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30 Apr 2012

Volume 100, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 181901 (2012); http://dx.doi.org/10.1063/1.4705414 (4 pages)

Etienne Brasselet, Arnaud Royon, and Lionel Canioni
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Enforced c-axis growth of ZnO epitaxial chemical vapor deposition films on a-plane sapphire

Yong Xie, Manfred Madel, Thilo Zoberbier, Anton Reiser, Wanqi Jie, Benjamin Neuschl, Johannes Biskupek, Ute Kaiser, Martin Feneberg, and Klaus Thonke

Appl. Phys. Lett. 100, 182101 (2012); http://dx.doi.org/10.1063/1.4709430 (4 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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To enforce perfect c-axis orientation of ZnO epitaxial films grown on a-plane sapphire, we first grew perfectly perpendicularly aligned (i.e., c axis oriented) ZnO nanopillars on such sapphire substrates, and then over-grew these by a closed epitaxial film using a modified chemical vapor deposition process at atmospheric pressure. X-ray diffraction and low temperature photoluminescence measurements confirm the desired epitaxial relationship and very high crystalline quality. This growth scheme is an efficient method to suppress dislocations and polycrystalline growth of ZnO and could work equally well for other heteroepitaxial epilayer/substrate systems.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Band gap engineering in BiNbO4 for visible-light photocatalysis

B. C. Wang, J. Nisar, B. Pathak, T. W. Kang, and R. Ahuja

Appl. Phys. Lett. 100, 182102 (2012); http://dx.doi.org/10.1063/1.4709488 (5 pages) | Cited 2 times

Online Publication Date: 30 April 2012

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We have investigated the electronic structure of anionic mono- (S, N, and C) and co-doping (N-N, C-N, S-C, and S-N) on BiNbO4 for the visible-light photocatalysis. The maximum band gap reduction of pure BiNbO4 is possible with the (C-S) co-doping and minimum with N mono-doping. The calculated binding energies show that the co-doped systems are more stable than their mono-doped counterparts. Our optical absorption curves indicate that the mono- (C) and co-anionic doped (N-N and C-S) BiNbO4 systems are promising materials for visible light photocatalysis.
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71.20.Ps Other inorganic compounds
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
71.15.Nc Total energy and cohesive energy calculations

Suppress temperature instability of InGaZnO thin film transistors by N2O plasma treatment, including thermal-induced hole trapping phenomenon under gate bias stress

Geng-Wei Chang, Ting-Chang Chang, Jhe-Ciou Jhu, Tsung-Ming Tsai, Yong-En Syu, Kuan-Chang Chang, Ya-Hsiang Tai, Fu-Yen Jian, and Ya-Chi Hung

Appl. Phys. Lett. 100, 182103 (2012); http://dx.doi.org/10.1063/1.4709417 (3 pages) | Cited 2 times

Online Publication Date: 2 May 2012

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An abnormal subthreshold leakage current is observed at high temperature, which causes a notable stretch-out phenomenon in amorphous InGaZnO thin film transistors (a-IGZO TFTs). This is due to trap-induced thermal-generated holes accumulating at the source region, which leads to barrier lowering on the source side and causes an apparent subthreshold leakage current. In order to obtain superior thermal stability performance of a-IGZO TFTs, conducting N2O plasma treatment on active layer was expected to avert defects generation during SiO2 deposition process. Reducing defects generation not only suppresses subthreshold current stretch-out phenomenon but also significantly improves the bias stress stability in a-IGZO TFTs at high temperature.
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85.30.Tv Field effect devices

Plasmon-enhanced mid-infrared luminescence from polar and lattice-structure-mismatched CdTe/PbTe single heterojunctions

Chunfeng Cai, Shuqiang Jin, Huizhen Wu, Bingpo Zhang, Lian Hu, and P. J. McCann

Appl. Phys. Lett. 100, 182104 (2012); http://dx.doi.org/10.1063/1.4711042 (5 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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We propose by exploring CdTe/PbTe single heterojunctions (SHs) that the abnormal enhancement of mid-infrared light emission from CdTe/PbTe heterostructures is due to coupling with surface plasmons. It is discovered that the observed intense mid-infrared luminescence in the SHs comes from the inherent polar interface character and coupling of surface plasmons localized at the metallic CdTe/PbTe interface to light emitted from the narrow gap PbTe. The finding offers an approach to manipulate mid-infrared light and to fabricate improved mid-infrared optoelectronic devices.
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78.55.Hx Other solid inorganic materials
61.66.Fn Inorganic compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Reduced longitudinal optical phonon-exciton interaction in InGaN/GaN nanorod structures

P. Renwick, H. Tang, J. Bai, and T. Wang

Appl. Phys. Lett. 100, 182105 (2012); http://dx.doi.org/10.1063/1.4711210 (4 pages)

Online Publication Date: 3 May 2012

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Photoluminescence measurements have been performed on a series of InGaN/GaN multiple quantum well (MQW) nanorod array structures in order to investigate the influence of a nanorod structure on longitudinal optical (LO) phonon-exciton interaction. The nanorod array structures were fabricated on InGaN/GaN MQW epi-wafers using a self-organised Ni nano-mask technique. Compared with their corresponding as-grown samples, all the nanorod structures exhibit a significant reduction in Huang-Rhys factor, indicating a reduced coupling between LO-phonon and exciton. This is attributed to strain relaxation as a result of being fabricated into nanorod structures. Our excitation power dependent measurements have demonstrated that the nanorod structures exhibit a clear reduction in efficiency droop at a high excitation power. This proves a theoretical prediction previously reported, namely, LO-phonon-exciton coupling contributes to an indirect Auger recombination, leading to the efficiency droop of InGaN/GaN based emitters. The nanorod structures offering a reduced phonon-exciton coupling can pave the way for reducing or eliminating efficiency droop, one of the major challenges in the field of III-nitride optoelectronics.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
63.20.kk Phonon interactions with other quasiparticles
78.55.Cr III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells

In-situ oxygen x-ray absorption spectroscopy investigation of the resistance modulation mechanism in LiNbO2 memristors

Jordan D. Greenlee, Cole F. Petersburg, W. Laws Calley, Cherno Jaye, Daniel A. Fischer, Faisal M. Alamgir, and W. Alan Doolittle

Appl. Phys. Lett. 100, 182106 (2012); http://dx.doi.org/10.1063/1.4709422 (4 pages)

Online Publication Date: 4 May 2012

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In situ near edge x-ray absorption fine structure spectroscopy (NEXAFS) is performed on LiNbO2 analog memristors to identify the underlying analog resistance modulation mechanism. Empty electronic state gradients in the NEXAFS difference spectra are observed in biased devices indicating a gradual movement of lithium. This movement of lithium supports the assertion that simple ion dopant drift and diffusion dominate the analog memristor’s resistance response. By identifying the physical memristance mechanism in analog LiNbO2 memristors, suggestions are made for additions to the memristor to modify device performance for both neuromorphic computing and memory applications.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
78.70.Dm X-ray absorption spectra
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