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15 Oct 2007

Volume 91, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 91, 162101 (2007); http://dx.doi.org/10.1063/1.2794995 (3 pages)

D. J. Reilly, C. M. Marcus, M. P. Hanson, and A. C. Gossard
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Fast single-charge sensing with a rf quantum point contact

D. J. Reilly, C. M. Marcus, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 91, 162101 (2007); http://dx.doi.org/10.1063/1.2794995 (3 pages) | Cited 30 times

Online Publication Date: 15 October 2007

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We report high-bandwidth charge sensing measurements using a GaAs quantum point contact embedded in a radio frequency impedance matching circuit (rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to charge, we demonstrate a conductance sensitivity of 5×10−6 e2/h Hz−1/2 with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron double quantum dot is investigated in a mode where the rf-QPC back action is rapidly switched.
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73.63.Rt Nanoscale contacts
73.63.Kv Quantum dots
73.21.La Quantum dots
85.35.Gv Single electron devices

Efficient visible light detection using individual germanium nanowire field effect transistors

Y. H. Ahn and Jiwoong Park

Appl. Phys. Lett. 91, 162102 (2007); http://dx.doi.org/10.1063/1.2799253 (3 pages) | Cited 30 times

Online Publication Date: 15 October 2007

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We report photoconductivity (PC) in individual germanium nanowire field effect transistors (GeFETs). PC measurements with a global illumination reveal that GeFETs can be used as a polarization-sensitive nanoscale light detector in the visible range. It is also found that the PC shows sensitive optical response especially in the low intensity regime. We observe a high internal gain in PC in conjunction with strong saturation behavior, which is attributed to the filling of surface trapping states. This mechanism for high internal gain is consistent with spatially resolved scanning photocurrent measurements, whose results confirm that optical absorption is in the linear regime.
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73.63.Bd Nanocrystalline materials
73.50.Pz Photoconduction and photovoltaic effects
85.30.Tv Field effect devices
73.63.Nm Quantum wires
73.40.-c Electronic transport in interface structures

Low-resistance Ni-based Schottky diodes on freestanding n-GaN

L. Lewis, B. Corbett, D. O Mahony, and P. P. Maaskant

Appl. Phys. Lett. 91, 162103 (2007); http://dx.doi.org/10.1063/1.2799739 (3 pages) | Cited 3 times

Online Publication Date: 15 October 2007

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Schottky diodes formed on a low doped (5×1016 cm−3) n-type GaN epilayer grown on a n+ freestanding GaN substrate were studied. The temperature dependent electrical characteristics of Ni contacts on the as-grown material are compared with an aqueous, potassium hydroxide (KOH) treated surface. In both cases the diodes are dominated by thermionic emission in forward bias, with low idealities (1.04 at room temperature) which decrease with increasing temperature, reaching 1.03 at 413 K. The Schottky barrier height is 0.79±0.05 eV for the as-grown surface compared with 0.85±0.05 eV for the KOH treated surface at room temperature. This is consistent with an inhomogeneous barrier distribution. The specific on-state resistance of the diodes is 0.57 mΩ cm2 The KOH treatment reduces the room temperature reverse leakage current density at −30 V to 1×10−5 A cm−2 compared to 6×10−2 A cm−2 for the as-grown samples.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.De Semiconductor-device characterization, design, and modeling

Determination of the valence band offset of wurtzite InN/ZnO heterojunction by x-ray photoelectron spectroscopy

Riqing Zhang, Panfeng Zhang, Tingting Kang, Haibo Fan, Xianglin Liu, Shaoyan Yang, Hongyuan Wei, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 91, 162104 (2007); http://dx.doi.org/10.1063/1.2800311 (3 pages) | Cited 18 times

Online Publication Date: 17 October 2007

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The valence band offset (VBO) of the wurtzite InN/ZnO heterojunction is directly determined by x-ray photoelectron spectroscopy to be 0.82±0.23 eV. The conduction band offset is deduced from the known VBO value to be 1.85∓0.23 eV, which indicates a type-I band alignment for InN/ZnO heterojunction.
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71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Conductivity fluctuation within a crystalline domain and its origin in pentacene thin-film transistors

Noboru Ohashi, Hiroshi Tomii, Ryousuke Matsubara, Masatoshi Sakai, Kazuhiro Kudo, and Masakazu Nakamura

Appl. Phys. Lett. 91, 162105 (2007); http://dx.doi.org/10.1063/1.2799743 (3 pages) | Cited 13 times

Online Publication Date: 18 October 2007

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Surface topography and high-resolution potential images in a thin-film transistor with a polycrystalline pentacene active layer have been measured by atomic-force-microscope potentiometry. A potential fluctuation independent of topographic features was found in large flat molecular terraces. The origin of the potential fluctuation was concluded to be the fluctuation of the top level of the highest-occupied-molecular-orbital band, which results in the variation of local carrier concentration. The full width at half maximum of the band fluctuation was estimated to be 12 meV, which might reduce the mean carrier velocity in crystalline domains.
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85.30.Tv Field effect devices

Forming single molecular junctions between indium tin oxide electrodes

Fang Chen, Zhifeng Huang, and Nongjian Tao

Appl. Phys. Lett. 91, 162106 (2007); http://dx.doi.org/10.1063/1.2800303 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2007

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We have demonstrated that indium tin oxide (ITO) can be used as contact electrodes to form molecular junctions via ITO-carboxylic acid bonds. We measured the conductance of n-alkane terminated with dicarboxylic acids using conducting atomic force microscope break junction. The conductance decreases exponentially with molecular length with a decay constant of ∼ 0.80 Å−1, which is similar to that of Au-carboxylic acid junctions. However, the contact conductance of ITO-carboxylic acid is smaller than that of Au-carboxylic acid, reflecting different electronic couplings between the linker group and electrodes. From the average breakdown force and stretching length, we estimated the binding energy of ITO-carboxylic acid.
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73.40.Ns Metal-nonmetal contacts

Nonvolatile programmable metallization cell memory switching element based on Ag-doped SbTe solid electrolyte

Young Sam Park, Seung Yun Lee, Sung Min Yoon, Soon Won Jung, Byoung Gon Yu, Soo Jin Lee, and Soon Gil Yoon

Appl. Phys. Lett. 91, 162107 (2007); http://dx.doi.org/10.1063/1.2789663 (3 pages) | Cited 4 times

Online Publication Date: 18 October 2007

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We report that industrially qualified SbTe chalcogenide film can be applied to programmable metallization cell memory switching device. To fabricate the switching device, Sb35Te65, Ag, and W (top electrode) were consequently sputtered on TiW (bottom electrode)/SiO2/Si substrate, and Ag diffusion process was not added. During Ag sputtering, it is apparent that Ag is diffused into Sb35Te65 film to form Ag-doped Sb35Te65 solid electrolyte, and that some of the diffused Ag reacts with Te to form Ag–Te bond in the solid electrolyte.
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84.32.Dd Connectors, relays, and switches
84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices

Investigation on the diffusion barrier properties of sputtered Mo/W–N thin films in Cu interconnects

Prodyut Majumder and Christos G. Takoudis

Appl. Phys. Lett. 91, 162108 (2007); http://dx.doi.org/10.1063/1.2800382 (3 pages) | Cited 21 times

Online Publication Date: 18 October 2007

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Mo/W–N bilayer thin film structures deposited on Si using sputtering have been studied as a copper diffusion barrier. The thermal stability of the barrier structure after annealing Cu/Mo/W–N/〈Si〉 samples in N2 for 5 min is studied using x-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy, and four point probe measurements. The failure of the barrier structure is indicated by the abrupt increase in sheet resistance value and the formation of Cu3Si phase as probed by XRD. Our results suggest that the Mo (5 nm)/W–N (5 nm) barrier is stable and can prevent the formation of Cu3Si at least up to 775 °C.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
85.40.Ls Metallization, contacts, interconnects; device isolation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Memory effect of nonvolatile bistable devices based on CdSe/ZnS nanoparticles sandwiched between C60 layers

Fushan Li, Dong-Ick Son, Jung-Hun Ham, Bong-Jun Kim, Jae Hun Jung, and Tae Whan Kim

Appl. Phys. Lett. 91, 162109 (2007); http://dx.doi.org/10.1063/1.2801357 (3 pages) | Cited 18 times

Online Publication Date: 19 October 2007

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Current-voltage and conductance-voltage (G-V) measurements on three-layer Al/C60/CdSe nanoparticles/C60/indium tin oxide (ITO) structures fabricated by using a spin-coating method showed a nonvolatile electrical bistable behavior. Capacitance-voltage (C-V) measurements on Al/C60/CdSe nanoparticles/C60/ITO structures showed a clockwise hysteresis with a flatband voltage shift due to the existence of the CdSe nanoparticles, indicative of memory effects in the devices. Current-time measurements showed that the devices exhibited excellent memory retention ability at ambient conditions. Possible operating mechanisms for the memory effects in the Al/C60/CdSe nanoparticles/C60/ITO devices are described on the basis of the G-V and the C-V results.
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85.30.-z Semiconductor devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Bd Nanocrystalline materials

The metal-insulator transition in VO2 studied using terahertz apertureless near-field microscopy

Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, and Yong-Sik Lim

Appl. Phys. Lett. 91, 162110 (2007); http://dx.doi.org/10.1063/1.2801359 (3 pages) | Cited 11 times

Online Publication Date: 19 October 2007

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We have studied the metal-insulator transition in a vanadium dioxide (VO2) thin film using terahertz apertureless near-field optical microscopy. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of micron-scale metallic domains in inhomogeneous VO2 thin films.
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71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
68.37.Uv Near-field scanning microscopy and spectroscopy
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