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8 Sep 1997

Volume 71, Issue 10, pp. 1285-1432

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Free-space electro-optics sampling of mid-infrared pulses

Q. Wu and X.-C. Zhang

Appl. Phys. Lett. 71, 1285 (1997); http://dx.doi.org/10.1063/1.119873 (2 pages) | Cited 109 times

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We report on the coherent detection of ultra-broadband mid-infrared electromagnetic pulses using a 30-μm-thick ZnTe electro-optic sensor. The detected frequency spectrum exceeds 37 THz, extending from microwave to the mid-infrared. The frequency response can be further improved by reducing the sensor thickness to 10 μm. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Shock-wave generation during rear- and front-side ablation of calcite

O. Yavas, E. L. Maddocks, M. R. Papantonakis, and R. F. Haglund

Appl. Phys. Lett. 71, 1287 (1997); http://dx.doi.org/10.1063/1.119930 (3 pages) | Cited 8 times

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Shock waves generated by rear- and front-side infrared (λ = 1.064 μm) laser irradiation of calcite were measured using time-resolved surface-plasmon resonance spectroscopy. The shock waves generated in the two cases are found to be distinctly different: Rear-side ablation gives rise to planar shock waves, while the front-side ablation is more nearly spherical. The observed differences are related to differing material-removal mechanisms at the two surfaces. © 1997 American Institute of Physics.
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62.65.+k Acoustical properties of solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.47.-p Spectroscopy of solid state dynamics

A model for the current–voltage characteristics and the quantum efficiency of single-layer organic light emitting diodes

Y. Kawabe, G. E. Jabbour, S. E. Shaheen, B. Kippelen, and N. Peyghambarian

Appl. Phys. Lett. 71, 1290 (1997); http://dx.doi.org/10.1063/1.119874 (3 pages) | Cited 18 times

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A model for the current–voltage characteristics and the quantum efficiency of single-layer organic light emitting diodes is presented. With variables such as the electric field, the hole, and electron carrier densities, a set of coupled nonlinear differential equations is derived by using classical electrostatics and by assuming Fowler–Nordheim injection. Numerical calculations for different carrier mobility and barrier height conditions show that low barrier height at both electrodes leads to higher efficiency and higher carrier mobility leads to higher brightness. We find that for applications that require high current injection such as lasers, materials with high mobility are desired to reduce space charge effects. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling

Polymer light-emitting electrochemical cells with frozen p-i-n junction

Jun Gao, Gang Yu, and Alan J. Heeger

Appl. Phys. Lett. 71, 1293 (1997); http://dx.doi.org/10.1063/1.119875 (3 pages) | Cited 81 times

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The p-i-n junction in a polymer light-emitting electrochemical cell (LEC) is stabilized by cooling the device below the glass transition temperature of the ion-transport polymer. LECs with frozen p-i-n junctions exhibit typical light emitting diode (LED) behavior including diode rectification, unipolar light emission (same polarity as that used for generating the junction), and fast response. The freezeout of ion motion allows polymer LECs to be driven at bias voltages well beyond the electrochemical stability window, and thereby extends the potential applications of polymer LECs to high pixel density, column-row addressable displays. © 1997 American Institute of Physics.
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85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices
85.30.Kk Junction diodes

Stable single-frequency operation of a high-power external cavity tapered diode laser at 780 nm

A. K. Goyal, P. Gavrilovic, and H. Po

Appl. Phys. Lett. 71, 1296 (1997); http://dx.doi.org/10.1063/1.119876 (3 pages) | Cited 5 times

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We report on grating-tuned tapered lasers that oscillate on a single external-cavity mode at powers as high as 720 mW. Frequency stabilization and side-mode discrimination are achieved through the use of an intracavity etalon. The emission frequency was stabilized against mode hops for a period of >2000 s and exhibited a short term jitter of ∼ 85 MHz over a period of 300 s. The single-frequency emission was tunable over a 17 nm range centered at 783 nm. Furthermore, the far-field emission remained near-diffraction limited throughout the measured current range (<2 A). © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Stimulated emission from optically pumped GaN quantum dots

Satoru Tanaka, Hideki Hirayama, Yoshinobu Aoyagi, Yukio Narukawa, Yoichi Kawakami, Shizuo Fujita, and Shigeo Fujita

Appl. Phys. Lett. 71, 1299 (1997); http://dx.doi.org/10.1063/1.119877 (3 pages) | Cited 41 times

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Stimulated emission was observed from optically pumped GaN quantum dots in an AlxGa1−xN separate confinement heterostructure fabricated on 6H-SiC(0001) substrate by metal organic chemical vapor deposition. Nanostructural GaN quantum dots, with an average size of ∼10 nm width, ∼1–2 nm height, and density of ∼1011 cm−2, were self-assembled on the AlxGa1−xN cladding layer surface. The stimulated emission peak was observed at ∼3.48 eV, which is ∼50 meV lower than that of spontaneous emission. The excitation power dependence on the emission intensity clearly indicates threshold pump power density of 0.75 MW/cm2 for the onset of stimulated emission. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.45.+h Stimulated emission
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Single-layer organic electroluminescent devices by vapor deposition polymerization

Weng-Kou Wen, Jwo-Huei Jou, Jeng-Feng Chiou, Win-Pin Chang, and Wha-Tzong Whang

Appl. Phys. Lett. 71, 1302 (1997); http://dx.doi.org/10.1063/1.119878 (3 pages) | Cited 3 times

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A novel method is presented herein regarding the preparation of a single-layer organic electroluminescent (EL) polymer thin film device. The device was made by simultaneously co-depositing two polymer thin film forming monomers, a hole-transporting molecule triphenyldiamine derivative (TPD) and an EL active molecule 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) on an indium-tin-oxide (ITO) glass substrate. The device structure was composed of the ITO glass, the TPD, and TPB co-doped polymer thin film, and a thermally evaporated aluminum electrode. Carrier injection from the two electrodes was significantly observed and the blue light in EL spectra, with an emission maximum at 435 nm, was triggered at a driving voltage of 17 V. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.35.-x Polymers: properties; reactions; polymerization
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Multiple optical paths in a self-seeding scheme for multiwavelength short pulse generation

D. N. Wang and C. Shu

Appl. Phys. Lett. 71, 1305 (1997); http://dx.doi.org/10.1063/1.119879 (3 pages) | Cited 4 times

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A simultaneous generation of multiwavelength short pulses is demonstrated by self-injection seeding of a laser diode. The wavelengths are selected by the use of multiple optical paths in an external cavity consisting of a grating, a beam splitter, and two mirrors. By adjusting the grating and either one of the mirrors, the wavelengths and their spacings can be readily tuned in a flexible manner. The system is simple, robust, and is of low cost. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Terahertz wave amplification, stimulated by dc electric current, in grating coupled low-dimensional electron systems

S. A. Mikhailov and N. A. Savostianova

Appl. Phys. Lett. 71, 1308 (1997); http://dx.doi.org/10.1063/1.119880 (3 pages) | Cited 7 times

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We present an analytic theory of the transmission of electromagnetic waves through a structure “two-dimensional electron system with a flowing current – grating coupler.” The transmission coefficient T(ω,vdr) is calculated as a function of frequency, drift velocity vdr, and other physical and geometrical parameters of the structure. Threshold conditions for amplification [T(ω,vdr)>1] are analyzed. A number of ideas for a reduction of the threshold velocity and an enhancement of the amplification are proposed. Our results can be used for designing tunable solid-state terahertz wave amplifiers (generators), based on the grating coupled low-dimensional electron systems. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Dj Gratings
84.40.Az Waveguides, transmission lines, striplines

Measurement of interdiffusion by high angle hollow cone illumination

J. C. Ewert, F. Hartung, and G. Schmitz

Appl. Phys. Lett. 71, 1311 (1997); http://dx.doi.org/10.1063/1.119881 (3 pages) | Cited 6 times

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High angle hollow cone darkfield or Z-contrast imaging is used to supress dynamical contributions like bend or extinction contours to electron imaging. Using a multiple scattering model it is possible to interpret image intensities quantitatively and to analyze specimen composition on a nanometer scale without specialized detectors like energy-energy-loss spectroscopy or energy dispersive spectroscopy. This method is practically tested on the interdiffusion of Cu-Au couples. Measured thin film interdiffusion coefficents, are comparable to literature data of the bulk diffusion coefficent in this system. © 1997 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness

Self-limiting growth of quantum dot heterostructures on nonplanar {111}B substrates

A. Hartmann, L. Loubies, F. Reinhardt, and E. Kapon

Appl. Phys. Lett. 71, 1314 (1997); http://dx.doi.org/10.1063/1.119882 (3 pages) | Cited 30 times

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We study the evolution of AlGaAs/GaAs growth during organometallic chemical vapor deposition on pyramidal recess patterns etched into GaAs {111}B substrates. Cross-sectional atomic force microscopy clearly demonstrates the self-organized growth behavior in the inverted pyramid structures. During AlGaAs deposition, the side corners and the tip of the pyramid sharpen up to a self-limited radius of curvature of less than 10 nm. In addition, vertical Ga-rich AlGaAs quantum wells are formed at these corners. Subsequent GaAs growth results in the formation of GaAs quantum wires along the corners of the pyramid. These wires meet at the tip of the pyramid, forming a quantum dot structure at this point. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of hydrogen dilution on the structure of amorphous silicon alloys

D. V. Tsu, B. S. Chao, S. R. Ovshinsky, S. Guha, and J. Yang

Appl. Phys. Lett. 71, 1317 (1997); http://dx.doi.org/10.1063/1.119928 (3 pages) | Cited 109 times

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We investigate why high levels of hydrogen dilution of the process gas lead to enhanced light soaking stability of amorphous silicon (a-Si) alloy solar cells by studying the microstructural properties of the material using high-resolution transmission electron microscopy (TEM) and Raman spectroscopy. The TEM results show that a-Si alloy (with or without hydrogen dilution) is a heterogeneous mixture of amorphous network and linear-like objects that show evidence of order along their length. The volume fraction of these ordered regions increases with increasing hydrogen dilution. © 1997 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
84.60.Jt Photoelectric conversion
78.30.Am Elemental semiconductors and insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses

Improved field emission of electrons from ion irradiated carbon

K. C. Walter, H. H. Kung, and C. J. Maggiore

Appl. Phys. Lett. 71, 1320 (1997); http://dx.doi.org/10.1063/1.119883 (3 pages) | Cited 8 times

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Electron field emission from allotropes of carbon (graphite, diamondlike carbon, and diamond) have been reported many times in the literature. This work explores the use of ion irradiation for improving electron field emission from carbon fibers. Carbon fibers have been irradiated with H, C, Ar, and Xe ions. Field emission characteristics have been measured as a function of ion dose. A reversible reduction in the required field for a fixed current level has been observed. The critical dose, Dc, defines the dose corresponding to the lowest field necessary to emit a fixed current (5 μA). The critical dose appears to correlate with the nuclear energy loss (collisions with atoms) of the ion in the carbon fiber. Transmission electron microscopy and parallel electron energy loss spectroscopy analysis indicate an amorphous surface, and an increase in the sp3 content of the fiber surface to 20%–30%. A corresponding decrease in the work function is expected and may account for the improvement in electron emission. © 1997 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.80.Jh Ion radiation effects
61.82.Ms Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Er Other amorphous solids
79.20.Kz Other electron-impact emission phenomena
73.30.+y Surface double layers, Schottky barriers, and work functions

Fast proton-conducting P2O5–ZrO2–SiO2 glasses

Masayuki Nogami, Ritsuko Nagao, Kensuke Makita, and Yoshihiro Abe

Appl. Phys. Lett. 71, 1323 (1997); http://dx.doi.org/10.1063/1.119884 (3 pages) | Cited 11 times

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Fast proton-conducting P2O5–ZrO2–2SiO2 glasses were successfully prepared by the hydrolysis of metal alkoxides. The glasses obtained by heating at 150 to 400 °C are chemically stable and exhibit high conductivities of ∼ 104 S/cm at room temperature, conductivities that are higher by ∼ 4 order than that of glasses containing no P2O5. These high conductivities were regarded as the fast proton transfer accelerated by molecular water bonded with POH groups. These glasses have a high potential for practical applications. © 1997 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
81.20.-n Methods of materials synthesis and materials processing
61.43.Fs Glasses
66.30.H- Self-diffusion and ionic conduction in nonmetals

Chemical erosion of amorphous hydrogenated boron films

A. Annen and W. Jacob

Appl. Phys. Lett. 71, 1326 (1997); http://dx.doi.org/10.1063/1.119885 (3 pages) | Cited 10 times

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Amorphous-hydrogenated boron (a-B:H) and carbon (a-C:H) thin films were prepared by radio-frequency plasma deposition using (B2H6+H2) or CH4 as a precursor gas. The film composition and density were investigated by ion-beam analysis. The films were eroded by hydrogen electron cyclotron resonance plasmas at floating potential and by atomic hydrogen dissociated by a hot filament. The temperature of the substrates was increased during the erosion process from 330 to 680 K. Erosion rates were measured in situ by ellipsometry. a-B:H films are shown to be much more resistant to erosion by hydrogen ions (H+) and atomic hydrogen (H0) than a-C:H films. In contrast to a-C:H films, no chemical erosion of a-B:H films by H0 was observed at temperatures below 600 K. Ion energies lower than the threshold energy for physical sputtering cause measurable erosion rates for a-B:H films. It is concluded that this is a synergistic effect of simultaneous H0 and H+ bombardment and it is designated as ion-induced chemical erosion. © 1997 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
61.80.Jh Ion radiation effects
68.55.-a Thin film structure and morphology

Influence of the microstructure on the thermal properties of thin polycrystalline diamond films

H. Verhoeven, A. Flöter, H. Reiß, R. Zachai, D. Wittorf, and W. Jäger

Appl. Phys. Lett. 71, 1329 (1997); http://dx.doi.org/10.1063/1.119886 (3 pages) | Cited 12 times

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Highly oriented and columnar grained diamond layers only a few microns thick, deposited at different substrate temperatures (500, 550, and 800 °C) on silicon using microwave-plasma-assisted chemical vapor deposition, are investigated by special photothermal techniques and high-resolution transmission electron microscopy (HRTEM). Small effective diamond–silicon boundary resistances of <4×10−9 m2 K/W are determined for thermal conduction normal to the interface. Thermal conductivities normal to the interface, k⊥, are found to be about an order of magnitude greater than the conductivities parallel to the interface, k∥ (k⊥/k∥ = 9–18). The boundary resistances measured are in good agreement with limits estimated from the interface structure observed by HRTEM, which indicate a low near-interfacial disorder for the layers. © 1997 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
65.90.+i Other topics in thermal properties of condensed matter (restricted to new topics in section 65)

Electroluminescence and electron transport in a perylene dye

P. Ranke, I. Bleyl, J. Simmerer, D. Haarer, A. Bacher, and H. W. Schmidt

Appl. Phys. Lett. 71, 1332 (1997); http://dx.doi.org/10.1063/1.119929 (3 pages) | Cited 57 times

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Charge carrier transport in vapor-deposited films of 1,6,7,12-tetraphenoxy-N,N′-bis-(2,6-diisopropylphenyl)-perylene-3,4,9,10-bis(dicarboximide) was investigated using two different methods, the time-of-flight (TOF) technique and time-resolved electroluminescence. Electron mobilities of 10−5 cm2/V s were measured in the bulk using a time-of-flight technique. Hole transport was found to be dispersive and, thus, a transit time for holes could not be obtained. The above dye was also used to fabricate single layer light emitting diodes showing clearly visible red electroluminescence under ambient conditions. Our experiments on transit electroluminescence confirmed the measured electron mobility and ruled out the possibility that the transit time of holes is shorter than the time range investigated in our time-of-flight experiments. © 1997 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
78.47.-p Spectroscopy of solid state dynamics
72.20.Fr Low-field transport and mobility; piezoresistance
85.60.Jb Light-emitting devices
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance

Enhanced conductivity in ionic conductor-insulator composites: Experiments and numerical model

Jean-Marc Debierre, P. Knauth, and Gilbert Albinet

Appl. Phys. Lett. 71, 1335 (1997); http://dx.doi.org/10.1063/1.120418 (3 pages) | Cited 8 times

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We study ionic conductivity of the model composites, copper(I) bromide-titanium dioxyde, in a large domain of composition. The experimentally observed enhancement of conductivity is interpreted by a numerical model taking into account grain size effects and interactions between ionic conductor and insulator grains. © 1997 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.Mm Grain and twin boundaries

Pyroelectrically induced optical emission from potassium titanyl phosphate crystals

D. W. Cooke, B. L. Bennett, R. E. Muenchausen, and D. M. Wayne

Appl. Phys. Lett. 71, 1338 (1997); http://dx.doi.org/10.1063/1.119887 (3 pages)

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We have observed optical scintillations and corresponding electric current pulses when uniformly heating potassium titanyl phosphate (KTP) crystals at 0.1–0.4 K/s over the temperature range 8–300 K. The scintillations correspond to molecular nitrogen emission occurring during the electrical breakdown of air near the crystal surface, and imply the existence of pyroelectrically induced peak electric fields at the crystal surface exceeding 30 kV/cm, which is ten times larger than dc electric fields reported to induce electrochromic (EC) damage in this material. Recent optical damage studies on KTP under high repetition rate, high average-power laser irradiation reveal an EC-like damage, implying the existence of an internal electric field arising during laser irradiation. Our observation of a sizable total pyroelectric response suggests one possible mechanism for the origin of these internal fields in KTP and other nonlinear optical materials. © 1997 American Institute of Physics.  
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78.60.Fi Electroluminescence
78.60.Kn Thermoluminescence
77.70.+a Pyroelectric and electrocaloric effects
42.70.Mp Nonlinear optical crystals
78.20.Jq Electro-optical effects
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.65.-k Nonlinear optics
77.84.Fa KDP- and TGS-type crystals

Structural and electrical properties of crystalline (1−x)Ta2O5–xAl2O3 thin films fabricated by metalorganic solution deposition technique

P. C. Joshi, S. Stowell, and S. B. Desu

Appl. Phys. Lett. 71, 1341 (1997); http://dx.doi.org/10.1063/1.119888 (3 pages) | Cited 10 times

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Polycrystalline (1−x)Ta2O5–xAl2O3 thin films were fabricated by metalorganic solution deposition technique on Pt-coated Si substrate at a temperature of 750 °C. Thin films with 0.9Ta2O5–0.1Al2O3 composition exhibited improved dielectric and insulating properties compared to Ta2O5 thin films. The measured small signal dielectric constant and dissipation factor at 100 kHz were 42.8 and 0.005, respectively. The temperature coefficient of capacitance was 20 ppm/°C in the measured temperature range of 25–125 °C. The leakage current density was lower than 6×10−8 A/cm2 up to an applied electric field of 1 MV/cm. A charge storage density of 18.9 fC/μm2 was obtained at an applied electric field of 0.5 MV/cm. The high dielectric constant, low dielectric loss, low leakage current density, and good temperature and bias stability suggest (1−x)Ta2O5–xAl2O3 thin films to be a suitable dielectric layer in integrated electronic devices in place of conventional dielectrics such as SiO2 or Si3N4. © 1997 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Gm Dielectric loss and relaxation
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Metastability modeling of compliant substrate critical thickness using experimental strain relief data

Carrie Carter-Coman, Robert Bicknell-Tassius, April S. Brown, and Nan Marie Jokerst

Appl. Phys. Lett. 71, 1344 (1997); http://dx.doi.org/10.1063/1.119889 (3 pages) | Cited 10 times

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A metastability model for GaAs compliant substrates is developed using the compliant substrate partitioning formula and experimental strain relief data. The developed model agrees with compliant substrate strain relief data deduced from double crystal x-ray diffraction and indicates that, for a set of growth conditions and compliant substrate thicknesses, layers of InGaAs of any thickness can be grown free of dislocations. The model developed in this letter is also compared to other compliant substrate critical thickness models, and the authors discuss the mechanisms of partitioning in mismatched layers grown on compliant substrates. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
62.20.-x Mechanical properties of solids
68.55.-a Thin film structure and morphology

Influence of atomic force microscope tip–sample interaction on the study of scaling behavior

J. Aué and J. Th. M. De Hosson

Appl. Phys. Lett. 71, 1347 (1997); http://dx.doi.org/10.1063/1.120415 (3 pages) | Cited 40 times

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Images acquired with atomic force microscopy are based on tip–sample interaction. It is shown that using scanning probe techniques for determining scaling parameters of a surface leads to an underestimate of the actual scaling dimension, due to the dilation of tip and surface. How much we underestimate the scaling exponent depends on the shape and aspect ratio of the tip, the actual fractal dimension of the surface, and its lateral–vertical ratio. © 1997 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Lh Atomic force microscopes

Switchable diffractive cholesteric gratings

D. Subacius, P. J. Bos, and O. D. Lavrentovich

Appl. Phys. Lett. 71, 1350 (1997); http://dx.doi.org/10.1063/1.119890 (3 pages) | Cited 29 times

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Electrically switchable diffractive gratings based on cholesteric liquid crystals are suggested. An electric field switches the cholesteric cell between three states: two with a uniform in-plane director and one with a periodic in-plane director modulation. The modulated state produces a Raman–Nath diffractive effect. Characteristic time of switching is of the order of 10 ms. Diffractive properties depend on the polarization of the incident beam and the direction of surface orientation. © 1997 American Institute of Physics.
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42.79.Dj Gratings
78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
42.79.Hp Optical processors, correlators, and modulators

Optical phonons of strained GaAs/GaP quantum wells studied by Raman spectroscopy

P. Castrillo, G. Armelles, J. P. Silveira, F. Briones, and J. Barbolla

Appl. Phys. Lett. 71, 1353 (1997); http://dx.doi.org/10.1063/1.119891 (3 pages) | Cited 4 times

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We have studied the optical phonons of GaAs quantum wells strained to GaP. The phonon frequencies have been measured by Raman spectroscopy. The results have been compared with calculations based on the linear chain model and the random isoamplitude model. The comparison suggests a certain degree of atomic intermixing at the interfaces, mainly due to a limited but measurable arsenic carry-over during growth. © 1997 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation

Deposition and doping of silicon carbide by gas-source molecular beam epitaxy

R. S. Kern and R. F. Davis

Appl. Phys. Lett. 71, 1356 (1997); http://dx.doi.org/10.1063/1.119892 (3 pages) | Cited 7 times

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Thin films of silicon carbide (SiC) have been deposited at 1400–1450 °C on vicinal and on-axis 6H-SiC(0001) substrates by gas-source molecular beam epitaxy using the SiH4-C2H4-H2 gas system. Polytype control (6H- or 3C-SiC) was established by utilizing substrates of particular orientations. Residual, unintentionally incorporated nitrogen impurity levels were affected by changing the SiH4/C2H4 gas flow ratio, in agreement with the “site-competition epitaxy” model. In situ doping was achieved by intentional introduction of nitrogen and aluminum into the growing crystal. © 1997 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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