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1 Aug 2005

Volume 87, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 87, 054101 (2005); http://dx.doi.org/10.1063/1.2006209 (3 pages)

Xiuqin Chen, S. Yang, M Hasegawa, K. Kawabe, and S. Motojima
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Aluminum arsenide cleaved-edge overgrown quantum wires

J. Moser, T. Zibold, D. Schuh, M. Bichler, F. Ertl, G. Abstreiter, M. Grayson, S. Roddaro, and V. Pellegrini

Appl. Phys. Lett. 87, 052101 (2005); http://dx.doi.org/10.1063/1.1994955 (3 pages) | Cited 11 times

Online Publication Date: 26 July 2005

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We report conductance measurements in quantum wires made of aluminum arsenide, a heavy-mass, multivalley one-dimensional (1D) system. Zero-bias conductance steps are observed as the electron density in the wire is lowered, with additional steps observable upon applying a finite dc bias. We attribute these steps to depopulation of successive 1D subbands. The quantum conductance is substantially reduced with respect to the anticipated value for a spin- and valley-degenerate 1D system. This reduction is consistent with disorder-induced, intrawire backscattering that suppresses the transmission of 1D modes. Calculations are presented to demonstrate the role of strain in the 1D states of this cleaved-edge structure.
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81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
73.63.Nm Quantum wires
72.20.-i Conductivity phenomena in semiconductors and insulators

Electronic transport properties of pentacene single crystals upon exposure to air

Oana D. Jurchescu, Jacob Baas, and Thomas T. M. Palstra

Appl. Phys. Lett. 87, 052102 (2005); http://dx.doi.org/10.1063/1.2001130 (3 pages) | Cited 67 times

Online Publication Date: 26 July 2005

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We report the effect of air exposure on the electronic properties of pentacene single crystals. Air can diffuse reversibly in and out of the crystals and influences the physical properties. We discern two competing mechanisms that modulate the electronic transport. The presence of oxygen increases the hole conduction, as in dark four O2 molecules introduce one charge carrier. This effect is enhanced by the presence of visible light. Contrarily, water, present in ambient air, is incorporated in the crystal lattice and forms trapping sites for injected charges.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
66.30.J- Diffusion of impurities
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Spiroconjugation-enhanced intermolecular charge transport

Chung-Chih Wu, Wei-Guang Liu, Wen-Yi Hung, Tsung-Li Liu, Yu-Ting Lin, Hao-Wu Lin, Ken-Tsung Wong, Yuh-Yih Chien, Ruei-Tang Chen, Tsung-Hsi Hung, Teng-Chih Chao, and You-Ming Chen

Appl. Phys. Lett. 87, 052103 (2005); http://dx.doi.org/10.1063/1.2001140 (3 pages) | Cited 19 times

Online Publication Date: 26 July 2005

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We report charge-transport and related physical properties of terfluorenes with various C9 substitutions. Results show that by introducing slight spiroconjugation between a core chromophore and conjugated substitutions through spiro-linking, the bulky substitution not only serves as a spatial hindrance to enhance morphological stability and emission efficiency in thin films, but also bridges and enhances intermolecular charge transport under certain situations. Interestingly, such characteristics are acquired without altering major electronic properties of core chromophores, rendering it a flexible molecular scheme for tuning characteristics of functional molecules to meet various demands of different applications.
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73.61.Ph Polymers; organic compounds

Screening of external electric field by photoinduced carriers in Bragg multiple quantum wells

V. I. Puller, L. I. Deych, M. V. Erementchouk, and A. A. Lisyansky

Appl. Phys. Lett. 87, 052104 (2005); http://dx.doi.org/10.1063/1.2001743 (3 pages)

Online Publication Date: 26 July 2005

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We study screening of external bias in a multiple-quantum-well structure by optically injected excess carriers. By solving self-consistently the Poisson equation and the equations for the electron and hole densities, we analyze how realization of different screening regimes depends on the applied bias, excitation power, temperature, and the parameters of the structure. Our calculations show the feasibility of using the proposed setup as an optically controlled electric switch in photonic circuits.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
73.50.Pz Photoconduction and photovoltaic effects

Field electron emission of Si nanotips with apexes of various compositions

J. C. She, K. Zhao, S. Z. Deng, J. Chen, and N. S. Xu

Appl. Phys. Lett. 87, 052105 (2005); http://dx.doi.org/10.1063/1.2001733 (3 pages) | Cited 9 times

Online Publication Date: 26 July 2005

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We report procedure with use of self-assembled silicon carbide (SiC) nanomasks for preparation of ultrahigh-density Si nanotips. Si nanotips with SiC apex may be firstly prepared in a CH4/H2 plasma treatment and in a subsequent H2 plasma etching a SiC apex may be converted into an amorphous silicon (a-Si) one with an additional function of sharpening the nanotips. A comparative study of the field electron emission from the Si nanotips with apexes of SiC, a-Si and pure Si is carried out, and shows that nanotips with a-Si apexes have not only the highest field enhancement factor but also the best emission uniformity. The physical origins for the above two improvements in field emission are discussed.
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81.07.Bc Nanocrystalline materials
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
61.43.Dq Amorphous semiconductors, metals, and alloys
52.77.Bn Etching and cleaning

High mobility two-dimensional electron system on hydrogen-passivated silicon(111) surfaces

K. Eng, R. N. McFarland, and B. E. Kane

Appl. Phys. Lett. 87, 052106 (2005); http://dx.doi.org/10.1063/1.2001734 (3 pages) | Cited 17 times

Online Publication Date: 26 July 2005

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We have fabricated and characterized a field-effect transistor in which an electric field is applied through an encapsulated vacuum cavity and induces a two-dimensional electron system on a hydrogen-passivated Si(111) surface. This vacuum cavity preserves the ambient sensitive surface and is created via room temperature contact bonding of two Si substrates. Hall measurements are made on the H–Si(111) surface prepared in aqueous ammonium fluoride solution. We obtain electron densities up to 6.5×1011 cm−2 and peak mobilities of ∼ 8000 cm2/V s at 4.2 K.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Room-temperature plasma waves resonant detection of sub-terahertz radiation by nanometer field-effect transistor

F. Teppe, W. Knap, D. Veksler, M. S. Shur, A. P. Dmitriev, V. Yu. Kachorovskii, and S. Rumyantsev

Appl. Phys. Lett. 87, 052107 (2005); http://dx.doi.org/10.1063/1.2005394 (3 pages) | Cited 54 times

Online Publication Date: 27 July 2005

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We report on room-temperature, resonant detection of 0.6 THz radiation by 250 nm gate length GaAs/AlGaAs heterostructure field-effect transistor. We show that the detection is strongly increased (and becomes resonant) when the drain current increases and the transistor is driven into the current saturation region. We interpret the results as due to resonant plasma wave detection that is enhanced by increasing the electron drift velocity.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.30.Tv Field effect devices

Three-dimensional atom mapping of dopants in Si nanostructures

Keith Thompson, John H. Booske, David J. Larson, and Thomas F. Kelly

Appl. Phys. Lett. 87, 052108 (2005); http://dx.doi.org/10.1063/1.2005368 (3 pages) | Cited 29 times

Online Publication Date: 27 July 2005

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Atom-probe tomography has successfully mapped three-dimensional (3D) dopant atom distributions in nanoscale volumes of Si subjected to various processing procedures. The 3D evolution of dopants, specifically effects such as dopant clustering and grain-boundary segregation, were analyzed in implanted polycrystalline Si gate contacts and implanted shallow junctions. A cluster of dimensions 2×7×8 nm3 and containing 264 B atoms, was identified at the intersection of three poly-Si grains, verifying that annealing highly overdoped thin poly-Si layers does not facilitate uniformly doped and highly conductive gate contact layers.
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61.72.uf Ge and Si
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials

Modulation of the work function of silicon gate electrode using thin TaN interlayers

H. N. Alshareef, H. C. Wen, H. R. Harris, K. Choi, H. F. Luan, P. Lysaght, P. Majhi, B. H. Lee, M. El-Bouanani, and V. Ukride

Appl. Phys. Lett. 87, 052109 (2005); http://dx.doi.org/10.1063/1.2006977 (3 pages) | Cited 4 times

Online Publication Date: 27 July 2005

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The impact of thin TaN layers (0.5–10 nm) on the effective work function of polycrystalline silicon (poly-Si)∕TaN stacks has been investigated. It is found that when the TaN layer is as thin as 0.5 nm, it can have a significant effect on the effective work function of poly-Si, and that n-type and p-type poly-Si behave differently. The observed results are explained by reactions between poly-Si and the TaN layer leading to the formation of TaxSiyNz at the poly-Si-gate dielectric interface. Electrical tests show minimal poly-Si depletion with the TaN layers, and gate leakage current and fixed charges that are comparable to conventional poly-Si electrodes. The results show that these stacked electrodes can be useful for nearly n-type effective work functions (4.2–4.3 eV).
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions

W2B-based rectifying contacts to n-GaN

Rohit Khanna, S. J. Pearton, F. Ren, I. Kravchenko, C. J. Kao, and G. C. Chi

Appl. Phys. Lett. 87, 052110 (2005); http://dx.doi.org/10.1063/1.2007865 (3 pages) | Cited 11 times

Online Publication Date: 28 July 2005

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Schottky contact formation on n-GaN using a novel W2B/Ti/Au metallization scheme was studied using current-voltage, scanning electron microscopy and Auger electron spectroscopy measurements. A maximum barrier height of 0.55 eV was achieved on as-deposited samples, with a negative temperature coefficient of 8×10−4 eV/°C over the range 25–150 °C. There was also a negative temperature coefficient for the reverse breakdown of the Schottky diodes with W2B contacts. The barrier height was essentially independent of annealing temperature up to 500 °C and decreased thereafter due to the onset of metallurgical reactions with the GaN. The Ti began to out-diffuse to the surface at temperatures of >500 °C. The reverse current magnitude was larger than predicted by thermionic emission alone.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices
79.20.Fv Electron impact: Auger emission
61.72.Cc Kinetics of defect formation and annealing
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
79.40.+z Thermionic emission

Electrical characterization of band gap states in C-doped TiO2 films

Yoshitaka Nakano, Takeshi Morikawa, Takeshi Ohwaki, and Yasunori Taga

Appl. Phys. Lett. 87, 052111 (2005); http://dx.doi.org/10.1063/1.2008376 (3 pages) | Cited 30 times

Online Publication Date: 28 July 2005

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We report on band gap states in C-doped TiO2 films that were prepared by oxidative annealing of sputtered TiC films at 550 °C in flowing O2 gas. Deep-level optical spectroscopy measurements revealed three deep levels located at ∼ 0.86, ∼ 1.30, and ∼ 2.34 eV below the conduction band. The first level is probably attributable to the intrinsic nature of TiO2, whereas the latter two levels are newly introduced by the C-doping. In particular, the pronounced 2.34 eV band contributes to band gap narrowing by mixing with the O 2p valence band. Additionally, the 0.86 and 1.30 eV levels can be active as an efficient generation-recombination center.
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71.55.Ht Other nonmetals
61.72.S- Impurities in crystals
73.61.Le Other inorganic semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing

Metalorganic chemical vapor deposition of atomically flat SrRuO3 films on stepped SrTiO3 substrates

Akihiro Sumi, Kenji Takahashi, Shintaro Yokoyama, Hitoshi Morioka, Hiroshi Funakubo, and Mamoru Yoshimoto

Appl. Phys. Lett. 87, 052112 (2005); http://dx.doi.org/10.1063/1.2006989 (3 pages) | Cited 8 times

Online Publication Date: 28 July 2005

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Epitaxial SrRuO3 films with thicknesses of 50–80 nm were systematically grown at 750 °C on (100)SrTiO3 substrates by metalorganic chemical vapor deposition with different supply rates of the Sr and Ru source gases. Stoichiometric films with a low resistivity of 240–260 μΩ cm can be grown on polished (100)SrTiO3 substrates over a wide range of source gas supply rates. However, the surface flatness of the deposited film was very sensitive to changes the input source gas supply rate. SrRuO3 films having step and trace structured surfaces were grown on polished and atomically flat SrTiO3 substrates under an optimized input gas supply rate. A height of 7–8 nm with a terrace width of 500–1000 nm were obtained on polished SrTiO3 substrates, but a single unit cell height of about 0.4 nm was obtained with a 200–300 nm terrace width on atomically flat SrTiO3 substrates. This opens the possibility of the mass production of atomically flat conductive perovskite layers.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
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