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5 Sep 2011

Volume 99, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 103701 (2011); http://dx.doi.org/10.1063/1.3633066 (3 pages)

Yinan Zhang, David J. S. Birch, and Yu Chen
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Thermoelectric figure of merit as a function of carrier propagation angle in semiconducting superlattices

Shuo Liu and E. W. Carlson

Appl. Phys. Lett. 99, 102101 (2011); http://dx.doi.org/10.1063/1.3633112 (3 pages)

Online Publication Date: 7 September 2011

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Superlattices have been a fruitful approach for enhancing the figure of merit, ZT, of thermoelectric materials. Generally, superlattice transport is measured either parallel or perpendicular to the superlattice planes. We show here that the figure of merit is a function of carrier propagation angle in the superlattice and that ZT generically exhibits a maximum at an oblique angle, near θ ≈ π/6.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.Pa Thermoelectric and thermomagnetic effects

Graphene/GaN Schottky diodes: Stability at elevated temperatures

S. Tongay, M. Lemaitre, T. Schumann, K. Berke, B. R. Appleton, B. Gila, and A. F. Hebard

Appl. Phys. Lett. 99, 102102 (2011); http://dx.doi.org/10.1063/1.3628315 (3 pages) | Cited 10 times

Online Publication Date: 7 September 2011

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Rectification and thermal stability of diodes formed at graphene/GaN interfaces have been investigated using Raman Spectroscopy and temperature-dependent current-voltage measurements. The Schottky barriers formed between GaN and mechanically transferred graphene display rectification that is preserved up to 550 K with the diodes eventually becoming non-rectifying above 650 K. Upon cooling, the diodes show excellent recovery with improved rectification. We attribute these effects to the thermal stability of graphene, which acts like an impenetrable barrier to the diffusion of contaminants across the interface, and to changes in the interface band alignment associated with thermally induced dedoping of graphene.
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85.30.Kk Junction diodes

Suppression in the negative bias illumination instability of Zn-Sn-O transistor using oxygen plasma treatment

Shinhyuk Yang, Kwang Hwan Ji, Un Ki Kim, Cheol Seong Hwang, Sang-Hee Ko Park, Chi-Sun Hwang, Jin Jang, and Jae Kyeong Jeong

Appl. Phys. Lett. 99, 102103 (2011); http://dx.doi.org/10.1063/1.3634053 (3 pages) | Cited 5 times

Online Publication Date: 7 September 2011

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This study examined the effect of oxygen plasma treatment on light-enhanced bias instability in Zn-Sn-O (ZTO) thin film transistors (TFTs). The treated ZTO TFT exhibited only a threshold voltage (Vth) shift of −2.05 V under negative bias illumination stress (NBIS) conditions, whereas the pristine device suffered from a negative Vth shift of 3.76 V under identical conditions. X-ray photoelectron spectroscopic analysis revealed that the oxygen vacancy defect density was diminished via the oxygen plasma treatment. This suggests the Vth degradation under NBIS is due to photo-transition of oxygen vacancy defects.
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85.30.Tv Field effect devices
52.77.-j Plasma applications
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Do we really need high thermoelectric figures of merit? A critical appraisal to the power conversion efficiency of thermoelectric materials

Dario Narducci

Appl. Phys. Lett. 99, 102104 (2011); http://dx.doi.org/10.1063/1.3634018 (3 pages) | Cited 8 times

Online Publication Date: 8 September 2011

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This paper will show that, while ZT is an appropriate performance index when optimizing the heat conversion rate, it may mislead research in view of applications aiming at large electric power production. This is of special relevance when related to the surge of research in the area of low-dimensionality semiconductors where ZT is increased by lowering the thermal conductivity κ. It will be shown that, when operating between sources at fixed temperature, the highest power output can be obtained by increasing κ, not decreasing it, the larger electric power output economically enabling thermoelectric generators for massive electric power production.
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72.20.Pa Thermoelectric and thermomagnetic effects
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
66.70.Df Metals, alloys, and semiconductors

Properties of the SiO2- and SiNx-capped GaAs(100) surfaces of GaInAsN/GaAs quantum-well heterostructures studied by photoelectron spectroscopy and photoluminescence

J. Dahl, V. Polojärvi, J. Salmi, P. Laukkanen, and M. Guina

Appl. Phys. Lett. 99, 102105 (2011); http://dx.doi.org/10.1063/1.3634046 (3 pages) | Cited 2 times

Online Publication Date: 8 September 2011

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SiO2 and SiNx layers are routinely deposited onto III-V(100) surfaces at different device processing steps. We elucidate these insulator-interface properties with photoemission and photoluminescence (PL) of SiO2- and SiNx-capped GaAs(100) surfaces of GaInAsN/GaAs quantum wells (QWs). Post-growth annealing led to an increase of the QW-PL intensity, of which origin can be clearly linked to the SiO2 and SiNx interfaces. Concomitantly, Ga2O–related photoemission increased, indicating useful formation of Ga2O at both insulator interfaces. Furthermore, higher Ga-oxidation-state emission, identified with Ga diffused into SiO2 and SiNx, correlates with the blue-shift of the QW-PL wavelength. Also, interfacial As-As related photoemission was identified.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications

PN junction rectification in electrolyte gated Mg-doped InN

E. Alarcón-Lladó, M. A. Mayer, B. W. Boudouris, R. A. Segalman, N. Miller, T. Yamaguchi, K. Wang, Y. Nanishi, E. E. Haller, and J. W. Ager

Appl. Phys. Lett. 99, 102106 (2011); http://dx.doi.org/10.1063/1.3634049 (3 pages) | Cited 3 times

Online Publication Date: 8 September 2011

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PN junction rectification is demonstrated in indium nitride. The junction is formed between the n-type surface accumulation layer and the Mg-doped, p-type bulk in a top-contacted thin film structure. The parasitic shorting path between the top contacts is controlled by gating with an electrolyte. For positive gate voltages, electrons accumulate at the surface and the current flows preferentially through n type regions, and linear current-voltage (I-V) behavior is observed. However, for negative gate voltages, surface electrons are depleted and current flows through the p-type bulk. This creates an n-p-n structure and a characteristic non-linear I-V curve is observed.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
78.66.Fd III-V semiconductors

Enhanced spin signal in nonlocal devices based on a ferromagnetic CoFeAl alloy

G. Bridoux, M. V. Costache, J. Van de Vondel, I. Neumann, and S. O. Valenzuela

Appl. Phys. Lett. 99, 102107 (2011); http://dx.doi.org/10.1063/1.3635391 (3 pages) | Cited 7 times

Online Publication Date: 9 September 2011

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We systematically study the nonlocal spin signal in lateral spin valves based on CoFeAl injectors and detectors and compare the results with identically fabricated devices based on CoFe. The devices are fabricated by electron beam evaporation at room temperature. We observe a > 10-fold enhancement of the spin signal in the CoFeAl devices. We explain this increase as due to the formation of a highly spin-polarized Co2FeAl Heusler compound with large resistivity. These results suggest that Heusler compounds are promising candidates as spin polarized electrodes in lateral spin devices for future spintronic applications.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.-b Spin polarized transport
75.50.Bb Fe and its alloys

Dielectric dipole mitigated Schottky barrier height tuning using atomic layer deposited aluminum oxide for contact resistance reduction

Brian E. Coss, Wei-Yip Loh, Herman Carlo Floresca, Moon J. Kim, Prashant Majhi, Robert M. Wallace, Jiyoung Kim, and Raj Jammy

Appl. Phys. Lett. 99, 102108 (2011); http://dx.doi.org/10.1063/1.3633117 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2011

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Schottky barrier height tuning is reported from the insertion of thin layers of AlOx and SiO2 at the interface between tantalum nitride and p-type silicon. The magnitude of the change in the barrier height is found to be dependent on the conditions of AlOx and SiO2 formation. The largest change in barrier height is over 350 meV and correlates well with the intrinsic dipole found at this interface. These findings are then interpreted using a model of the dipole formation at the high-κ and SiO2 interface. The application of these findings for low resistance contacts as well as options to achieve greater performance are discussed.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Cg Contact resistance, contact potential

Low-temperature photocarrier dynamics in monolayer MoS2

T. Korn, S. Heydrich, M. Hirmer, J. Schmutzler, and C. Schüller

Appl. Phys. Lett. 99, 102109 (2011); http://dx.doi.org/10.1063/1.3636402 (3 pages) | Cited 38 times

Online Publication Date: 9 September 2011

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The band structure of MoS2 strongly depends on the number of layers, and a transition from indirect to direct-gap semiconductor has been observed recently for a single layer of MoS2. Single-layer MoS2 therefore becomes an efficient emitter of photoluminescence even at room temperature. Here, we report on scanning Raman and on temperature-dependent, as well as time-resolved photoluminescence measurements on single-layer MoS2 flakes prepared by exfoliation. We observe the emergence of two distinct photoluminescence peaks at low temperatures. The photocarrier recombination at low temperatures occurs on the few-picosecond timescale, but with increasing temperatures, a biexponential photoluminescence decay with a longer-lived component is observed.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Le Other inorganic semiconductors
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Effect of cationic substitution on the thermoelectric properties of In4−xMxSe2.95 compounds (M = Na, Ca, Zn, Ga, Sn, Pb; x = 0.1)

Kyunghan Ahn, Eunseog Cho, Jong-Soo Rhyee, Sang Il Kim, Sang Mock Lee, and Kyu Hyoung Lee

Appl. Phys. Lett. 99, 102110 (2011); http://dx.doi.org/10.1063/1.3637053 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2011

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We report an electrical and thermal transport study for polycrystalline samples of In4Se3−x substituted with various metals. Our experimental and theoretical investigation revealed that the Na, Ca, and Pb substitutions at the In4 site in the 4:3 indium selenide lattice are more effective for increase in electron concentration than the Zn, Ga, and Sn substitutions at other sites, and the Peierls distortion in cationic substituted compounds may not be as strong as In4Se3−x based on higher lattice thermal conductivities of the former than the latter. It is found that the cationic substitutions may weaken the effect of Peierls distortion on thermal properties for In4Se3−x while they maintain the same trend for electrical properties of In4Se3−x with different electron concentrations.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
66.70.Df Metals, alloys, and semiconductors
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