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17 Jan 2005

Volume 86, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 033101 (2005); http://dx.doi.org/10.1063/1.1851002 (3 pages)

Kun Chen, Allen Taflove, Young L. Kim, and Vadim Backman
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Properties of nonpolar a-plane InGaN∕GaN multiple quantum wells grown on lateral epitaxially overgrown a-plane GaN

Arpan Chakraborty, Stacia Keller, Cedrik Meier, Benjamin A. Haskell, Salka Keller, Patrick Waltereit, Steven P. DenBaars, Shuji Nakamura, James S. Speck, and Umesh K. Mishra

Appl. Phys. Lett. 86, 031901 (2005); http://dx.doi.org/10.1063/1.1851007 (3 pages) | Cited 38 times

Online Publication Date: 7 January 2005

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The properties of nonpolar a-plane InGaN∕GaN multiple-quantum wells (MQWs), grown simultaneously on lateral epitaxially overgrown (LEO) a-plane GaN and planar a-plane GaN, were studied. High-resolution x-ray diffraction analysis revealed that the In mol fraction in the MQWs grown on LEO-GaN was significantly lower than that on planar a-plane GaN. The lower In incorporation was confirmed by microphotoluminescence (μ-PL) and wide-area photoluminescence measurements, which showed a redshift of the MQW emission from 413 nm for the nearly defect-free laterally overgrown regions to 453 nm for the defective “window” regions of the LEO a-plane GaN, to 478 nm for the high-defect density planar a-plane GaN. μ-PL measurements also demonstrated that the emission from the nearly defect-free wings of the LEO a-plane GaN was more than ten times stronger than the emission from the defective windows.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.Fg Quantum wells
68.37.Ps Atomic force microscopy (AFM)
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Plasmon scattering from a single gold nanoparticle collected through an optical fiber

Sang-Kee Eah, Heinrich M. Jaeger, Norbert F. Scherer, Gary P. Wiederrecht, and Xiao-Min Lin

Appl. Phys. Lett. 86, 031902 (2005); http://dx.doi.org/10.1063/1.1851011 (3 pages) | Cited 19 times

Online Publication Date: 7 January 2005

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A single gold nanoparticle is attached to the end of a chemically etched fiber axicon microlens tip by modifying the tip surface with linker molecules. The high collection efficiency of the fiber axicon microlens allows plasmon scattering of a single nanoparticle to be measured directly through the optical fiber. The portable nature of this probe allows direct optical sensing of environmental changes using a single nanoparticle.
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07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Anomalous behaviors of E1/E2 deep level defects in 6H silicon carbide

X. D. Chen, C. C. Ling, M. Gong, S. Fung, C. D. Beling, G. Brauer, W. Anwand, and W. Skorupa

Appl. Phys. Lett. 86, 031903 (2005); http://dx.doi.org/10.1063/1.1853523 (3 pages) | Cited 4 times

Online Publication Date: 7 January 2005

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Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n-type 6H–SiC. Similar to others’ results, the behaviors of E1 and E2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E1/E2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E1/E2. The activation energy and the capture cross section of this defect are EC−0.31 eV and σ ∼ 8×10−14 cm2, respectively.
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71.55.-i Impurity and defect levels
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Fe Electron and positron radiation effects

Investigation of plasma hydrogenation and trapping mechanism for layer transfer

Peng Chen, Paul K. Chu, T. Höchbauer, J.-K. Lee, M. Nastasi, D. Buca, S. Mantl, R. Loo, M. Caymax, T. Alford, J. W. Mayer, N. David Theodore, M. Cai, B. Schmidt, and S. S. Lau

Appl. Phys. Lett. 86, 031904 (2005); http://dx.doi.org/10.1063/1.1852087 (3 pages) | Cited 13 times

Online Publication Date: 7 January 2005

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Hydrogen ion implantation is conventionally used to initiate the transfer of Si thin layers onto Si wafers coated with thermal oxide. In this work, we studied the feasibility of using plasma hydrogenation to replace high dose H implantation for layer transfer. Boron ion implantation was used to introduce H-trapping centers into Si wafers to illustrate the idea. Instead of the widely recognized interactions between boron and hydrogen atoms, this study showed that lattice damage, i.e., dangling bonds, traps H atoms and can lead to surface blistering during hydrogenation or upon postannealing at higher temperature. The B implantation and subsequent processes control the uniformity of H trapping and the trap depths. While the trap centers were introduced by B implantation in this study, there are many other means to do the same without implantation. Our results suggest an innovative way to achieve high quality transfer of Si layers without H implantation at high energies and high doses.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments
71.55.Cn Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si

Estimation of elastic compliances of planar interfacial cracks from homogeneous solutions

Larissa Gorbatikh and Marina Popova

Appl. Phys. Lett. 86, 031905 (2005); http://dx.doi.org/10.1063/1.1850196 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2005

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Formation of cracks in a material as a result of the damage accumulation may change (weaken) material effective properties. The present letter suggests an approach to estimate such changes when cracks form at interfaces of dissimilar materials (for example, at matrix/inclusion boundaries or film/substrate interfaces). Generally, solution of an interface problem is required to predict compliances of interfacial cracks, with the exception of planar cracks. We show that planar cracks possess a special property in the sense that their normal compliances may be approximated from solutions in a homogeneous medium. The method is then applied to analyze elastic compliances of the rectilinear, penny-shaped, elliptical, and annular interfacial cracks.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains
62.20.M- Structural failure of materials
62.20.D- Elasticity

Investigation of the initial stage of growth of HfO2 films on Si(100) grown by atomic-layer deposition using in situ medium energy ion scattering

Hyo Sik Chang, Hyunsang Hwang, Mann-Ho Cho, and Dae Won Moon

Appl. Phys. Lett. 86, 031906 (2005); http://dx.doi.org/10.1063/1.1850596 (3 pages) | Cited 7 times

Online Publication Date: 10 January 2005

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The initial stage of growth of HfO2 films on p-type Si(100) grown by atomic-layer deposition (ALD) was investigated using in situ medium energy ion scattering (MEIS). The interaction between adsorbed HfCl4 molecules and the oxidized Si surface was examined as a function of growth cycles. The results clearly show that island-like growth occurs during the initial HfO2 growth and the islands are then merged into a continuous atomic layer with an increase in ALD cycles. The morphology of thicker HfO2 films remained essentially unchanged with growth cycles. Interfacial reactions between Hf and Si during the initial growth stage were minimal. As a result, the effect of insufficient nucleation density is a dominant factor in the initial stage of growth of hafnium oxide on the oxidized Si substrate, resulting in nonlinear growth behavior.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.43.Fg Adsorbate structure (binding sites, geometry)

Junction and carrier temperature measurements in deep-ultraviolet light-emitting diodes using three different methods

Y. Xi, J.-Q. Xi, Th. Gessmann, J. M. Shah, J. K. Kim, E. F. Schubert, A. J. Fischer, M. H. Crawford, K. H. A. Bogart, and A. A. Allerman

Appl. Phys. Lett. 86, 031907 (2005); http://dx.doi.org/10.1063/1.1849838 (3 pages) | Cited 51 times

Online Publication Date: 11 January 2005

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The junction temperature of AlGaN ultraviolet light-emitting diodes emitting at 295 nm is measured by using the temperature coefficients of the diode forward voltage and emission peak energy. The high-energy slope of the spectrum is explored to measure the carrier temperature. A linear relation between junction temperature and current is found. Analysis of the experimental methods reveals that the diode-forward voltage is the most accurate (±3 °C). A theoretical model for the dependence of the diode forward voltage (Vf) on junction temperature (Tj) is developed that takes into account the temperature dependence of the energy gap. A thermal resistance of 87.6 K/W is obtained with the device mounted with thermal paste on a heat sink.
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85.60.Jb Light-emitting devices
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Role of silicon interstitials in boron cluster dissolution

Maria Aboy, Lourdes Pelaz, Luis A. Marqués, Pedro López, Juan Barbolla, R. Duffy, V. C. Venezia, and Peter B. Griffin

Appl. Phys. Lett. 86, 031908 (2005); http://dx.doi.org/10.1063/1.1852728 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2005

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We present kinetic nonlattice Monte Carlo atomistic simulations to investigate the role of Si interstitials in B cluster dissolution. We show that the presence of Si interstitials from an oxidizing anneal stabilize B clusters and slow down B cluster dissolution, compared to anneal in inert ambient. We have also analyzed the influence of injected Si interstitials from end of range defects, due to preamorphizing implants, on B deactivation and reactivation processes. We have observed that the B cluster evolution can be clearly correlated to the evolution of Si interstitial defects at the end of range. The minimum level of activation occurs when the Si interstitial supersaturation is low because the end of range defects have dissolved or reach very stable configurations, such as dislocation loops.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
02.70.Uu Applications of Monte Carlo methods

Synthesis and optical properties of well-aligned ZnO nanorod array on an undoped ZnO film

Jiansheng Jie, Guanzhong Wang, Yiming Chen, Xinhai Han, Qingtao Wang, Bo Xu, and J. G. Hou

Appl. Phys. Lett. 86, 031909 (2005); http://dx.doi.org/10.1063/1.1854737 (3 pages) | Cited 78 times

Online Publication Date: 12 January 2005

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High-density well-aligned ZnO nanorod array was successfully synthesized on a PLD prepared undoped ZnO film by a catalyst-free method. X-ray diffraction and scanning electron microscopy show that the nanorods are well-oriented perpendicular to the substrate. The photoluminescence from free excitons and Raman spectra of the ZnO nanorods reflect the high purity and nearly defect free structure of nanorods. The well-aligned feature of the nanorod array is attributed to the nanorods’ epitaxial growth from the ZnO film.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations

Elastic and electromechanical properties of polypropylene foam ferroelectrets

M. Dansachmüller, R. Schwödiauer, S. Bauer-Gogonea, S. Bauer, M. Paajanen, and J. Raukola

Appl. Phys. Lett. 86, 031910 (2005); http://dx.doi.org/10.1063/1.1854740 (3 pages) | Cited 15 times

Online Publication Date: 12 January 2005

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Internally charged closed-cell polymer electrets exhibit ferroelectric-like behavior and have been called ferroelectrets. They are attractive for soft electroactive transducers, the high compressibility leads to d33 transducer coefficients exceeding those of ferroelectric polymers. A technique for the measurement of the elastic modulus and the transducer coefficient of ferroelectrets is reported. The elastic behavior of ferroelectretic polypropylene foams is correlated with the piezoelectric-like properties. Prestress treatments linearize the transducer properties.
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77.84.Jd Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.70.Rr Aerosols and foams
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
77.22.-d Dielectric properties of solids and liquids

Theoretical study of nitrogen vacancies in Ti4AlN3

Denis Music, Rajeev Ahuja, and Jochen M. Schneider

Appl. Phys. Lett. 86, 031911 (2005); http://dx.doi.org/10.1063/1.1854744 (3 pages) | Cited 11 times

Online Publication Date: 12 January 2005

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We have investigated the energetics of the N vacancy formation in Ti4AlN3 by ab initio calculations. We identify N 2a sites (Wyckoff notation) in Ti4AlN2.75 as the most probable vacancy sites based on the energetics of vacancy formation. Furthermore, Ti4AlN3 does not exhibit any states at the Fermi level. Introducing N vacancies causes states to appear at the Fermi level, which may enable electron transport. Recently measured conductivity data [ Finkel et al., Phys. Rev. B 67, 235108 (2003) ] for Ti4AlN3 can be understood based on our calculations.
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61.72.Bb Theories and models of crystal defects
61.72.J- Point defects and defect clusters
71.55.Ht Other nonmetals
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states

Concentration and ion-energy-independent annealing kinetics during ion-implanted-defect annealing

R. Karmouch, J.-F. Mercure, Y. Anahory, and F. Schiettekatte

Appl. Phys. Lett. 86, 031912 (2005); http://dx.doi.org/10.1063/1.1852733 (3 pages) | Cited 5 times

Online Publication Date: 12 January 2005

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Nanocalorimetry revealed that the annealing kinetics of ion-implanted defects in polycrystalline Si is independent of ion fluence and implantation energy. Ion implantation of 30 keV Si−, 15 keV Si−, and 15 keV C− was performed at fluences ranging from 6×1011 to 1×1015 atoms/cm2, followed by temperature scans between 30 and 450 °C. The rate of heat release has the same shape for all fluences, featuring no peaks but rather a smooth, continuously increasing signal. This suggests that the heat release is dominated by the annealing of highly disordered zones generated by each implantation cascade. Such annealing depends primarily on the details of the damage zone–crystal interface kinetics, and not on the point defect concentration.
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61.72.uf Ge and Si

Continuous grey scale image printing on the liquid crystal cell

Rumiko Yamaguchi and Susumu Sato

Appl. Phys. Lett. 86, 031913 (2005); http://dx.doi.org/10.1063/1.1851009 (3 pages) | Cited 11 times

Online Publication Date: 13 January 2005

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The continuous grey scale image is printed on the liquid crystal (LC) cell through the similar printing process on a photographic paper. The LC cell is prepared with a rubbed photo-cross-linkable polymer coated substrate whose azimuthal anchoring strength increases by exposing the unpolarized UV light. The cell filled with the LC is exposed to the UV light through a negative film, and is thermally developed and fixed. The twist angle continuously changes from 0° to about 90° by increasing the exposure, and the positive image with continuous grey levels appears in the LC cell between parallel polarizers.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals

Optical properties of InAs/GaAs surface quantum dots

Z. L. Miao, Y. W. Zhang, S. J. Chua, Y. H. Chye, P. Chen, and S. Tripathy

Appl. Phys. Lett. 86, 031914 (2005); http://dx.doi.org/10.1063/1.1854199 (3 pages) | Cited 23 times

Online Publication Date: 13 January 2005

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We report long-wavelength photoluminescence emission ( ∼ 1.6–1.7 μm) from self-organized InAs surface quantum dots (SQDs) grown on GaAs substrate without any capping layers. Photoluminescence (PL) properties of these quantum dots (QDs) are strongly affected by the surface states and strain relaxation mechanism. Compared to the case of capped InAs QDs, a large redshift of about 466 nm observed in the PL spectrum of SQDs can be attributed to the strain relaxation and the strong coupling of the confined states with the surface states. The PL properties of these SQDs can also be influenced by the presence of quasi-infinite surface potential.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
78.68.+m Optical properties of surfaces
68.65.Hb Quantum dots (patterned in quantum wells)
73.20.At Surface states, band structure, electron density of states
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Effect of growth polarity on vacancy defect and impurity incorporation in dislocation-free GaN

F. Tuomisto, K. Saarinen, B. Lucznik, I. Grzegory, H. Teisseyre, T. Suski, S. Porowski, P. R. Hageman, and J. Likonen

Appl. Phys. Lett. 86, 031915 (2005); http://dx.doi.org/10.1063/1.1854745 (3 pages) | Cited 29 times

Online Publication Date: 13 January 2005

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We have used positron annihilation, secondary ion mass spectrometry, and photoluminescence to study the point defects in GaN grown by hydride vapor phase epitaxy (HVPE) on GaN bulk crystals. The results show that N polar growth incorporates many more donor and acceptor type impurities and also Ga vacancies. Vacancy clusters with a positron lifetime τD = 470±50 ps were found near the N polar surfaces of both the HVPE GaN layers and bulk crystals.
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81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
78.66.Fd III-V semiconductors
78.70.Bj Positron annihilation
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Enhanced room-temperature luminescence efficiency through carrier localization in AlxGa1−xN alloys

C. J. Collins, A. V. Sampath, G. A. Garrett, W. L. Sarney, H. Shen, M. Wraback, A. Yu. Nikiforov, G. S. Cargill, and V. Dierolf

Appl. Phys. Lett. 86, 031916 (2005); http://dx.doi.org/10.1063/1.1856702 (3 pages) | Cited 29 times

Online Publication Date: 14 January 2005

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AlGaN samples grown by plasma-assisted molecular-beam epitaxy on sapphire (0001) substrates, with 20%–50% Al content and without the use of indium, show intense room-temperature photoluminescence that is significantly redshifted, 200–400 meV, from band edge. This intense emission is characterized by a long room-temperature lifetime ( ∼ 375 ps) comparable to that seen in low defect density ( ∼ 108 cm−2) GaN. Room-temperature monochromatic cathodoluminescence images at the redshifted peak reveal spatially nonuniform emission similar to that observed in In(Al)GaN alloys and attributed to compositional inhomogeneity. These observations suggest that spatial localization enhances the luminescence efficiency despite the high defect density (>1010 cm−2) of the films by inhibiting movement of carriers to nonradiative sites.
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78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Angle-dispersive neutron diffraction under high pressure to 10 GPa

S. Klotz, Th. Strässle, G. Rousse, G. Hamel, and V. Pomjakushin

Appl. Phys. Lett. 86, 031917 (2005); http://dx.doi.org/10.1063/1.1855419 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2005

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We present a method which allows high-quality powder neutron diffraction patterns to be obtained under pressure by angle-dispersive diffraction to at least 10 GPa. This technique uses a new type of Paris–Edinburgh press in conjunction with sintered boron nitride anvils. As an example, we show NiO diffraction patterns obtained under purely hydrostatic pressures up to 10 GPa. These data were collected within a few hours, and are free from any contaminating signal from the pressure cell. High-resolution nuclear and magnetic structural information can be readily extracted by Rietveld refinements, without additional data correction. This technique will allow powder neutron diffraction at elevated pressures to become a standard tool on continuous neutron facilities.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.43.Gt Powders, porous materials
62.50.-p High-pressure effects in solids and liquids
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.05.fm Neutron diffraction
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