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17 Mar 2003

Volume 82, Issue 11, pp. 1649-1799

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 1709 (2003); http://dx.doi.org/10.1063/1.1560575 (3 pages)

Ji-Won Oh, Masahiro Yoshita, Hidefumi Akiyama, Loren N. Pfeiffer, and Ken W. West
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Void channel microstructures in resin solids as an efficient way to infrared photonic crystals

M. J. Ventura, M. Straub, and M. Gu

Appl. Phys. Lett. 82, 1649 (2003); http://dx.doi.org/10.1063/1.1560870 (3 pages) | Cited 32 times

Online Publication Date: 10 March 2003

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Microvoid channels were generated by local melting in a solidified polymer resin sample moving perpendicular to the focus of a high numerical-aperture objective under visible femtosecond-pulsed illumination. Channel size, surface quality, and high density channel vicinity depended on laser intensity and scanning speed. Electron microscope images revealed elliptical channel cross sections of 0.7–1.3 μm in lateral diameter and an elongation in the focusing direction of approximately 50%. A 20 layer woodpile-type photonic crystal structure with a 1.7 μm layer spacing and a 1.8 μm in-plane channel spacing provided a sharp peak in reflection and a suppression of infrared transmission in the stacking direction by 85% at wavelength 4.8 μm with a gap/midgap ratio of 0.11. © 2003 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
42.62.-b Laser applications
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.47.-p Spectroscopy of solid state dynamics

Temporally multiplexed holographic polymer-dispersed liquid crystals

J. Qi, M. E. Sousa, A. K. Fontecchio, and G. P. Crawford

Appl. Phys. Lett. 82, 1652 (2003); http://dx.doi.org/10.1063/1.1557767 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2003

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We report on a temporal multiplexing technique to fabricate multiple reflection gratings in holographic polymer-dispersed liquid crystals. By time-sequentially exposing the sample, two switchable reflection gratings are formed in a single film. The reflectance of the resulting gratings is well controlled by the individual exposure time. The observed transmission spectra are in excellent agreement with our model based on the reaction-diffusion equation to predict the kinetics of formation and the 2×2 matrix method to model the optical performance. © 2003 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems

Spectral and time-resolved photoluminescence studies of Eu-doped GaN

Ei Ei Nyein, U. Hömmerich, J. Heikenfeld, D. S. Lee, A. J. Steckl, and J. M. Zavada

Appl. Phys. Lett. 82, 1655 (2003); http://dx.doi.org/10.1063/1.1560557 (3 pages) | Cited 76 times

Online Publication Date: 10 March 2003

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We report on spectral and time-resolved photoluminescence (PL) studies performed on Eu-doped GaN prepared by solid-source molecular-beam epitaxy. Using above-gap excitation, the integrated PL intensity of the main Eu3+ line at 622.3 nm (5D0→7F2 transition) decreased by nearly 90% between 14 K and room temperature. Using below-gap excitation, the integrated intensity of this line decreased by only ∼ 50% for the same temperature range. In addition, the Eu3+ PL spectrum and decay dynamics changed significantly compared to above-gap excitation. These results suggest the existence of different Eu3+ centers with distinct optical properties. Photoluminescence excitation measurements revealed resonant intra-4f absorption lines of Eu3+ ions, as well as a broad excitation band centered at ∼ 400 nm. This broad excitation band overlaps higher lying intra-4f Eu3+ energy levels, providing an efficient pathway for carrier-mediated excitation of Eu3+ ions in GaN. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.47.-p Spectroscopy of solid state dynamics

Growth of room-temperature “arsenic free” infrared photovoltaic detectors on GaSb substrate using metamorphic InAlSb digital alloy buffer layers

E. Plis, P. Rotella, S. Raghavan, L. R. Dawson, S. Krishna, D. Le, and C. P. Morath

Appl. Phys. Lett. 82, 1658 (2003); http://dx.doi.org/10.1063/1.1556167 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2003

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We report the growth of a high-quality graded InAlSb digital alloy buffer layer on GaSb substrates. The metamorphic buffer layer relaxes the lattice matching constraint and allows the growth of heterostructures without the use of a second group V element. Cross-sectional transmission electronic microscopy images reveal a very low dislocation density in the buffer layer. Using such a buffer layer, a room-temperature InGaSb photovoltaic detector with λcutoff ∼ 3 μm has been fabricated with an external quantum efficiency >70%. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.65.Cd Superlattices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.Lk Linear defects: dislocations, disclinations

Theoretical investigation of a two-dimensional photonic crystal slab with truncated cone air holes

Yoshinori Tanaka, Takashi Asano, Yoshihiro Akahane, Bong-Shik Song, and Susumu Noda

Appl. Phys. Lett. 82, 1661 (2003); http://dx.doi.org/10.1063/1.1559947 (3 pages) | Cited 66 times

Online Publication Date: 10 March 2003

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The effects of truncated cone air holes on propagation losses from line defect waveguides in two-dimensional (2D) photonic crystal (PC) slabs are investigated. It is shown that coupling between TE-like waveguide modes and TM-like slab modes due to out-of-plane structural asymmetries can result in large propagation losses. It is also shown that coupling, and therefore propagation loss, does not occur in a frequency range where wave vectors of TE-like waveguide modes do not match projections of those of TM-like slab modes. The results are thought to be applicable to other structures exhibiting out-of-plane asymmetries, such as 2D PC slabs attached to silicon on insulator substrates. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Interferometric study of thermal dynamics in GaAs-based quantum-cascade lasers

C. Pflügl, M. Litzenberger, W. Schrenk, D. Pogany, E. Gornik, and G. Strasser

Appl. Phys. Lett. 82, 1664 (2003); http://dx.doi.org/10.1063/1.1561582 (3 pages) | Cited 26 times

Online Publication Date: 10 March 2003

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The thermal dynamics in quantum-cascade lasers under pulsed operation is investigated by a scanning interferometric thermal mapping technique. An infrared laser beam probes the change in the refractive index caused by current-induced heating of the working devices. The measured phase shift provides a quantitative information on the thermal characteristics with a micrometer spatial and a nanosecond time resolution. Comparing the experiments with a two-dimensional thermal model enables us to determine the anisotropic heat conductivity in the multilayered active region, found to be much lower than the one of bulk GaAs, as well as the temperature increase in the active region during pulsed operation. © 2003 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.66.Fd III-V semiconductors

Fabrication of three-dimensional polymer photonic crystal structures using single diffraction element interference lithography

Ivan Divliansky, Theresa S. Mayer, Kito S. Holliday, and Vincent H. Crespi

Appl. Phys. Lett. 82, 1667 (2003); http://dx.doi.org/10.1063/1.1560860 (3 pages) | Cited 53 times

Online Publication Date: 10 March 2003

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This letter describes an approach for recording three-dimensional (3D) periodic structures in a photosensitive polymer using a single diffraction element mask. The mask has a central opening surrounded by three diffraction gratings oriented 120° relative to one another such that the three first order diffracted beams and the nondiffracted laser beam give a 3D spatial light intensity pattern. Structures patterned in this polymer using 1.0 and 0.56 μm grating periods have hexagonal symmetry with micron- to submicron-periodicity over large substrate area. Band structure calculations of these low index contrast materials predict photonic gaps in certain high symmetry directions. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Jk Polymers and organics
42.79.Dj Gratings
42.86.+b Optical workshop techniques

Ultrashort, nonlinear, optical time response of Fe-doped InGaAs/InP multiple quantum wells in 1.55-μm range

M. Guézo, S. Loualiche, J. Even, A. Le Corre, H. Folliot, C. Labbé, O. Dehaese, and G. Dousselin

Appl. Phys. Lett. 82, 1670 (2003); http://dx.doi.org/10.1063/1.1557333 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2003

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Pump-probe experiments are used to characterize Fe-doped InGaAs/InP multiple quantum wells for ultrafast saturable absorption applications. Sample photoresponse time is well controlled by iron doping from the nanosecond range to a value as short as 0.45 ps for an iron concentration of 6×1018 cm−3. Furthermore, the switching amplitude, that is, the differential transmission ratio (DTR), of samples having increasing Fe doping (null to 6×1018 cm−3) presents two decreasing regimes at moderate optical excitation levels. The first one is explained well by the degree of quality of the material, whereas the second one is interpreted as an inhibition of exciton formation at high doping levels. This interpretation is highlighted by an analysis of the temporal evolution of the DTR. The influence of the doping localization (in the well, in the barrier, or in the whole structure) is studied as well. Finally, an attractive way to maintain a constant value of the DTR with an ultrafast response time (2.6 ps) is proposed and demonstrated. © 2003 American Institute of Physics.
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78.67.De Quantum wells
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.30.Fs III-V and II-VI semiconductors

Parametric study of Ga1−xInxNyAs1−y/GaAs quantum wells for 1.3-μm laser operation

W. W. Chow and J. S. Harris

Appl. Phys. Lett. 82, 1673 (2003); http://dx.doi.org/10.1063/1.1561154 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2003

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A microscopic laser theory was used to investigate gain properties in Ga1−xInxNyAs1−y/GaAs quantum wells. We considered combinations of x and y giving laser emission around 1.30 μm. Optical properties affecting laser threshold and dynamical response are described for structures with strain ranging from compressive to tensile. A parametric study of this kind should provide useful information for the optimization of GaInNAs vertical-cavity surface-emitting laser gain media for telecommunications applications. © 2003 American Institute of Physics.
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42.70.Hj Laser materials
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells

Near-field scanning optical microscopy of photonic crystal nanocavities

Koichi Okamoto, Marko Lončar, Tomoyuki Yoshie, Axel Scherer, Yueming Qiu, and Pawan Gogna

Appl. Phys. Lett. 82, 1676 (2003); http://dx.doi.org/10.1063/1.1559646 (3 pages) | Cited 24 times

Online Publication Date: 10 March 2003

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Near-field scanning optical microscopy was used to observe high-resolution images of confined modes and photonic bands of planar photonic crystal (PPC) nanocavities fabricated in active InGaAsP material. We have observed the smallest optical cavity modes, which are intentionally produced by fractional edge dislocation high-Q cavity designs. The size of the detected mode was roughly four by three lattice spacings. We have also observed extended dielectric-band modes of the bulk PPC surrounding the nanocavity by geometrically altering the bands in emission range and eliminating localized modes out of the emission range. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.55.Tv Photonic crystal lasers and coherent effects
68.65.Fg Quantum wells
68.37.Uv Near-field scanning microscopy and spectroscopy
42.55.Sa Microcavity and microdisk lasers
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
63.20.Pw Localized modes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.55.Cr III-V semiconductors
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Potential for a hydrogen water-plasma laser

R. L. Mills, P. C. Ray, and R. M. Mayo

Appl. Phys. Lett. 82, 1679 (2003); http://dx.doi.org/10.1063/1.1558213 (3 pages) | Cited 14 times

Online Publication Date: 10 March 2003

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A stationary, electronically excited, population inversion of atomic hydrogen, H, has been observed in a low-pressure water-vapor microwave discharge plasma. The inverted H population was evident from the relative intensities of the transitions within the Lyman series (n=2, 3, 4, and 5 to n=1) and within the Balmer series (n=3, 4, 5, 6, 7, and 8 to n=2). Back illumination with a broadband (vis/IR) lamp source showed depopulation of the n=5 state. Lines of the Balmer series of n=5, and 6 to n=2 and the Paschen series of n=5 to n=3 were of particular importance because of the potential to design blue and 1.3 μm infrared lasers, respectively, which are ideal for many communications and microelectronics applications. High-power hydrogen gas lasers are anticipated at wavelengths over a broad spectral range from far infrared to violet which may be miniaturized to micron dimensions. Such a hydrogen laser may prove to be the most versatile and useful of all. © 2003 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
52.75.-d Plasma devices
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Improving the mechanical properties of single-walled carbon nanotube sheets by intercalation of polymeric adhesives

Jonathan N. Coleman, Werner J. Blau, Alan B. Dalton, Edgar Muñoz, Steve Collins, Bog G. Kim, Joselito Razal, Miles Selvidge, Guillermo Vieiro, and Ray H. Baughman

Appl. Phys. Lett. 82, 1682 (2003); http://dx.doi.org/10.1063/1.1559421 (3 pages) | Cited 83 times

Online Publication Date: 10 March 2003

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Organic polymers, such as poly(vinyl alcohol), poly(vinyl pyrrolidone), and poly(styrene), were intercalated into single-walled carbon nanotube sheets by soaking the sheets in polymer solutions. Even for short soak times, significant polymer intercalation into existing free volume was observed. Tensile tests on intercalated sheets showed that the Young’s modulus, strength, and toughness increased by factors of 3, 9, and 28, respectively, indicating that the intercalated polymer enhances load transmission between nanotubes. © 2003 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
81.07.De Nanotubes
81.05.ub Fullerenes and related materials
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Np Adhesion
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

High-temperature resistive surface grating for spectral control of thermal radiation

Hitoshi Sai, Yoshiaki Kanamori, and Hiroo Yugami

Appl. Phys. Lett. 82, 1685 (2003); http://dx.doi.org/10.1063/1.1560867 (3 pages) | Cited 48 times

Online Publication Date: 10 March 2003

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Spectral emittance and thermal stability of two-dimensional W gratings are investigated to obtain high-temperature resistive selective emitters. Numerical calculations based on rigorous coupled-wave analysis are performed to determine the structural profile of gratings with good spectral selectivity. According to the determined parameters, two-dimensional W gratings composed of rectangular microcavities with the period of 1.0 μm are fabricated on single crystalline and polycrystalline W substrates. The grating shows a strong emission peak which can be explained by the confined modes inside the cavities. The grating with 200 nm wall thickness made from a single crystalline W shows very high thermal stability over 1400 K, while the polycrystalline grating is deformed at a high temperature because of the grain growth. © 2003 American Institute of Physics.
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42.79.Dj Gratings
44.40.+a Thermal radiation

Strain-driven facet formation on self-assembled InAs islands on GaAs (311)A

Z. M. Wang, H. Wen, V. R. Yazdanpanah, J. L. Shultz, and G. J. Salamo

Appl. Phys. Lett. 82, 1688 (2003); http://dx.doi.org/10.1063/1.1559945 (3 pages) | Cited 12 times

Online Publication Date: 10 March 2003

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The shape of InAs three-dimensional islands grown on GaAs(311)A substrates by molecular-beam epitaxy was investigated by in situ scanning tunneling microscopy. The island is found to be laterally surrounded by (111)A and {110} facets together with a convex curved region close to the (100) facet. The top ridge of the islands is atomically resolved to be the most recently discovered high-index surface {11,5,2}. This observation points to the importance of the study of nanostructure growth on high-index surfaces and their characterization. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.47.Fg Semiconductor surfaces
81.07.Bc Nanocrystalline materials

Thermally induced oxide crystallinity and interface destruction in Ga2O3–GaAs structures

M. Passlack, J. K. Abrokwah, Z. Yu, R. Droopad, C. Overgaard, and H. Kawayoshi

Appl. Phys. Lett. 82, 1691 (2003); http://dx.doi.org/10.1063/1.1560875 (3 pages) | Cited 13 times

Online Publication Date: 10 March 2003

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Amorphous Ga2O3 films are deposited onto the GaAs(001) surface using effusive evaporation from a high-purity polycrystalline Ga2O3 source. The Ga2O3–GaAs structure is characterized by cross-sectional transmission electron microscopy, electron diffraction, and photoluminescence intensity measurements. As-deposited Ga2O3 films are found to be amorphous forming an atomically abrupt interface of low interface state density Dit with GaAs. For oxide films with a thickness tox ≥ 127 Å, rapid thermal annealing above a critical temperature Tc = 720 °C induces Ga2O3 bulk crystallization resulting in structural deformation of the Ga2O3–GaAs interface and complete destruction of its low Dit character. Preliminary data suggest that the critical temperature Tc may increase in the limit of very thin Ga2O3 films. © 2003 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing

Deep ultraviolet picosecond time-resolved photoluminescence studies of AlN epilayers

K. B. Nam, J. Li, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 82, 1694 (2003); http://dx.doi.org/10.1063/1.1559659 (3 pages) | Cited 49 times

Online Publication Date: 10 March 2003

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AlN epilayers with high optical qualities have been obtained by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in AlN epilayers. Two PL emission lines associated with the donor bound exciton (D0X, or I2) and free exciton (FX) transitions have been observed, from which the binding energy of the donor bound excitons in AlN epilayers was determined to be around 16 meV. Time-resolved PL measurements revealed that the recombination lifetimes of the I2 and free exciton transitions in AlN epilayers were around 80 and 50 ps, respectively. The temperature dependencies of the free exciton radiative decay lifetime and emission intensity were investigated, from which a value of about 80 meV for the free exciton binding energy in AlN epilayer was deduced. This value is believed to be the largest free exciton binding energy ever reported in semiconductors, implying excitons in AlN are an extremely robust system that would survive well above room temperature. This together with other well-known physical properties of AlN may considerably expand future prospects for the application of III-nitride materials. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.35.-y Excitons and related phenomena

Alloy states in dilute GaAs1−xNx alloys (x<1%)

X. D. Luo, J. S. Huang, Z. Y. Xu, C. L. Yang, J. Liu, W. K. Ge, Y. Zhang, A. Mascarenhas, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 82, 1697 (2003); http://dx.doi.org/10.1063/1.1560872 (3 pages) | Cited 14 times

Online Publication Date: 10 March 2003

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A set of GaAs1−xNx samples with small nitrogen composition (x<1%) were investigated by continuous-wave photoluminescence (PL), pulse-wave excitation PL, and time-resolved PL. In the PL spectra, an extra transition located at the higher-energy side of the commonly reported N-related emissions was observed. By measuring the PL dependence on temperature and excitation power, the PL peak was identified as a transition of alloy band edge-related recombination in GaAsN. The PL dynamics further confirms its intrinsic nature as being associated with the band edge rather than N-related bound states. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Control of spin functionality in ZnMnSe-based structures: Spin switching versus spin alignment

I. A. Buyanova, G. Yu. Rudko, W. M. Chen, A. A. Toropov, S. V. Sorokin, S. V. Ivanov, and P. S. Kop’ev

Appl. Phys. Lett. 82, 1700 (2003); http://dx.doi.org/10.1063/1.1561570 (3 pages) | Cited 14 times

Online Publication Date: 10 March 2003

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The ability of attaining desired spin functionality by adjusting structural design is demonstrated in diluted magnetic semiconductor (DMS) quantum structures based on II–VI semiconductors. The following spin enabling functions are achieved by tuning the ratio between the rates of exciton spin relaxation within the DMS and exciton escape from it to an adjacent nonmagnetic spin detector. Spin switching is realized when using a thin layer of Zn0.95Mn0.05Se as a spin manipulator and is attributed to a fast exciton escape from the DMS preceding the spin relaxation. Spin alignment is accomplished in tunneling structures where the presence of an energy barrier inserted between a spin manipulator (a DMS-based superlattice) and a spin detector ensures a slow escape rate from the DMS layer. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.50.Pp Magnetic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.21.Cd Superlattices
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Femtosecond laser-induced periodic surface structure on diamond film

Qihong Wu, Yurong Ma, Rongchuan Fang, Yuan Liao, Qingxuan Yu, Xiangli Chen, and Kelvin Wang

Appl. Phys. Lett. 82, 1703 (2003); http://dx.doi.org/10.1063/1.1561581 (3 pages) | Cited 72 times

Online Publication Date: 10 March 2003

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We report the laser-induced periodic surface structure (LIPSS) with periodicity about a quarter of the laser wavelength on unpolished diamond film treated by a P-polarized femtosecond laser. The short period LIPSS is parallel to the laser polarization and independent on the incidence angle. The LIPSS perpendicular to the laser polarization with periodicity shorter than a third of the laser wavelength slightly dependent on the incidence angle is also observed as well as the LIPSS perpendicular to the laser polarization with periodicity dependent on the incidence angle. The results are explained by interference of the incident laser and surface scattered wave related to the excited electrons during laser interactions with diamond, being in excellent agreement with a previously developed theory. © 2003 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
81.05.U- Carbon/carbon-based materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.82.Fk Semiconductors

Formation of InAs self-assembled quantum rings on InP

T. Raz, D. Ritter, and G. Bahir

Appl. Phys. Lett. 82, 1706 (2003); http://dx.doi.org/10.1063/1.1560868 (3 pages) | Cited 59 times

Online Publication Date: 10 March 2003

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Shape transformations of partially capped self-assembled InAs quantum dots grown on InP are studied. Atomic force microscopy images show large anisotropic redistribution of the island material after coverage by a 1-nm-thick InP layer. The anisotropic material redistribution occurs within a few minutes and leads to a change from lens-like to elongated ring-like islands. The shape transformation is not accompanied by dot material compositional change. The formation of InAs/InP quantum rings disagrees with a previous model of InAs/GaAs ring formation that assumes that the driving force for the dot to ring transformation is the difference in surface diffusion velocity of indium and gallium atoms. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)

Step-edge kinetics driving the formation of atomically flat (110) GaAs surfaces

Ji-Won Oh, Masahiro Yoshita, Hidefumi Akiyama, Loren N. Pfeiffer, and Ken W. West

Appl. Phys. Lett. 82, 1709 (2003); http://dx.doi.org/10.1063/1.1560575 (3 pages) | Cited 9 times

Online Publication Date: 10 March 2003

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Atomically flat (110) GaAs surfaces fabricated by the cleaved-edge overgrowth method and high-temperature growth-interrupt annealing are characterized at the atomic scale. We observe atomically flat (110) surfaces extending over areas more than 100 μm in size. Moreover, deposition of slightly less or more than integral monolayers (MLs) causes the appearance of characteristic step-edge shapes such as 1-ML-deep pits, or 2-to-3-ML-high isolated islands. Statistical analysis on the size and shape distribution of the 1-ML-deep pits supports a simple model based on the stability of Ga and As atoms on step edges with different bonding configurations, and reveals driving force to form an atomically flat (110) surface. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
61.72.Cc Kinetics of defect formation and annealing

Exciton quenching in Pt/GaN Schottky diodes with Ga- and N-face polarity

S. Shokhovets, D. Fuhrmann, R. Goldhahn, G. Gobsch, O. Ambacher, M. Hermann, U. Karrer, and M. Eickhoff

Appl. Phys. Lett. 82, 1712 (2003); http://dx.doi.org/10.1063/1.1561160 (3 pages) | Cited 8 times

Online Publication Date: 10 March 2003

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We observed a peculiar dependence of low-temperature electroreflectance spectra of Pt/GaN Schottky diodes with Ga- and N-face polarity on the bias voltage (so-called “rotation” spectra), indicating the quenching of discrete exciton states and the formation of an exciton dead layer (EDL) beneath the gate. Data analysis is carried out using the field-dependent dielectric function of GaN. It yields parameters of excitons for the zero-field limit and the depth of the EDL, as well as the surface band bending and the ionized impurity concentration. © 2003 American Institute of Physics.
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85.30.Kk Junction diodes
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
78.20.Jq Electro-optical effects
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Formation of regular arrays of silicon microspikes by femtosecond laser irradiation through a mask

M. Y. Shen, C. H. Crouch, J. E. Carey, R. Younkin, E. Mazur, M. Sheehy, and C. M. Friend

Appl. Phys. Lett. 82, 1715 (2003); http://dx.doi.org/10.1063/1.1561162 (3 pages) | Cited 46 times

Online Publication Date: 10 March 2003

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We report fabrication of regular arrays of silicon microspikes by femtosecond laser irradiation of a silicon wafer covered with a periodic mask. Without a mask, microspikes form, but they are less ordered. We believe that the mask imposes order by diffracting the laser beam and providing boundary conditions for capillary waves in the laser-melted silicon. © 2003 American Institute of Physics.
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81.65.-b Surface treatments
81.05.Cy Elemental semiconductors
85.40.Hp Lithography, masks and pattern transfer
79.20.Ds Laser-beam impact phenomena
68.47.Fg Semiconductor surfaces
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
64.70.D- Solid-liquid transitions
06.60.Jn High-speed techniques (microsecond to femtosecond)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Stable protocrystalline silicon and unstable microcrystalline silicon at the onset of a microcrystalline regime

Jun Yong Ahn, Kyung Hoon Jun, Koeng Su Lim, and Makoto Konagai

Appl. Phys. Lett. 82, 1718 (2003); http://dx.doi.org/10.1063/1.1561161 (3 pages) | Cited 9 times

Online Publication Date: 10 March 2003

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We investigated the structural, electrical, and optical properties as well as light-induced degradation characteristics of silicon films prepared by photochemical vapor deposition at various hydrogen dilution ratios. The protocrystalline silicon deposited before the onset of the microcrystalline regime was most stable against light soaking. However, the films deposited at the onset of the microcrystalline regime, known to have the most competent device quality and stability, were observed to be less stable. Such instability at the onset of the microcrystalline regime is correlated with the existence of the clustered phase hydrogen that indicates microvoids in the films. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.82.Fk Semiconductors
78.30.-j Infrared and Raman spectra
78.66.Db Elemental semiconductors and insulators
73.50.Pz Photoconduction and photovoltaic effects
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Fe valency-induced effect on the magnetic and electrotransport properties in Nd0.67Sr0.33Mn1−xFexO3 polycrystalline system

Y. L. Chang and C. K. Ong

Appl. Phys. Lett. 82, 1721 (2003); http://dx.doi.org/10.1063/1.1555259 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2003

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Systematic study is conducted on the effect of Fe valency-induced magnetic and electrotransport properties in Nd0.67Sr0.33Mn1−xFexO3 polycrystalline system. The system is found to display the properties of Nd0.67Sr0.33MnO3 and Nd0.67Sr0.33FeO3 depending on the Fe concentration. It is found that, while Mn3+ and Mn4+ enhance the double exchange in the system, Fe3+ and Fe4+ enhance the superexchange interaction in the system. Although Fe3+ weakens the ferromagnetism, Fe4+ ions enhance the electrical conductivity in the system. The large variations in resistivity with temperature for some of these compounds has potential application in the development of new magnetic recording medias, optoelectronics devices and bolometric detectors. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.30.Et Exchange and superexchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.28.+d Narrow-band systems; intermediate-valence solids
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