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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages)

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis
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Flexible, compressible, hydrophobic, floatable, and conductive carbon nanotube-polymer sponge

Jin-Woo Han, Beomseok Kim, Jing Li, and M. Meyyappan

Appl. Phys. Lett. 102, 051903 (2013); http://dx.doi.org/10.1063/1.4790437 (4 pages)

Online Publication Date: 4 February 2013

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A flexible, compressible, hydrophobic, ice-repelling, floatable, and conductive carbon nanotube (CNT)-polydimethylsiloxane (PDMS) sponge is presented. The microporous sponge-like PDMS scaffold fabricated with a sugar cube template is capable of CNT uptake. The CNT-PDMS sponge (CPS) is deformable and compressible up to 90%. The Young's modulus varies from 22 KPa to 200 KPa depending on the applied strain. The conductive pathways via the CNT network increase with compressive strain similar to a variable resistor or pressure sensor. The softness of the CPS can be utilized for artificial skin to grip sensitive objects. In addition, the contact angle of water droplets on CPS shows 141°, and thus the hydrophobic nature of the CPS can be exploited as a floating electrode. Furthermore, the hydrophobicity is maintained below freezing temperature, allowing an ice-repelling electrode.
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81.40.Lm Deformation, plasticity, and creep
62.20.de Elastic moduli
62.20.F- Deformation and plasticity
68.03.Cd Surface tension and related phenomena
81.40.Jj Elasticity and anelasticity, stress-strain relations

Enhancement of the performance of InAs quantum dots solar cell by surface modification using Poly-L-Lysine homopolymers

Y. F. Makableh, R. Vasan, S. Lee, and O. M. Manasreh

Appl. Phys. Lett. 102, 051904 (2013); http://dx.doi.org/10.1063/1.4789908 (3 pages)

Online Publication Date: 4 February 2013

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The enhancement of InAs quantum dots solar cell was reported for surface modification by implementing Poly-L-Lysine (PLL) homopolymers as an anti-reflection coating. Dip coating method was used to coat the solar cell surface with PLL. The current-voltage, spectral response, and external quantum efficiency measurements were performed to characterize the solar cell. Furthermore, the transmission spectra of GaAs were obtained before and after PLL coating. At least 25% increase in the performance of the InAs quantum dots solar cell was achieved as depicted in the current voltage, external quantum efficiency, and spectral response measurements.
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88.40.jm Thin film III-V and II-VI based solar cells
42.79.Wc Optical coatings
88.40.hj Efficiency and performance of solar cells

Differential scanning calorimetric determination of the thermal properties of amorphous Co60Fe20B20 and Co40Fe40B20 thin films

Yuan-Tsung Chen, S. H. Lin, and W. H. Hsieh

Appl. Phys. Lett. 102, 051905 (2013); http://dx.doi.org/10.1063/1.4775375 (5 pages)

Online Publication Date: 4 February 2013

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The thermal stability of Co60Fe20B20 and Co40Fe40B20 thin films are investigated by non-isothermal and isothermal thermal analysis. The differential scanning calorimetry results of amorphous Co60Fe20B20 and Co40Fe40B20 thin films showed the crucial glass forming ability index, γ and γm. The Kissinger formula was applied to calculate the activation energy (Q) of crystallization to measure its resistance of crystallization; 3000 Å was a critical thickness. Based on the non-isothermal and isothermal thermal analysis, it reveals that the thermal stability and incubation time of Co60Fe20B20 films are better than Co40Fe40B20 films.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.60.Dv Thermal stability; thermal effects
64.70.P- Glass transitions of specific systems

The growth of microcrystalline silicon oxide thin films studied by in situ plasma diagnostics

S. Kirner, O. Gabriel, B. Stannowski, B. Rech, and R. Schlatmann

Appl. Phys. Lett. 102, 051906 (2013); http://dx.doi.org/10.1063/1.4790279 (4 pages)

Online Publication Date: 5 February 2013

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The crystallinity and refractive index of microcrystalline silicon oxide (μc-SiOx:H) n-layers and their dependence on the pressure and radio frequency power during the deposition process is correlated with plasma properties derived from in situ diagnostics. From process gas depletion measurements, the oxygen content of the layers was calculated. High crystallinities were observed for increased pressures and decreased powers, indicating clear differences to trends previously shown for microcrystalline silicon (μc-Si:H) material, which are explained by the varying oxygen incorporation. Amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cells with μc-SiOx:H intermediate reflector layers deposited at optimized pressures showed greatly improved series resistances.
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68.55.at Other materials
52.77.Dq Plasma-based ion implantation and deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Submicron-diameter phase-separated scintillator fibers for high-resolution X-ray imaging

Yoshihiro Ohashi, Nobuhiro Yasui, Yuui Yokota, Akira Yoshikawa, and Toru Den

Appl. Phys. Lett. 102, 051907 (2013); http://dx.doi.org/10.1063/1.4790295 (4 pages)

Online Publication Date: 5 February 2013

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We demonstrated micrometer-scale resolution X-ray imaging by using phase-separated scintillator fibers. Hexagonally well-aligned 680-nm-diameter GdAlO3(GAP):Ce3+ scintillator fibers surrounded with α-Al2O3 were fabricated from directionally solidified eutectics. The GAP:Ce3+ fibers convert X-rays to lights and emitted lights are confined and transported along the fiber direction by a total reflection mode. High-resolution X-ray image of a gold grating phantom with a 4 μm aperture, corresponding to a bundle of 12 fibers, was achieved even with a 150 -μm-thick scintillator. These scintillator fibers overcome resolution reduction caused by light scattering and almost reach the resolution limit of the material nature itself.
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07.85.-m X- and γ-ray instruments
42.81.Wg Other fiber-optical devices
07.60.Vg Fiber-optic instruments

Microstructural defects in GaN thin films grown on chemically vapor-deposited graphene layers

Hyobin Yoo, Kunook Chung, Suk In Park, Miyoung Kim, and Gyu-Chul Yi

Appl. Phys. Lett. 102, 051908 (2013); http://dx.doi.org/10.1063/1.4790385 (4 pages)

Online Publication Date: 5 February 2013

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Microstructural defects in GaN thin films grown on graphene produced via chemical vapor deposition have been investigated using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD analysis reveals the preferred orientations of the GaN films. We further examined the microstructural defects such as grain boundaries and threading dislocations present in the films using TEM. Plan-view TEM analysis showed presence of both high- and low-angle grain boundaries and the threading dislocations mostly bound to those grain boundaries. Moreover, the characteristics and behavior of the threading dislocations were also investigated using cross-section TEM analysis.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
79.20.Kz Other electron-impact emission phenomena

Structural evolution in bulk metallic glass under high-temperature tension

X. D. Wang, H. B. Lou, J. Bednarcik, H. Franz, H. W. Sheng, Q. P. Cao, and J. Z. Jiang

Appl. Phys. Lett. 102, 051909 (2013); http://dx.doi.org/10.1063/1.4790393 (4 pages)

Online Publication Date: 5 February 2013

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The tensile behavior of a Cu46Zr46Al8 bulk metallic glass (BMG) at elevated temperatures has been studied using in situ x-ray diffraction and molecular dynamics simulation. It is demonstrated that excess open volume is generated during elastic deformation and accumulated enough before plastic flow starts. The open volume almost keeps constant during homogeneous deformation, suggesting that a high content of open volume is a key point for developing BMGs with pronounced tensile plasticity.
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81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Optical contrast and laser-induced phase transition in GeCu2Te3 thin film

Yuta Saito, Yuji Sutou, and Junichi Koike

Appl. Phys. Lett. 102, 051910 (2013); http://dx.doi.org/10.1063/1.4791567 (5 pages)

Online Publication Date: 6 February 2013

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Fast crystallization and low power amorphization are essential to achieve rapid data recording and low power consumption in phase-change memory. This work investigated the laser-induced phase transition behaviors of GeCu2Te3 film based on the reflectance of amorphous and crystalline states. The GeCu2Te3 film showed a reflectance decrease upon crystallization, which was the opposite behavior in Ge2Sb2Te5 film. The crystallization starting time of the as-deposited GeCu2Te3 film was as fast as that of the as-deposited Ge2Sb2Te5 film. Furthermore, the GeCu2Te3 crystalline film was found to be reamorphized by laser irradiation at lower power and shorter pulse width than the Ge2Sb2Te5.
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78.66.Nk Insulators
64.70.K- Solid-solid transitions
61.82.Ms Insulators
78.30.Hv Other nonmetallic inorganics
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Ha Other nonmetallic inorganics
78.40.Pg Disordered solids

A method to determine the Young's modulus of thin-film elements assisted by dark-field electron holography

S. Reboh, P. Benzo, P. Morin, R. Cours, M. J. Hÿtch, and A. Claverie

Appl. Phys. Lett. 102, 051911 (2013); http://dx.doi.org/10.1063/1.4790617 (4 pages)

Online Publication Date: 6 February 2013

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We present a method to determine the isotropic elastic modulus of nanometer-thick films of unknown or imprecise microstructure and composition. First, the mesoscopic stress of the film is determined using Stoney's method. Then, after fabricating film-stripes by lithography, dark-field electron holography is used to image the strain fields (3 nm spatial resolution, ∼2 × 10−4 precision) resulting from the local interactions between the stripes and an underlying silicon crystal. By comparing the experimental results with finite element method modeling, we deduce Young's modulus of the film. Silicon nitride films on Si substrates are presented as a model system.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
68.60.Bs Mechanical and acoustical properties

Oxidation induced softening in Al nanowires

Fatih G. Sen, Yue Qi, Adri C. T. van Duin, and Ahmet T. Alpas

Appl. Phys. Lett. 102, 051912 (2013); http://dx.doi.org/10.1063/1.4790181 (5 pages) | Cited 1 time

Online Publication Date: 7 February 2013

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The mechanical properties of metallic nanowires depend dramatically on the atmospheric conditions. Molecular-dynamics simulations with ReaxFF were conducted to study tensile elastic deformation of oxidized Al nanowires. The thin amorphous oxide shell formed around Al nanowires had a very low Young's modulus of 26 GPa, due to its low density and low Al-O coordination. Consequently, for diameters less than 100 nm, the composite Young's modulus of oxide-covered Al nanowires showed a size dependence implying that in this case “smaller is softer.” The model developed also explained the discrepancies in the reported modulus values of nanometer-scale Al thin films.
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62.23.Hj Nanowires
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
62.20.de Elastic moduli
62.20.F- Deformation and plasticity

Observation of rhombohedral nanostructures in the orthorhombic phase of KNbO3 using convergent-beam electron diffraction

Kenji Tsuda, Rikiya Sano, and Michiyoshi Tanaka

Appl. Phys. Lett. 102, 051913 (2013); http://dx.doi.org/10.1063/1.4791679 (4 pages)

Online Publication Date: 7 February 2013

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Symmetries of nanometer-scale local structures in the rhombohedral and orthorhombic phases of potassium niobate (KNbO3) have been examined using convergent-beam electron diffraction. Nanometer-size local structures with rhombohedral symmetry have been discovered in the orthorhombic phase of KNbO3. It has been found that the structure of the orthorhombic phase of KNbO3 is formed as an average of two variants with rhombohedral symmetry. This fact indicates that the phase transformation between the orthorhombic and rhombohedral phases has an order-disorder character. The result is analogous to the case of BaTiO3, which we already reported [Tsuda et al., Phys. Rev. B 86, 214106 (2012)].
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64.60.Cn Order-disorder transformations
64.70.Nd Structural transitions in nanoscale materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.46.-w Structure of nanoscale materials

Growth of highly near-c-axis oriented ferroelectric LiNbO3 thin films on Si with a ZnO buffer layer

Peng You, Chaojing Lu, Wanneng Ye, Lanzhong Hao, Jun Zhu, and Yichun Zhou

Appl. Phys. Lett. 102, 051914 (2013); http://dx.doi.org/10.1063/1.4791680 (5 pages)

Online Publication Date: 7 February 2013

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Ferroelectric LiNbO3 thin film of high near-c-axis orientation was grown on Si by pulsed laser deposition using a thin ZnO buffer layer of high c-axis orientation. Both the LiNbO3 film and the ZnO layer consist of columnar grains with random in-plane twist relative to each other. The c axes of LiNbO3 grains tilt small angles with respect to the film growth direction and the deviation angles follow nearly Gaussian probability distribution within 5°. The out-of-plane tilt nucleation of LiNbO3 lattices on the waved surfaces of the ZnO layer leads to the near-c-axis oriented growth of the LiNbO3 film.
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81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
77.84.Ek Niobates and tantalates
77.80.-e Ferroelectricity and antiferroelectricity

Transient lattice distortion induced by ultrashort heat pulse propagation through thin film metal/metal interface

Ali Oguz Er, Jie Chen, Jau Tang, and Peter M. Rentzepis

Appl. Phys. Lett. 102, 051915 (2013); http://dx.doi.org/10.1063/1.4790378 (5 pages)

Online Publication Date: 7 February 2013

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Phonon propagation across the Cu/Ag(111) interface and transient structural disorder in Ag(111) crystal, after excitation of 18 nm copper layer with UV femtosecond pulses has been studied by means of picosecond time resolved X-ray diffraction. The lattice disorder was measured by the changes in peak shift and broadening of the XRD rocking curve. A blast force was formed within 2 ps after fs UV irradiation. After fast initial expansion and contraction, a sharp oscillation is observed, while the subsequent oscillations were found to be broader due to out-of phase relationship between the sound waves in the copper and silver layers.
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68.35.Ja Surface and interface dynamics and vibrations
62.65.+k Acoustical properties of solids
68.35.Ct Interface structure and roughness

Reduced threading dislocation densities in high-T/N-rich grown InN films by plasma-assisted molecular beam epitaxy

Bernhard Loitsch, Fabian Schuster, Martin Stutzmann, and Gregor Koblmüller

Appl. Phys. Lett. 102, 051916 (2013); http://dx.doi.org/10.1063/1.4789983 (5 pages)

Online Publication Date: 7 February 2013

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We explore the effect of growth kinetics on the structural properties of In-polar InN films on GaN templates grown near the thermal dissociation limit by plasma-assisted molecular beam epitaxy. Unlike the common growth temperature limit (T ≈ 500 °C) for In-polar InN grown under In-rich conditions, slightly N-rich conditions are demonstrated to shift the available growth temperature window to much higher temperatures (by >50 °C). InN films grown in this high-T/N-rich regime show significantly reduced off-axis X-ray diffraction rocking curve peak widths and record low threading dislocation densities (TDD ∼ 4 × 109 cm−2) even for film thicknesses <1 μm, as compared to state of the art In-rich growth. The reduction of TDD is attributed to more effective TD inclination and annihilation under N-rich growth, delineating prospective routes for improved InN-based materials.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Jj Ion and electron beam-assisted deposition; ion plating
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Pressure-induced tetragonal-orthorhombic phase transitions in CeRuPO

S. Hirai, Y. Kamihara, A. Wakatsuki, M. Matoba, and W. L. Mao

Appl. Phys. Lett. 102, 051917 (2013); http://dx.doi.org/10.1063/1.4791690 (4 pages)

Online Publication Date: 8 February 2013

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CeRuPO, a ferromagnetic Kondo lattice, undergoes two novel pressure-induced structural phase transitions. CeRuPO undergoes an isostructural transition to a collapsed tetragonal structure near 7.5 GPa. Since pressure suppresses the initial ferromagnetic ordering of Ce3+, our observation suggests a quantum critical point for CeRuPO near this pressure. The collapsed tetragonal phase transforms into an orthorhombic Cmma structure. This phase is isostructural with the low temperature phase of LaFeAsO, which is superconducting under high pressure. Since CeRuPO exhibits a similar relationship between the two phases of LaFeAsO, the collapsed tetragonal and orthorhombic phases of CeRuPO may adopt a novel magnetic ground state.
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64.70.K- Solid-solid transitions
74.40.Kb Quantum critical phenomena
61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids

Why specific mixed solvent composition leads to appropriate film formation of composite during spin coating?

S. S. Ghosh, A. P. Zerwal, G. G. Bisen, G. S. Lonkar, J. V. Sali, V. S. Waman, and S. R. Jadkar

Appl. Phys. Lett. 102, 051918 (2013); http://dx.doi.org/10.1063/1.4791696 (5 pages)

Online Publication Date: 8 February 2013

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In this paper, we explain why specific mixed solvent composition leads to appropriate film formation of composite (polymer: inorganic nanoparticle) during spin coating. As a typical case, P3HT:TiO2 film formation has been discussed by taking chloroform as good solvent for P3HT while ethanol, methanol, and 2-propanol are used as co-solvents for dispersing TiO2. Mixed solvent evaporation dynamics during film drying has been simulated to explain the experimental results. Present study can be immensely useful for selecting proper solvents and their initial ratio for blend film formation of a particular phase separation.
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81.05.Qk Reinforced polymers and polymer-based composites
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.F- Liquid-vapor transitions
64.75.Ef Mixing
68.03.Fg Evaporation and condensation of liquids
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Identification of the native defect doping mechanism in amorphous indium zinc oxide thin films studied using ultra high pressure oxidation

Sunghwan Lee and David C. Paine

Appl. Phys. Lett. 102, 052101 (2013); http://dx.doi.org/10.1063/1.4790187 (5 pages) | Cited 1 time

Online Publication Date: 4 February 2013

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The mechanism of native defect doping in amorphous In-Zn-O (a-IZO) has not previously been established but is likely associated with native oxygen defect doping. We have used high pressure oxidation and defect equilibrium analysis to show a −1/6 power dependence of carrier density on oxygen fugacity in a-IZO. This dependency is predicted for oxygen vacancy-like donor defects. Extrapolation of equilibrium constants established at high pressures to atmospheric pressure reveals that the equilibrium carrier density in a-IZO at 200 °C is higher (>1020/cm3) than typical as-deposited channel carrier densities (<1017/cm3). This is consistent with observed increases in channel carrier density and negative threshold voltage shift in annealed a-IZO thin film transistor devices.
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61.72.uj III-V and II-VI semiconductors
68.35.bj Amorphous semiconductors, glasses
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
82.60.Hc Chemical equilibria and equilibrium constants

The source of the threading dislocation in GaSb/GaAs hetero-structures and their propagation mechanism

Yi Wang, P. Ruterana, S. Kret, S. El Kazzi, L. Desplanque, and X. Wallart

Appl. Phys. Lett. 102, 052102 (2013); http://dx.doi.org/10.1063/1.4790296 (5 pages)

Online Publication Date: 4 February 2013

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The misfit and threading dislocations during GaSb epitaxy on GaAs substrate were investigated by weak beam dark field and high angle dark field scanning transmission electron microscopy. The geometric phase analysis and dislocation density tensor analysis were next used to analyze the strain around the threading dislocations and quantify the corresponding Burgers vectors. It is shown that there are three types of threading dislocations (mixed, edge, and pair of mixed types) close to the interface, which originate from the 60°, Lomer, and 60° pair misfit dislocations, respectively. During the growth of the epitaxial layer, the edge type as well as the pair of mixed threading dislocations split into two mixed type dislocations for the glide in {111} planes. Eventually, only mixed type dislocations have been observed at the surface of thick GaSb layers.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Correlation between Ti source/drain contact and performance of InGaZnO-based thin film transistors

Kwang-Hyuk Choi and Han-Ki Kim

Appl. Phys. Lett. 102, 052103 (2013); http://dx.doi.org/10.1063/1.4790357 (5 pages)

Online Publication Date: 4 February 2013

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Ti contact properties and their electrical contribution to an amorphous InGaZnO (a-IGZO) semiconductor-based thin film transistor (TFT) were investigated in terms of chemical, structural, and electrical considerations. TFT device parameters were quantitatively studied by a transmission line method. By comparing various a-IGZO TFT parameters with those of different Ag and Ti source/drain electrodes, Ti S/D contact with an a-IGZO channel was found to lead to a negative shift in VT (−Δ 0.52 V). This resulted in higher saturation mobility (8.48 cm2/Vs) of a-IGZO TFTs due to effective interfacial reaction between Ti and an a-IGZO semiconducting layer. Based on transmission electron microcopy, x-ray photoelectron depth profile analyses, and numerical calculation of TFT parameters, we suggest a possible Ti contact mechanism on semiconducting a-IGZO channel layers for TFTs.
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73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices

Phosphorus doping of 4H SiC by liquid immersion excimer laser irradiation

Akihiro Ikeda, Koji Nishi, Hiroshi Ikenoue, and Tanemasa Asano

Appl. Phys. Lett. 102, 052104 (2013); http://dx.doi.org/10.1063/1.4790621 (4 pages)

Online Publication Date: 4 February 2013

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Phosphorus doping of 4H SiC is performed by KrF excimer laser irradiation of 4H SiC immersed in phosphoric acid. Phosphorus is incorporated to a depth of a few tens of nanometers at a concentration of over 1020/cm3 without generating significant crystal defects. Formation of a pn junction diode with an ideality factor of 1.06 is demonstrated.
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61.72.up Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Scattering due to large cluster embedded in quantum wells

Changbo Liu, Guijuan Zhao, Guipeng Liu, Yafeng Song, Heng Zhang, Dongdong Jin, Zhiwei Li, Xianglin Liu, Shaoyan Yang, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 102, 052105 (2013); http://dx.doi.org/10.1063/1.4782218 (4 pages)

Online Publication Date: 5 February 2013

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Two dimensional electron gas mobility limited by the scattering of large cluster is studied. From this study, we find that the scattering caused by conduction band offset between host well and multiple mini-quantum well (mini-QW) series aligned along the QW channel, i.e., quantum pits, can be treated as a variable in our calculation. The results show that the mobility increases with increasing barrier height, which is opposite to the well-known interface roughness scattering mobility. To make the calculation simple, the InxGa1−xN/InyGa1−yN QW double-heterostructure is selected to along (11math0) non-polarized direction, along which the barrier and well are both flat.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Ct Interface structure and roughness

Tensile strained GeSn on Si by solid phase epitaxy

R. R. Lieten, J. W. Seo, S. Decoster, A. Vantomme, S. Peters, K. C. Bustillo, E. E. Haller, M. Menghini, and J.-P. Locquet

Appl. Phys. Lett. 102, 052106 (2013); http://dx.doi.org/10.1063/1.4790302 (5 pages)

Online Publication Date: 5 February 2013

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We demonstrate single crystalline GeSn with tensile strain on silicon substrates. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single crystalline GeSn by solid phase epitaxy. Excellent structural quality is demonstrated for layers with up to 6.1% of Sn. The GeSn layers show tensile strain (up to +0.34%), which lowers the difference between direct and indirect band transition and makes this method promising for obtaining direct band gap group IV layers. GeSn with 4.5% Sn shows increased optical absorption compared to Ge and an optical band gap of 0.52 eV.
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81.15.Np Solid phase epitaxy; growth from solid phases
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.at Other materials
73.61.At Metal and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

Carrier transport mechanism of low resistance Ti/Al/Au ohmic contacts to AlInN/GaN heterostructures

Seongjun Kim, Jae-Hyun Ryou, Russell D. Dupuis, and Hyunsoo Kim

Appl. Phys. Lett. 102, 052107 (2013); http://dx.doi.org/10.1063/1.4790384 (4 pages)

Online Publication Date: 5 February 2013

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The carrier transport mechanism of a low resistance Ti/Al/Au Ohmic contact to AlInN/GaN heterostructures was investigated. The Ohmic contact produced upon thermal annealing was due to the generation of TiN contact inclusions with a density of 2.8 × 108 cm−2, i.e., spike mechanism. The sheet resistance of channel layer was found to follow power law, yielding the power index of −1.57. Temperature dependent contact resistance could be understood based on the parallel network model consisting of distributed resistance components of TiN contact inclusion (predominant) and the rest sound region (negligible), giving the barrier height of 0.65 eV and the carrier density of 2.3 × 1019 cm−3 at the TiN/GaN interfaces.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Diameter-dependent boron diffusion in silicon nanowire-based transistors

Andreas Schulze, Antonios Florakis, Thomas Hantschel, Pierre Eyben, Anne S. Verhulst, Rita Rooyackers, Anne Vandooren, and W. Vandervorst

Appl. Phys. Lett. 102, 052108 (2013); http://dx.doi.org/10.1063/1.4790438 (4 pages)

Online Publication Date: 5 February 2013

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We analyzed the carrier profile in silicon nanowire-based tunnel-FETs as a function of nanowire diameter using scanning spreading resistance microscopy. The nanowires were etched into an epitaxially grown stack, of which the top layer was in situ boron doped and the top contact was implanted. We revealed a significantly reduced boron diffusion inside narrower nanowires and a nonuniform diffusion depth in wider nanowires. Using process simulations, we attribute the latter to a reduced transient enhanced diffusion close to the nanowire sidewall caused by the recombination of excess interstitials. The shallower profile in narrower nanowires is related to an enhanced interstitial annihilation.
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85.30.Tv Field effect devices
66.30.J- Diffusion of impurities

Spatially resolved investigation of strain and composition variations in (In,Ga)N/GaN epilayers

Benjamin Wilsch, Uwe Jahn, Bernd Jenichen, Jonas Lähnemann, Holger T. Grahn, Hui Wang, and Hui Yang

Appl. Phys. Lett. 102, 052109 (2013); http://dx.doi.org/10.1063/1.4790591 (4 pages)

Online Publication Date: 5 February 2013

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The strain state and composition of a 400 nm thick (In,Ga)N layer grown by metal-organic chemical vapor deposition on a GaN template are investigated by spatially integrated x-ray diffraction and cathodoluminescence (CL) spectroscopy as well as by spatially resolved CL and energy dispersive x-ray analysis. The CL investigations confirm a process of strain relaxation accompanied by an increasing indium content toward the surface of the (In,Ga)N layer, which is known as the compositional pulling effect. Moreover, we identify the strained bottom, unstrained top, and gradually relaxed intermediate region of the (In,Ga)N layer. In addition to an increase of the indium content along the growth direction, the strain relaxation leads to an enhancement of the lateral variations of the indium distribution toward the surface.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
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