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25 Jul 2011

Volume 99, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 99, 041102 (2011); http://dx.doi.org/10.1063/1.3615051 (3 pages)

M. Davanço, M. T. Rakher, D. Schuh, A. Badolato, and K. Srinivasan
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Low temperature solution-processed graphene oxide/Pr0.7Ca0.3MnO3 based resistive-memory device

Insung Kim, Manzar Siddik, Jungho Shin, Kuyyadi P Biju, Seungjae Jung, and Hyunsang Hwang

Appl. Phys. Lett. 99, 042101 (2011); http://dx.doi.org/10.1063/1.3617426 (3 pages) | Cited 3 times

Online Publication Date: 26 July 2011

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We propose a graphene oxide (GO)/Pr0.7Ca0.3MnO3 (PCMO) based resistance random access memory (RRAM) device. Both active layers were prepared by a sol-gel spin-coating method at low temperature (<300 °C).The fabricated Pt/GO/PCMO/Pt RRAM device shows good switching performance with an on/off ratio of about 100 and a retention property of more than 104 at 85 °C and reliable endurance characteristics. Moreover, the observed bipolar switching phenomena could be explained by the movement of oxygen ions across the GO–PCMO interface. These results suggest that the GO/PCMO device is a good candidate for use in resistive memory applications.
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84.30.Sk Pulse and digital circuits

Quantum efficiency of GaN photocathode under different illumination

Xiaohui Wang (王晓晖), Benkang Chang (常本康), Yujie Du (杜玉杰), and Jianliang Qiao (乔建良)

Appl. Phys. Lett. 99, 042102 (2011); http://dx.doi.org/10.1063/1.3614555 (3 pages) | Cited 2 times

Online Publication Date: 26 July 2011

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GaN samples are activated by Cs/O under illumination of deuterium lamp, 300 nm monochromatic light with power of 70 μW and 300 nm monochromatic light with power of 35 μW, respectively. Photocurrent is detected before activation under illumination of deuterium lamp. Quantum efficiency (QE) is tested after activation. The results indicate that GaN activated under 300 nm monochromatic light have higher QE than that under deuterium lamp, and no obvious difference is detected between different power 300 nm monochromatic light. The photocurrent before activation inhibits the adsorption of Cs on the GaN surface, which decrease the QE of GaN.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Weak antilocalization effect in high-mobility two-dimensional electron gas in an inversion layer on p-type HgCdTe

Rui Yang, Kuanghong Gao, Laiming Wei, Xinzhi Liu, Gujin Hu, Guolin Yu, Tie Lin, Shaoling Guo, Yanfeng Wei, Jianrong Yang, Li He, Ning Dai, Junhao Chu, and D. G. Austing

Appl. Phys. Lett. 99, 042103 (2011); http://dx.doi.org/10.1063/1.3615303 (3 pages) | Cited 2 times

Online Publication Date: 26 July 2011

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Magnetoconductance of a gated two-dimensional electron gas (2DEG) in an inversion layer on a p-type HgCdTe film is investigated. At strong magnetic fields, characteristic features such as the quantum Hall effect of a 2DEG with single subband occupation are observed. At weak magnetic fields, the weak antilocalization effect in the ballistic regime is observed. Phase coherence time and zero-field spin-splitting are extracted following Golub’s model [L. E. Golub, Phys. Rev. B 71, 235310 (2005)]. The temperature dependence of the dephasing rate is consistent with the Nyquist mechanism.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance
68.55.ag Semiconductors

Determining contact potential barrier effects on electronic transport in single molecular junctions

Jianfeng Zhou and Bingqian Xu

Appl. Phys. Lett. 99, 042104 (2011); http://dx.doi.org/10.1063/1.3615803 (3 pages) | Cited 4 times

Online Publication Date: 27 July 2011

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The authors introduced a simplified multiple-barrier model based on the widely accepted traditional tunneling model to describe the electron transport behaviors in single molecule junction systems. The contact potential barrier height Φc and the contact decay constant βc were taken as the key indexes to represent certain contact conformations. By monitoring the dynamic changes of contact potential barriers corresponding to the mechanical extension of contact conformations with our newly developed Scanning Probe Microscope (SPM)-break junction technique and then fitting into the model, we established an in-depth and detailed understanding of the molecule-metal contact effects on electronic transport properties in single molecular junctions. © 2011 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling

Giant effect of negative differential conductance in graphene nanoribbon p-n hetero-junctions

V. Hung Nguyen, F. Mazzamuto, J. Saint-Martin, A. Bournel, and P. Dollfus

Appl. Phys. Lett. 99, 042105 (2011); http://dx.doi.org/10.1063/1.3616143 (3 pages) | Cited 9 times

Online Publication Date: 27 July 2011

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The I-V characteristics of graphene nanoribbon (GNR) p-n junctions have been investigated using atomistic quantum simulation. On the basis of results obtained for simple armchair GNR structures with large bandgap, it is suggested to improve significantly the device operation by inserting a small-bandgap section in the transition region between n and p zones. A giant peak-to-valley ratio (PVR) of negative differential conductance (higher than 103) can be achieved in such hetero-junctions. Additionally, the PVR is proved to be weakly sensitive to the transition length and not strongly degraded by the edge disorder, which is an important feature regarding applications.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

SrTiO3 modified TiO2 electrodes and improved dye-sensitized TiO2 solar cells

Sujuan Wu, Xingsen Gao, Minghui Qin, J.-M. Liu, and Shejun Hu

Appl. Phys. Lett. 99, 042106 (2011); http://dx.doi.org/10.1063/1.3617460 (3 pages)

Online Publication Date: 28 July 2011

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The SrTiO3-coated TiO2 (TiO2/SrTiO3) electrodes prepared by radio frequency magnetron sputtering are used to improve the performance of dye-sensitized TiO2 solar cells by means of surface modification. The structural and performance characterizations reveal that the TiO2/SrTiO3 electrodes, in comparison with fresh TiO2 electrodes, have low density of oxygen vacancies, passivated surface states, and suppressed interfacial recombination effect, thus resulting in improved performance parameters of the cells. An optimized coating of SrTiO3 layer on the TiO2 film surface allows an enhancement of the power conversion efficiency from 4.78% to 5.91%.
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88.40.H- Solar cells (photovoltaics)
81.15.Cd Deposition by sputtering
81.65.Rv Passivation
61.72.jd Vacancies

The effect of Bi composition to the optical quality of GaAs1−xBix

A. R. Mohmad, F. Bastiman, C. J. Hunter, J. S. Ng, S. J. Sweeney, and J. P. R. David

Appl. Phys. Lett. 99, 042107 (2011); http://dx.doi.org/10.1063/1.3617461 (3 pages) | Cited 7 times

Online Publication Date: 28 July 2011

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GaAs1−xBix alloys grown by molecular beam epitaxy for x up to 0.06 were studied by photoluminescence (PL). The results indicate that dilute fractions of bismuth (Bi) with x < 0.025 improve the material quality of this low temperature growth alloys by reducing the density of gallium (Ga) and/or arsenic related defects. The crystal quality starts to degrade at higher Bi concentration probably due to significant amount of Bi-related defects, BiGa. However, the room temperature PL intensity continues to increase with Bi content for the range studied due to greater band-gap offset between GaAs and GaAs1−xBix. Analysis carried out shows no correlation between localization effects and the room temperature PL enhancement.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
78.55.Cr III-V semiconductors

Highly reproducible memory effect of organic multilevel resistive-switch device utilizing graphene oxide sheets/polyimide hybrid nanocomposite

Chaoxing Wu, Fushan Li, Yongai Zhang, Tailiang Guo, and Ting Chen

Appl. Phys. Lett. 99, 042108 (2011); http://dx.doi.org/10.1063/1.3619815 (3 pages) | Cited 9 times

Online Publication Date: 29 July 2011

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The functionalization of graphene oxide (GO) sheets with polyimide (PI) enables the layer-by-layer fabrication of a GO-PI hybrid resistive-switch device and leads to high reproducibility of the memory effect. The current-voltage curves for the as-fabricated device exhibit multilevel resistive-switch properties under various reset voltages. The capacitance-voltage characteristics for a capacitor based on GO-PI nanocomposite indicate that the electrical switching may originate from the charge trapping in GO sheets. The high device-to-device uniformity and unique memory properties of the device make it an attractive candidate for applications in next-generation high-density nonvolatile flash memories.
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84.30.Sk Pulse and digital circuits

Robust bi-stable memory operation in single-layer graphene ferroelectric memory

Emil B. Song, Bob Lian, Sung Min Kim, Sejoon Lee, Tien-Kan Chung, Minsheng Wang, Caifu Zeng, Guangyu Xu, Kin Wong, Yi Zhou, Haider I. Rasool, David H. Seo, Hyun-Jong Chung, Jinseong Heo, Sunae Seo, et al.

Appl. Phys. Lett. 99, 042109 (2011); http://dx.doi.org/10.1063/1.3619816 (3 pages) | Cited 19 times

Online Publication Date: 29 July 2011

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With the motivation of realizing an all graphene-based circuit for low power, we present a reliable nonvolatile graphene memory device, single-layer graphene (SLG) ferroelectric field-effect transistor (FFET). We demonstrate that exfoliated single-layer graphene can be optically visible on a ferroelectric lead-zirconate-titanate (PZT) substrate and observe a large memory window that is nearly equivalent to the hysteresis of the PZT at low operating voltages in a graphene FFET. In comparison to exfoliated graphene, FFETs fabricated with chemical vapor deposited (CVD) graphene exhibit enhanced stability through a bi-stable current state operation with long retention time. In addition, we suggest that the trapping/de-trapping of charge carriers in the interface states is responsible for the anti-hysteresis behavior in graphene FFET on PZT.
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85.50.Gk Non-volatile ferroelectric memories
81.05.ue Graphene
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Giant magnetoresistance in zigzag graphene nanoribbon

Z. F. Wang and Feng Liu

Appl. Phys. Lett. 99, 042110 (2011); http://dx.doi.org/10.1063/1.3619817 (3 pages) | Cited 2 times

Online Publication Date: 29 July 2011

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Based on the mean-field Hubbard model (J. Guo et al., Appl. Phys. Lett. 92, 163109 (2008)), ballistic spin transport in zigzag graphene nanoribbons is investigated theoretically. A giant magnetoresistance effect is found with 100% change in resistance as the two transverse electrodes switch from the parallel to antiparallel magnetic configuration. Such change is shown to arise from different coupling between the subbands near the Fermi level, which is dependent of the orbital symmetry. In addition, the operating energy window of giant magnetoresistance exists in a wide range of ribbon widths, easing the way for experimental validation of the proposed device.
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61.48.Gh Structure of graphene
61.46.-w Structure of nanoscale materials
72.20.Ht High-field and nonlinear effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.20.At Surface states, band structure, electron density of states
73.23.Ad Ballistic transport

Analysis of untreated cross sections of Cu(In,Ga)Se2 thin-film solar cells with varying Ga content using Kelvin probe force microscopy

Zhenhao Zhang, Xiaochen Tang, Uli Lemmer, Wolfram Witte, Oliver Kiowski, Michael Powalla, and Hendrik Hölscher

Appl. Phys. Lett. 99, 042111 (2011); http://dx.doi.org/10.1063/1.3607954 (3 pages) | Cited 4 times

Online Publication Date: 29 July 2011

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The potential distribution of the Cu(In,Ga)Se2/CdS/ZnO layer structure on untreated cross sections of Cu(In,Ga)Se2 thin-film solar cells are analyzed by Kelvin probe force microscopy under ambient conditions. The potential differences between the Cu(In,Ga)Se2 absorber and the ZnO window layer are systematically investigated, providing direct evidence for a Fermi energy shifting in Cu(In,Ga)Se2 absorbers with different Ga content.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
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