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5 Jun 2000

Volume 76, Issue 23, pp. 3337-3483

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The Meyer–Neldel rule in organic thin-film transistors

E. J. Meijer, M. Matters, P. T. Herwig, D. M. de Leeuw, and T. M. Klapwijk

Appl. Phys. Lett. 76, 3433 (2000); http://dx.doi.org/10.1063/1.126669 (3 pages) | Cited 40 times

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We have measured and analyzed the temperature and gate voltage dependencies of the field-effect mobility in organic thin-film transistors. We find that the mobility prefactor increases exponentially with the activation energy in agreement with the Meyer–Neldel rule. This behavior is demonstrated in the mobility data of solution-processed pentacene, poly(2,5-thienylene vinylene) and in mobility data reported in literature. Surprisingly, the characteristic Meyer–Neldel energy for all analyzed materials is close to 40 meV. Possible implications for the charge transport mechanism in these materials are discussed. © 2000 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Electron tunneling experiments on skutterudite Co1−xFexSb3 semiconductors

Jiro Nagao, Marhoun Ferhat, Hiroaki Anno, Kakuei Matsubara, Eiji Hatta, and Kōichi Mukasa

Appl. Phys. Lett. 76, 3436 (2000); http://dx.doi.org/10.1063/1.126670 (3 pages) | Cited 10 times

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Electron tunneling experiments were performed on p-Co1−xFexSb3–Al-oxide–Al junctions for x = 0 and x = 0.1 at 4.2 K. A U-shaped tunneling conductance curve obtained for polycrystalline p-CoSb3 clearly shows an energy-band gap of ∼50 meV. For p-Co0.9Fe0.1Sb3 skutterudites, a strong zero-bias conductance anomaly is observed. This anomaly may be due to a structural disorder arising from defects such as vacancies and interstitial Fe atoms. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.05.Hd Other semiconductors
73.40.Gk Tunneling
61.72.J- Point defects and defect clusters
71.20.Nr Semiconductor compounds

From N isoelectronic impurities to N-induced bands in the GaNxAs1−x alloy

P. J. Klar, H. Grüning, W. Heimbrodt, J. Koch, F. Höhnsdorf, W. Stolz, P. M. A. Vicente, and J. Camassel

Appl. Phys. Lett. 76, 3439 (2000); http://dx.doi.org/10.1063/1.126671 (3 pages) | Cited 108 times

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GaNxAs1−x samples with x<3% grown by metalorganic vapor phase epitaxy were studied by low-temperature photoluminescence under hydrostatic pressure and photomodulated reflectance spectroscopy. The transformation from N acting as an isoelectronic impurity to N-induced band formation takes place at x ≈ 0.2%. The N level does not shift with respect to the valence band edge of GaNxAs1−x. Concentration as well as hydrostatic-pressure dependence of the GaNxAs1−x bands can be described by a three band kp description of the conduction band state E− and E+ and the valence band at k = 0. The model parameters for T<20 and T = 300 K were determined by fitting the model to the experimental data. Modeling the linewidth of the E− transition by combining the kp model and ion statistics leads to the conclusion that the electron-hole pairs are strongly localized. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds

Low-frequency noise and mobility fluctuations in AlGaN/GaN heterostructure field-effect transistors

J. A. Garrido, B. E. Foutz, J. A. Smart, J. R. Shealy, M. J. Murphy, W. J. Schaff, L. F. Eastman, and E. Muñoz

Appl. Phys. Lett. 76, 3442 (2000); http://dx.doi.org/10.1063/1.126672 (3 pages) | Cited 19 times

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The 1/f low-frequency noise characteristics of AlGaN/GaN heterostructure field-effect transistors, grown on sapphire and SiC substrates by molecular beam epitaxy and organometallic vapor phase epitaxy, are reported. The Hooge parameter is deduced taking into account the effect of the contact noise and the noise originating in the ungated regions. A strong dependence between the Hooge parameter and the sheet carrier density is obtained, and it is explained using a model in which mobility fluctuations are produced by dislocations. A Hooge parameter as low as αCH ≈ 8×10−5 is determined for devices grown on SiC substrates. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Td Noise processes and phenomena
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Focused-ion-beam writing of electrical connections into platinum oxide films

F. Machalett, K. Edinger, L. Ye, J. Melngailis, T. Venkatesan, M. Diegel, and K. Steenbeck

Appl. Phys. Lett. 76, 3445 (2000); http://dx.doi.org/10.1063/1.125945 (3 pages) | Cited 4 times

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A focused Ga+ ion-beam (FIB) writing system has been used to directly change an insulating platinum oxide film into a conducting film with a dose in the order of 1014 Ga+/cm2 at 30 keV ion energy. The sheet resistance of a PtO2 film, which is prepared by magnetron sputtering, was reduced from 4×109 Ω/□ to approximately 5×102 Ω/□. Electron microprobe measurements indicate that oxygen loss in the irradiated regions causes the large decrease in resistivity. Scanning electron microscope pictures show that the film quality after ion irradiation is more homogeneous than after laser irradiation, which has been used to pattern these materials by thermal processes. Compared with laser patterning, the resolution of FIB patterning is more than one order of magnitude higher and is suitable for possible applications in nanotechnology. © 2000 American Institute of Physics.
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73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions
61.80.Jh Ion radiation effects
61.82.Ms Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Ls Metallization, contacts, interconnects; device isolation

The benzene molecule as a molecular resonant-tunneling transistor

M. Di Ventra, S. T. Pantelides, and N. D. Lang

Appl. Phys. Lett. 76, 3448 (2000); http://dx.doi.org/10.1063/1.126673 (3 pages) | Cited 104 times

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Experiments and theory have so far demonstrated that single molecules can form the core of a two-terminal device. Here we report first-principles calculations of transport through a benzene-1, 4-dithiolate molecule with a third capacitive terminal (gate). We find that the resistance of the molecule rises from its zero-gate-bias value to a value roughly equal to the quantum of resistance (12.9 kΩ) when resonant tunneling through the π∗ antibonding orbitals occurs. © 2000 American Institute of Physics.
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85.65.+h Molecular electronic devices
73.23.-b Electronic transport in mesoscopic systems

Low resistance Ti/Pt/Au ohmic contacts to p-type GaN

L. Zhou, W. Lanford, A. T. Ping, I. Adesida, J. W. Yang, and A. Khan

Appl. Phys. Lett. 76, 3451 (2000); http://dx.doi.org/10.1063/1.126674 (3 pages) | Cited 50 times

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Electrical properties of Ti (15 nm)/Pt (50 nm)/Au (80 nm) contacts on moderately doped p-GaN (NA = 3.0×1017 cm−3) are reported. Linear current–voltage characteristics were observed after annealing the contacts for 1 min at temperatures above 700 °C. The best ohmic contacts were obtained after annealing in a N2 ambient at 800 °C for 2 min. These contacts exhibited a specific contact resistance Rc of 4.2×10−5 Ω cm2 and contact resistivity ρc of 21 Ω mm. Possible mechanisms for the lower contact resistivity of Ti/Pt/Au contacts are discussed. The processing for the Ti/Pt/Au ohmic contacts is compatible with routine fabrication steps for GaN devices. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Role of interfacial compound formation associated with the use of ZnO buffers layers in the hydride vapor phase epitaxy of GaN

Shulin Gu, Rong Zhang, Jingxi Sun, Ling Zhang, and T. F. Kuech

Appl. Phys. Lett. 76, 3454 (2000); http://dx.doi.org/10.1063/1.126675 (3 pages) | Cited 20 times

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ZnO buffer layers have been used in the hydride vapor phase epitaxy of GaN in order to improve the initial nucleation and growth of the GaN and hence the subsequent materials properties. The specific role of the ZnO buffer layer was investigated by x-ray photoelectron spectroscopy and x-ray diffraction. The improvements in the GaN growth behavior are attributed to the formation of a thin surface layer of ZnAl2O4 that results from a reaction-diffusion process between the ZnO and Al2O3. This layer can provide an improved lattice match to GaN as well as change in surface energy affecting the initial growth of the GaN. © 2000 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
66.30.Ny Chemical interdiffusion; diffusion barriers
64.60.Q- Nucleation
82.60.Nh Thermodynamics of nucleation
79.60.Dp Adsorbed layers and thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.Md Surface thermodynamics, surface energies
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
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