wavenumber, confirming that gm enhancement is due to tensile stress introduced by the PADOX approach.
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85.30.Tv Field effect devices
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