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6 Jul 2009

Volume 95, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 95, 013107 (2009); http://dx.doi.org/10.1063/1.3167775 (3 pages)

T. Y. Tsai, C. Y. Lee, N. H. Tai, and W. H. Tuan
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In-plane anisotropic photoluminescence of C-plane GaN under asymmetric biaxial strain

Z. Zhang, D. Y. Fu, R. Zhang, B. Liu, Z. L. Xie, X. Q. Xiu, P. Han, Y. D. Zheng, and G. Edwards

Appl. Phys. Lett. 95, 011901 (2009); http://dx.doi.org/10.1063/1.3157132 (3 pages) | Cited 1 time

Online Publication Date: 6 July 2009

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The effects of anisotropic strain on wurtzite GaN valence subbands are investigated both theoretically and experimentally. k•p perturbation theory reveals that the in-plane asymmetric strain not only affects the transition energies, but also determines the polarization properties, which is analyzed to be the essential cause of the optical anisotropy. Considerable in-plane anisotropy of strained C-plane GaN in polarized photoluminescence is reported. The experimental result in good agreement with theoretical study directly proves the strain effects on the transitions polarization states. The fine accordance of observed and simulated photoluminescence dependences on strain asymmetry degree demonstrates a primary realization of strain controlled optical anisotropy, and such modulation indicates the great potential of utilizing GaN-based semiconductors in polarization-sensitive optoelectronics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds

Observation of Γ-point phonon frequency in ultrathin metallic films confirmed by ab initio calculation and lattice dynamics

H. Tanei, K. Kusakabe, H. Ogi, N. Nakamura, and M. Hirao

Appl. Phys. Lett. 95, 011902 (2009); http://dx.doi.org/10.1063/1.3157138 (3 pages) | Cited 4 times

Online Publication Date: 6 July 2009

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Vibrations in ultrathin metallic films excited by ultrafast light pulses have been studied based on continuum mechanics. However, this paper shows that they are Γ-point phonon vibrations of plate-phonon modes. Ab initio and lattice dynamics calculations are made to compare Γ-point phonon vibrational frequencies with measurements obtained by the picosecond ultrasound spectroscopy. The standing-wave frequencies of specific Γ-point phonon modes of the slab model show good agreement with measurements without any fitting parameters. This study informs us of a limitation of the continuum-mechanics theory for explaining the mechanics of ultrathin metallic films.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Surface acoustic waves with negative group velocity in a thin film structure on silicon

A. A. Maznev and A. G. Every

Appl. Phys. Lett. 95, 011903 (2009); http://dx.doi.org/10.1063/1.3168509 (3 pages) | Cited 7 times

Online Publication Date: 6 July 2009

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A surface acoustic wave dispersion curve of a thin film structure on silicon measured with the laser-induced transient grating technique displays a local minimum in frequency at nonzero wavenumber. For a range of wavenumbers to one side of this minimum the dispersion curve is of negative slope, implying the existence of surface waves with negative group velocity. Unlike in the well studied case of “backward traveling” Lamb waves in plates, the anomalous behavior here is exhibited by the lowest acoustic mode of the structure. The existence of the local minimum in the dispersion curve is corroborated by numerical simulations.
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68.60.Bs Mechanical and acoustical properties
68.65.Ac Multilayers
61.41.+e Polymers, elastomers, and plastics
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology

Analysis of the electric field induced elemental separation of Ge2Sb2Te5 by transmission electron microscopy

Dongmin Kang, Dongbok Lee, Hyun-Mi Kim, Sung-Wook Nam, Min-Ho Kwon, and Ki-Bum Kim

Appl. Phys. Lett. 95, 011904 (2009); http://dx.doi.org/10.1063/1.3168517 (3 pages) | Cited 9 times

Online Publication Date: 6 July 2009

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The chemical instability of line patterned Ge2Sb2Te5 was studied by transmission electron microscopy after electrically inducing melt and solidification. Compositional analysis showed elemental separation of Te to the anode side, while Ge and Sb mutually separated at the cathode side. Such elemental separation of Ge2Sb2Te5 is explained by the electric field effects and thermodynamic driving forces.
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68.55.ag Semiconductors
68.37.Og High-resolution transmission electron microscopy (HRTEM)
64.70.D- Solid-liquid transitions
64.75.Qr Phase separation and segregation in semiconductors
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epifilms

C. C. Kuo, W.-R. Liu, W. F. Hsieh, C.-H. Hsu, H. C. Hsu, and L. C. Chen

Appl. Phys. Lett. 95, 011905 (2009); http://dx.doi.org/10.1063/1.3159470 (3 pages) | Cited 7 times

Online Publication Date: 7 July 2009

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Crystal symmetry breaking of wurtzite C6V to orthorhombic C2V due to in-plane anisotropic strain was investigated for nonpolar (11math0) ZnO epifilms grown on the R-sapphire. X-ray diffraction results reveal the epilayer is subjected to a compressive strain along the polar c-axis and tensile strains along both a-[11math0] surface normal and in-plane p-[1math00] axis. The polarized Raman spectra of E2 modes reveal violation of the C6V selection rules. Oppositely, the C2V configuration satisfies the selection rules for the Raman modes. The observed E1 and E2 bands in polarized optical reflection and photoluminescence spectra confirm the anisotropic strain causes the structure change to the orthorhombic one.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors

Bulk metallic glass formation near intermetallic composition through liquid quenching

W. F. Wu and Y. Li

Appl. Phys. Lett. 95, 011906 (2009); http://dx.doi.org/10.1063/1.3168411 (3 pages) | Cited 10 times

Online Publication Date: 7 July 2009

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Metallic glass is typically formed either by liquid quenching near deep-eutectics or by solid-state reaction near the intermetallic in center of the phase diagram. In our research, two optimum bulk glass formers are synthesized in the vicinity of the intermetallic compound of Cu–Zr system through liquid quenching. It is shown that such a pair of unique glass formation is only feasible in a narrow composition range close to but clearly separated by the intermetallic composition where both the kinetic and thermodynamic conditions for the amorphous formation are matched. The discovery of this “intermetallic glass” pair through quenching allows us to find a potentially applicable host of metallic glass systems. This is followed by a discussion on its impact on understanding the formation and physics of bulk metallic glasses.
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61.43.Fs Glasses
64.70.pe Metallic glasses
64.70.qd Thermodynamics and statistical mechanics
81.30.Bx Phase diagrams of metals, alloys, and oxides

Crystal orientation of GaAs islands grown on SrTiO3 (001) by molecular beam epitaxy

L. Largeau, J. Cheng, P. Regreny, G. Patriarche, A. Benamrouche, Y. Robach, M. Gendry, G. Hollinger, and G. Saint-Girons

Appl. Phys. Lett. 95, 011907 (2009); http://dx.doi.org/10.1063/1.3168500 (3 pages) | Cited 2 times

Online Publication Date: 7 July 2009

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The growth of GaAs islands on (001)-oriented SrTiO3 (STO) substrates by molecular beam epitaxy is studied. A competition between (111)- and (001)-oriented islands takes place. It is shown that this competition is driven by the interface energy and the critical nucleation volume of the GaAs/STO system. Perspectives are proposed to control this competition in order to define reliable growth procedures for the monolithic integration of GaAs based heterostructures on crystalline STO/Si(001) templates.
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81.10.Bk Growth from vapor
61.50.-f Structure of bulk crystals

First-principles study to obtain evidence of low interface defect density at Ge/GeO2 interfaces

Shoichiro Saito, Takuji Hosoi, Heiji Watanabe, and Tomoya Ono

Appl. Phys. Lett. 95, 011908 (2009); http://dx.doi.org/10.1063/1.3168501 (3 pages) | Cited 11 times

Online Publication Date: 7 July 2009

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We present evidence of low defect density at Ge/GeO2 interfaces on the basis of first-principles total energy calculations. The energy advantages of atom emission from the Ge/GeO2 interface to release stress due to lattice mismatch are compared with those from the Si/SiO2 interface. The advantages of Ge/GeO2 are found to be less than those of Si/SiO2 because of the high flexibility of the bonding networks in GeO2. Thus, the suppression of Ge-atom emission during the oxidation process leads to improved electrical properties of the Ge/GeO2 interfaces.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.15.Nc Total energy and cohesive energy calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.05.Cy Elemental semiconductors

Accessing nanomechanical resonators via a fast microwave circuit

Mika A. Sillanpää, Jayanta Sarkar, Jaakko Sulkko, Juha Muhonen, and Pertti J. Hakonen

Appl. Phys. Lett. 95, 011909 (2009); http://dx.doi.org/10.1063/1.3173826 (3 pages) | Cited 9 times

Online Publication Date: 8 July 2009

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We demonstrate how to fully electrically detect the vibrations of conductive nanomechanical resonators up to the microwave regime. We use the electrically actuated vibrations to modulate an LC tank circuit, which blocks the stray capacitance and detect the created sideband voltage by a microwave analyzer. We prove the technique up to mechanical frequencies of 200 MHz. Finally, we estimate how one could approach the quantum limit of mechanical systems.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Spectroscopic ellipsometry study of GaAs1−xBix material grown on GaAs substrate by atmospheric pressure metal-organic vapor-phase epitaxy

Nebiha Ben Sedrine, Imed Moussa, Hedi Fitouri, Ahmed Rebey, Belgacem El Jani, and Radhouane Chtourou

Appl. Phys. Lett. 95, 011910 (2009); http://dx.doi.org/10.1063/1.3167359 (3 pages) | Cited 1 time

Online Publication Date: 8 July 2009

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The optical properties in terms of complex dielectric function of GaAs1−xBix alloys (0% ≤ x ≤ 3.7%), grown by atmospheric pressure metal-organic vapor-phase epitaxy, are determined by using room temperature spectroscopic ellipsometry. The interband transition energies in the energy range of 1.4–5.4 eV are resolved using a line shape fitting on the numerically calculated dielectric function second derivatives. The bismuth effect on the critical point parameters is then determined. We have found that, as for GaAs1−xBix alloys E0 transition, the bismuth incorporation shifts the E1, E1+Δ1, E2, and E0′ transition energies but with a lower magnitude. We also observed a root-square-like increase of the E1 broadening parameter (Γ1) with respect to the bismuth composition.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Direct gap photoluminescence of n-type tensile-strained Ge-on-Si

Xiaochen Sun, Jifeng Liu, Lionel C. Kimerling, and Jurgen Michel

Appl. Phys. Lett. 95, 011911 (2009); http://dx.doi.org/10.1063/1.3170870 (3 pages) | Cited 45 times

Online Publication Date: 9 July 2009

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Room temperature direct gap photoluminescence (PL) was observed from n-type tensile-strained epitaxial Ge-on-Si. The PL intensity increases with n-type doping due to a higher electron population in the direct Γ valley as a result of increased Fermi level. The direct gap emission also increases with temperature due to thermal excitation of electrons into the direct Γ valley, exhibiting robustness to heating effects. These unique properties of direct gap emission in an indirect gap material agree with our theoretical model and make Ge a promising light emitting material in 1550 nm communication band.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
71.20.Mq Elemental semiconductors
68.47.Fg Semiconductor surfaces
61.72.uf Ge and Si
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