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12 May 2008

Volume 92, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 92, 193301 (2008); http://dx.doi.org/10.1063/1.2920199 (3 pages)

Wei Chen, Hong Liang Zhang, Han Huang, Lan Chen, and Andrew Thye Shen Wee
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Stable ZnO thin film transistors by fast open air atomic layer deposition

David H. Levy, Diane Freeman, Shelby F. Nelson, Peter J. Cowdery-Corvan, and Lyn M. Irving

Appl. Phys. Lett. 92, 192101 (2008); http://dx.doi.org/10.1063/1.2924768 (3 pages) | Cited 67 times

Online Publication Date: 12 May 2008

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We report stable, high performance zinc oxide thin film transistors grown by an atmospheric pressure atomic layer deposition system. With all deposition and processing steps kept at or below 200 °C, the alumina gate dielectric shows low leakage (below 10−8 A/cm2) and high breakdown fields. Zinc oxide thin film transistors in a bottom gate geometry yield on/off ratios above 108, near zero turn-on voltage, little or no hysteresis, and mobility greater than 10 cm2/V s. With alumina passivation, shifts in threshold voltage under gate bias stress compare favorably to those reported in the literature.
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81.05.Dz II-VI semiconductors
85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.Rv Passivation

Tunnel spectroscopy in ac-driven quantum dot nanoresonators

J. Villavicencio, I. Maldonado, R. Sánchez, E. Cota, and G. Platero

Appl. Phys. Lett. 92, 192102 (2008); http://dx.doi.org/10.1063/1.2919797 (3 pages) | Cited 2 times

Online Publication Date: 12 May 2008

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Electronic transport in a triple quantum dot shuttle device in the presence of an ac field is analyzed within a fully quantum mechanical framework. A generalized density matrix formalism is used to describe the time evolution for electronic state occupations in a dissipative phonon bath. In the presence of an ac gate voltage, the electronic states are dressed by photons and the interplay between photon and vibrational sidebands produces current characteristics that obey selection rules. Varying the ac parameters allows to tune the tunneling current features. In particular, we show that coherent destruction of tunneling can be achieved in our device.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.-p Nanoelectronic devices
85.65.+h Molecular electronic devices

c-erbB-2 sensing using AlGaN/GaN high electron mobility transistors for breast cancer detection

K. H. Chen, B. S. Kang, H. T. Wang, T. P. Lele, F. Ren, Y. L. Wang, C. Y. Chang, S. J. Pearton, D. M. Dennis, J. W. Johnson, P. Rajagopal, J. C. Roberts, E. L. Piner, and K. J. Linthicum

Appl. Phys. Lett. 92, 192103 (2008); http://dx.doi.org/10.1063/1.2926656 (3 pages) | Cited 14 times

Online Publication Date: 12 May 2008

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Antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect c-erbB-2, which is a breast cancer marker. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 s when target c-erbB-2 antigen in a buffer at clinically relevant concentrations was added to the antibody-immobilized surface. We could detect a range of concentrations from 16.7 to 0.25 μg/ml. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN/GaN HEMTs for breast cancer screening.
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87.19.xj Cancer
87.85.-d Biomedical engineering

Efficient suppression of charge trapping in ZnO-based transparent thin film transistors with novel Al2O3/HfO2/Al2O3 structure

Seongpil Chang, Yong-Won Song, Sanggyu Lee, Sang Yeol Lee, and Byeong-Kwon Ju

Appl. Phys. Lett. 92, 192104 (2008); http://dx.doi.org/10.1063/1.2924769 (3 pages) | Cited 26 times

Online Publication Date: 13 May 2008

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Charge trapping is dramatically suppressed in ZnO transparent thin film transistors (TFTs) employing a multilayered gate insulator with HfO2 layer sandwiched by Al2O3 layers. In spite of its high dielectric constant, HfO2 has critical drawbacks including huge charge trap density in interfaces. We suggest and demonstrate an elegant solution to minimize the charge trapping introducing Al2O3 buffer layers. The operation of Al2O3/HfO2/Al2O3 multilayered gate-insulator structure in the ZnO transparent TFT is evaluated to ensure the voltage difference in the hysteresis loop as low as 0.2 V, and the immunization to the threshold voltage shift induced by repeated sweeps of gate voltage.
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85.30.Tv Field effect devices

Conductive atomic force microscopy of InAs/GaAs quantum rings

Tomaž Mlakar, Giorgio Biasiol, Stefan Heun, Lucia Sorba, T. Vijaykumar, G. U. Kulkarni, Vittorio Spreafico, and Stefano Prato

Appl. Phys. Lett. 92, 192105 (2008); http://dx.doi.org/10.1063/1.2928220 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2008

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The properties of self-assembled InAs/GaAs quantum rings are investigated by conductive atomic force microscopy. Our two-dimensional current maps and current-voltage curves show a lower conductivity of the central ring hole as compared to rim and surrounding planar region. This result is quite surprising if we take into account the compositional profile of quantum rings: being the region with the highest In concentration, one would expect the central hole to be the region with the highest conductivity. However, including the presence of a surface oxide into numerical simulations yields consistent results, which show the same qualitative behavior as the measured conductivities.
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73.63.Hs Quantum wells
68.37.Ps Atomic force microscopy (AFM)
68.35.bg Semiconductors

Robust single-parameter quantized charge pumping

B. Kaestner, V. Kashcheyevs, G. Hein, K. Pierz, U. Siegner, and H. W. Schumacher

Appl. Phys. Lett. 92, 192106 (2008); http://dx.doi.org/10.1063/1.2928231 (3 pages) | Cited 14 times

Online Publication Date: 14 May 2008

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This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs–GaAs gated nanowire. We find a remarkable robustness of the quantized regime against variations in the driving signal, which increases with applied rf power. This feature, together with its simple configuration, makes this device a potential module for a scalable source of quantized current.
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85.35.Gv Single electron devices
85.30.-z Semiconductor devices

Valence band offset of ZnO/4H-SiC heterojunction measured by x-ray photoelectron spectroscopy

H. B. Fan, G. S. Sun, S. Y. Yang, P. F. Zhang, R. Q. Zhang, H. Y. Wei, C. M. Jiao, X. L. Liu, Y. H. Chen, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 92, 192107 (2008); http://dx.doi.org/10.1063/1.2926679 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2008

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The valence band offset (VBO) of the wurtzite ZnO/4H-SiC heterojunction is directly determined to be 1.61±0.23 eV by x-ray photoelectron spectroscopy. The conduction band offset is deduced to be 1.50±0.23 eV from the known VBO value, which indicates a type-II band alignment for this heterojunction. The experimental VBO value is confirmed and in good agreement with the calculated value based on the transitive property of heterojunctions between ZnO, SiC, and GaN.
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71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces

ZnO metal-semiconductor field-effect transistors with Ag-Schottky gates

H. Frenzel, A. Lajn, M. Brandt, H. von Wenckstern, G. Biehne, H. Hochmuth, M. Lorenz, and M. Grundmann

Appl. Phys. Lett. 92, 192108 (2008); http://dx.doi.org/10.1063/1.2926684 (3 pages) | Cited 27 times

Online Publication Date: 14 May 2008

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Metal-semiconductor field-effect transistors (MESFETs) were fabricated by reactive dc sputtering of Ag-Schottky gate contacts on ZnO thin-film channels grown by pulsed-laser deposition on sapphire. The n-type conductivity (normally on) of typical MESFETs is tunable over 8 decades in a voltage range of 2.5 V with an off voltage of −1.5 V and very low off-current density in the range of 10−6 A/cm2. Channel mobilities of up to 27 cm2/V s have been achieved.
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85.30.Tv Field effect devices

Giant positive magnetoresistance in Co-doped ZnO nanocluster films

Y. F. Tian, J. Antony, R. Souza, S. S. Yan, L. M. Mei, and Y. Qiang

Appl. Phys. Lett. 92, 192109 (2008); http://dx.doi.org/10.1063/1.2921051 (3 pages) | Cited 6 times

Online Publication Date: 15 May 2008

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We have studied nanostructures and magnetoresistance of 0.5%, 12%, and 30% Co-doped ZnO nanocluster films which were deposited by a third generation sputtering-gas-aggregation source on Si wafer. Microstructure analysis is performed by x-ray photoelectron spectrometer, transmission electron microscopy, and x-ray diffraction and shows a uniform mean nanocrystallite size of 20 nm with perfect wurtzite ZnO structure. Magnetoresistance (MR) increases at 5 K with Co doping concentration, that is, 0.5% Co-doped ZnO with 469% MR, while the other two samples have 744% and 811%. The large positive MR is explained by the suppression of spin-dependent hopping paths when localized states with onsite correlation undergo a relatively large spin (Zeeman) splitting in a magnetic field due to strong s,p-d interactions in Co-doped ZnO nanocluster films.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ga II-VI semiconductors
61.72.U- Doping and impurity implantation
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.ag Semiconductors
72.20.Ee Mobility edges; hopping transport

Effect of molecular beam epitaxy growth conditions on the Bi content of GaAs1−xBix

X. Lu, D. A. Beaton, R. B. Lewis, T. Tiedje, and M. B. Whitwick

Appl. Phys. Lett. 92, 192110 (2008); http://dx.doi.org/10.1063/1.2918844 (3 pages) | Cited 21 times

Online Publication Date: 15 May 2008

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We describe how the Bi content of GaAs1−xBix epilayers grown on GaAs can be controlled by the growth conditions in molecular beam epitaxy. Nonstandard growth conditions are required because of the strong tendency for Bi to surface segregate under usual growth conditions for GaAs. A maximum Bi content of 10% is achieved at low substrate temperature and low arsenic pressure, as inferred from x-ray diffraction measurements. A model for bismuth incorporation is proposed that fits a large body of experimental data on Bi content for a wide range of growth conditions. Low growth rates are found to facilitate the growth of bismide alloys with a low density of Bi droplets.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

High quality GaN grown on silicon(111) using a SixNy interlayer by metal-organic vapor phase epitaxy

Kai Cheng, M. Leys, S. Degroote, M. Germain, and G. Borghs

Appl. Phys. Lett. 92, 192111 (2008); http://dx.doi.org/10.1063/1.2928224 (3 pages) | Cited 18 times

Online Publication Date: 15 May 2008

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High quality GaN layers with dislocation density of (3.0±0.5)×108/cm2 have been grown on silicon(111) substrates using a combination of AlGaN intermediate layers and a SixNy interlayer. A smooth and fully coalesced layer was obtained by virtue of a high temperature growth process which accelerates coalescence and improves at the same time the crystalline quality. This was confirmed by high resolution x-ray diffraction showing a full width of half maximum of 415 arc sec for the asymmetric (−2201) rocking curve.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Study on threading dislocations blocking mechanism of GaN/AlxGa1−xN superlattices

L. W. Sang, Z. X. Qin, H. Fang, X. R. Zhou, Z. J. Yang, B. Shen, and G. Y. Zhang

Appl. Phys. Lett. 92, 192112 (2008); http://dx.doi.org/10.1063/1.2929377 (3 pages) | Cited 5 times

Online Publication Date: 15 May 2008

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GaN/AlxGa1−xN superlattices (SLs) with different period thicknesses tp were grown as interlayers between GaN and AlyGa1−yN epilayers. The effect of threading dislocations (TDs) blocking became more evident with increasing tp. Transmission electron microscopy analysis shows that TDs are inclined to be bended in SLs and terminated in GaN wells as a result of strain. X-ray diffraction measurement also validated that GaN wells played a more important role as a TDs filter. The blocking of TDs in SLs resulted in an abnormal decrease in relaxation factors R(SLs) with increasing tp.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.65.Cd Superlattices
68.35.Gy Mechanical properties; surface strains
68.35.Dv Composition, segregation; defects and impurities

Effect of frequency and temperature on microwave-induced magnetoresistance oscillations in two-dimensional electron systems

Jesús Iñarrea

Appl. Phys. Lett. 92, 192113 (2008); http://dx.doi.org/10.1063/1.2920170 (3 pages) | Cited 14 times

Online Publication Date: 15 May 2008

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Experimental results on microwave-induced magnetoresistance oscillations in two-dimensional electron systems show a similar behavior regarding temperature and microwave frequency. It is found that these oscillations tend to quench when frequency or temperature increases, approaching magnetoresistance to the response of the dark system. In this work, we show that this experimental behavior can be addressed on the same theoretical basis. Microwave radiation forces the electron orbits to move back and forth being damped by interaction with the lattice. We show that this damping dramatically depends on microwave frequency and also on temperature.
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73.63.-b Electronic transport in nanoscale materials and structures
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.30.+q High-frequency effects; plasma effects

Lifetime and diffusion length of photogenerated minority carriers in single-crystalline n-type β-FeSi2 bulk

Teruhisa Ootsuka, Takashi Suemasu, Jun Chen, Takashi Sekiguchi, and Yoshiaki Hara

Appl. Phys. Lett. 92, 192114 (2008); http://dx.doi.org/10.1063/1.2929744 (3 pages) | Cited 11 times

Online Publication Date: 15 May 2008

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We have evaluated the lifetime and diffusion length of photogenerated minority carriers (holes) in single-crystalline n-type β-FeSi2 bulk grown by chemical vapor transport. The diffusion length measured by optical-beam-induced current agreed well with that measured by electron-beam-induced current, that is, 51 and 38 μm, respectively, for samples annealed at 800 °C for 8 h. The decay curve of photoconductivity obtained by 1.31 and 1.55 μm light pulses was well fitted by assuming a carrier lifetime of approximately a few microseconds. The mobility of photogenerated minority carriers was estimated to be approximately 200–360 cm2/V s from the measured lifetime and diffusion length.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors
72.40.+w Photoconduction and photovoltaic effects

A hydrogen storage layer on the surface of silicon nitride films

Ziyuan Liu, Shuu Ito, Markus Wilde, Katsuyuki Fukutani, Ichiro Hirozawa, and Tomoyuki Koganezawa

Appl. Phys. Lett. 92, 192115 (2008); http://dx.doi.org/10.1063/1.2921052 (3 pages) | Cited 3 times

Online Publication Date: 16 May 2008

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Composition, layer structure, and H-retaining stability of 980 °C N2-annealed silicon nitride-oxide (ON) stacks were analyzed using high resolution rutherford backscattering, synchrotron x-ray specular reflectometry, and nuclear reaction analysis. The formation of a Si2N2O layer in the near-surface part of N2-annealed nitride films was discovered. The Si2N2O layer can store hydrogen species that are resistant against energetic electron damage due to their reduced diffusion mobility. Although degrading in air, the Si2N2O layer thus provides reliable hydrogen species, which are desirable in the integrated circuit processing of silicon transistors and silicon ONO trap memories.
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84.60.-h Direct energy conversion and storage
81.40.Gh Other heat and thermomechanical treatments

Valence-band offset of epitaxial ZnO/MgO (111) heterojunction determined by x-ray photoelectron spectroscopy

Y. F. Li, B. Yao, Y. M. Lu, B. H. Li, Y. Q. Gai, C. X. Cong, Z. Z. Zhang, D. X. Zhao, J. Y. Zhang, D. Z. Shen, and X. W. Fan

Appl. Phys. Lett. 92, 192116 (2008); http://dx.doi.org/10.1063/1.2924279 (3 pages) | Cited 14 times

Online Publication Date: 16 May 2008

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The valence-band offset of ZnO/MgO (111) heterojunction has been directly measured by x-ray photoelectron spectroscopy. Excluding the strain effect, the valence-band offset is determined to be 0.87±0.20 eV, and the conduction-band offset ΔEC is deduced to be −3.59±0.20 eV, indicating that ZnO/MgO heterojunction has a type-I band alignment. The conduction-band and valence-band offset of MgO/ZnO is used to interpret the origination of p-type conduction in undoped MgxZn1−xO alloy and deeper acceptor level in undoped and N-doped p-type MgxZn1−xO alloy than in ZnO.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures

High-temperature quenching of electrical resistance in graphene interconnects

Q. Shao, G. Liu, D. Teweldebrhan, and A. A. Balandin

Appl. Phys. Lett. 92, 192117 (2008); http://dx.doi.org/10.1063/1.2927371 (3 pages)

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The authors reported on the experimental investigation of the high-temperature electrical resistance of graphene. The test structures were fabricated by using the focused ion beam from the single and bilayer graphene produced by mechanical exfoliation. It was found that as temperature increases from 300 to 500 K, the resistance of the single, and bilayer graphene interconnects drops down by 30% and 70%, respectively. The quenching and temperature dependence of the resistance were explained by the thermal generation of the electron-hole pairs and carrier scattering by acoustic phonons. The obtained results are important for the proposed graphene interconnect applications in integrated circuits.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
81.40.Gh Other heat and thermomechanical treatments
85.40.Ls Metallization, contacts, interconnects; device isolation
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
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