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7 Mar 2011

Volume 98, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 98, 104101 (2011); http://dx.doi.org/10.1063/1.3560505 (3 pages)

Zhongchang Wang, Susumu Tsukimoto, Rong Sun, Mitsuhiro Saito, and Yuichi Ikuhara
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Surface band bending and electron affinity as a function of hole accumulation density in surface conducting diamond

M. T. Edmonds, C. I. Pakes, S. Mammadov, W. Zhang, A. Tadich, J. Ristein, and L. Ley

Appl. Phys. Lett. 98, 102101 (2011); http://dx.doi.org/10.1063/1.3561760 (3 pages) | Cited 4 times

Online Publication Date: 7 March 2011

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Simultaneous measurements of work function (ϕ) and C 1s core level shift were employed to determine the change in electron affinity (χ) and band bending as a function of hole sheet density on H-terminated diamond for atmospheric and fullerene (C60F48) induced surface conductivity. Contrary to earlier investigations, it is shown that changes in work function do not reflect variations in the position of the surface Fermi level in response to surface transfer doping. Instead, with a transition from −0.96 to −0.33 eV, χ accounts for a significant amount of the change in ϕ for hole densities between 5×108 and 4×1013 cm−2.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.25.+i Surface conductivity and carrier phenomena
81.05.ug Diamond

Nonlinear transport properties and Joule heating effect in charge ordered LuFe2O4

S. Cao, J. Li, H. F. Tian, Y. B. Qin, L. J. Zeng, H. X. Yang, and J. Q. Li

Appl. Phys. Lett. 98, 102102 (2011); http://dx.doi.org/10.1063/1.3562314 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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The nonlinear current-voltage (I-V) relation of charge ordered (CO) LuFe2O4 has been studied in the temperature range from 220 to 520 K. Strong nonlinear effects are identified in the CO state and disappear in high-temperature charge disordered state. Alternation of the CO state under applied electric field is directly revealed by in situ transmission electron microscopy observations. Careful investigations of time-dependent resistance under the applied electric field near the threshold value (Eth) often show three distinct steps for the nonlinear transitions. The CO collapse likely at a critical conductivity yields a sharp drop in resistance.
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72.60.+g Mixed conductivity and conductivity transitions
72.80.Sk Insulators
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.

Photocarrier relaxation through the manifold of localized states in a polymer-fullerene bulk heterojunction material

Nelson E. Coates, Daniel Moses, and Alan J. Heeger

Appl. Phys. Lett. 98, 102103 (2011); http://dx.doi.org/10.1063/1.3562371 (3 pages) | Cited 2 times

Online Publication Date: 7 March 2011

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We investigate the transport and relaxation of photogenerated carriers in a polymer-fullerene bulk-heterojunction (BHJ) material by measuring the transient photoconductivity as a function of the sample temperature. Data in the nanosecond time regime indicate that following the initial trapping (within ∼ 100 ps), the photogenerated carriers relax into the manifold of disorder-induced localized states near the band edge, and the transport becomes thermally activated. By measuring the temporal dependence of the transport activation energy, we are able to monitor the relaxation of carriers into deeper traps, with a corresponding reduction in carrier mobility. A comparison of BHJs made from different molecular weight poly(3-hexylthiophene) (P3HT) (21 and 95 kDa), indicates that higher molecular weight polymer in the BHJ material yields a consistently higher activation energy. The reduction in the carrier mobility in BHJ materials made with higher molecular weight P3HT is confirmed by steady-state photoconductivity measurements. In contrast to disordered inorganic semiconductors (e.g., amorphous silicon), the activation energies associated with the density of states in the disorder-induced band tails are a small fraction (<10%) of the band gap energy of P3HT.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.-c Electronic transport in interface structures

Influence of electric field on persistent photoconductivity in unintentionally doped n-type GaN

Qifeng Hou, Xiaoliang Wang, Hongling Xiao, Cuimei Wang, Cuibai Yang, Haibo Yin, Qingwen Deng, Jinmin Li, Zhanguo Wang, and Xun Hou

Appl. Phys. Lett. 98, 102104 (2011); http://dx.doi.org/10.1063/1.3562008 (3 pages)

Online Publication Date: 8 March 2011

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The influence of electric field on persistent photoconductivity in unintentionally doped n-GaN is investigated. It was found that under higher electric field the build-up course was slowed down while the decay course was accelerated. After a higher-voltage pulse, it was observed that the current dropped to a value lower than the dark current, and a current increase that lasted for thousands of seconds was observed. It is suggested that the above phenomena should be caused by the increase in capture rate of electron traps with electric field and are related to the Coulomb-repulsive characteristic of defects related to persistent photoconductivity.
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72.40.+w Photoconduction and photovoltaic effects
73.23.Hk Coulomb blockade; single-electron tunneling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Ea III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Charge transfer dynamics in Cu-doped ZnO nanowires

Guozhong Xing, Guichuan Xing, Mingjie Li, Edbert Jarvis Sie, Dandan Wang, Arief Sulistio, Quan-lin Ye, Cheng Hon Alfred Huan, Tom Wu, and Tze Chien Sum

Appl. Phys. Lett. 98, 102105 (2011); http://dx.doi.org/10.1063/1.3558912 (3 pages) | Cited 11 times

Online Publication Date: 8 March 2011

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Time resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy reveal an ultrafast charge transfer (CT) process, with an electron localization time constant 39±9 ps, between the ZnO host and the Cu dopants in Cu-doped ZnO nanowires. This CT process effectively competes with the ZnO band edge emission, resulting in the quenching of the ZnO UV emission. TRPL measurements show that the UV decay dynamics coincides with the buildup of the Cu-related green emission. TA measurements probing the state-filling of the band edge and defect states provide further support to the CT model where the bleaching dynamics concur with the TRPL lifetimes.
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73.63.Nm Quantum wires
78.67.Lt Quantum wires
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.67.Uh Nanowires

Thin-film transistors based on poly(3,3‴-dialkyl-quarterthiophene) and zinc oxide nanowires with improved ambient stability

Sara M. C. Vieira, Gen-Wen Hsieh, Husnu E. Unalan, Sefa Dag, Gehan A. J. Amaratunga, and William I. Milne

Appl. Phys. Lett. 98, 102106 (2011); http://dx.doi.org/10.1063/1.3560982 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2011

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The ambient stability of thin-film transistors (TFTs) based on zinc oxide (ZnO) nanowires embedded in poly(3,3‴-dialkyl-quarterthiophene) was monitored through time dependence of electrical characteristics over a period of 16 months. The hybrid-based TFT showed an initial hole mobility in the linear regime of 4.2×10−4 cm2/V s. After 16 months storage in ambient conditions (exposed to air, moisture, and light) the mobility decreased to 2.3×10−5 cm2/V s. Comparatively the organic-based TFT lost total carrier mobility after one month storage making the hybrid-based TFTs more suitable for transistor applications when improved stability combined with structural flexibility are required.
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85.30.Tv Field effect devices
81.05.Dz II-VI semiconductors
81.07.Gf Nanowires

Correlation of photoconductivity response of amorphous In–Ga–Zn–O films with transistor performance using microwave photoconductivity decay method

Satoshi Yasuno, Toshihiro Kugimiya, Shinya Morita, Aya Miki, Futoshi Ojima, and Shingo Sumie

Appl. Phys. Lett. 98, 102107 (2011); http://dx.doi.org/10.1063/1.3561755 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2011

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The film quality of amorphous In–Ga–Zn–O (a-IGZO), an amorphous oxide semiconductor (AOS), was studied by the microwave photoconductivity decay (μ-PCD) method. Also, μ-PCD mappings over a 6 in. wafer were undertaken. It was found that the peak signal of the decay curve had a strong correlation with the a-IGZO transistor performance and hence the film quality. The film annealed under a wet condition showed the highest mobility and had the highest peak signal. The μ-PCD method was found to be a very useful tool to evaluate the film quality and predict the performance of AOS transistors fabricated under different process conditions.
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73.61.Jc Amorphous semiconductors; glasses
73.61.Ga II-VI semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.50.Mx High-frequency effects; plasma effects
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.Tv Field effect devices

Reversible electron pumping and negative differential resistance in two-step barrier diode under strong terahertz ac field

G. Murillo, P. A. Schulz, and J. C. Arce

Appl. Phys. Lett. 98, 102108 (2011); http://dx.doi.org/10.1063/1.3562309 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2011

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A computational study, employing a Floquet-transfer-matrix approach, of the current in a model two-step barrier diode under intense ac fields in the terahertz range is reported. It is demonstrated that the field pumps a net tunnel current through the structure, which can exhibit a negative differential resistance and whose direction can be controlled by the ac-bias amplitude. These behaviors are seen to originate from the inelastic scattering of incoming electrons by absorption or emission of field quanta from a shape resonance present in the field-free structure.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling
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Effects of tip induced carrier density in local tunnel spectra of graphene

Shyam K. Choudhary and Anjan K. Gupta

Appl. Phys. Lett. 98, 102109 (2011); http://dx.doi.org/10.1063/1.3555344 (3 pages)

Online Publication Date: 9 March 2011

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We report on tip induced carrier density changes in local tunnel spectra of single layer graphene (SLG) with backgate using room-temperature scanning tunneling microscopy (STM) and spectroscopy. The SLG samples, prepared by exfoliation method and verified by Raman spectra, show atomically resolved honeycomb lattice. Local tunnel spectra show two minima with the two moving in opposite directions along the bias axis. One minimum shows nearly a square-root dependence, and the other shows a linear dependence on gate voltage. We understand these features as arising from the STM tip induced and bias voltage dependent change in carrier density in SLG.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Gk Tunneling

Influence of the substrate temperature on the Curie temperature and charge carrier density of epitaxial Gd-doped EuO films

T. Mairoser, A. Schmehl, A. Melville, T. Heeg, W. Zander, J. Schubert, D. E. Shai, E. J. Monkman, K. M. Shen, T. Z. Regier, D. G. Schlom, and J. Mannhart

Appl. Phys. Lett. 98, 102110 (2011); http://dx.doi.org/10.1063/1.3563708 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2011

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Rare earth doping is a standard, yet experimentally poorly understood method to increase the Curie temperature (TC) of the ferromagnetic semiconductor EuO. Here, we report on the charge carrier density (n) and the TC of commonly used 4.2 at. % Gd-doped EuO films grown by molecular-beam epitaxy on (110) oriented YAlO3 substrates at various substrate temperatures (Tsub). Increasing Tsub leads to a decrease in n and TC. For high substrate temperatures the Gd-doping is rendered completely inactive: n and TC drop to the values of undoped EuO.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Le Other inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials

Mode-filtered electron injection into a waveguide interferometer

Sven S. Buchholz, Ulrich Kunze, Dirk Reuter, Andreas D. Wieck, and Saskia F. Fischer

Appl. Phys. Lett. 98, 102111 (2011); http://dx.doi.org/10.1063/1.3563714 (3 pages)

Online Publication Date: 10 March 2011

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Injection of mode-filtered electrons into a phase-sensitive four-terminal waveguide Aharonov–Bohm (AB) ring is studied. An individually tuneable quantum point contact (QPC) in a waveguide lead of the GaAs/AlGaAs-ring allows to selectively couple to one-dimensional modes in the ring. Thus, we demonstrate single-mode transport in a multimode waveguide structure. Coherent mode-filtering by the lowest QPC subband is verified by nonlocal bend resistance and phase-sensitive AB interference measurements.
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73.23.-b Electronic transport in mesoscopic systems
81.05.Ea III-V semiconductors

Room temperature electrical injection and detection of spin polarized carriers in silicon using MgO tunnel barrier

Nathan W. Gray and Ashutosh Tiwari

Appl. Phys. Lett. 98, 102112 (2011); http://dx.doi.org/10.1063/1.3564889 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2011

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We are reporting room-temperature, all electrical injection and detection of spin polarized carriers in silicon using NiFe/MgO tunnel-barrier-contacts. From the magnetic field dependence of the spin accumulation voltage, spin-lifetime, and diffusion-length of the carriers were determined to be 276 ps and 328 nm, respectively. For comparison, similar experiments were also performed using NiFe/Al2O3 tunnel-barrier-contacts. However, in the latter case spin-lifetime and diffusion-length were found to be lower ( ∼ 107 ps, 204 nm) demonstrating the superiority of MgO barrier for spin-injection application. Attaining spin diffusion lengths of >320 nm in Si channels is a ground breaking step and opens tremendous opportunities for integrating spin functionality into post-Moore-era electronic devices.
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72.25.Hg Electrical injection of spin polarized carriers
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Schottky-barrier lowering in silicon nanowire field-effect transistors prepared by metal-assisted chemical etching

M. Zaremba-Tymieniecki and Z. A. K. Durrani

Appl. Phys. Lett. 98, 102113 (2011); http://dx.doi.org/10.1063/1.3565971 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2011

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We investigate the influence of Schottky barrier lowering in Si nanowire field-effect transistors, using nanowires prepared by metal-assisted chemical etching. The experimental electrical characteristics of a p-channel transistor are modeled using thermionic emission of holes across the reverse-biased source Schottky barrier. This barrier is lowered by the image-force potential, and by the electric field generated by both source-drain and gate voltages. The gate voltage lowers the barrier height directly and in addition, modulates the effect of the source-drain voltage on barrier lowering.
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85.30.Tv Field effect devices
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