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12 Sep 2011

Volume 99, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 113501 (2011); http://dx.doi.org/10.1063/1.3634072 (3 pages)

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan, Ramamoorthy Ramesh, and Sayeef Salahuddin
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Influence of the silicon carbide surface morphology on the epitaxial graphene formation

M. H. Oliveira, Jr., T. Schumann, M. Ramsteiner, J. M. J. Lopes, and H. Riechert

Appl. Phys. Lett. 99, 111901 (2011); http://dx.doi.org/10.1063/1.3638058 (3 pages) | Cited 5 times

Online Publication Date: 12 September 2011

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Graphene grown on SiC(0001) by Si depletion has a stepped surface with terraces and step heights up to 10 times larger than those observed in the original SiC surface. This is due to an additional step bunching that usually occurs during graphene formation. In this work, we show that such process can be suppressed by controlling the initial step structure of the SiC surface. In this case, the graphene monolayer is formed on the SiC without modification of the original surface morphology. We observe that the absence of step bunching during growth has no influence on the graphene structural quality.
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81.05.ue Graphene
68.35.bg Semiconductors
68.55.ap Fullerenes
61.48.Gh Structure of graphene
68.65.Pq Graphene films

First-principles studies on the dominant acceptor and the activation mechanism of phosphorus-doped ZnO

Ping Li, Sheng-Hua Deng, and Jing Huang

Appl. Phys. Lett. 99, 111902 (2011); http://dx.doi.org/10.1063/1.3638460 (3 pages) | Cited 5 times

Online Publication Date: 12 September 2011

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Based on first-principles calculations, we suggest that the PZn-2VZn complex is the dominant acceptor in phosphorus-doped ZnO with a calculated transition level of 150 meV. We suggest that the out-diffusion of zinc interstitials will indirectly favor the formation of the PZn-2VZn complex. According to this mechanism, an upper limit of annealing temperature of about 860 °C is obtained, which is high enough to activate the doped ZnO from n- to p-type. This mechanism applies to the other group-V dopants. The above results are in agreement with the experimental reports.
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71.55.Gs II-VI semiconductors
61.72.jj Interstitials
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

Cd diffusion and thermal stability of CdZnO/ZnO heterostructures

A. Yu. Azarov, T. C. Zhang, B. G. Svensson, and A. Yu. Kuznetsov

Appl. Phys. Lett. 99, 111903 (2011); http://dx.doi.org/10.1063/1.3639129 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2011

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Structural properties and thermal stability of CdZnO/ZnO heterostructures grown on sapphire substrate by metal-organic vapor phase epitaxy (MOVPE) have been studied. Zn/Cd interdiffusion and Cd evaporation appear as key factors limiting the thermal stability of CdZnO/ZnO heterostructures. Cd diffusion in MOVPE ZnO is found to start already at 600 °C with an activation energy of ∼2.2 eV and yields a saturation in the Cd concentration at 0.1-1 at. %. The actual Cd content remaining in the samples upon annealing is determined by a competition between Cd evaporation via the surface and diffusion/segregation in the bulk.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Dv Composition, segregation; defects and impurities
68.35.Fx Diffusion; interface formation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Bidirectional bending splitter of designer surface plasmons

Yong Jin Zhou, Quan Jiang, and Tie Jun Cui

Appl. Phys. Lett. 99, 111904 (2011); http://dx.doi.org/10.1063/1.3639277 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2011

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We propose and experimentally verify a bidirectional bending splitter of designer surface plasmons which is composed of two metallic gratings of trapezoid grooves. A metal wire is used to excite the designer surface plasmons propagating along the gratings. A full-wave numerical method has been used to simulate the performance of the bending splitter. The experimental verifications in the microwave frequencies have excellent agreements to the simulations. It is demonstrated that the splitter can not only split the electromagnetic waves at different frequencies, but also guide the electromagnetic waves effectively for large-angle bending.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Dj Gratings

Calculating the specific contact resistance from the nanostructure at the interface of silver thick film contacts on n-type silicon

Stefan Kontermann, Ralf Preu, and Gerhard Willeke

Appl. Phys. Lett. 99, 111905 (2011); http://dx.doi.org/10.1063/1.3635383 (3 pages) | Cited 1 time

Online Publication Date: 14 September 2011

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Nanoscale silver crystals located on the silicon surface at the interface of silver thick film contacts carry the current across the contacts. By quantifying the interface area between the silver crystals and the silicon from scanning electron microscopy images of the silicon surface beneath the contact, we calculate the macroscopic specific contact resistance for contacts of different quality. We find good agreement with experimental contact resistance measurements. The presented results enable the prediction of the macroscopic specific contact resistance from the nanostructure found at the contact interface.
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73.40.Cg Contact resistance, contact potential
73.63.Rt Nanoscale contacts
81.07.Lk Nanocontacts
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.40.Ns Metal-nonmetal contacts

Defect migration and recombination in nanoindentation of silica glass

Ken-ichi Nomura, Yi-Chun Chen, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

Appl. Phys. Lett. 99, 111906 (2011); http://dx.doi.org/10.1063/1.3637052 (3 pages) | Cited 2 times

Online Publication Date: 14 September 2011

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Deformation, plasticity, and flow in silica-based glasses have been studied for decades, and yet important questions remain about the atomistic mechanisms underlying these processes. Our molecular dynamics simulations of nanoindentation indicate that these mechanical processes have a unified underlying atomistic mechanism. The simulations reveal that indentation nucleates under-coordinated silicon and oxygen defects, which migrate by switching bonds in string-like processes. We also observe defect annihilation in the plastic region underneath and the pileup region around the indenter. These defects have also been observed in simulations of nanovoid coalescence under hydrostatic tension and in nanovoid deformation and breakup in shearing silica glass.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.fq Plasticity and superplasticity
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.40.Lm Deformation, plasticity, and creep

Tetrahedral chalcopyrite quantum dots for solar-cell applications

Juho Ojajärvi, Esa Räsänen, Sascha Sadewasser, Sebastian Lehmann, Philipp Wagner, and Martha Ch. Lux-Steiner

Appl. Phys. Lett. 99, 111907 (2011); http://dx.doi.org/10.1063/1.3640225 (3 pages)

Online Publication Date: 15 September 2011

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Chalcopyrite structures are candidates for efficient intermediate-band solar cells in thin-film technology. Here, we examine a material combination of CuInSe2 dots embedded in CuGaS2 matrix and show that epitaxial growth leads to distinctive tetrahedral nanostructures. Our model calculations provide us with the optimal nanodot size to reach the maximum efficiency—in principle up to 61%. The optimal quantum dot satisfies the known physical constraints, and it is in excellent qualitative agreement with our grown samples.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
73.21.La Quantum dots
78.67.Hc Quantum dots

The role of plasmons and interband transitions in the color of AuAl2, AuIn2, and AuGa2

V. J. Keast, K. Birt, C. T. Koch, S. Supansomboon, and M. B. Cortie

Appl. Phys. Lett. 99, 111908 (2011); http://dx.doi.org/10.1063/1.3638061 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2011

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First principles calculations of the optical properties of the intermetallic compounds AuAl2, AuIn2, and AuGa2 have been performed. Analysis of the dielectric functions showed that AuAl2 is unique because a bulk plasmon is seen in the optical region and contributes to the purple color of this material. An experimental electron energy-loss spectrum showed excellent agreement with the theoretical prediction and confirmed the presence of the bulk plasmon.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.20.Uv Electron energy loss spectroscopy

Formation of optical barriers with excellent thermal stability in single-crystal sapphire by hydrogen ion implantation and thermal annealing

William T. Spratt, Mengbing Huang, Chuanlei Jia, Lei Wang, Vimal K. Kamineni, Alain C. Diebold, and Hua Xia

Appl. Phys. Lett. 99, 111909 (2011); http://dx.doi.org/10.1063/1.3637613 (3 pages) | Cited 1 time

Online Publication Date: 16 September 2011

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We report a study on the use of hydrogen ion implantation to form optical barriers with excellent thermal stability in single-crystal sapphire. Sapphire crystals are implanted with H ions of energies 0.2–1 MeV to doses 1016–1017 cm−2, followed by thermal annealing between 600–1200 °C. Prism coupling experiments and spectroscopic ellipsometry indicate the formation of an optical barrier with decreased refractive index around the projected range of H ions in sapphire. The refractive index reduction is found to increase with annealing temperatures, reaching a maximum of ∼3.2% following annealing at 1200 °C. The correlation of the structural properties with the formation of optical barriers and their thermal stability in sapphire crystals, is duscussed.
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61.72.up Other materials
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.43.Nr Desorption kinetics
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments

Magnesium, nitrogen codoped Cr2O3: A p-type transparent conducting oxide

E. Arca, K. Fleischer, and I. V. Shvets

Appl. Phys. Lett. 99, 111910 (2011); http://dx.doi.org/10.1063/1.3638461 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2011

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A p-type transparent conductive oxide (TCO) was synthesised by codoping of poorly conducting chromium oxide (Cr2O3) with magnesium and nitrogen. We demonstrated that the codoping produced a TCO with good figure of merit despite using spray pyrolysis for deposition. The nitrogen enhances the specular transparency of the films in the visible range (400-700 nm), and Mg improves the conductivity while retaining the p-type character of the material. Co-doping with both elements produces a p-type oxide with a low resistivity of 3 Ω cm and transmission up to 65% for a 150 nm thick film. A comparison with other known p-type materials is given.
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81.05.Hd Other semiconductors
81.15.Rs Spray coating techniques
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.66.Li Other semiconductors

Dislocation reduction in heteroepitaxial Ge on Si using SiO2 lined etch pits and epitaxial lateral overgrowth

Darin Leonhardt and Sang M. Han

Appl. Phys. Lett. 99, 111911 (2011); http://dx.doi.org/10.1063/1.3632113 (3 pages)

Online Publication Date: 16 September 2011

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We report a technique that significantly reduces threading dislocations in Ge on Si heteroepitaxy. Germanium is first grown on Si and etched to produce pits in the surface where threading dislocations terminate. Further processing leaves a layer of SiO2 only within etch pits. Subsequent selective epitaxial Ge growth results in coalescence above the SiO2. The SiO2 blocks the threading dislocations from propagating into the upper Ge epilayer. With annealed Ge films grown on Si, the said method reduces the defect density from 2.6 × 108 to 1.7 × 106 cm−2, potentially making the layer suitable for electronic and photovoltaic devices.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
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