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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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Two photon absorption in quantum dot-in-a-well infrared photodetectors

P. Aivaliotis, E. A. Zibik, L. R. Wilson, J. W. Cockburn, M. Hopkinson, and N. Q. Vinh

Appl. Phys. Lett. 92, 023501 (2008); http://dx.doi.org/10.1063/1.2833691 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2008

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Two photon absorption processes in InAs/In01.5Ga0.85As/GaAs quantum dot-in-a-well photodetectors are studied using free electron laser excitation. Two photon induced, normal incidence photocurrent, observed in the range of 20–30 μm, arises from sequential near-resonant two-step transitions involving electron ground to first excited states in the dot, to quantum well final states. We find a two photon absorption coefficient of β ∼ 1×107 cm/GW at 26.5 μm (47 meV) and 0.8 V applied bias. Second-order autocorrelation measurements exhibit two characteristic time constants of ∼ 3 and ∼ 40 ps. The latter is associated with the intermediate state electron lifetime, whereas the short decay is explained by the involvement of acoustic phonon assisted transitions.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Electrical behavior of zinc oxide layers grown by low temperature atomic layer deposition

N. Huby, S. Ferrari, E. Guziewicz, M. Godlewski, and V. Osinniy

Appl. Phys. Lett. 92, 023502 (2008); http://dx.doi.org/10.1063/1.2830940 (3 pages) | Cited 35 times

Online Publication Date: 14 January 2008

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We report on the electrical properties of thin film transistors based on zinc oxide (ZnO) layers grown by low temperature (100–170 °C) atomic layer deposition. As evidenced through Hall effect measurements, a drastic decrease of the carrier concentration occurred for ZnO films grown at 100 °C. Time of flight–secondary ions mass spectroscopy analysis revealed that this decrease is associated with an increase of the hydroxide groups in the ZnO layer which suppressed oxygen vacancy formation. Transistors fabricated from ZnO films grown at 100 °C exhibit a high Ion/Ioff ratio ( ∼ 107) and an encouraging intrinsic channel mobility ( ∼ 1 cm2/V s).
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.30.Tv Field effect devices

Experimental study of the minimum metal gate thickness required to fix the effective work function in metal-oxide-semiconductor capacitors

F. Fillot, S. Maîtrejean, I. Matko, and B. Chenevier

Appl. Phys. Lett. 92, 023503 (2008); http://dx.doi.org/10.1063/1.2833697 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2008

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We have investigated the dependence of the effective work function (EWF) of a poly-p+/TiN/SiO2/Si capacitor as a function of the TiN layer thickness. By using a pulsing chemical vapor deposition process, the nitride layer was demonstrated to be continuous from 2.2 nm. It was also shown that the EWF of capacitors, made with TiN layer thickness ranging between 2.2 and 7.1 nm, is independent of the thickness and similar to that of bulk TiN. Our study indicates that the EWF of the entire gate electrode stack is determined by the first metallic monolayers (<2.2 nm) in contact with the gate dielectric.
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84.32.Tt Capacitors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High-efficiency hole extraction/electron-blocking layer to replace poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) in bulk-heterojunction polymer solar cells

Alexander W. Hains and Tobin J. Marks

Appl. Phys. Lett. 92, 023504 (2008); http://dx.doi.org/10.1063/1.2834697 (3 pages) | Cited 48 times

Online Publication Date: 14 January 2008

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An anode interfacial layer is reported for bulk-heterojunction (BHJ) polymer solar cells to replace the commonly used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). A poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB)+4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2) blend is crosslinked, forming robust ∼ 10 nm thick films covalently bound to indium tin oxide, which transport holes while blocking misdirected electrons. The thermal stability and photovoltaic performance metrics of TFB:TPDSi2-modified BHJ cells are significantly greater than those of cells fabricated in parallel with PEDOT:PSS or with no interfacial layer. For a poly[2-methoxy-5-(3′,7′-dimethyloctyloxyl]-1,4-phenylene vinylene: methanofullerene[6 6]-phenyl C61-butyric acid methyl ester cell, Voc = 0.89 V, Jsc = 4.62 mA/cm2, FF = 54.4%, and ηp = 2.23%.
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84.60.Jt Photoelectric conversion

In situ synthesizing molecular materials between coplanar gold microgap electrodes for the fabrication of molecular devices

Yaling Liu, Zhuoyu Ji, Hongxiang Li, Wenping Hu, and Daoben Zhu

Appl. Phys. Lett. 92, 023505 (2008); http://dx.doi.org/10.1063/1.2831731 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2008

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In this paper, a way to integrate the synthesis of molecular materials and the fabrication of molecular devices was demonstrated by using copper tetracyanoquinodimethane (CuTCNQ). Coplanar gold microgap electrodes were prepared by photolithography or electrobeam lithography. CuTCNQ was in situ synthesized between Au gap electrodes by electrochemical deposition for the fabrication of molecular devices.
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85.65.+h Molecular electronic devices
81.20.-n Methods of materials synthesis and materials processing
82.45.Fk Electrodes

Electrically stable low voltage ZnO transistors with organic/inorganic nanohybrid dielectrics

Sung Hoon Cha, Min Suk Oh, Kwang H. Lee, Seongil Im, Byoung H. Lee, and Myung M. Sung

Appl. Phys. Lett. 92, 023506 (2008); http://dx.doi.org/10.1063/1.2827588 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2008

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We report on the fabrication of top-gate ZnO thin-film transistors (TFTs) with organic and inorganic nanohybrid dielectric layers that take superlattice form in their inside structure. The nanohybrid dielectrics were prepared by the alternate deposition of organic self-assembled monolayer and oxide monolayer on sputter-deposited ZnO channel. With a 22-nm-thin AlOx-based hybrid dielectric layer ( ∼ 130 nFcm2), our ZnO TFT showed a field mobility of 0.36 cm2V s operating at 8 V, while the mobility increased up to 0.66 cm2V s with a 22-nm-thin AlOx-based/TiOx-based/AlOx-based (5.5 nm11 nm5.5 nm and ∼ 220 nFcm2) triple hybrid layer under 2 V operation. Since both ZnO-TFTs display little gate hysteresis, we conclude that our nanohybrid dielectric approach is promising to achieve a gate-stable low voltage top-gate ZnO-TFTs.
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85.30.Tv Field effect devices

In situ preparation of CdS nanoparticles imbedded in a polyelectrolyte multilayer for photocurrent generation

Wonjoo Lee, Sun-Ki Min, Seunghoon Shin, Sung-Hwan Han, and Soo-Hyoung Lee

Appl. Phys. Lett. 92, 023507 (2008); http://dx.doi.org/10.1063/1.2831718 (3 pages) | Cited 6 times

Online Publication Date: 15 January 2008

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CdS nanoparticles (NPs) were prepared and imbedded in polyelectrolyte multilayers (PEMs) in situ and applied to the photocurrent generation. The PEM films of the poly(propylviologen)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) were prepared using layer-by-layer deposition. The Br− ions of the viologen groups were exchanged with S2− ion by dipping the PEMs films in a Na2S solution. Then, the films were dipped in a solution containing Cd2+ to give CdS NPs of less than 10 nm in size. The CdS NP-PEM films form an efficient acceptor-sensitizer dyad system, which showed a good photocurrent of 70 nA/cm2 at 380 nm for a 3.5 bilayer sample.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.66.Hf II-VI semiconductors
79.60.Fr Polymers; organic compounds
68.55.ag Semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.20.-n Methods of materials synthesis and materials processing

High photoexcited carrier multiplication by charged InAs dots in AlAs/GaAs/AlAs resonant tunneling diode

Wangping Wang, Ying Hou, Dayuan Xiong, Ning Li, Wei Lu, Wenxing Wang, Hong Chen, Junming Zhou, E. Wu, and Heping Zeng

Appl. Phys. Lett. 92, 023508 (2008); http://dx.doi.org/10.1063/1.2832368 (3 pages) | Cited 12 times

Online Publication Date: 15 January 2008

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We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77 K. The detection structure is based on an AlAs/GaAs/AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10 nA photocurrent in this structure, corresponding to the photoexcited carrier multiplication factor of 107. This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes

Ion irradiation in liquid of μm3 region for cell surgery

Yoshio Iwai, Tokihiro Ikeda, Takao M. Kojima, Yasunori Yamazaki, Kazuhiro Maeshima, Naoko Imamoto, Tomohiro Kobayashi, Takuya Nebiki, Tadashi Narusawa, and Grigory P. Pokhil

Appl. Phys. Lett. 92, 023509 (2008); http://dx.doi.org/10.1063/1.2834695 (3 pages) | Cited 18 times

Online Publication Date: 17 January 2008

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We present here a cell surgery scheme involving selective inactivation or disruption of cellular structures. Energetic ions are injected into a cell through a tapered glass capillary like a microinjection method. A slight but essential difference from microinjection is that a thin window is prepared at the outlet so that no liquid material can flow in or back through the outlet while still allowing energetic ions to penetrate into the cell. An ∼ MeV He ion beam from such a capillary having 10 μm outlet diameter inactivated a selected volume ( ∼ μm3) of fluorescent molecules located in a HeLa cell nucleus.
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87.53.Ay Biophysical mechanisms of interaction
87.17.-d Cell processes
87.16.Zg Nuclear morphology

Band gaps of lower-order Lamb wave in thin plate with one-dimensional phononic crystal layer: Effect of substrate

Jian Gao, Xin-Ye Zou, Jian-Chun Cheng, and Baowen Li

Appl. Phys. Lett. 92, 023510 (2008); http://dx.doi.org/10.1063/1.2834700 (3 pages) | Cited 13 times

Online Publication Date: 17 January 2008

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We study the substrate effect on the band gaps of lower-order Lamb waves propagating in thin plate with one-dimensional phononic crystal layer coated on uniform substrate. The transmitted power spectra are calculated by using the finite element method (FEM). The results show that when the substrate is hard, the influences on band gap are significant and the band gaps disappear rapidly as the substrate becomes thicker. However, when the substrate is soft, the depth of band gaps becomes larger as the thickness of the substrate increases. A virtual plane wave expansion method is developed to calculate the dispersion curves of Lamb wave. The locations and widths of band gaps on the dispersion curves are in good agreement with the results from the transmitted power spectra by FEM.
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68.35.Iv Acoustical properties
63.22.Np Layered systems

Role of hydrogen in Ge/HfO2/Al gate stacks subjected to negative bias temperature instability

N. Rahim and D. Misra

Appl. Phys. Lett. 92, 023511 (2008); http://dx.doi.org/10.1063/1.2827567 (3 pages) | Cited 1 time

Online Publication Date: 17 January 2008

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This work investigates the role of hydrogen and nitrogen in a Ge/HfO2/Al gate stack by comparing the negative bias temperature instability (NBTI) characteristics with and without the surface nitridation of Ge surface prior to HfO2 deposition. Flatband voltage shift, change in interface state density, and stress induced leakage current were also monitored as a function of stress time. Virtually unchanged interface state density as a function of NBTI indicates no atomic hydrogen release from the dangling bond sites. However, the low n value in power law dependence of flatband voltage shift suggests diffusion of molecular hydrogen absorbed at the interface.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.43.Mn Adsorption kinetics

Bias-stress induced contact and channel degradation in staggered and coplanar organic field-effect transistors

Tim Richards and Henning Sirringhaus

Appl. Phys. Lett. 92, 023512 (2008); http://dx.doi.org/10.1063/1.2825584 (3 pages) | Cited 22 times

Online Publication Date: 18 January 2008

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We have investigated the dependence of bias-stress induced degradation in organic field-effect transistors on the device configuration. We show that separation of contact and channel effects is essential for understanding bias-stress instabilities. In coplanar device configurations, an increase in source contact resistance during current flow is primarily responsible for a rapid device degradation. In contrast, in staggered device configurations, the significantly slower reduction in current is primarily due to charge trapping in the channel leading to an increase in threshold voltage, while the contacts themselves do not exhibit significant degradation.
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85.30.Tv Field effect devices

Stable efficiency roll-off in phosphorescent organic light-emitting diodes

Sung Hyun Kim, Jyongsik Jang, Kyoung Soo Yook, and Jun Yeob Lee

Appl. Phys. Lett. 92, 023513 (2008); http://dx.doi.org/10.1063/1.2836270 (3 pages) | Cited 44 times

Online Publication Date: 18 January 2008

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Origin of efficiency roll-off in phosphorescent organic light-emitting diodes was investigated with triplet mixed host devices and stable devices with little efficiency roll-off was developed. Efficiency roll-off was significant in the device with narrow recombination zone (RZ) and charge leakage out of emitting layer at high luminance was critical to efficiency roll-off. Efficiency roll-off could be reduced in triplet mixed host device with broad RZ and little charge leakage at high driving voltage. Triplet mixed host devices with an exciton blocking layer showed a quantum efficiency over 90% of maximum quantum efficiency at a luminance of 20 000 cd/m2.
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85.60.Jb Light-emitting devices

Demonstration of a multiplexer of dissipationless superconducting quantum interference devices

J. A. B. Mates, G. C. Hilton, K. D. Irwin, L. R. Vale, and K. W. Lehnert

Appl. Phys. Lett. 92, 023514 (2008); http://dx.doi.org/10.1063/1.2803852 (3 pages) | Cited 23 times

Online Publication Date: 18 January 2008

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We report on the development of a microwave superconducting quantum interference device (SQUID) multiplexer to read out arrays of low-temperature detectors. In this frequency-division multiplexer, superconducting resonators with different frequencies couple to a common transmission line and each resonator couples to a different dissipationless SQUID. We demonstrate multiple designs, with high-Q values (4100–18 000), noise as low as 0.17μΦ0/math, and a naturally linear readout scheme based on flux modulation. This multiplexing approach is compatible with superconducting transition-edge sensors and magnetic calorimeters and is capable of multiplexing more than a thousand detectors in a single transmission line.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
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