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9 Jan 2012

Volume 100, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 023701 (2012); http://dx.doi.org/10.1063/1.3673335 (3 pages)

Biswarup Pathak, Henrik Löfås, Jariyanee Prasongkit, Anton Grigoriev, Rajeev Ahuja, and Ralph H. Scheicher
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Effect of strain and barrier composition on the polarization of light emission from AlGaN/AlN quantum wells

J. E. Northrup, C. L. Chua, Z. Yang, T. Wunderer, M. Kneissl, N. M. Johnson, and T. Kolbe

Appl. Phys. Lett. 100, 021101 (2012); http://dx.doi.org/10.1063/1.3675451 (4 pages) | Cited 6 times

Online Publication Date: 9 January 2012

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For AlGaN-based multi-quantum-well light emitters grown on c-plane substrates there is a tendency for the polarization of the emitted light to switch from transverse electric (TE) polarization to transverse magnetic (TM) polarization as the wavelength decreases. This transition depends on various factors that include the strain in the quantum well. Experimental results are presented that illustrate the phenomenon for nitride light emitting diodes (LEDs) grown on sapphire and on bulk AlN. Model calculations are presented which quantify the dependence of the TE/TM switch on the quantum well strain and the Al composition in the barriers surrounding the well.
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85.60.Jb Light-emitting devices

Efficient optical trapping using small arrays of plasmonic nanoblock pairs

Yoshito Tanaka and Keiji Sasaki

Appl. Phys. Lett. 100, 021102 (2012); http://dx.doi.org/10.1063/1.3675550 (3 pages) | Cited 5 times

Online Publication Date: 9 January 2012

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We report that a small two-dimensional array of gold nanoblock pairs separated by a nanometric gap significantly improves the performance of optical trapping compared to a single nanoblock pair. The array of 4 × 4 pairs suppresses the Brownian motion of a trapped 1 μm diameter particle by a factor of six compared to the single pair. In addition, the array enables particle trapping for a longer period of time. These results are essential for biological applications where intense optical irradiation is a concern.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.79.-e Optical elements, devices, and systems
05.40.Jc Brownian motion

Structural and optical studies of nitrogen incorporation into GaSb-based GaInSb quantum wells

Hari P. Nair, Adam M. Crook, Kin M. Yu, and Seth R. Bank

Appl. Phys. Lett. 100, 021103 (2012); http://dx.doi.org/10.1063/1.3675618 (3 pages) | Cited 2 times

Online Publication Date: 9 January 2012

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We investigate the incorporation of nitrogen into (Ga,In)Sb grown on GaSb and report room temperature photoluminescence from GaInSb(N) quantum wells. X-ray diffraction and channeling nuclear reaction analysis, together with Rutherford backscattering, were employed to identify the optimal molecular beam epitaxial growth conditions that minimized the incorporation of non-substitutional nitrogen into GaNSb. Consistent with this hypothesis, GaInSb(N) quantum wells grown under the conditions that minimized non-substitutional nitrogen exhibited room temperature photoluminescence, indicative of significantly improved radiative efficiency. Further development of this material system could enable type-I laser diodes emitting throughout the (3-5 μm) wavelength range.
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78.67.De Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

444.9 nm semipolar (11math2) laser diode grown on an intentionally stress relaxed InGaN waveguiding layer

Po Shan Hsu, Matthew T. Hardy, Feng Wu, Ingrid Koslow, Erin C. Young, Alexey E. Romanov, Kenji Fujito, Daniel F. Feezell, Steven P. DenBaars, James S. Speck, and Shuji Nakamura

Appl. Phys. Lett. 100, 021104 (2012); http://dx.doi.org/10.1063/1.3675850 (4 pages) | Cited 10 times

Online Publication Date: 9 January 2012

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We demonstrate an electrically injected semipolar (11math2) laser diode (LD) grown on an intentionally stress relaxed n-In0.09Ga0.91N waveguiding layer. Detrimental effects of misfit dislocations (MDs) in the proximity of the active region were effectively suppressed by utilizing a p/n-Al0.2Ga0.8N electron/hole blocking layer between the dislocated heterointerfaces and the active region. The threshold current density of the LD was ∼20.3 kA/cm2 with a lasing wavelength of 444.9 nm. This LD demonstrates an alternative approach in semipolar AlInGaN LD waveguide design where the thickness and composition of the waveguiding and/or cladding layers are not limited by the critical thickness for MD formation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Photovoltaic quantum dot quantum cascade infrared photodetector

A. V. Barve and S. Krishna

Appl. Phys. Lett. 100, 021105 (2012); http://dx.doi.org/10.1063/1.3675905 (3 pages) | Cited 1 time

Online Publication Date: 9 January 2012

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Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared photodetection (λpeak = 5.5 μm) is demonstrated. The quantum cascade barrier region provides the internal electric field to transfer photoexcited electrons into quantum dots of the next stack, enabling zero bias operation. Increased carrier relaxation time for intersubband transitions in quantum dots provides a distinct advantage for the carrier transport. Responsivity of 10 mA/W and detectivity of 9 × 109 cm Hz1/2 W−1 at 77 K for f/2 optics has been obtained at zero bias. Dark current density is 6.5 × 10−7A cm−2, at 80 K at zero bias.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Ultrafast dynamics of the Mn3+ d-d transition and spin-lattice interaction in YMnO3 film

Zuanming Jin, Hong Ma, Gaofang Li, Yue Xu, Guohong Ma, and Zhenxiang Cheng

Appl. Phys. Lett. 100, 021106 (2012); http://dx.doi.org/10.1063/1.3675906 (4 pages) | Cited 2 times

Online Publication Date: 9 January 2012

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We investigate the photo-induced carrier dynamics and spin-lattice interaction in hexagonal YMnO3 film by the temperature-dependent femtosecond pump-probe spectroscopy. The spin-lattice interaction is identified from the slow component of the transient transmittance change with the excitation energies tuned to 1.7 eV and 2.0 eV, which are close to Mn3+ ions d(xz),(yz)→d(z2) and d(x2-y2),(xy)→d(z2) transition, respectively. Temperature dependences of the spin-lattice relaxation parameters demonstrate that the spin-lattice interaction is strongly connected with the d-d transition within Mn3+ ions and enhanced by spin ordering.
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75.70.Ak Magnetic properties of monolayers and thin films
78.47.J- Ultrafast spectroscopy (<1 psec)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Improvement of temperature-stability in a quantum well laser with asymmetric barrier layers

Alexey E. Zhukov, Natalia V. Kryzhanovskaya, Fedor I. Zubov, Yuri M. Shernyakov, Mikhail V. Maximov, Elizaveta S. Semenova, Kresten Yvind, and Levon V. Asryan

Appl. Phys. Lett. 100, 021107 (2012); http://dx.doi.org/10.1063/1.3676085 (3 pages) | Cited 1 time

Online Publication Date: 10 January 2012

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We fabricated and tested a quantum well laser with asymmetric barrier layers. Such a laser has been proposed earlier to suppress bipolar carrier population in the optical confinement layer and thus to improve temperature-stability of the threshold current. As compared to the conventional reference laser structure, our laser with asymmetric barrier layers demonstrates reduced internal optical loss, lower threshold current density at elevated temperatures, and higher characteristic temperature (143 vs. 99 K at 20 °C).
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.86.+b Optical workshop techniques
42.87.-d Optical testing techniques

Experimental controlling of Fano resonance in indirectly coupled whispering-gallery microresonators

Bei-Bei Li, Yun-Feng Xiao, Chang-Ling Zou, Xue-Feng Jiang, Yong-Chun Liu, Fang-Wen Sun, Yan Li, and Qihuang Gong

Appl. Phys. Lett. 100, 021108 (2012); http://dx.doi.org/10.1063/1.3675571 (3 pages) | Cited 6 times

Online Publication Date: 10 January 2012

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We experimentally studied the transmission spectrum of a coupled resonator structure in which a low-Q microdisk and a high-Q microtoroid indirectly interact with each other mediated by a fiber taper. Asymmetric Fano resonances were observed and could be controlled to change periodically by adjusting the distance between the two microresonators. It is revealed that the Fano resonance originates from the coupling of the two modes belonging to the two microresonators. The observed period of distance change is around 8 μm, which shows good agreement with the theoretical prediction by the beat of multiple propagating modes in the fiber taper.
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07.10.Cm Micromechanical devices and systems

Nonlinear optical properties of low temperature annealed silicon-rich oxide and silicon-rich nitride materials for silicon photonics

S. Minissale, S. Yerci, and L. Dal Negro

Appl. Phys. Lett. 100, 021109 (2012); http://dx.doi.org/10.1063/1.3675882 (4 pages) | Cited 6 times

Online Publication Date: 10 January 2012

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We investigate the nonlinear optical properties of Si-rich silicon oxide (SRO) and Si-rich silicon nitride (SRN) samples as a function of silicon content, annealing temperature, and excitation wavelength. Using the Z-scan technique, we measure the non-linear refractive index n2 and the nonlinear absorption coefficient β for a large number of samples fabricated by reactive co-sputtering. Moreover, we characterize the nonlinear optical parameters of SRN in the broad spectral region 1100-1500 nm and show the strongest nonlinearity at 1500 nm. These results demonstrate the potential of the SRN matrix for the engineering of compact devices with enhanced Kerr nonlinearities for silicon photonics applications.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments

High-reflectivity, high-Q micromechanical membranes via guided resonances for enhanced optomechanical coupling

Catvu H. Bui, Jiangjun Zheng, S. W. Hoch, Lennon Y. T. Lee, J. G. E. Harris, and Chee Wei Wong

Appl. Phys. Lett. 100, 021110 (2012); http://dx.doi.org/10.1063/1.3658731 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2012

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Using Fano-type guided resonances (GRs) in photonic crystal (PhC) slab structures, we numerically and experimentally demonstrate optical reflectivity enhancement of high-Q SiNx membrane-type resonators used in membrane-in-the-middle optomechanical (OM) systems. Normal-incidence transmission and mechanical ringdown measurements of 50-nm-thick PhC membranes demonstrate GRs near 1064 nm, leading to a ∼4 × increase in reflectivity while preserving high mechanical Q factors of up to ∼5 × 106. The results would allow improvement of membrane-in-the-middle OM systems by virtue of increased OM coupling, presenting a path towards ground state cooling of such a membrane and observations of related quantum effects.
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07.10.Cm Micromechanical devices and systems
07.60.-j Optical instruments and equipment
42.70.Qs Photonic bandgap materials

Wavelength selective uncooled infrared sensor by plasmonics

Shinpei Ogawa, Kazuya Okada, Naoki Fukushima, and Masafumi Kimata

Appl. Phys. Lett. 100, 021111 (2012); http://dx.doi.org/10.1063/1.3673856 (4 pages) | Cited 2 times

Online Publication Date: 11 January 2012

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A wavelength selective uncooled infrared (IR) sensor using two-dimensional plasmonic crystals (2D PLCs) has been developed. The numerical investigation of 2D PLCs demonstrates that the wavelength of absorption can be mainly controlled by the period of the surface structure. A microelectromechanical systems-based uncooled IR sensor with 2D PLCs as the IR absorber was fabricated through a complementary metal oxide semiconductor and a micromachining technique. The selective enhancement of responsivity was observed at the wavelength that coincided with the period of the 2D-PLC absorber.
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07.10.Cm Micromechanical devices and systems
02.60.-x Numerical approximation and analysis
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Monolayer graphene growth on Ni(111) by low temperature chemical vapor deposition

Rafik Addou, Arjun Dahal, Peter Sutter, and Matthias Batzill

Appl. Phys. Lett. 100, 021601 (2012); http://dx.doi.org/10.1063/1.3675481 (3 pages) | Cited 10 times

Online Publication Date: 9 January 2012

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In contrast to the commonly employed high temperature chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the bulk, we demonstrate that below 600 °C graphene can be grown in a self-limiting monolayer growth process. Optimum growth is achieved at ∼550 °C. Above this temperature, carbon diffusion into the bulk is limiting the surface growth rate, while at temperatures below ∼500 °C a competing surface carbide phase impedes graphene formation.
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81.05.ue Graphene
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Fx Diffusion; interface formation
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On the polarized emission from exciton complexes in GaN quantum dots

S. Amloy, K. F. Karlsson, T. G. Andersson, and P. O. Holtz

Appl. Phys. Lett. 100, 021901 (2012); http://dx.doi.org/10.1063/1.3675572 (4 pages) | Cited 3 times

Online Publication Date: 9 January 2012

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The optical linear polarization properties of exciton complexes in asymmetric Stranski-Krastanov grown GaN quantum dots have been investigated experimentally and theoretically. It is demonstrated that the polarization angle and the polarization degree can be conveniently employed to associate emission lines in the recorded photoluminescence spectra to a specific dot. The experimental results are in agreement with configuration interaction computations, which predict similar polarization degrees for the exciton and the biexciton (within 10%) in typical GaN quantum dots. The theory further predicts that the polarization degree can provide information about the charge state of the dot.
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78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
71.35.-y Excitons and related phenomena
73.21.La Quantum dots
78.55.Cr III-V semiconductors

Optimizing non-radiative energy transfer in hybrid colloidal-nanocrystal/silicon structures by controlled nanopillar architectures for future photovoltaic cells

O. Seitz, L. Caillard, H. M. Nguyen, C. Chiles, Y. J. Chabal, and A. V. Malko

Appl. Phys. Lett. 100, 021902 (2012); http://dx.doi.org/10.1063/1.3675634 (4 pages) | Cited 4 times

Online Publication Date: 9 January 2012

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To optimize colloidal nanocrystals/Si hybrid structures, nanopillars are prepared and organized via microparticle patterning and Si etching. A monolayer of CdSe nanocrystals is then grafted on the passivated oxide-free nanopillar surfaces, functionalized with carboxy-alkyl chain linkers. This process results to a negligible number of non-radiative surface state defects with a tightly controlled separation between the nanocrystals and Si. Steady-state and time-resolved photoluminescence measurements confirm the close-packing nanocrystal arrangement and the dominance of non-radiative energy transfer from nanocrystals to Si. We suggest that radially doped p-n junction devices based on energy transfer offer a viable approach for thin film photovoltaic devices.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Rv Passivation
82.70.Dd Colloids
61.46.-w Structure of nanoscale materials
78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Formation mechanism of cellular structures during unidirectional growth of binary semiconductor Si-rich SiGe materials

Raira Gotoh, Kozo Fujiwara, Xinbo Yang, Haruhiko Koizumi, Jun Nozawa, and Satoshi Uda

Appl. Phys. Lett. 100, 021903 (2012); http://dx.doi.org/10.1063/1.3675860 (4 pages) | Cited 2 times

Online Publication Date: 9 January 2012

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The formation mechanism of a cellular structure during the growth of Si-rich SiGe crystals was studied by in situ observation. We directly observed the morphological transformation of the crystal-melt interface during the unidirectional growth of Si-rich SiGe. It was found that the morphology of the interface transformed from a planar to a zigzag facets to a faceted cellular interface with increasing growth rate. It is clarified that Ge segregation at valleys of zigzag facets leads to the formation of a cellular structure in Si-rich SiGe crystals.
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81.10.Fq Growth from melts; zone melting and refining
81.30.Fb Solidification
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Effects of scandium on the bandgap and location of Ce3+ levels in Lu1−xScxBO3:Ce scintillators

Yuntao Wu, Guohao Ren, Dongzhou Ding, Fan Yang, and Shangke Pan

Appl. Phys. Lett. 100, 021904 (2012); http://dx.doi.org/10.1063/1.3675881 (4 pages) | Cited 3 times

Online Publication Date: 9 January 2012

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Transparent Lu1−xScxBO3:Ce (x = 0.3, 0.5, 0.7, 0.8) scintillation crystals were grown by Czochralski method. Vacuum ultraviolet excitation spectra and thermoluminescence glow curves revealed the narrowing of bandgap and the redshift of the first electric dipole-allowed fd transition of Ce3+ with the increase of Sc content. The ionization energy evaluated from the photoluminescence decays as a function of temperature indicated that, with increasing Sc content, the thermal ionization probability occurring from 5d1 relaxed state of Ce3+ was enhanced, which degraded the scintillation efficiency of Lu1−xScxBO3:Ce crystals.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials
78.60.Kn Thermoluminescence
78.70.Ps Scintillation

Theoretical investigation of high velocity, temperature compensated Rayleigh waves along AlN/SiC substrates for high sensitivity mass sensors

Cinzia Caliendo

Appl. Phys. Lett. 100, 021905 (2012); http://dx.doi.org/10.1063/1.3675619 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2012

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The operation of electroacoustic devices based on surface acoustic waves (SAW) propagation along β-SiC/AlN and amorphous-SiC/AlN substrates is theoretically studied with respect to the AlN film thickness, the SAW propagation direction, temperature and electric boundary conditions. GHz-range, enhanced electroacoustic coupling coefficient, temperature compensated around 20 °C electroacoustic devices are the advantages of SiC/AlN composite structures. These structures are also suitable for the implementation of sensors with improved performances with respect to SAW devices based on bulk single crystal piezoelectric substrates. The structures feasibility was confirmed by structural investigation and quantitative analysis of sputtered amorphous-SiC and AlN films on Si substrates.
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43.58.-e Acoustical measurements and instrumentation
68.35.Iv Acoustical properties

Correlating the supercooled liquid region width with the fragility parameter in bulk metallic glasses

L. Hu, F. Ye, Y. F. Liang, and J. P. Lin

Appl. Phys. Lett. 100, 021906 (2012); http://dx.doi.org/10.1063/1.3675910 (3 pages) | Cited 1 time

Online Publication Date: 10 January 2012

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A linear correlation of fragility parameter D* with supercooled liquid region width ΔTx for Ca-based bulk metallic glasses (BMGs) was revealed. This relationship is found in La- and Zr-based BMGs as well and extended to several glass-forming systems. The origin of this phenomenon lies in the close relation between crystallization and temperature dependence of viscosity. This relationship can be formulated by ΔTx0.33 = 6.8×10-3×(D*)(Tg0.33)+2(K), indicating that the unique variation of the viscosity with the temperature correlates with the location and width of the supercooled liquid region. Moreover, an approximation of fragility parameter D* for BMGs can be evaluated by the formula.
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64.70.pe Metallic glasses
66.20.-d Viscosity of liquids; diffusive momentum transport
61.43.Fs Glasses

Computational study on entanglement length and pore size of carbon nanotube buckypaper

Ying Li and Martin Kröger

Appl. Phys. Lett. 100, 021907 (2012); http://dx.doi.org/10.1063/1.3675912 (5 pages) | Cited 2 times

Online Publication Date: 10 January 2012

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In this letter, both entanglement length and pore size of carbon nanotube (CNT) buckypaper are studied numerically and found to scale with a characteristic length math, where EI and γ denote the bending stiffness and binding energy of a CNT, respectively. For math<40 nm, the CNTs in buckypaper are “interwound” with a short entanglement length and a small pore size. However, when math>40 nm, CNT “ring”/“racket” structures dominate the buckypaper, exhibiting longer entanglement length and larger pore size. The acquired understanding of microscopic structures allows us to propose that CNT buckypaper with different mechanical properties and pore size can be designed through the choice of math values.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
62.20.dq Other elastic constants
62.20.F- Deformation and plasticity
61.43.Gt Powders, porous materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep

Theoretical investigation of Fe substitution for Mn in complex hydride YMn2H6

Shigeyuki Takagi, Kazutoshi Miwa, Tamio Ikeshoji, Motoaki Matsuo, Mika Kano, and Shin-ichi Orimo

Appl. Phys. Lett. 100, 021908 (2012); http://dx.doi.org/10.1063/1.3675913 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2012

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Complex hydride YMn2H6 with a space group Fmmathm has two sorts of Mn, in which one presents as a divalent cation Mn2+ on the 8c site and the other forms a complex anion [MnH6]5− on the 4a site. We investigate the stabilities of Fe substitutions for a part of Mn atoms on either the site using first-principles calculations. Our results reveal that an Fe atom prefers the 4a occupation, and the origin of this site preference can be understood by the balance of two competing energy gains brought by the 3d bands for either the 4a or 8c site substituted Fe.
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71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

High (pressure, temperature) phase diagrams of ZnO and AlN from second harmonic generation measurements

Lkhamsuren Bayarjargal and Björn Winkler

Appl. Phys. Lett. 100, 021909 (2012); http://dx.doi.org/10.1063/1.3676057 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2012

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The pressure-induced B4 → B1 structural phase boundaries of ZnO and AlN have been determined with the second harmonic generation (SHG) technique at high temperature. The SHG measurements of AlN show that between 15.6 and 18 GPa, the phase boundary has a negative slope of nearly −627 K/GPa, and that below 15.6 GPa, the slope is significantly smaller (−77 K/GPa). ZnO has a phase boundary with a negative slope of nearly −1427 K/GPa around 5.3–6 GPa and −228 K/GPa below 5 GPa. The phase transition pressure of AlN is sensitive to deviatoric stress and varies from 18 to 24.5 GPa.
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81.30.Dz Phase diagrams of other materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids
64.70.kg Semiconductors

Observation of a snap-through instability in graphene

Scott Scharfenberg, Nikhita Mansukhani, Cesar Chialvo, Richard L. Weaver, and Nadya Mason

Appl. Phys. Lett. 100, 021910 (2012); http://dx.doi.org/10.1063/1.3676059 (3 pages) | Cited 5 times

Online Publication Date: 12 January 2012

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We examine the competition between adhesive and bending energies for few-layer graphene (FLG) samples placed on microscale-corrugated metallic substrates. Using atomic force microscopy, we show that the graphene undergoes a sharp “snap-through” transition as a function of layer thickness, where the material transitions between conforming to the substrate and lying flat on top of the substrate. By utilizing the critical snap-through thickness in an elasticity model for the FLG’s bending, we extract a value for graphene-surface adhesion energy of 1.1 eV/nm2.
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68.65.Pq Graphene films
68.35.Md Surface thermodynamics, surface energies
68.35.Np Adhesion
68.55.-a Thin film structure and morphology
68.60.Wm Other nonelectronic physical properties
62.20.F- Deformation and plasticity

Enhanced crystallization of GeTe from an Sb2Te3 template

R. E. Simpson, P. Fons, A. V. Kolobov, M. Krbal, and J. Tominaga

Appl. Phys. Lett. 100, 021911 (2012); http://dx.doi.org/10.1063/1.3675635 (4 pages) | Cited 4 times

Online Publication Date: 12 January 2012

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Crystalline Sb2Te3 templates reduce the crystallization time of the phase change material GeTe by four orders of magnitude to 20 ns. Structural measurements and density functional theory molecular dynamics atomistic modeling show that this reduction is a direct consequence of textured crystal growth from a plane of octahedral crystal nucleation centers. The nucleation template serves to reduce the crystallization activation energy by 2.6 eV allowing crystallization to proceed at a temperature 95 °C lower than that of the untemplated GeTe film.
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81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.70.dg Crystallization of specific substances

Direct evidence of type II band alignment in ZnO nanorods/poly(3-hexylthiophene) heterostructures

M. H. Chan, J. Y. Chen, T. Y. Lin, and Y. F. Chen

Appl. Phys. Lett. 100, 021912 (2012); http://dx.doi.org/10.1063/1.3676267 (3 pages) | Cited 1 time

Online Publication Date: 13 January 2012

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The emission from ZnO nanorods/poly(3-hexylthiophene) (P3HT) heterostructures with type II band alignment has been investigated. The additional emission due to the formation of the heterojunction around 950 nm has been found and attributed to the type II transition related to the recombination of electrons in conduction band of ZnO and holes in highest occupied molecular orbital band of P3HT. The consistency of excitation power density dependent photoluminescence (PL) spectra with the theoretical prediction offers a firm evidences for the type II transition. In addition, lifetime of P3HT measured by time-resolved PL also strongly supports that the infrared light indeed arises from the type II transition. Our results shown here provide the first direct evidence of the type II band alignment in ZnO nanorods/P3HT heterostructure, which should be very useful for the realization of underpinned mechanism of the developed optoelectronic devices.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Et II-VI semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Metalorganic chemical vapor deposition of N-polar GaN films on vicinal SiC substrates using indium surfactants

Dongjin Won, Xiaojun Weng, and Joan M. Redwing

Appl. Phys. Lett. 100, 021913 (2012); http://dx.doi.org/10.1063/1.3676275 (4 pages) | Cited 2 times

Online Publication Date: 13 January 2012

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The effect of indium surfactants on the growth of N-polar GaN films on vicinal C-face SiC substrates by metalorganic chemical vapor deposition was investigated. Triangular hillocks formed on the surface of N-polar GaN without indium, resulting in a rough surface. When indium surfactants were introduced during GaN growth, the surface roughness was reduced from 18.1 to 3.5 nm over a 20 × 20 μm2 area. The photoluminescence characteristics of N-polar GaN film were also improved because of a reduction of carbon caused by the presence of indium, demonstrating that indium is a useful surfactant in the growth of N-polar GaN.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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