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1 Sep 2004

Volume 96, Issue 5, pp. 2417-3034

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WO3∕metal thin-film bilayered structures as optical recording materials

Yasuhiko Takeda, Naohiko Kato, Tatsuo Fukano, Akihiro Takeichi, Tomoyoshi Motohiro, and Shoichi Kawai

J. Appl. Phys. 96, 2417 (2004); http://dx.doi.org/10.1063/1.1775051 (6 pages) | Cited 7 times

Online Publication Date: 1 September 2004

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Interface reactions in WO3∕metal thin-film bilayered structures were examined for applications to optical recording materials. Decreases in the reflectance of the structures caused by temperature elevation were observed and were attributed to (i) coloration of the WO3 layers, and (ii) decreases in the reflectance of the metal layers resulting from redox reactions between the WO3 and the metals. The reflectance spectra of the structures before temperature elevation showed moderate wavelength dependence over a wide range, from the visible to the near infrared. Decreases in the reflectance due to temperature elevation occurred over a wide wavelength range. Examination of the WO3∕Al–Ti bilayered structures as potential optical disk memories revealed that the redox reactions occurred within submicrosecond time periods during irradiation with the recording laser. The results indicate that these structures possess promising properties for applications to optical recording materials that can be used over a wide wavelength range.
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42.79.Vb Optical storage systems, optical disks
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
68.55.-a Thin film structure and morphology
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.-b Specific chemical reactions; reaction mechanisms

Effect of outermost layers on resonant cavity enhanced devices

Il-Sug Chung, Yong Tak Lee, Jae-Eun Kim, and Hae Yong Park

J. Appl. Phys. 96, 2423 (2004); http://dx.doi.org/10.1063/1.1775302 (5 pages) | Cited 2 times

Online Publication Date: 1 September 2004

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Both the reflectivity and the reflection delay of a quarter wave mirror (QWM) can be controlled by choosing the outermost layer of the QWM appropriately. For a GaAs∕Al0.75Ga0.25As QWM, depositing a Si layer as the incoming outermost layer decreases the reflectivity to the same degree as removing 19.6 layers, and increases the reflection delay by 12.0 times. Likewise, when using a TiO2 layer, the reflectivity decreases to a level similar to the removal of 16.1 layers while the reflection delay is 7.9 times longer. Therefore, an efficient method to fabricate resonant cavity enhanced photodetectors for bidirectional optical interconnects is proposed. This method needs no subsequent etching process while giving a quantum efficiency of approximately 90% using currently available deposition techniques. Furthermore, the tunable wavelength and bandwidth ranges of microelectromechanical system tunable filters can be controlled separately by the outermost layer, thereby allowing filters with different bandwidths to be fabricated on the same wafer.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Ds Interconnects, including holographic interconnects
42.79.Ci Filters, zone plates, and polarizers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Holographic method for a direct growth of three-dimensional photonic crystals by chemical vapor deposition

Michel Duneau, François Delyon, and Marc Audier

J. Appl. Phys. 96, 2428 (2004); http://dx.doi.org/10.1063/1.1776322 (9 pages) | Cited 2 times

Online Publication Date: 1 September 2004

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A method to obtain three-dimensional (3D) photonic crystals by chemical vapor deposition (CVD) is presented. Campbell et al. [N. Campbell, N. Sharp, M. T. Harrison, R. G. Denning, and A. J. Tuberfield, Nature 404, 53 (2000)] have developed a method of holographic lithography for producing 3D periodic structures with photoresists. Their method is adapted in two main directions. First, we optimize the geometry of the interferometer with respect to polarizations and relative intensities of the beams. The construction of an interferometer adapted to a ultraviolet laser source at 355 nm is described and direct observations of the interference field obtained by a video camera are presented. Second, we show that a laser source with short pulses could induce a suitable thermal contrast on a convenient substrate in order to grow a 3D photonic crystal by CVD.
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42.70.Qs Photonic bandgap materials
07.60.Ly Interferometers
42.40.Kw Holographic interferometry; other holographic techniques
42.30.Ms Speckle and moiré patterns
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Raman spectroscopic studies of TeO2-BaO-SrO-Nb2O5 glasses: Structure-property correlations

G. Senthil Murugan and Yasutake Ohishi

J. Appl. Phys. 96, 2437 (2004); http://dx.doi.org/10.1063/1.1772890 (6 pages) | Cited 9 times

Online Publication Date: 1 September 2004

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The structure of technologically important tellurite glasses has been studied by Raman spectroscopy. The present investigation revealed the presence of TeO4 trigonal bipyramid, TeO3 trigonal pyramid, and NbO6 octahedra in these glasses. The influence of a gradual addition of the modifier oxides on the glass structure has been elucidated. The evolution of TeO3 units with the modifier addition was different from the earlier reports on the tellurite glasses. Even at higher modifier concentrations TeO4 units were dominating in the glass network compared to TeO3, though NbO6 octahedra also come into the picture. The ratio of TeO4∕TeO3 structural units was discussed for different series of glass compositions. An attempt has been made based on these structural details obtained via Raman studies to explain the origin of the greatly improved thermal stabilities and refractive indices of these glass compositions.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.43.Fs Glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Nonlocal photopolymerization effect in the formation of reflective holographic polymer-dispersed liquid crystals

Jun Qi, Liuliu Li, Mousumi De Sarkar, and Gregory P. Crawford

J. Appl. Phys. 96, 2443 (2004); http://dx.doi.org/10.1063/1.1778480 (8 pages) | Cited 12 times

Online Publication Date: 1 September 2004

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The optical performance of reflective holographic polymer-dispersed liquid crystals (H-PDLCs) is investigated as a function of sample thickness and laser exposure intensity, and, the data are analyzed in terms of a nonlocal photopolymerization model. The intensity of laser exposure is proven to have a strong influence on the reflection efficiency of H-PDLCs. We have found that the experimental results cannot be completely interpreted by the previous local diffusion model. Combined with transfer matrix analysis, a modified diffusion model with a nonlocal photopolymerization term is proposed herein, which qualitatively describes our experimental observations. The experimental data demonstrates our assertion that the nonlocal effect is strongly correlated to the exposure conditions. Under the low exposure condition, the diffusion effect is screened by this nonlocal effect, and effectively a small diffusion constant is observed. Under the high exposure condition, the nonlocal effect can be suppressed and the modified diffusion model can be deduced to the original local diffusion model. Also, within the framework of this nonlocal model, overexposure can be properly explained.
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42.70.Df Liquid crystals
42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.50.-m Photochemistry
42.40.Eq Holographic optical elements; holographic gratings
66.30.-h Diffusion in solids
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O2(1Δ) production in He∕O2 mixtures in flowing low pressure plasmas

D. Shane Stafford and Mark J. Kushner

J. Appl. Phys. 96, 2451 (2004); http://dx.doi.org/10.1063/1.1768615 (15 pages) | Cited 58 times

Online Publication Date: 1 September 2004

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Chemical oxygen-iodine lasers (COIL) are attractive for diverse industrial applications because they are capable of high efficiency, high power operation, and because the 1.315 μm wavelength can be transmitted through fiber optics and couples efficiently with most metals. Conventional COILs are pumped with O2(1Δ) that is generated by reaction of Cl2 in a basic H2O2 solution. Current trends in pumping COILs involve producing the O2(1Δ) in electric discharges, thereby circumventing the hazards, complexity, and weight associated with pumping and storing caustic liquids. In this work, we have investigated the scaling of O2(1Δ) yields with specific energy deposition in He∕O2 mixtures in flowing radio frequency (rf) discharges at pressures of a few to tens of Torr using a global plasma kinetics model. We found that O2(1Δ) yield increases nearly linearly with specific energy deposition in O2 molecules up to a few eV per molecule, with yields peaking around 30% by 5–8 eV. Further increases in specific energy deposition serve only to increase O2 dissociation and gas heating, thereby reducing the O2(1Δ) yield. We also found that variations in peak yields at a given specific energy deposition are caused by secondary effects resulting from dilution, pressure, and power level. We show that these secondary effects alter the O2(1Δ) yield by shifting the O2(1Σ)∕O2(1Δ) ratio.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
52.25.Dg Plasma kinetic equations
42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Mechanism of silicon etching in the presence of CF2, F, and Ar+

David Humbird and David B. Graves

J. Appl. Phys. 96, 2466 (2004); http://dx.doi.org/10.1063/1.1769602 (6 pages) | Cited 15 times

Online Publication Date: 1 September 2004

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Molecular dynamics simulations of CF2, F, and Ar+ impacting silicon surfaces reveal the spontaneous formation of segregated layers of Si-C and SiFx, formed due to Ar+ ion impact and ion-induced mixing. The mechanisms of steady-state etching under these conditions involve a leading front of SiFx that fluorinates the Si substrate, followed by a region or zone of Si-C. The SiFx and Si-C layers move through the substrate Si during steady-state etching. Si is generally etched from the surface of the Si-C layer by an ion impact. Carbon reaction with Si in the Si-C zone raises the total atomic density in the Si-C layer to nearly three times the value observed in undisturbed Si and reduces the Si etch rate by limiting ion mixing. Etching stops completely if the Si-C layer becomes so impervious that ions cannot reach the SiFx front. The importance of the depth profile of ion energy deposition in sustaining etching is very clearly observed in the simulations.
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81.65.Cf Surface cleaning, etching, patterning
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Dv Composition, segregation; defects and impurities

An empirical formula for negative corona discharge current in point-grid electrode geometry

Kimio Yamada

J. Appl. Phys. 96, 2472 (2004); http://dx.doi.org/10.1063/1.1775301 (4 pages) | Cited 5 times

Online Publication Date: 1 September 2004

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A series of measurements carried out with a point-grid electrode system has clarified that the current-voltage characteristics of the negative corona discharge obey the Townsend relation, further, in which the coefficient is proportional to temperature and the power of the electrode gap independently, and the corona onset voltage is proportional to the product of the reciprocal of temperature and the power of the electrode gap. The empirical formula derived from their relations has estimated negative corona currents with an accuracy of 1 μA for a given parameter set, which will allow application to ion generator design.
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52.80.Hc Glow; corona
52.80.Dy Low-field and Townsend discharges

Radio frequency induced ionized collisional flow model for application at atmospheric pressures

Subrata Roy and Datta Gaitonde

J. Appl. Phys. 96, 2476 (2004); http://dx.doi.org/10.1063/1.1778474 (6 pages) | Cited 11 times

Online Publication Date: 1 September 2004

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We present the development and application of a versatile finite-element method to discretize direct current and radio frequency (rf) induced plasma-sheath dynamics, using multifluid equations. For the former, argon gas is assumed, and the solution is verified by comparison with a theoretical model obtained from the literature. For rf discharges, partially ionized helium gas is considered between two electrodes coated in a dielectric material. The computed solutions for charge densities, the ion velocity and the neutral gas density and crossflow distributions show expected trends. Specifically, ion and electron number densities at the peak discharge current are compared with published numerical results. The derived electric field is utilized with a simple phenomenological model applicable to the transverse velocity in a one-dimensional situation to predict the anticipated hump in the near wall profile. The next step of extending the model, through future work, to two dimensions and for polyphase supply as implemented in realistic configurations is greatly facilitated by the generality of the chosen finite-element method.
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52.40.Kh Plasma sheaths
52.80.Pi High-frequency and RF discharges
02.70.Dh Finite-element and Galerkin methods
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Chirally oriented heteroepitaxial thin films grown by pulsed laser deposition: Pt(621) on SrTiO3(621)

Andrew J. Francis and Paul A. Salvador

J. Appl. Phys. 96, 2482 (2004); http://dx.doi.org/10.1063/1.1768609 (12 pages) | Cited 7 times

Online Publication Date: 1 September 2004

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Pulsed laser deposition has been used to grow Pt(621) thin films having a chiral orientation on SrTiO3(621) substrates. Films were deposited over a range of conditions, then characterized for their crystallinity and epitaxy using x-ray diffraction and for their surface morphologies using atomic force microscopy (AFM). Films deposited at 600 °C grew epitaxially, but with an island growth mode. Pt deposited at 250 °C displayed smooth surfaces but did not grow epitaxially. A three-step process wherein films were seeded at 600 °C, deposited at 250 °C, and postannealed was shown to result in excellent epitaxial growth and flat surface morphologies. Films grown using the three-step process exhibited excellent epitaxy, having the orientation relationship (621)Pt∥(621)SrTiO3:[0math2]Pt∥[0math2]SrTiO3. When postannealed at 800 °C, they exhibited flat surfaces (rms≈20 math) having long terraces separated by steps running along the expected [0math2] direction of the SrTiO3(621) substrate. Films postannealed at 600 °C were flatter (rms≈10 math) with no evident step directionality. The SrTiO3(621) substrates were observed to be extremely flat (rms≈2 math) and to have morphologically featureless surfaces, as expected for a (621) surface. The good crystalline quality of the SrTiO3 substrate surface is considered to drive the growth of the chirally oriented heteroepitaxial Pt films. Similarities and differences between Pt growth on chiral surfaces and on low-index achiral surfaces are discussed.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Effect of temperature cycling on the static fatigue of double-coated optical fibers

Sham-Tsong Shiue, Ting-Ying Shen, and Kun-Ming Lin

J. Appl. Phys. 96, 2494 (2004); http://dx.doi.org/10.1063/1.1772882 (7 pages) | Cited 3 times

Online Publication Date: 1 September 2004

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This study theoretically investigates the effect of temperature cycling on the static fatigue of double-coated optical fibers. The tensile force and temperature cycling induced tensile stresses on the glass fiber of double-coated optical fibers are determined using the viscoelastic theory. Optical fibers lifetime is dominated by the tensile stress on the glass fibers, which is a function of the material properties and thickness of the polymeric coating. To minimize these stresses on the glass fiber, the radius, Young’s modulus, and thermal expansion coefficient of the secondary coating should be reduced, while the relaxation time of the secondary coating should be increased. Additionally, based on strength consideration, the radius and Young’s modulus of the polymeric coating should be sufficiently thick or hard to support the external mechanical stresses. Meanwhile, based on the microbending-insensitivity consideration, the relaxation time of the primary coating should be reduced.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Molecular dynamics simulation for evaluating melting point of wurtzite-type GaN crystal

Kenji Harafuji, Taku Tsuchiya, and Katsuyuki Kawamura

J. Appl. Phys. 96, 2501 (2004); http://dx.doi.org/10.1063/1.1772878 (12 pages) | Cited 16 times

Online Publication Date: 1 September 2004

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A two-phase molecular dynamics simulation of coexisting solid and liquid has been carried out to investigate the melting point of wurtzite-type GaN crystals. The melting point is determined by examining the movement of the interface between the solid and liquid during the simulation. The potential is a two-body interatomic one composed of the long-range Coulomb interaction, the Gilbert-type short-range repulsion, the covalent bonding and covalent repulsion of the modified Morse type, and the van der Waals interaction. The melting point and the interface morphology depend on the crystallization direction. The melting point Tm (K) increases with pressure P (GPa), but there appears a discontinuity in the vicinity of 8–9 GPa. This is due to the solid-electrolyte-like behavior of Ga atoms with a partial charge in the high-pressure region. The discontinuity has not yet been confirmed by experiment. The least-squares fitted result is Tm=2538+177P−4.62P2 at pressures lower than 8 GPa and Tm=2825+210P−5P2 at pressures higher than 9 GPa. The Clausius-Clapeyron relation is confirmed using calculated thermodynamic data.
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64.70.D- Solid-liquid transitions
62.50.-p High-pressure effects in solids and liquids

Molecular dynamics simulation of dislocations in wurtzite-type GaN crystal

Kenji Harafuji, Taku Tsuchiya, and Katsuyuki Kawamura

J. Appl. Phys. 96, 2513 (2004); http://dx.doi.org/10.1063/1.1772879 (12 pages) | Cited 6 times

Online Publication Date: 1 September 2004

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Microscopic dislocation structures in wurtzite-type GaN crystal have been studied by the use of molecular dynamics simulation. Parameters for a two-body interatomic potential are determined by the Hartree-Fock ab initio method. A dislocation is generated by the coalescence of the facing planes of a semi-infinite trench structure in the crystal. Six types of trench structures with different depth-directions and extension-directions are examined. Temperatures of 1000 and 1500 K are considered. A core structure with an eightfold ring has been confirmed for edge dislocations along the c axis, though there appear a few atoms that are shifted from the ring core structure. The ring core structure is consistent with reported theoretical expectations and experimental observations. A tenfold ring core structure is also observed for edge dislocations along the c axis. A screw dislocation is generated by an attracting force between gallium and nitrogen atoms across the trench space when the attracting force has a large component parallel to the trench extension direction.
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61.72.Bb Theories and models of crystal defects
61.43.Bn Structural modeling: serial-addition models, computer simulation

Nonlinear optical properties of tungstate fluorophosphate glasses

E. L. Falcão-Filho, Cid B. de Araújo, C. A. C. Bosco, L. H. Acioli, G. Poirier, Y. Messaddeq, G. Boudebs, and M. Poulain

J. Appl. Phys. 96, 2525 (2004); http://dx.doi.org/10.1063/1.1758309 (5 pages) | Cited 10 times

Online Publication Date: 1 September 2004

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The optical nonlinearity of tungstate fluorophosphate glasses, synthesized in the NaPO3-BaF2-WO3 system, was investigated through experiments based on the third-order susceptibility, χ(3). Nonlinear (NL) refraction and NL absorption measurements in the picosecond regime were performed using the Z-scan technique at 532 nm. NL refractive index, n2∝Re χ(3), ranging from 0.4×10−14 cm2/W to 0.6×10−14 cm2/W were determined. The two-photon absorption coefficient, α2∝Im χ(3), for excitation at 532 nm, vary from 0.3 to 0.5 cm/GW. Light induced birefringence experiments performed in the femtosecond regime indicate that the response time of the nonlinearity at 800 nm is faster than 100 fs. The experiments show that χ(3) is enhanced when the WO3 concentration increases and this behavior is attributed to the hyperpolarizabilities associated to W–O bonds. © 2004 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
78.47.-p Spectroscopy of solid state dynamics

Dynamics of energy transfer and frequency upconversion in Tm3+ doped fluoroindate glass

Vladimir A. Jerez, Cid B. de Araújo, and Y. Messaddeq

J. Appl. Phys. 96, 2530 (2004); http://dx.doi.org/10.1063/1.1769596 (5 pages) | Cited 11 times

Online Publication Date: 1 September 2004

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Blue and ultraviolet upconversion (UC) emissions at 455 and 363 nm were observed from Tm3+ doped fluoroindate glasses pumped at 650 nm. The time behavior of the UC signals was studied for different Tm3+ concentrations. The measurements revealed the origin of the UC process as well as allowed to quantify the interaction between Tm3+ ions. The results indicate that a two-step one-photon absorption process is responsible for the UC emissions, and dipole-dipole interaction provides the main contribution for energy transfer (ET) among active ions. The critical distance between Tm3+ ions at which the ET rate is equal to the decay rate of noninteracting Tm3+ ions was determined.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz
78.55.Hx Other solid inorganic materials
42.55.Rz Doped-insulator lasers and other solid state lasers

Magnetophotoluminescence study of the influence of substrate orientation and growth interruption on the electronic properties of InAs∕GaAs quantum dots

S. Godefroo, J. Maes, M. Hayne, V. V. Moshchalkov, M. Henini, F. Pulizzi, A. Patanè, and L. Eaves

J. Appl. Phys. 96, 2535 (2004); http://dx.doi.org/10.1063/1.1767972 (5 pages) | Cited 11 times

Online Publication Date: 1 September 2004

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We have used photoluminescence in pulsed (⩽50 T) and dc (⩽12 T) magnetic fields to investigate the influence of substrate orientation and growth interruption (GI) on the electronic properties of InAs∕GaAs quantum dots, grown by molecular beam epitaxy at 480 °C. Dot formation is very efficient on the (100) substrate: electronic confinement is already strong without GI and no significant change in confinement is observed with GI. On the contrary, for the (311)B substrate strong confinement of the charges only occurs after a GI is introduced. When longer GIs are applied the dots become higher.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ls Magneto-optical effects

Structural and Mössbauer characterization of the ball-milled Fex(Al2O3)100−x system

A. Paesano, C. K. Matsuda, L. F. Cótica, S. N. de Medeiros, J. B. M. da Cunha, B. Hallouche, and S. L. Silva

J. Appl. Phys. 96, 2540 (2004); http://dx.doi.org/10.1063/1.1771480 (7 pages)

Online Publication Date: 1 September 2004

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Metal-oxide composites were synthesized by high-energy ball milling of metallic iron (α-Fe) and alumina (α-Al2O3) powders, varying the starting relative concentration and the milling time. The samples were characterized by scanning electron microscopy, x-ray diffraction, and Mössbauer spectroscopy. The results revealed the formation of a FeAl2O3+W spinel phase (hercynite) and of iron (super)paramagnetic nanoprecipitates, in addition to residual magnetic iron and alumina. We also observed that the relative amounts of nanoprecipitates and hercynite for isochronally milled samples were correlated with the sample nominal concentration x, with the precursor iron being relatively more converted in those phases for low x values. Particularly for x=10 milled sample, the relative amounts of the (super)paramagnetic and spinel phases were observed to increase linearly with the milling time. An x=20∕24 h milled sample was annealed in H2 atmosphere and revealed the reduction of hercynite, with iron phase separation.
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75.20.Ck Nonmetals
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Mh Cermets, ceramic and refractory composites
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.46.-w Structure of nanoscale materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
81.30.Mh Solid-phase precipitation
81.40.Gh Other heat and thermomechanical treatments

Bistability in deformed helix ferroelectric liquid crystal

S. Kaur, A. K. Thakur, R. Chauhan, S. S. Bawa, and A. M. Biradar

J. Appl. Phys. 96, 2547 (2004); http://dx.doi.org/10.1063/1.1775047 (5 pages) | Cited 15 times

Online Publication Date: 1 September 2004

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Bistability in deformed helix ferroelectric liquid crystal (DHFLC) has been investigated by electro-optical and dielectric methods and compared with the bistability phenomenon in surface stabilized ferroelectric liquid crystal (SSFLC). Bistability in DHFLC as well as SSFLC is based on different physical phenomena. In SSFLC, it occurs due to surface effect and in DHFLC, by the critical deformation of the helix, under the application of time delayed square voltage pulse of known magnitude and frequency. Memory behavior of DHFLC and SSFLC cells has been compared by optical, electrical, dielectric, and hysteresis methods and the difference has been analyzed. It has been observed that memory effect in DHFLC is independent of surface effect but critically depends on the applied voltage and frequency of time delayed square wave pulse.
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
77.80.Dj Domain structure; hysteresis
78.20.Jq Electro-optical effects
77.22.Ch Permittivity (dielectric function)

Polarization tuning the Stokes photoluminescence spectra of erbium doped KNbO3 ceramics

Sheng-Yuan Chu, Cheng-Hung Wen, Sing-Long Tyan, Yuu-Ging Lin, Yung-Der Juang, and Cheng-Kuo Wen

J. Appl. Phys. 96, 2552 (2004); http://dx.doi.org/10.1063/1.1774261 (4 pages) | Cited 7 times

Online Publication Date: 1 September 2004

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The poling effect in Stokes photoluminescence (PL) spectroscopy of erbium doped potassium niobate (KNbO3) ceramics has been investigated by studying the relations between PL spectra with the poling electric field, poling time, and annealing conditions, respectively. All the Stark splitting components of 4S3∕2→4I13∕2 transition were evident after the poling process. The experiments also showed that the polarization enhances the fine structure and modifies the intensity ratio of the 4S3∕2→4I15∕2, 4F9∕2→4I15∕2, and 4S3∕2→4I15∕2 transitions at different poling electric fields and poling times for the samples doped with 5% of erbium. Comparing the poling spectra with annealing spectra, we can see that both polarization and annealing can modify the intensity of PL. However, the mechanisms of the two effects are different. The frequency shift Δν of the peaks depended on the wavelength after poling demonstrates that the Stark splitting was produced by the dipole moment of erbium ions interacting with the internal local electric field due to polarization.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.55.Hx Other solid inorganic materials
78.20.Jq Electro-optical effects
77.22.Ej Polarization and depolarization
81.40.Gh Other heat and thermomechanical treatments

Transient photovoltage in GaN as measured by atomic force microscope tip

M. A. Reshchikov, S. Sabuktagin, D. K. Johnstone, and H. Morkoç

J. Appl. Phys. 96, 2556 (2004); http://dx.doi.org/10.1063/1.1774245 (5 pages) | Cited 15 times

Online Publication Date: 1 September 2004

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We studied restoration of the band bending at the surface of undoped GaN layers after illumination with above-bandgap light. The photovoltage saturated with illumination at about 0.2–0.3 eV at room temperature, although the upward band bending for GaN in the dark is of the order of 1 eV. We attribute the photovoltage effect to charging of the surface states, the density of which is estimated at about 1012 cm−2. Restoration of the barrier after a light pulse is simulated by a phenomenological model whereby the acceptorlike surface states are emptied of electrons under illumination and filled back in dark due to thermionic transfer of free electrons from the bulk to the surface states over the near-surface barrier. Photoinduced desorption of oxygen also affects the value of the photovoltage if the illumination is prolonged.
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68.47.Fg Semiconductor surfaces
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
73.25.+i Surface conductivity and carrier phenomena
72.80.Ey III-V and II-VI semiconductors
73.50.Pz Photoconduction and photovoltaic effects
79.40.+z Thermionic emission

Growth of Si∕β-FeSi2∕Si double-heterostructures on Si(111) substrates by molecular-beam epitaxy and photoluminescence using time-resolved measurements

M. Takauji, N. Seki, T. Suemasu, F. Hasegawa, and M. Ichida

J. Appl. Phys. 96, 2561 (2004); http://dx.doi.org/10.1063/1.1774246 (5 pages) | Cited 14 times

Online Publication Date: 1 September 2004

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Highly [110]∕[101]-oriented semiconducting iron disilicide β-FeSi2 continuous films were grown on Si(111) by molecular-beam epitaxy (MBE) using a β-FeSi2 epitaxial template formed by reactive deposition epitaxy. The optimum MBE growth temperature was determined to be about 750°C. At this temperature, the full width at half maximum β-FeSi2(220)∕(202) x-ray diffraction peak was at a minimum. Subsequent MBE overgrowth of an undoped Si layer was performed on the β-FeSi2 at 500°C, resulting in the Si∕β-FeSi2∕Si double heterostructure. After annealing the wafers at 800°C in Ar for 14 h, 1.55 μm photoluminescence (PL) was obtained at low temperatures. Time-resolved PL measurements elucidated that the luminescence originated from two sources, one with a short decay time (τ∼10 ns) and the other with a long decay time (τ∼100 ns). The short decay time was thought to be due to carrier recombination in β-FeSi2, whereas the long decay time was due probably to a dislocation-related D1 line in Si.
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81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Modulated photothermal radiometry applied to semitransparent samples: Models and experiments

S. André, B. Rémy, D. Maillet, A. Degiovanni, and J.-J. Serra

J. Appl. Phys. 96, 2566 (2004); http://dx.doi.org/10.1063/1.1774260 (10 pages) | Cited 7 times

Online Publication Date: 1 September 2004

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Mathematical modeling is presented of the combined conductive and radiative heat transfer occurring in a semitransparent material (STM) subjected to a periodic heat flux. The models rely on the quadrupole method, which is a very powerful tool to obtain analytical solutions in the Fourier or Laplace domain. Photoacoustic or photothermal radiometry techniques are reviewed. Two groups of methods are discussed depending on whether the sample has natural or opaque interfaces to simulate radiative exchanges with the surroundings. The metrological problem of measuring the phonic thermal diffusivity of semitransparent materials is investigated. Theoretical simulations are given. They explain some typical features of the phase-lag signal of temperature responses. Experimental measurements on pure silica validate the results and prove that these methods are efficient for the thermal characterization of STM.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Photoreflectance evidence of multiple band gaps in dilute GaInNAs layers lattice-matched to GaAs

R. Kudrawiec, E.-M. Pavelescu, J. Wagner, G. Sęk, J. Misiewicz, M. Dumitrescu, J. Konttinen, A. Gheorghiu, and M. Pessa

J. Appl. Phys. 96, 2576 (2004); http://dx.doi.org/10.1063/1.1776312 (4 pages) | Cited 35 times

Online Publication Date: 1 September 2004

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Dilute Ga1−xInxNyAs1−y∕GaAs quantum wells with high In-content, which are under compressive strain, have been shown previously to exhibit multiple band gaps, likely due to the presence of different nitrogen nearest-neighbor environments, i.e., N‐Ga4−mInm (0⩽m⩽4) short-range-order clusters. Here, photoreflectance (PR) measurements on lattice-matched dilute GaInNAs-on-GaAs layers with low indium and nitrogen content are reported, which give evidence that these layers also exhibit several distinct band gaps. These distinct band gaps, which were found to coexist, are associated with different nitrogen bonding configurations, as revealed by Raman spectroscopy. Thus, the metastable nature of GaInNAs seems to be a persistent intrinsic property, irrespective of strain and indium content. The annealing-induced blueshift of GaInNAs band gap energy, which is usually observed in this system, has been associated with the change in the intensity of PR resonances related to different N‐Ga4−mInm configurations.
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73.21.Fg Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.60.Bs Mechanical and acoustical properties

Band gap tuning of InAs∕GaSb type-II superlattices for mid-infrared detection

H. J. Haugan, F. Szmulowicz, G. J. Brown, and K. Mahalingam

J. Appl. Phys. 96, 2580 (2004); http://dx.doi.org/10.1063/1.1776321 (6 pages) | Cited 19 times

Online Publication Date: 1 September 2004

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The superlattice (SL) of a 40 period InAs∕GaSb SL structure were varied around the 20.5 math InAs∕24 math GaSb design in order to produce a device with an optimum mid-infrared photoresponse and a sharpest photoresponse cutoff. The samples for this study were grown by molecular beam epitaxy with precisely calibrated growth rates. Varying individual layer width around the nominal design, we were able to systematically change the photoresponse cutoff wavelength between 4.36 to 3.45 um by decreasing the InAs width from 23.5 to 17.5 math, and between 4.55 to 4.03 μm by increasing the GaSb width from 18 to 27 math. Therefore, the cutoff changes faster with decreasing InAs rather than increasing GaSb width. However, increasing GaSb width more effectively enhances the sharpness of photoresponse near band edge. The effect of design parameters on the photoresponse cutoff and other effects are explained by a nonperturbative, modified envelope function approximation (EFA) calculation that includes the interface coupling of heavy, light, and spin-orbit holes resulting from the in-plane asymmetry at InAs∕GaSb interfaces. Using the modified EFA model, the SL design at fixed period of 44.5 math was adjusted for the optimum performance.
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81.05.Ea III-V semiconductors
73.21.Cd Superlattices
68.65.Cd Superlattices
72.40.+w Photoconduction and photovoltaic effects
78.30.Fs III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

A quantitative model for the blueshift induced by rapid thermal annealing in GaNAs∕GaAs triple quantum wells

Yijun Sun, Takashi Egawa, and Hiroyasu Ishikawa

J. Appl. Phys. 96, 2586 (2004); http://dx.doi.org/10.1063/1.1776638 (6 pages) | Cited 1 time

Online Publication Date: 1 September 2004

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The effects of rapid thermal annealing (RTA) on the optical properties of GaNAs∕GaAs triple quantum wells grown by chemical beam epitaxy are studied in detail by photoluminescence (PL) spectroscopy at 77 K. Special emphasis is put on the RTA-induced PL peak blueshift. It is found that the blueshift is neither due to nitrogen diffusion from well layer to barrier layer nor due to homogenization of nitrogen composition fluctuations. The blueshift is due to the coupling between the radiative recombination of PL emission and the nonradiative recombination of nonradiative centers. A quantitative model is proposed in which the blueshift is proportional to the relative change of the concentration of nonradiative centers. This model quantitatively explains not only our present results but also previous observations.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Fd III-V semiconductors
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