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25 Jun 2007

Volume 90, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 90, 262501 (2007); http://dx.doi.org/10.1063/1.2752015 (3 pages)

Ian Appelbaum and Douwe J. Monsma
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Anharmonic behavior in microwave-driven resistivity oscillations in Hall bars

Jesús Iñarrea

Appl. Phys. Lett. 90, 262101 (2007); http://dx.doi.org/10.1063/1.2751585 (3 pages) | Cited 13 times

Online Publication Date: 25 June 2007

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The authors analyzed the magnetoresistivity of a two-dimensional electron system excited by microwave radiation in a regime of high intensities and low frequencies. In such a regime, recent experiments show that different features appear in the magnetoresistivity response which suggest an anharmonic behavior. These features consist mainly of distorted oscillations and new resonance peaks at the subharmonics of the cyclotron frequency. They follow the model of microwave-driven electron orbit motions which become anharmonic when the ratio of microwave intensity to microwave frequency is large enough.
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72.30.+q High-frequency effects; plasma effects
73.63.-b Electronic transport in nanoscale materials and structures

Microphotoreflectance spectroscopy of heterojunction bipolar transistors under biasing voltage: Measurement of the net doping concentration

Houssam Chouaib and Catherine Bru-Chevallier

Appl. Phys. Lett. 90, 262102 (2007); http://dx.doi.org/10.1063/1.2751591 (3 pages) | Cited 3 times

Online Publication Date: 25 June 2007

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The authors present a microphotoreflectance (micro-PR) spectroscopic study of a biased InGaAlAs/GaAsSb/InP heterojunction bipolar transistor. Franz Keldysh oscillations from an InGaAlAs emitter are studied as a function of the static biasing voltage applied to the emitter-base junction. The electric field value from the InGaAlAs emitter is decreasing under direct biasing voltage. The change in electric field value is shown to be in good agreement within the expected operation of forward biased junction, and making possible a straight measurement of the net doping concentration. Results show the feasibility of a micro-PR spectroscopy analysis of devices under operation.
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85.30.Pq Bipolar transistors

Molecular-based light-activated thyristor

Toshifumi Iimori, Nobuhiro Ohta, and Toshio Naito

Appl. Phys. Lett. 90, 262103 (2007); http://dx.doi.org/10.1063/1.2749845 (3 pages) | Cited 10 times

Online Publication Date: 25 June 2007

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A photoinduced electrical conductivity switching is observed in the molecular conductor of α-[bis(ethylenedithio)tetrathiafulvalene]2I3 at different temperatures with different irradiation light intensities. The threshold voltage for the differential-negative-resistance effect appearing in the current-voltage characteristic curve decreases and increases, respectively, as the light intensity is increased and as the temperature decreases below the insulator-metal phase transition. The potential application of molecular conductor in bidirectional light-activated thyristor devices is demonstrated.
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85.65.+h Molecular electronic devices
85.60.-q Optoelectronic devices

Ambipolar field-effect transistor based on organic-inorganic hybrid structure

Hajime Nakanotani, Masayuki Yahiro, Chihaya Adachi, and Koki Yano

Appl. Phys. Lett. 90, 262104 (2007); http://dx.doi.org/10.1063/1.2752023 (3 pages) | Cited 13 times

Online Publication Date: 26 June 2007

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The authors developed an ambipolar field-effect transistor (FET) based on an organic-inorganic hybrid structure that consisted of an indium zinc oxide and pentacene double layer fabricated on a SiO2/n++-Si substrate. Although the FETs based on an indium zinc oxide or pentacene single layer only showed unipolar FET characteristics, the hybrid FET showed definite ambipolar FET characteristics. The authors obtained a highly saturated field-effect hole and electron mobilities of 0.14 and 13.8 cm2/V s. Furthermore, the authors demonstrated electroluminescence from hybrid FETs using tetracene as an emitting layer. The authors’ success shows that the hybridization of organic and inorganic materials opens up a new field in electronics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

14 MHz organic diodes fabricated using photolithographic processes

Yuming Ai, Srinivas Gowrisanker, Huiping Jia, Isaac Trachtenberg, Eric Vogel, Robert M. Wallace, Bruce E. Gnade, Raymond Barnett, Harvey Stiegler, and Hal Edwards

Appl. Phys. Lett. 90, 262105 (2007); http://dx.doi.org/10.1063/1.2752533 (3 pages) | Cited 15 times

Online Publication Date: 26 June 2007

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Organic semiconductor-based Schottky diodes operating at 14 MHz, fabricated using conventional photolithographic and etching processes, have been demonstrated. Copper phthalocyanine is the semiconductor, with gold and aluminum as the Ohmic and Schottky contacts, respectively. The organic diode based rectifier circuit generated a dc output voltage of approximately 2 V at 14 MHz, using an input ac signal with a zero-to-peak voltage amplitude of 5 V. These devices showed little degradation under continuous ac voltage stress when operated in vacuum.
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85.30.Kk Junction diodes
85.40.Hp Lithography, masks and pattern transfer

Improvements in the device characteristics of amorphous indium gallium zinc oxide thin-film transistors by Ar plasma treatment

Jin-Seong Park, Jae Kyeong Jeong, Yeon-Gon Mo, Hye Dong Kim, and Sun-Il Kim

Appl. Phys. Lett. 90, 262106 (2007); http://dx.doi.org/10.1063/1.2753107 (3 pages) | Cited 99 times

Online Publication Date: 26 June 2007

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The effect of Ar plasma treatment on amorphous indium gallium zinc oxide (a-IGZO) thin films was investigated. The net electron carrier concentration (1020–1021 cm−3) of the a-IGZO thin films dramatically increased upon their exposure to the Ar plasma compared to that (1014 cm−3) of the as-deposited thin film. The authors attempted to reduce the contact resistance between the Pt/Ti (source/drain electrode) and a-IGZO (channel) by using the Ar plasma treatment. Without the treatment, the a-IGZO thin film transistors (TFTs) with W/L = 50/4 μm exhibited a moderate field-effect mobility (μFE) of 3.3 cm2/V s, subthreshold gate swing (S) of 0.25 V/decade, and Ion/off ratio of 4×107. The device performance of the a-IGZO TFTs was significantly improved by the Ar plasma treatment. As a result, an excellent S value of 0.19 V/decade and high Ion/off ratio of 1×108, as well as a high μFE of 9.1 cm2/V s, were achieved for the treated a-IGZO TFTs.
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85.30.Tv Field effect devices
73.40.Cg Contact resistance, contact potential
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Jc Amorphous semiconductors; glasses

Polymer functionalized piezoelectric-FET as humidity/chemical nanosensors

Chang Shi Lao, Qin Kuang, Zhong L. Wang, Myung-Chul Park, and Yulin Deng

Appl. Phys. Lett. 90, 262107 (2007); http://dx.doi.org/10.1063/1.2748097 (3 pages) | Cited 32 times

Online Publication Date: 27 June 2007

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By coating one side of the surface of a ZnO nanobelt (NB) with multilayer polymers using an electrostatic self-assembling process, a humidity/chemical nanosensor based on piezoelectric field effect transistor (PE-FET) is demonstrated. The working principle of the PE-FET relies on the self-contraction/expansion of the polymer, which builds up a strain in the piezoelectric NB and induces a potential drop across the NB that serves as the gate voltage for controlling the current flowing through the NB. The response of PE-FET to the phase transition of the coating polymer was also demonstrated. The device is a component for nanopiezotronics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.35.-p Nanoelectronic devices

Graphitization of polymer surfaces by low-energy ion irradiation

I. Lazareva, Y. Koval, M. Alam, S. Strömsdörfer, and P. Müller

Appl. Phys. Lett. 90, 262108 (2007); http://dx.doi.org/10.1063/1.2752738 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2007

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The surface of several polymers was graphitized by low-energy ion irradiation. Their conducting properties were studied as a function of the energy of the ions and the irradiation temperature. It was found that at rather modest ion energies ( ∼ 1000 eV) and irradiation temperatures (<400 °C), polymer surfaces transform to a graphitized state. The graphitized layer consists of overlapping graphite islands with a diameter of 1–3 nm and exhibits a semimetallic conductivity. Gradually reducing the energy of the ions and the irradiation temperature, the authors observed a transition from semimetallic to variable range hopping conductivity.
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68.47.Mn Polymer surfaces
68.35.Rh Phase transitions and critical phenomena
72.20.Ee Mobility edges; hopping transport
72.60.+g Mixed conductivity and conductivity transitions
61.82.Pv Polymers, organic compounds
61.80.Jh Ion radiation effects

Defect generation at the Si–SiO2 interface following corona charging

Hao Jin, K. J. Weber, N. C. Dang, and W. E. Jellett

Appl. Phys. Lett. 90, 262109 (2007); http://dx.doi.org/10.1063/1.2749867 (3 pages) | Cited 7 times

Online Publication Date: 28 June 2007

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A combination of capacitance-voltage and lifetime decay measurements is used to show that corona biasing of silicon oxidized samples results in the generation of additional interface defects and an increase in surface recombination. The onset of interface degradation occurs at relatively low electric fields, estimated to be less than ∼ +/−1.2 MV/cm. The majority of the defects generated by corona biasing can be removed by a short annealing at 400 °C. The results are consistent with the hypothesis that atomic hydrogen is chiefly responsible for the observed degradation. Corona biasing, even at low electric fields, cannot be relied on as a noninvasive characterization tool.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
81.65.Rv Passivation

Evidence of electron accumulation at nonpolar surfaces of InN nanocolumns

E. Calleja, J. Grandal, M. A. Sánchez-García, M. Niebelschütz, V. Cimalla, and O. Ambacher

Appl. Phys. Lett. 90, 262110 (2007); http://dx.doi.org/10.1063/1.2749871 (3 pages) | Cited 37 times

Online Publication Date: 28 June 2007

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High-quality InN nanocolumns grown by molecular beam epitaxy on n-type Si(111) have been electrically characterized by atomic force microscopy. Current-voltage characteristics were measured on InN nanocolumns with similar heights but different diameters. The conductivity scales the nanocolumns reciprocal diameter, pointing to the nanocolumn lateral surface as the main conduction path. These results, opposing those found in undoped GaN nanocolumns where the conductivity is rather independent of the diameter (conduction through the volume), agree well with a model that predicts electron accumulation by Fermi level pinning within the conduction band on nonpolar (m plane) InN surfaces reconstructed under In-rich conditions.
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73.63.Bd Nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states

Direct observation of relaxation dynamics of spin-polarized electrons excited at a higher-energy spin-split subband in a diluted magnetic semiconductor quantum well

K. Saito, J. H. Park, I. Souma, Y. Oka, and A. Murayama

Appl. Phys. Lett. 90, 262111 (2007); http://dx.doi.org/10.1063/1.2753091 (3 pages) | Cited 2 times

Online Publication Date: 28 June 2007

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The authors observe relaxation dynamics of spin-polarized electrons excited at a higher-energy spin-split subband in a diluted magnetic semiconductor quantum well by means of pump-probe absorption spectroscopy. Time dependences of the circularly polarized saturated absorbance directly show the relaxation of spin-polarized electrons, which is inaccessible by photoluminescence. The probe-energy dependence of the relaxation time is obtained ranging from 2 to 100 ps at 2.5 T within the absorption band. This dependence is systematically explained by both the intraband energy relaxation of the spin-polarized electrons and the subsequent electron-spin relaxation that is modified by effects of the exciton localization.
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73.63.Hs Quantum wells
78.67.De Quantum wells
72.25.Dc Spin polarized transport in semiconductors
75.50.Pp Magnetic semiconductors
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena

Defect reduction in GaN epilayers grown by metal-organic chemical vapor deposition with in situ SiNx nanonetwork

Jinqiao Xie, Serguei A. Chevtchenko, Ümit Özgür, and Hadis Morkoç

Appl. Phys. Lett. 90, 262112 (2007); http://dx.doi.org/10.1063/1.2753096 (3 pages) | Cited 4 times

Online Publication Date: 28 June 2007

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Line and point defect reductions in thin GaN epilayers with single and double in situ SiNx nanonetworks on sapphire substrates grown by metal-organic chemical vapor deposition were studied by deep-level transient spectroscopy (DLTS), augmented by x-ray diffraction (XRD), and low temperature photoluminescence (PL). All samples measured by DLTS in the temperature range from 80 to 400 K exhibited trap A (peak at ∼ 325 K) with an activation energy of 0.55–0.58 eV, and trap B (peak at ∼ 155 K) with an activation energy of 0.21–0.28 eV. The concentrations of both traps were much lower for layers with SiNx nanonetwork compared to the reference sample. The lowest concentration was achieved for the sample with 6 min deposition SiNx nanonetwork, which was also lower than that for a sample prepared by conventional epitaxial lateral overgrowth. In concert with the DLTS results, PL and XRD linewidths were reduced for the samples with SiNx network indicating improved material quality. Consistent trend among optical, structural, and DLTS results suggests that SiNx network can effectively reduce both point and line defects.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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