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24 Sep 2012

Volume 101, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 101, 133101 (2012); http://dx.doi.org/10.1063/1.4752467 (5 pages)

Yen Husn Su and Wei-Yu Chen
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Strain dependent stabilization of metallic paramagnetic state in epitaxial NdNiO3 thin films

Yogesh Kumar, R. J. Choudhary, S. K. Sharma, M. Knobel, and Ravi Kumar

Appl. Phys. Lett. 101, 132101 (2012); http://dx.doi.org/10.1063/1.4754593 (5 pages)

Online Publication Date: 24 September 2012

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We report here the strain dependent study of epitaxial NdNiO3 films deposited on LaAlO3 and SrTiO3 substrates using pulsed laser deposition. Electrical transport and magnetic properties of films are found to be controlled by the substrate induced strain. NdNiO3 film on SrTiO3 substrate exhibits behaviour similar to that of bulk NdNiO3, while stabilization of low temperature metallic paramagnetic phase has been observed for film deposited on LaAlO3 substrate. Invariance of Raman spectra, with temperature, of the film on LaAlO3 reveals that the melting of charge ordering under compressive strain is responsible for the stabilization of metallic phase at lower temperature.
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68.60.Bs Mechanical and acoustical properties
73.61.Ng Insulators
75.20.Ck Nonmetals
75.70.Ak Magnetic properties of monolayers and thin films
78.30.Hv Other nonmetallic inorganics
81.15.Fg Pulsed laser ablation deposition

Suppression of m-plane and c-plane slip through Si and Mg doping in partially relaxed (20math1) InGaN/GaN heterostructures

Matthew T. Hardy, Erin C. Young, Po Shan Hsu, Daniel A. Haeger, Ingrid L. Koslow, Shuji Nakamura, Steven P. DenBaars, and James S. Speck

Appl. Phys. Lett. 101, 132102 (2012); http://dx.doi.org/10.1063/1.4754693 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2012

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Several series of (20math1) oriented InGaN/GaN heterostructures were grown to examine the impact of Si and Mg doping on stress relaxation by misfit dislocation formation. Si doping greatly reduced m-plane slip misfit dislocation lines as observed in cathodoluminescence, as well as reducing relaxation from c-plane slip as measured using x-ray diffraction reciprocal space maps. However, samples with the same degree of relaxation still showed reduced m-plane slip for the highly Si doped case. Mg doping showed a similar effect while experiments with Si–Mg co-doping reversed the effect.
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61.72.uj III-V and II-VI semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.sd Impurity concentration

Enhanced thermoelectric performance through energy-filtering effects in nanocomposites dispersed with metallic particles

M. Liu and X. Y. Qin

Appl. Phys. Lett. 101, 132103 (2012); http://dx.doi.org/10.1063/1.4755768 (4 pages)

Online Publication Date: 24 September 2012

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The thermoelectric properties of semiconductor materials with metallic nanoinclusions were investigated by using the Boltzmann transport equation under the relaxation time approximation. The results showed that the Seebeck coefficient can be significantly enhanced due to interface potential barrier induced by metallic nanoinclusions, leading to the optimized power factor at T < 700 K as barrier height is around kBT larger than the Fermi energy (here, kB is the Boltzmann constant). Additionally, it was found that high-concentration nanoinclusions with radius 1–2 nm can effectively enhance the thermoelectric performance of nanocomposites through energy-selective carrier scattering.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials

Highly conductive p-type amorphous oxides from low-temperature solution processing

Jinwang Li (李金望), Eisuke Tokumitsu (徳光永輔), Mikio Koyano (小矢野幹夫), Tadaoki Mitani (三谷忠興), and Tatsuya Shimoda (下田達也)

Appl. Phys. Lett. 101, 132104 (2012); http://dx.doi.org/10.1063/1.4754608 (4 pages)

Online Publication Date: 26 September 2012

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We report solution-processed, highly conductive (resistivity 1.3–3.8 mΩ cm), p-type amorphous A-B-O (A = Bi, Pb; B = Ru, Ir), processable at temperatures (down to 240 °C) that are compatible with plastic substrates. The film surfaces are smooth on the atomic scale. Bi-Ru-O was analyzed in detail. A small optical bandgap (0.2 eV) with a valence band maximum (VBM) below but very close to the Fermi level (binding energy EVBM = 0.04 eV) explains the high conductivity and suggests that they are degenerated semiconductors. The conductivity changes from three-dimensional to two-dimensional with decreasing temperature across 25 K.
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73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Pronounced Purcell enhancement of spontaneous emission in CdTe/ZnTe quantum dots embedded in micropillar cavities

T. Jakubczyk, W. Pacuski, T. Smoleński, A. Golnik, M. Florian, F. Jahnke, C. Kruse, D. Hommel, and P. Kossacki

Appl. Phys. Lett. 101, 132105 (2012); http://dx.doi.org/10.1063/1.4754078 (4 pages) | Cited 1 time

Online Publication Date: 26 September 2012

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The coupling of CdTe/ZnTe quantum dot (QD) emission to micropillar cavity eigenmodes in the weak coupling regime is demonstrated. We analyze photoluminescence spectra of QDs embedded in monolithic micropillar cavities based on Bragg mirrors which contain MgSe/ZnTe/MgTe superlattices as low-index material. The pillar emission shows pronounced cavity eigenmodes, and their spectral shape is in good agreement with simulations. QD emission in resonance with the cavity mode is shown to be efficiently guided toward the detector, and an experimental Purcell enhancement by a factor of 5.7 is determined, confirming theoretical expectations.
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78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots

Schottky barrier height of Au on the transparent semiconducting oxide β-Ga2O3

M. Mohamed, K. Irmscher, C. Janowitz, Z. Galazka, R. Manzke, and R. Fornari

Appl. Phys. Lett. 101, 132106 (2012); http://dx.doi.org/10.1063/1.4755770 (5 pages)

Online Publication Date: 26 September 2012

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The Schottky barrier height of Au deposited on (100) surfaces of n-type β-Ga2O3 single crystals was determined by current-voltage characteristics and high-resolution photoemission spectroscopy resulting in a common effective value of 1.04 ± 0.08 eV. Furthermore, the electron affinity of β-Ga2O3 and the work function of Au were determined to be 4.00 ± 0.05 eV and 5.23 ± 0.05 eV, respectively, yielding a barrier height of 1.23 eV according to the Schottky-Mott rule. The reduction of the Schottky-Mott barrier to the effective value was ascribed to the image-force effect and the action of metal-induced gap states, whereas extrinsic influences could be avoided.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Sx Metal-semiconductor-metal structures
79.60.Bm Clean metal, semiconductor, and insulator surfaces

15% efficient Cu(In,Ga)Se2 solar cells obtained by low-temperature pulsed electron deposition

S. Rampino, N. Armani, F. Bissoli, M. Bronzoni, D. Calestani, M. Calicchio, N. Delmonte, E. Gilioli, E. Gombia, R. Mosca, L. Nasi, F. Pattini, A. Zappettini, and M. Mazzer

Appl. Phys. Lett. 101, 132107 (2012); http://dx.doi.org/10.1063/1.4755772 (4 pages) | Cited 2 times

Online Publication Date: 26 September 2012

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An approach to low-cost production of Cu(In,Ga)Se2 (CIGS) solar cells based on pulsed electron deposition (PED) has achieved a crucial milestone. Lab-scale solar cells with efficiencies exceeding 15% were obtained by depositing CIGS from a stoichiometric quaternary target at 270 °C and without any post-growth treatment. An effective control of the p-doping level in CIGS was achieved by starting the PED deposition with a layer of NaF tailored to generate the optimum Na diffusion. These results show that PED is a promising technology for the development of a competitive low-cost production process for CIGS solar cells.
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88.40.H- Solar cells (photovoltaics)
61.66.Bi Elemental solids
61.66.Dk Alloys
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Anomalous behavior of epitaxial indium nano-contacts on cadmium-zinc-telluride

A. Ruzin, O. Sinkevich, G. Cohen-Taguri, and I. Goldfarb

Appl. Phys. Lett. 101, 132108 (2012); http://dx.doi.org/10.1063/1.4754706 (4 pages)

Online Publication Date: 28 September 2012

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In this work, experimental characterization results of indium nano-contacts are presented. The indium nano-contacts are epitaxially grown on a two-dimensional surface of high-resistivity, n-type Cd0.9Zn0.1Te in ultra-high vacuum. The scaling effect in these contacts is systematic, but not linear. It is shown that the contacts exhibit a profoundly asymmetric behavior. It is argued that the “rectifying” behavior of these contacts is due to tunneling and that the tunneling does not necessarily imply Schottky nature.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
73.40.Gk Tunneling

High electron mobility through the edge states in random networks of c-axis oriented wedge-shaped GaN nanowalls grown by molecular beam epitaxy

H. P. Bhasker, S. Dhar, A. Sain, Manoj Kesaria, and S. M. Shivaprasad

Appl. Phys. Lett. 101, 132109 (2012); http://dx.doi.org/10.1063/1.4755775 (5 pages)

Online Publication Date: 28 September 2012

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Transport and optical properties of random networks of c-axis oriented wedge-shaped GaN nanowalls grown spontaneously on c-plane sapphire substrates through molecular beam epitaxy are investigated. Our study suggests a one dimensional confinement of carriers at the top edges of these connected nanowalls, which results in a blue shift of the band edge luminescence, a reduction of the exciton-phonon coupling, and an enhancement of the exciton binding energy. Not only that, the yellow luminescence in these samples is found to be completely suppressed even at room temperature. All these changes are highly desirable for the enhancement of the luminescence efficiency of the material. More interestingly, the electron mobility through the network is found to be significantly higher than that is typically observed for GaN epitaxial films. This dramatic improvement is attributed to the transport of electrons through the edge states formed at the top edges of the nanowalls.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
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