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31 May 2010

Volume 96, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 96, 223101 (2010); http://dx.doi.org/10.1063/1.3439728 (3 pages)

Seokho Yun, Jeremy A. Bossard, Theresa S. Mayer, and Douglas H. Werner
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Permanent optical doping of amorphous metal oxide semiconductors by deep ultraviolet irradiation at room temperature

Hyungtak Seo, Young-Je Cho, Jinwoo Kim, Santosh M.bobade, Kyoung-Youn Park, Jaegab Lee, and Duck-Kyun Choi

Appl. Phys. Lett. 96, 222101 (2010); http://dx.doi.org/10.1063/1.3429586 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2010

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We report an investigation of two photon ultraviolet (UV) irradiation induced permanent n-type doping of amorphous InGaZnO (a-IGZO) at room temperature. The photoinduced excess electrons were donated to change the Fermi-level to a conduction band edge under the UV irradiation, owing to the hole scavenging process at the oxide interface. The use of optically n-doped a-IGZO channel increased the carrier density to ∼ 1018 cm−3 from the background level of 1016 cm−3, as well as the comprehensive enhancement upon UV irradiation of a-IGZO thin film transistor parameters, such as an on-off current ratio at ∼ 108 and field-effect mobility at 22.7 cm2/V s.
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61.82.Fk Semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
73.61.Ga II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Theory of electroluminescence intensity and insights into recombination in thin film solar cells

Gregory Brown, Vladimir Faifer, Ben Cardozo, Eugene Bykov, and Miguel Contreras

Appl. Phys. Lett. 96, 222102 (2010); http://dx.doi.org/10.1063/1.3443637 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2010

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Equations describing the electroluminescence (EL) intensity as a function of material properties are derived for thin film solar cells and experimentally validated using Cu(In,Ga)Se2 solar cells. EL intensity at constant voltage is controlled by the electronic properties of the neutral bulk even when the diode current is controlled by recombination in the space charge region. Using a combination of techniques, it is found that recombination in the quasineutral bulk does not correlate with recombination in the space charge region. Differences between EL measurements on thin film cells and crystalline silicon cells are discussed including the effects of secondary barriers.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
85.30.De Semiconductor-device characterization, design, and modeling

Morphology characterization of argon-mediated epitaxial graphene on C-face SiC

J. L. Tedesco, G. G. Jernigan, J. C. Culbertson, J. K. Hite, Y. Yang, K. M. Daniels, R. L. Myers-Ward, C. R. Eddy, J. A. Robinson, K. A. Trumbull, M. T. Wetherington, P. M. Campbell, and D. K. Gaskill

Appl. Phys. Lett. 96, 222103 (2010); http://dx.doi.org/10.1063/1.3442903 (3 pages) | Cited 18 times

Online Publication Date: 1 June 2010

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Epitaxial graphene layers were grown on the C-face of 4H–SiC and 6H–SiC using an argon-mediated growth process. Variations in growth temperature and pressure were found to dramatically affect the morphological properties of the layers. The presence of argon during growth slowed the rate of graphene formation on the C-face and led to the observation of islanding. The similarity in the morphology of the islands and continuous films indicated that island nucleation and coalescence is the growth mechanism for C-face graphene.
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81.05.ue Graphene
68.55.-a Thin film structure and morphology
68.55.J- Morphology of films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Enhanced conductivity of tunnel junctions employing semimetallic nanoparticles through variation in growth temperature and deposition

Hari P. Nair, Adam M. Crook, and Seth R. Bank

Appl. Phys. Lett. 96, 222104 (2010); http://dx.doi.org/10.1063/1.3442909 (3 pages) | Cited 5 times

Online Publication Date: 1 June 2010

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We report ErAs nanoparticle-enhanced tunnel junctions grown on GaAs with low specific resistances (<2×10−4 Ω cm−2), approximately tenfold lower than previous reports. A reduction in specific resistance was achieved by modifying the ErAs nanoparticle morphology through the molecular beam epitaxial growth conditions, particularly lower growth temperatures. A further investigation of the variation in tunnel junction resistance with the amount of ErAs deposited and growth temperature shows that nanoparticle surface coverage may not be the only factor determining tunnel junction resistance.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.A- Nucleation and growth
73.61.At Metal and metallic alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)

Self-confined GaN heterophased quantum wells

Ikai Lo, Yu-Chi Hsu, Chia-Ho Hsieh, Wen-Yuan Pang, Mitch M. C. Chou, Yen-Liang Chen, Cheng-Hung Shih, and Ying-Chieh Wang

Appl. Phys. Lett. 96, 222105 (2010); http://dx.doi.org/10.1063/1.3442497 (3 pages)

Online Publication Date: 2 June 2010

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Wurtzite/zinc-blende/wurtzite GaN heterophased quantum wells (QWs) were grown by plasma-assisted molecular beam epitaxy. A self-assembling mechanism was used to simulate the heterophased QW, in which a wurtzite/zinc-blende phase transition was created by rotating the threefold symmetric N-Ga vertical bond 60°. The GaN heterophased QW was attested by transmission electron microscopy, selective area electron diffraction and cathodoluminescence measurements.
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81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.ag Semiconductors

Band structure measurement of organic single crystal with angle-resolved photoemission

Huanjun Ding, Colin Reese, Antti J. Mäkinen, Zhenan Bao, and Yongli Gao

Appl. Phys. Lett. 96, 222106 (2010); http://dx.doi.org/10.1063/1.3446849 (3 pages) | Cited 8 times

Online Publication Date: 3 June 2010

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The electronic structure of bulk rubrene single crystal was studied with angle-resolved photoemission spectroscopy. Highly reproducible dispersive features were observed with nice symmetry about the Brillouin zone center and boundaries, representing the band structure measured for a bulk organic single crystal. The high quality of the surface was confirmed with scanning tunneling microscopy. The energy dispersion of the highest occupied molecular orbitals derived bands showed strong anisotropic behavior in the a-b plane of the unit cell. The measured band structure, however, differs unexpectedly from theoretical calculations in terms of the amount of the dispersion and the separation of the bands.
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71.20.Rv Polymers and organic compounds
79.60.Fr Polymers; organic compounds

Quantum confinement effects in Si/Ge heterostructures with spatially ordered arrays of self-assembled quantum dots

Oleksiy B. Agafonov, Christian Dais, Detlev Grützmacher, and Rolf J. Haug

Appl. Phys. Lett. 96, 222107 (2010); http://dx.doi.org/10.1063/1.3442508 (3 pages) | Cited 2 times

Online Publication Date: 3 June 2010

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Magnetotunneling spectroscopy was employed to probe the confinement in vertical Si/Ge double-barrier resonant tunneling diodes with regularly distributed Ge quantum dots. Their current-voltage characteristics reveal a steplike behavior in the vicinity of zero bias, indicating resonant tunneling of heavy-holes via three-dimensionally confined unoccupied hole states in Ge quantum dots. Assuming parabolic confinement, we extract the strength of the confinement potential of quantum dots.
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78.20.Ls Magneto-optical effects
73.21.La Quantum dots
75.75.Lf Electronic structure of magnetic nanoparticles
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.16.Dn Self-assembly
73.40.Jn Metal-to-metal contacts

Improvement of resistance switching characteristics in a thin FeOx transition layer of TiN/SiO2/FeOx/FePt structure by rapid annealing

Li-Wei Feng, Chun-Yen Chang, Yao-Feng Chang, Ting-Chang Chang, Shin-Yuan Wang, Shih-Ching Chen, Chao-Cheng Lin, Shih-Cheng Chen, and Pei-Wei Chiang

Appl. Phys. Lett. 96, 222108 (2010); http://dx.doi.org/10.1063/1.3428777 (3 pages) | Cited 5 times

Online Publication Date: 3 June 2010

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In this paper, the influence of a 600 °C rapid thermal annealing for 60 s on the improvements of resistance switching behaviors in a TiN/SiO2/FeOx/FePt structure is reported. It is found that besides the distinct reduction in memory switching parameters in forming voltage, set/reset voltages, and their dispersions, the resistance ratio of high-resistance state to low-resistance state is also enlarged after annealing. The effects of annealing on improving the resistance switching properties are discussed by x-ray diffraction and x-ray photon-emission spectra depth profile results. Additionally, good retention characteristics are exhibited in the annealed TiN/SiO2/FeOx/FePt resistance switching memory.
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84.30.Sk Pulse and digital circuits

Silicon surface passivation by an organic overlayer of 9,10-phenanthrenequinone

Sushobhan Avasthi, Yabing Qi, Grigory K. Vertelov, Jeffrey Schwartz, Antoine Kahn, and James C. Sturm

Appl. Phys. Lett. 96, 222109 (2010); http://dx.doi.org/10.1063/1.3429585 (3 pages) | Cited 8 times

Online Publication Date: 4 June 2010

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Merged organic-silicon heterojunction devices require the passivation of dangling bonds at the silicon surface, preferably with a low-temperature process. In this paper, we demonstrate the high-quality passivation of the silicon (100) surface using an organic molecule (9,10-phenanthrenequinone, PQ). PQ reacts with the dangling bonds, thus providing a bridge between organic semiconductors and silicon. We measure low recombination velocities ( ∼ 150 cm/s) at the PQ-silicon interface. Metal/organic-insulator/silicon capacitors and transistors prove that at PQ-silicon interface, the Fermi level can be modulated. The formation of an inversion layer with electron mobility of 600 cm2/V∙s further demonstrates the passivation quality of PQ.
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81.65.Rv Passivation
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
84.32.Tt Capacitors

Influence of the oxidizing species on the Ge dangling bonds at the (100)Ge/GeO2 interface

Silvia Baldovino, Alessandro Molle, and Marco Fanciulli

Appl. Phys. Lett. 96, 222110 (2010); http://dx.doi.org/10.1063/1.3446839 (3 pages) | Cited 10 times

Online Publication Date: 4 June 2010

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The nature of the defects present at various Ge/GeO2 interfaces has been investigated by means of electrically detected magnetic resonance (EDMR) spectroscopy. GeO2 thin films were grown by atomic oxygen, ozone, and molecular oxygen exposure. The defect microstructure is sensitive to the oxidizing species, i.e., to the oxidation mechanism. Different EDMR spectra are correlated with the specific electrical response of the corresponding Ge/GeO2 metal-oxide-semiconductor structures.
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68.35.Ct Interface structure and roughness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Extremely low drift of resistance and threshold voltage in amorphous phase change nanowire devices

Mukut Mitra, Yeonwoong Jung, Daniel S. Gianola, and Ritesh Agarwal

Appl. Phys. Lett. 96, 222111 (2010); http://dx.doi.org/10.1063/1.3447941 (3 pages) | Cited 16 times

Online Publication Date: 4 June 2010

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Time-dependent drift of resistance and threshold voltage in phase change memory (PCM) devices is of concern as it leads to data loss. Electrical drift in amorphous chalcogenides has been argued to be either due to electronic or stress relaxation mechanisms. Here we show that drift in amorphized Ge2Sb2Te5 nanowires with exposed surfaces is extremely low in comparison to thin-film devices. However, drift in stressed nanowires embedded under dielectric films is comparable to thin-films. Our results shows that drift in PCM is due to stress relaxation and will help in understanding and controlling drift in PCM devices.
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85.30.-z Semiconductor devices
85.35.-p Nanoelectronic devices
84.30.Sk Pulse and digital circuits
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