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23 Jun 2008

Volume 92, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 92, 254102 (2008); http://dx.doi.org/10.1063/1.2945893 (3 pages)

M. Trinker, S. Groth, S. Haslinger, S. Manz, T. Betz, S. Schneider, I. Bar-Joseph, T. Schumm, and J. Schmiedmayer
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Two-dimensional electron gas insulation by local surface thin thermal oxidation in AlGaN/GaN heterostructures

Fabrizio Roccaforte, Filippo Giannazzo, Ferdinando Iucolano, Corrado Bongiorno, and Vito Raineri

Appl. Phys. Lett. 92, 252101 (2008); http://dx.doi.org/10.1063/1.2946657 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2008

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In this letter, the physical effects of the local surface thin thermal oxidation on the current transport in AlGaN/GaN heterostructures are reported. Current-voltage measurements performed on appropriate test patterns demonstrated that a selective oxidation process at 900 °C enables the suppression of the current flow through the two-dimensional electron gas. The electrical insulation was achieved even though structural analysis showed that the formed oxide did not reach the depth of the AlGaN/GaN heterointerface. The combination of capacitance-voltage measurements with depth-resolved scanning capacitance microscopy enabled to correlate the electrical results to the doping and the compositional stability of the material during oxidation.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Mq Oxidation
61.72.uj III-V and II-VI semiconductors

Preparation and characterization of (001)- and (110)-oriented 0.6FeTiO3⋅0.4Fe2O3 films for room temperature magnetic semiconductors

Yusuke Takada, Makoto Nakanishi, Tatsuo Fujii, and Jun Takada

Appl. Phys. Lett. 92, 252102 (2008); http://dx.doi.org/10.1063/1.2951589 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2008

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Thin films of ilmenite-hematite solid solution 0.6FeTiO3⋅0.4Fe2O3 were prepared on α-Al2O3 (001) and (110) single-crystalline substrates. The oxide phases formed in the thin films strongly depended on the oxygen partial pressure (PO2) during deposition. At PO2 = 1.3×10−3 Pa, regardless of thesubstrate orientation, well-ordered 0.6FeTiO3⋅0.4Fe2O3 films with Rmath symmetry were epitaxially formed. Large saturation magnetization at room temperature was observed in both (001)- and (110)-oriented films. The differences in the magnetization and electrical resistivity curves between the (001)- and (110)-oriented films indicated the anisotropic nature of 0.6FeTiO3⋅0.4Fe2O3.
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81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
68.55.J- Morphology of films
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Gg Ferrimagnetics

Equal mobility of constituent cations in BaTiO3

Han-Ill Yoo, Chung-Eun Lee, Roger A. De Souza, and Manfred Martin

Appl. Phys. Lett. 92, 252103 (2008); http://dx.doi.org/10.1063/1.2951606 (3 pages) | Cited 1 time

Online Publication Date: 24 June 2008

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It is widely believed that in BaTiO3, Ba2+ cations are much more mobile than Ti4+ cations. Under a dc electric field, Ba cations are therefore expected at elevated temperatures to move at a faster rate to the cathode, leading to compositional demixing and eventually to decomposition of the BaTiO3. We have found that this is not the case. Overall mass transfer in BaTiO3 does occur but with no compositional demixing. This indicates that contrary to the general belief, Ba2+ and Ti4+ have the same electrochemical mobilities in BaTiO3. This suggests a common diffusion mechanism involving both cation sublattices.
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66.30.-h Diffusion in solids
82.45.-h Electrochemistry and electrophoresis

Electronic structure and optical properties of Nb-doped anatase TiO2

X. D. Liu, E. Y. Jiang, Z. Q. Li, and Q. G. Song

Appl. Phys. Lett. 92, 252104 (2008); http://dx.doi.org/10.1063/1.2949070 (3 pages) | Cited 17 times

Online Publication Date: 24 June 2008

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The electronic structure and optical properties of pure and Nb-doped TiO2 with anatase structure were calculated using local-density approximation based on the density-functional theory. For the undoped TiO2, the Fermi level locates in the band gap between the conduction band and valence band, while it moves into the conduction band and shows metal-like characteristic after Nb atom was introduced into the TiO2 supercell. The optical absorption coefficients for both compounds are very small in the visible light range. Our calculations provide electronic structure evidence that the Nb-doped anatase TiO2 is a new type transparent conducing metal.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Inversion capacitance-voltage studies on GaAs metal-oxide-semiconductor structure using transparent conducting oxide as metal gate

T. Yang, Y. Liu, P. D. Ye, Y. Xuan, H. Pal, and M. S. Lundstrom

Appl. Phys. Lett. 92, 252105 (2008); http://dx.doi.org/10.1063/1.2953080 (3 pages) | Cited 7 times

Online Publication Date: 27 June 2008

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A systematic capacitance-voltage (C-V) study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited Al2O3 as gate dielectrics and indium tin oxide (ITO) as the metal gate. The transparent conducting ITO gate allows homogeneous photoillumination on the whole MOS capacitance area, such that one can easily observe the low-frequency (LF) C-V and quasistatic C-V of GaAs at room temperature. The semiconductor capacitance effect on GaAs MOS devices has also been identified and insightfully discussed based on the obtained LF C-V curves. The semiconductor capacitance effect becomes more important for devices with high-mobility channel materials and aggressively scaled high-k gate dielectrics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
72.20.Fr Low-field transport and mobility; piezoresistance

Evidence for surface dipole modifications in In2O3-based transparent conductors

S. P. Harvey, T. O. Mason, C. Körber, Y. Gassenbauer, and A. Klein

Appl. Phys. Lett. 92, 252106 (2008); http://dx.doi.org/10.1063/1.2953435 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2008

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Surface dipole modifications were identified for contamination-free In2O3-based transparent conducting oxides by ultraviolet photoelectron spectroscopy on both thin film and bulk ceramic specimens. In particular, heating in air was found to result in an increase in ionization potential and work function. The formation of surface dipoles may be related to the unique structure (crystal, defect) of bixbyite-based materials. These findings have important ramifications for the tuning of work functions in In2O3-based transparent conductors.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.61.Ng Insulators
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