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10 May 2010

Volume 96, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 96, 193101 (2010); http://dx.doi.org/10.1063/1.3425776 (3 pages)

J. J. Zhang, N. Hrauda, H. Groiss, A. Rastelli, J. Stangl, F. Schäffler, O. G. Schmidt, and G. Bauer
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Viability of using near infrared PbS quantum dots as active materials in luminescent solar concentrators

G. V. Shcherbatyuk, R. H. Inman, C. Wang, R. Winston, and S. Ghosh

Appl. Phys. Lett. 96, 191901 (2010); http://dx.doi.org/10.1063/1.3422485 (3 pages) | Cited 19 times

Online Publication Date: 11 May 2010

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The performance of chemically synthesized lead sulfide (PbS) quantum dots (QDs) in planar, nontracking luminescent solar concentrators (LSCs) is evaluated using spectroscopic and photovoltaic techniques. Spatially resolved measurements are used to investigate and analyze the role of reduced self-absorption on the LSC efficiency. From comparative measurements of samples with Rhodamine B and CdSe/ZnS QDs it is established that PbS LSCs generate nearly twice the photocurrent in silicon cells than the other materials, achieving an integrated optical efficiency of 12.6%. This is attributed primarily to the broadband absorption of PbS which allows optimum harvesting of the solar spectrum.
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88.40.H- Solar cells (photovoltaics)
73.63.Kv Quantum dots
72.40.+w Photoconduction and photovoltaic effects
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics

Biexciton emission from sol-gel ZnMgO nanopowders

C. H. Chia, Y. J. Lai, W. L. Hsu, T. C. Han, J. W. Chiou, Y. M. Hu, Y. C. Lin, W. C. Fan, and W. C. Chou

Appl. Phys. Lett. 96, 191902 (2010); http://dx.doi.org/10.1063/1.3428780 (3 pages) | Cited 4 times

Online Publication Date: 11 May 2010

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We studied the power-dependent photoluminescence of Zn1−xMgxO nanopowders grown by sol-gel method, at temperature T = 100 K. At moderate optical pumping intensity, a nonlinear emission band due to the radiative recombination of free biexcitons was detected. We found that the free biexciton binding energies of Zn1−xMgxO nanopowder (0.01 ≤ x ≤ 0.05) are nearly constant (13.5±1.5 meV).
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations

Influence of the As2/As4 growth modes on the formation of quantum dot-like InAs islands grown on InAlGaAs/InP (100)

C. Gilfert, E.-M. Pavelescu, and J. P. Reithmaier

Appl. Phys. Lett. 96, 191903 (2010); http://dx.doi.org/10.1063/1.3428956 (3 pages) | Cited 4 times

Online Publication Date: 11 May 2010

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The formation process of InAs quantum dashes and quantum dots (QDs) grown on quaternary InAlGaAs surfaces lattice-matched to n-type InP(100) are investigated. A clear trend of the InAs to form dashes or dots depending on the species of supplied arsenic could be demonstrated. Using As4, elongated quantum dashes can be observed. Changing the growth mode to As2 molecules enables a shape transition from dashes to dome-shaped QDs. The dot ensembles exhibit improved photoluminescence (PL) intensity and linewidth over their elongated counterparts. With this basic concept, low temperature PL linewidths as low as 23 meV have been achieved.
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68.65.Hb Quantum dots (patterned in quantum wells)
64.70.Nd Structural transitions in nanoscale materials
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

The effect of nanocrystallite size in monoclinic HfO2 films on lattice expansion and near-edge optical absorption

M. C. Cisneros-Morales and C. R. Aita

Appl. Phys. Lett. 96, 191904 (2010); http://dx.doi.org/10.1063/1.3428965 (3 pages) | Cited 10 times

Online Publication Date: 11 May 2010

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Nanocrystalline monoclinic HfO2 films were sputter deposited on fused silica substrates, air annealed at 573 to 1273 K to affect crystallite growth, and analyzed by x-ray diffraction and spectrophotometry. Lattice expansion occurs with diminishing crystallite size. O 2p→Hf 5d interband absorption dominates the optical edge at energy E ≥ 6.24 eV, with an optical band gap, Eo = 5.48±0.023, which is independent of crystallite size. However, the strength of a localized resonant band, with onset at 5.65 eV and maximum at 5.94 eV, is affected by crystallite size. Its polaronic origin in a perfect HfO2 lattice is discussed.
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61.46.Hk Nanocrystals
77.55.D- High-permittivity gate dielectric films
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
68.55.aj Insulators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Structural defects working as active oxygen-reduction sites in partially oxidized Ta-carbonitride core-shell particles probed by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy

Hideto Imai, Masashi Matsumoto, Takashi Miyazaki, Shinji Fujieda, Akimitsu Ishihara, Motoko Tamura, and Ken-ichiro Ota

Appl. Phys. Lett. 96, 191905 (2010); http://dx.doi.org/10.1063/1.3430543 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2010

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We analyzed the local structure of the surface Ta-oxide phase of TaCN/Ta2O5 core-shell particles that have a high oxygen reduction activity by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy, suppressing the contribution from the TaCN cores. The radial structure analysis revealed that the catalytically-active Ta2O5 phase in the TaCN/Ta2O5 particle surface contains oxygen-vacancy defects with shorter Ta–O bonds leading to the slight expansion of the first Ta–O shell. Such oxygen defects are likely responsible for the oxygen reduction capability by creating electronically favorable oxygen adsorption sites and electron conduction pathways.
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71.55.Ht Other nonmetals
68.35.bt Other materials
61.72.jd Vacancies
78.70.Dm X-ray absorption spectra
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Kinetic roughening of a ZnO grain boundary

Sung Bo Lee, Young-Min Kim, Dong-Su Ko, Tae-Young Ahn, Young-Woon Kim, and Jucheol Park

Appl. Phys. Lett. 96, 191906 (2010); http://dx.doi.org/10.1063/1.3428369 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2010

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Using a model ZnO bicrystal, we examine grain boundary kinetics by high-resolution transmission electron microscopy. The grain boundary undergoes a transition from atomically stepped to undulating appearances with increasing driving force for migration at a given temperature, producing clear evidence that grain boundaries undergo kinetic roughening.
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61.72.Mm Grain and twin boundaries
79.20.Uv Electron energy loss spectroscopy
61.72.Cc Kinetics of defect formation and annealing

Thermal kinetics of OH− ions in LiNbO3:Mg crystals above the photorefractive threshold

K. Lengyel, L. Kovács, Á. Péter, K. Polgár, G. Corradi, A. Baraldi, and R. Capelletti

Appl. Phys. Lett. 96, 191907 (2010); http://dx.doi.org/10.1063/1.3428772 (3 pages)

Online Publication Date: 12 May 2010

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OH stretching vibrations in LiNbO3 (LN) crystals having various Li/Nb ratios and doped with Mg above the photorefractive threshold concentration were investigated in the 20–500 °C temperature range. Beside the 3534 cm−1 above-threshold band another peak at about 3465 cm−1, known from below-threshold stoichiometric LN, was found to appear at a temperature depending on the Mg surplus concentration and grow further with increasing temperature at the expense of the 3534 cm−1 band. The energy difference between the OH− ions was determined to be ΔE = 0.25±0.02 eV independently from the composition and Mg concentration. A kinetic model describing the thermal process predicts a linear Mg surplus dependence of the ratio of band areas at a given temperature.
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78.20.Mg Photorefractive effects
61.66.Bi Elemental solids
61.66.Dk Alloys
78.30.Hv Other nonmetallic inorganics

Radiation-induced metastable ordered phase in gallium nitride

Manabu Ishimaru

Appl. Phys. Lett. 96, 191908 (2010); http://dx.doi.org/10.1063/1.3430046 (3 pages)

Online Publication Date: 13 May 2010

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Energetic particle irradiation is one of the useful ways for realizing metastable phases far from the equilibrium state. In the present study, we performed electron-beam-irradiation into gallium nitride (GaN) with a wurtzite structure and examined its structural changes using transmission electron microscopy. It was found that superlattice Bragg reflections appear in the electron diffraction patterns of the irradiated GaN. This suggests that the wurtzite GaN transforms to another crystalline structure with atomic ordering.
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61.82.Fk Semiconductors
68.55.ag Semiconductors

Optical and microstructural properties versus indium content in InxGa1−xN films grown by metal organic chemical vapor deposition

A. Gokarna, A. Gauthier-Brun, W. Liu, Y. Androussi, E. Dumont, E. Dogheche, J. H. Teng, S. J. Chua, and D. Decoster

Appl. Phys. Lett. 96, 191909 (2010); http://dx.doi.org/10.1063/1.3425761 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2010

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We present comparative investigations of single phase InxGa1−xN alloys for a varying In content (x = 0.07 to 0.14) grown by metal organic chemical vapor deposition (MOCVD) technique. While the composition was determined using secondary ion mass spectroscopy, we have investigated the microstructures in InxGa1−xN/GaN films by using transmission electron microscopy and correlated these with the refractive index of the material. Based on ellipsometric analysis of the films, the dispersion of optical indices for InxGa1−xN films is determined by using Tauc–Lorentz dispersion equations.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.05.Ea III-V semiconductors

Epitaxial graphene on cubic SiC(111)/Si(111) substrate

A. Ouerghi, A. Kahouli, D. Lucot, M. Portail, L. Travers, J. Gierak, J. Penuelas, P. Jegou, A. Shukla, T. Chassagne, and M. Zielinski

Appl. Phys. Lett. 96, 191910 (2010); http://dx.doi.org/10.1063/1.3427406 (3 pages) | Cited 24 times

Online Publication Date: 14 May 2010

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Epitaxial graphene films grown on silicon carbide (SiC) substrate by solid state graphitization is of great interest for electronic and optoelectronic applications. In this paper, we explore the properties of epitaxial graphene films on 3C-SiC(111)/Si(111) substrate. X-ray photoelectron spectroscopy and scanning tunneling microscopy were extensively used to characterize the quality of the few-layer graphene (FLG) surface. The Raman spectroscopy studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples.
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68.55.Nq Composition and phase identification
68.55.jd Thickness
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
78.30.Na Fullerenes and related materials
81.05.uf Graphite

Photoluminescence studies of high-quality InAlN layer lattice-matched to GaN grown by metal organic chemical vapor deposition

Z. T. Chen, Y. Sakai, and T. Egawa

Appl. Phys. Lett. 96, 191911 (2010); http://dx.doi.org/10.1063/1.3430737 (3 pages) | Cited 7 times

Online Publication Date: 14 May 2010

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Temperature-dependent photoluminescence (PL) measurements have been performed on high-quality InAlN layers lattice-matched (LM) to GaN with different thicknesses. It is found that the PL is consisted of two components denoted as IH (high-energy side) and IL (low-energy side), respectively. IH is attributed to exciton luminescence of bulk InAlN with linewidth comparable to those calculated under the assumption of perfect random alloy. While IL is attributed to the emission from the quantum-dotlike structure on the surface of InAlN, revealing the importance of surface effect to the investigations related to InAlN LM to GaN.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.35.-y Excitons and related phenomena
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