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5 Jul 2010

Volume 97, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 97, 013301 (2010); http://dx.doi.org/10.1063/1.3458867 (3 pages)

M. Uno, Y. Hirose, T. Uemura, K. Takimiya, Y. Nakazawa, and J. Takeya
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Ge quantum dot tunneling diode with room temperature negative differential resistance

M. Oehme, A. Karmous, M. Sarlija, J. Werner, E. Kasper, and J. Schulze

Appl. Phys. Lett. 97, 012101 (2010); http://dx.doi.org/10.1063/1.3462069 (3 pages) | Cited 6 times

Online Publication Date: 7 July 2010

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We present current density-voltage characteristics of Ge quantum dot p+-i-n+ tunneling diodes. The diode structure with Ge quantum dots embedded in the intrinsic region was grown by low temperature molecular beam epitaxy without any postgrowth annealing steps. The quantum dot diodes were fabricated using a low thermal budget fabrication process which preserves the Ge quantum structure. A negative differential resistance at room temperature of a Ge quantum dot tunneling diode was observed. A maximum peak to valley ratio of 1.6 at room temperature was achieved.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
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Electron transport properties of InAs ultrathin films obtained by epitaxial lift-off and van der Waals bonding on flexible substrates

Hayato Takita, Norihiko Hashimoto, Cong Thanh Nguyen, Masahiro Kudo, Masashi Akabori, and Toshi-kazu Suzuki

Appl. Phys. Lett. 97, 012102 (2010); http://dx.doi.org/10.1063/1.3459137 (3 pages) | Cited 5 times

Online Publication Date: 7 July 2010

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We investigated InAs ultrathin films on flexible substrates. InAs layers grown on GaAs(001) are separated by epitaxial lift-off (ELO), followed by van der Waals bonding (VWB) on flexible substrates. We employed “normal” and “inverted” VWB; in the former, top and bottom sides are maintained during ELO and VWB, while inverted in the latter. From the InAs on flexible substrates, we fabricated Hall-bar devices with recess etch-thinning, using which electron transport properties depending on InAs layer thickness were characterized. For the inverted VWB, we observe very high electron mobilities of InAs ultrathin films, such as ∼ 10 000 cm2/V s for ∼ 100 nm thickness and ∼ 7000 cm2/V s for ∼ 20 nm. These carrier mobilities are highest not only for thin films on flexible substrates but also for InAs thin films; higher than those of InAs films grown on GaAs(111)A and membranes fabricated from them.
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73.61.Ey III-V semiconductors
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

High temperature conductance characteristics of LaAlO3/SrTiO3-heterostructures under equilibrium oxygen atmospheres

F. Gunkel, S. Hoffmann-Eifert, R. Dittmann, S. B. Mi, C. L. Jia, P. Meuffels, and R. Waser

Appl. Phys. Lett. 97, 012103 (2010); http://dx.doi.org/10.1063/1.3457386 (3 pages) | Cited 3 times

Online Publication Date: 7 July 2010

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The interface conductance of LaAlO3/SrTiO3 heterostructures was investigated under high temperature oxygen equilibrium. The dependence of the heterostructure’s conductance on oxygen partial pressure (from 10−22 to 1 bar) and temperature (800 to 1100 K) was compared to the characteristic of SrTiO3 single crystals, which is described in terms of a defect chemistry model. Up to 950 K the equilibrated heterostructures reveal an additional influence of a metallic-like conduction path with a very slight dependence on the oxygen partial pressure. Donor-type interface states which may result from either lattice distortions or A-site cation intermixing during processing are discussed as a possible origin for the exceptional interface conduction of LaAlO3/SrTiO3 heterostructures.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Band-gap narrowing of TiO2 doped with Ce probed with x-ray absorption spectroscopy

S. W. Chen, J. M. Lee, K. T. Lu, C. W. Pao, J. F. Lee, T. S. Chan, and J. M. Chen

Appl. Phys. Lett. 97, 012104 (2010); http://dx.doi.org/10.1063/1.3460916 (3 pages) | Cited 10 times

Online Publication Date: 7 July 2010

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The electronic structure of TiO2 doped with Ce was investigated with x-ray absorption and photoluminescence (PL) spectra. Ce doping narrows the band gap of TiO2, as evidenced by a redshift in the absorption edge in the O K-edge spectrum and PL. Narrowing is ascribed to the formation of an impurity band, composed of Ce 4f (Ce3+/Ce4+) and oxygen defect states, that induces tailing of the conduction band. Band gap narrowing extends the photoactivity of TiO2 to visible light. The impurity band located below the minimum of the conduction band traps excited electrons and suppresses recombination, enhancing the photocatalytic activity.
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71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
61.72.up Other materials

End-of-range defects in germanium and their role in boron deactivation

F. Panciera, P. F. Fazzini, M. Collet, J. Boucher, E. Bedel, and F. Cristiano

Appl. Phys. Lett. 97, 012105 (2010); http://dx.doi.org/10.1063/1.3456537 (3 pages) | Cited 4 times

Online Publication Date: 7 July 2010

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We investigated the thermal evolution of end-of-range (EOR) defects in germanium and their impact on junction thermal stability. After solid-phase epitaxial regrowth of a preamorphized germanium layer, EOR defects exhibiting dislocation loop-like contrast behavior are present. These defects disappear during thermal annealing at 400 °C, while boron electrical deactivation occurs. After the whole defect population vanishes, boron reactivation is observed. These results indicate that germanium self-interstitials, released by EOR defects, are the cause of B deactivation. Unlike in Si, the whole deactivation/reactivation cycle in Ge is found to take place while the maximum active B concentration exceeds its solubility limit.
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68.35.Fx Diffusion; interface formation
66.30.J- Diffusion of impurities
81.40.Gh Other heat and thermomechanical treatments
61.72.jj Interstitials

High performance atomic-layer-deposited LaLuO3/Ge-on-insulator p-channel metal-oxide-semiconductor field-effect transistor with thermally grown GeO2 as interfacial passivation layer

J. J. Gu, Y. Q. Liu, M. Xu, G. K. Celler, R. G. Gordon, and P. D. Ye

Appl. Phys. Lett. 97, 012106 (2010); http://dx.doi.org/10.1063/1.3462303 (3 pages) | Cited 7 times

Online Publication Date: 8 July 2010

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Enhancement-mode p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) on germanium-on-insulator substrate is fabricated with atomic-layer-deposited (ALD) LaLuO3 as gate dielectric. Significant improvement in both on-state current and effective hole mobility has been observed for devices with thermal GeO2 passivation. The negative threshold voltage (VT) shift in devices with GeO2 interfacial layer (IL) further demonstrates the effectiveness of surface passivation. Results from low temperature mobility characterization show that phonon scattering is the dominant scattering mechanism at a large inversion charge, indicating good interface quality. The combination of higher-k LaLuO3 and ultrathin GeO2 IL is a promising solution to the tradeoff between the aggressive equivalent oxide thickness scaling and good interface quality.
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85.30.Tv Field effect devices

Dramatic mobility enhancements in doped SrTiO3 thin films by defect management

Y. Kozuka, Y. Hikita, C. Bell, and H. Y. Hwang

Appl. Phys. Lett. 97, 012107 (2010); http://dx.doi.org/10.1063/1.3457994 (3 pages) | Cited 8 times

Online Publication Date: 8 July 2010

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We report bulk-quality n-type SrTiO3 (n-SrTiO3) thin films fabricated by pulsed laser deposition, with electron mobility as high as 6600 cm2 V−1 s−1 at 2 K and carrier density as low as 2.0×1018 cm−3 ( ∼ 0.02 at. %), far exceeding previous pulsed laser deposition films. This result stems from precise strontium and oxygen vacancy defect chemistry management, providing a general approach for defect control in complex oxide heteroepitaxy.
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68.55.ag Semiconductors
81.05.Hd Other semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
81.15.Fg Pulsed laser ablation deposition
61.72.jd Vacancies

Ion versus pH sensitivity of ungated AlGaN/GaN heterostructure-based devices

Anna Podolska, Martin Kocan, Alex M. Garces Cabezas, Timothy D. Wilson, Gilberto A. Umana-Membreno, Brett D. Nener, Giacinta Parish, Stacia Keller, and Umesh K. Mishra

Appl. Phys. Lett. 97, 012108 (2010); http://dx.doi.org/10.1063/1.3462323 (3 pages) | Cited 5 times

Online Publication Date: 9 July 2010

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We have investigated the pH and ion sensitivity of AlGaN/GaN heterostructure devices; these devices are sensitive to the ion concentration rather than to the pH of the solution. Sheet resistance as a function of pH for calibrated pH solutions and dilute NaOH, HCl, KOH, and NaCl showed an increase as a function of ionic concentration, regardless of whether the pH was acidic, basic, or neutral. An increase in resistance corresponds to accumulation of negative ions at the AlGaN surface, indicating device selectivity toward the negative ions. We attribute this to the formation of a double layer at the liquid/semiconductor interface.
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85.30.Tv Field effect devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
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