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17 May 2010

Volume 96, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages)

Qimin Quan, Parag B. Deotare, and Marko Loncar
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Mechanisms controlling the phase and dislocation density in epitaxial silicon films grown from silane below 800 °C

Charles W. Teplin, Kirstin Alberi, Maxim Shub, Carolyn Beall, Ina T. Martin, Manuel J. Romero, David L. Young, Robert C. Reedy, Paul Stradins, and Howard M. Branz

Appl. Phys. Lett. 96, 201901 (2010); http://dx.doi.org/10.1063/1.3422474 (3 pages) | Cited 7 times

Online Publication Date: 18 May 2010

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We construct a phase diagram for silicon layer growth on (001) Si by hot-wire chemical vapor deposition (HWCVD), for rates from 10 to 150 nm/min and for substrate temperatures from 500 to 800 °C. Our results show that a mixed mono and dihydride surface termination during growth causes polycrystalline growth; some H-free sites are needed for epitaxy. For epitaxial films (T>620 °C), the dislocation density decreases with increasing growth temperature because of reduced O contamination of the surface. The best HWCVD epitaxial layers have dislocation densities of 105 cm−2.
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81.05.Cy Elemental semiconductors
81.30.Dz Phase diagrams of other materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

The electronic consequences of multivalent elements in inorganic solar absorbers: Multivalency of Sn in Cu2ZnSnS4

Koushik Biswas, Stephan Lany, and Alex Zunger

Appl. Phys. Lett. 96, 201902 (2010); http://dx.doi.org/10.1063/1.3427433 (3 pages) | Cited 10 times

Online Publication Date: 18 May 2010

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Multivalent transition metal impurities in semiconductors are known to create deep levels inside the band gap that are associated with changes in the oxidation state. Some emerging functional semiconductor materials now contain multivalent elements not just as impurities, but as part of their structural skeleton (“multivalent semiconductors”). This raises the possibility that the performance of such materials may be affected by those skeleton elements transitioning from one oxidation state to another, in response to charge-altering perturbations such as illumination or doping. Here we address the correlation between multivalency and the electronic properties of these new semiconductor materials.
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71.55.Ht Other nonmetals
61.72.up Other materials

Electronic structure of wurtzite and rocksalt InN investigated by optical absorption under hydrostatic pressure

J. Ibáñez, A. Segura, F. J. Manjón, L. Artús, T. Yamaguchi, and Y. Nanishi

Appl. Phys. Lett. 96, 201903 (2010); http://dx.doi.org/10.1063/1.3431291 (3 pages) | Cited 4 times

Online Publication Date: 18 May 2010

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The pressure dependence of the optical absorption edge of InN is investigated. Owing to the strong nonparabolicity of the energy bands, wurtzite InN exhibits enhanced optical absorption well above the absorption edge. The direct band gap of wurtzite InN increases linearly with pressure at 29±1 meV/GPa. The wurtzite-to-rocsksalt phase transition is observed at 15.3±0.5 GPa as a clear change in the absorption edge. We find that rocksalt InN is an indirect semiconductor with a band gap energy of around 1.0 eV. A higher energy direct transition is found at ∼ 2 eV. These results are discussed in terms of theoretical band-structure calculations.
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71.20.Nr Semiconductor compounds
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.66.Fd III-V semiconductors

Strain induced suppression of silver agglomeration of indium-containing silver contact

Gwan Ho Jung, Jun Ho Son, Yang Hee Song, and Jong-Lam Lee

Appl. Phys. Lett. 96, 201904 (2010); http://dx.doi.org/10.1063/1.3430509 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2010

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The mechanism for thermally stable indium-containing silver [Ag(In)] Ohmic contact on p-type GaN has been investigated. The specific contact resistivity as low as 3.8×10−5 Ω cm2 and a high reflectance of 88.4% at a 460 nm wavelength were obtained by annealing Ag(0.5 wt % In) alloy contact at 450 °C in air ambient. The In atoms in Ag matrix made In–O chemical bonds, producing a tensile stress in the film. This compensated thermal compressive stress built in the Ag film. As a result, In atoms in Ag film play a role in preventing Ag contact from agglomeration, leading to high reflectance and good thermal stability.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
68.35.Gy Mechanical properties; surface strains
78.40.Kc Metals, semimetals, and alloys
68.60.Bs Mechanical and acoustical properties

Dynamics of charge leakage from self-assembled CdTe quantum dots

Ł. Kłopotowski, M. Goryca, T. Kazimierczuk, P. Kossacki, P. Wojnar, G. Karczewski, and T. Wojtowicz

Appl. Phys. Lett. 96, 201905 (2010); http://dx.doi.org/10.1063/1.3430524 (3 pages)

Online Publication Date: 19 May 2010

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We study the leakage dynamics of charge stored in an ensemble of CdTe quantum dots embedded in a field-effect structure. Optically excited electrons are stored and read out by a proper time sequence of bias pulses. We monitor the dynamics of electron loss and find that the rate of the leakage is strongly dependent on time, which we attribute to an optically generated electric field related to the stored charge. A rate equation model quantitatively reproduces the results.
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78.67.Hc Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.La Quantum dots

Transient enhanced diffusion of B mediated by self-interstitials in preamorphized Ge

E. Napolitani, G. Bisognin, E. Bruno, M. Mastromatteo, G. G. Scapellato, S. Boninelli, D. De Salvador, S. Mirabella, C. Spinella, A. Carnera, and F. Priolo

Appl. Phys. Lett. 96, 201906 (2010); http://dx.doi.org/10.1063/1.3429084 (3 pages) | Cited 12 times

Online Publication Date: 19 May 2010

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The dissolution of interstitial-type end-of-range (EOR) damage in preamorphized Ge is shown to induce a transient enhanced diffusion of an epitaxially grown boron delta at temperatures above 350 °C that saturates above 420 °C. The B diffusion events are quantitatively correlated with the measured positive strain associated with the EOR damage as a function of the annealing temperature with an energy barrier for the EOR damage dissolution of 2.1±0.3 eV. These results unambiguously demonstrate that B diffuses in Ge through a mechanism assisted by self-interstitials, and impose considering the interstitial implantation damage for the modeling of impurity diffusion in Ge.
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66.30.J- Diffusion of impurities
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
64.75.Bc Solubility
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Effect of oxygen partial pressure on the Fermi level of ZnO1−x films fabricated by pulsed laser deposition

Chul-Hee Min, Suyeon Cho, Seung-Hyuk Lee, Deok-Yong Cho, Won Goo Park, Jae Gwan Chung, Eunha Lee, Jae Cheol Lee, Benayad Anass, Jae Hak Lee, Cheol Seong Hwang, and Se-Jung Oh

Appl. Phys. Lett. 96, 201907 (2010); http://dx.doi.org/10.1063/1.3432398 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2010

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We investigated the influence of oxygen deficiency on the Fermi level (EF) of ZnO thin film prepared by pulsed laser deposition (PLD). For this purpose, we adopted in situ x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The oxygen deficiency was effectively controlled by varying the oxygen partial pressure [P(O2)] during the PLD. The EF shifted by +0.6 eV as the P(O2) decreased from 10 to 3.3 Pa. This shift indicates a significant change in the energy balance in the oxygen-deficient ZnO films. This fact suggests that the very large change in the resistivity of ZnO thin films resulting from the oxygen deficiency could be attributed to the EF shift rather than grain boundary formation in the ZnO film.
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71.20.Nr Semiconductor compounds
73.22.-f Electronic structure of nanoscale materials and related systems
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
79.60.Bm Clean metal, semiconductor, and insulator surfaces

GaN avalanche photodiodes grown on m-plane freestanding GaN substrate

Z. Vashaei, E. Cicek, C. Bayram, R. McClintock, and M. Razeghi

Appl. Phys. Lett. 96, 201908 (2010); http://dx.doi.org/10.1063/1.3432408 (3 pages) | Cited 9 times

Online Publication Date: 20 May 2010

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M-plane GaN avalanche p-i-n photodiodes on low dislocation density freestanding m-plane GaN substrates were realized using metal-organic chemical vapor deposition. High quality homoepitaxial m-plane GaN layers were developed; the root-mean-square surface roughness was less than 1 Å and the full-width-at-half-maximum value of the x-ray rocking curve for (10math0) diffraction of m-plane GaN epilayer was 32 arcsec. High quality material led to a low reverse-bias dark current of 8.11 pA for 225 μm2 mesa photodetectors prior to avalanche breakdown, with the maximum multiplication gain reaching about 8000.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Stripe/kink microstructures formed in mechanical peeling of highly orientated pyrolytic graphite

Ze Liu, Quan-shui Zheng, and Jefferson Z. Liu

Appl. Phys. Lett. 96, 201909 (2010); http://dx.doi.org/10.1063/1.3422484 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2010

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Mechanical exfoliation is nowadays the primary method to produce isolated graphenes. A stripe/kink microstructure is observed in our graphite flakes produced by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG). It composes a series of parallel stripes with width of about 100 microns separated by kinking microstructures ( ∼ 2 microns) in the graphite flake plane. The formation of such structure is attributed to the sliding between adjacent layers of the HOPG under the mechanical peeling. A theoretical model is presented to understand the persistence of such kinking structures in terms of the interlayer shear force locking effect.
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81.05.uf Graphite
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Formation of core/shell-like ZnSe1−xTex nanocrystals due to equilibrium surface segregation

Sumeet C. Pandey, T. J. Mountziaris, D. Venkataraman, and Dimitrios Maroudas

Appl. Phys. Lett. 96, 201910 (2010); http://dx.doi.org/10.1063/1.3428659 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2010

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We report results of equilibrium surface segregation in ZnSe1−xTex nanocrystals based on a computational analysis of coupled compositional, structural, and volume relaxation of the nanocrystals that employs Monte Carlo and conjugate-gradient methods according to a first-principles-parameterized description of interatomic interactions. We have determined the equilibrium concentration distribution as a function of nanocrystal size and composition for nanocrystal morphologies that include faceted equilibrium crystal shapes. The results identify the nanoparticle size and composition ranges that allow for self-assembly of core/shell-like nanocrystal structures characterized by a Te-deficient core and a Te-rich shell.
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61.46.-w Structure of nanoscale materials
02.60.-x Numerical approximation and analysis
02.50.Ng Distribution theory and Monte Carlo studies

Site-specific electronic configurations of Fe 3d states by energy loss by channeled electrons

Kazuyoshi Tatsumi, Shunsuke Muto, Ikuo Nishida, and Ján Rusz

Appl. Phys. Lett. 96, 201911 (2010); http://dx.doi.org/10.1063/1.3429593 (3 pages) | Cited 6 times

Online Publication Date: 21 May 2010

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Site-specific configurations of Fe 3d electrons in a spinel ferrite were investigated by electron energy loss spectroscopy under electron channeling conditions. Site-specific spectra were extracted by applying a multivariate curve resolution (MCR) technique to the data set. An electronic difference in the Fe sites caused by ligand field splitting of trivalent Fe was probed. This demonstrated the promise of site-specific valence and spin state analysis in spintronics applications of spinel ferrites.
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71.20.Ps Other inorganic compounds
71.70.Ch Crystal and ligand fields
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
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