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9 Oct 2000

Volume 77, Issue 15, pp. 2271-2423

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Silicon-based organic light-emitting diode operating at a wavelength of 1.5 μm

R. J. Curry, W. P. Gillin, A. P. Knights, and R. Gwilliam

Appl. Phys. Lett. 77, 2271 (2000); http://dx.doi.org/10.1063/1.1316064 (3 pages) | Cited 42 times

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1.5-μm light-emitting diodes which operate at room temperature have been fabricated on silicon substrates. The devices use an erbium-containing organic light-emitting diode (OLED) structure which utilizes p++ silicon as the hole injection contact. The OLEDs use N, N′-diphenyl-N,N′-bis(3-methyl)-1,1′-biphenyl-4,4′-diamine as the hole transporting layer and erbium tris(8-hydroxyquinoline) as the electron conducting and emitting layer. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices

Detection of volatile organic compound vapors by using a vapochromic material on a tapered optical fiber

C. Bariáin, I. R. Matías, I. Romeo, J. Garrido, and M. Laguna

Appl. Phys. Lett. 77, 2274 (2000); http://dx.doi.org/10.1063/1.1316074 (3 pages) | Cited 23 times

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A low-cost optical fiber sensor to detect volatile organic compounds has been developed. Changes of up to 13.5 dB in the transmitted optical power have been detected with different concentrations of acetone and dichloromethane vapors. The device uses a standard single-mode fiber. The sensing mechanism relies on a vapor-induced refractive index change in a film of a vapochromic material deposited on the thinner region of a tapered fiber. © 2000 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
82.80.-d Chemical analysis and related physical methods of analysis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Wc Optical coatings

Wavelength locking of multiple diode lasers by multiplexed gratings in a photorefractive crystal

Changxi Yang and Min Xiao

Appl. Phys. Lett. 77, 2277 (2000); http://dx.doi.org/10.1063/1.1315630 (3 pages)

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We propose a technique to simultaneously stabilize relative wavelengths among multiple diode lasers by using multiplexed photorefractive gratings. Each grating is designed to be Bragg matched for the counter-propagating reflection at a specific diode laser wavelength. Experimental results from stabilization of two diode laser wavelengths by using two photorefractive gratings exhibit excellent short- and long-term wavelength stability. We show that this technique can be extended to stabilize relative wavelengths of many diode lasers. The thermal stability of the photorefractive gratings and the signal-to-noise ratio (or the bit-error rate) are discussed. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.By Design of specific laser systems
42.79.Dj Gratings

Polymer phosphorescent light-emitting devices doped with tris(2-phenylpyridine) iridium as a triplet emitter

Chang-Lyoul Lee, Kyung Bok Lee, and Jang-Joo Kim

Appl. Phys. Lett. 77, 2280 (2000); http://dx.doi.org/10.1063/1.1315629 (3 pages) | Cited 136 times

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We have fabricated phosphorescent polymer light-emitting devices with tris(2-phenylpyridine) iridium [Ir(ppy)3] as a triplet emissive dopant in poly(vinylcarbazole) (PVK) host. The device with 8% doping concentration of [Ir(ppy)3] in PVK showed the external quantum efficiency of 1.9% and the peak luminance of 2,500 cd/m2. The emission spectrum of the device exhibited no emission from PVK, indicating that the energy transfer from PVK to [Ir(ppy)3] is efficient. This work demonstrates that efficient electrophosphorescent light-emitting devices can be realized with polymers. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.-b Other luminescence and radiative recombination
42.70.Jk Polymers and organics

Continuous-wave operation of phase-coupled vertical-cavity surface-emitting laser arrays

F. Monti di Sopra, M. Brunner, H.-P. Gauggel, H. P. Zappe, M. Moser, R. Hövel, and E. Kapon

Appl. Phys. Lett. 77, 2283 (2000); http://dx.doi.org/10.1063/1.1316772 (3 pages) | Cited 25 times

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Coupled arrays of vertical-cavity surface-emitting lasers were realized by patterning the reflectivity of the top-distributed Bragg reflector using a phase-matching layer and a metal grid. For improved current injection and better heat dissipation the devices were selectively oxidized. Continuous-wave room-temperature operation of these arrays has been achieved at 960 nm. Near- and far-field measurements confirm the phase-coupling in a typical out-of-phase mode pattern. Analysis of the differential efficiency reveals a strong decrease when the number of lasing pixels and hence the mesa size is increased. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.-k Nonlinear optics
42.60.Pk Continuous operation

Surface plasmon quantum cascade lasers at λ ∼ 19 μm

Alessandro Tredicucci, Claire Gmachl, Michael C. Wanke, Federico Capasso, Albert L. Hutchinson, Deborah L. Sivco, Sung-Nee G. Chu, and Alfred Y. Cho

Appl. Phys. Lett. 77, 2286 (2000); http://dx.doi.org/10.1063/1.1316768 (3 pages) | Cited 23 times

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The longest wavelength III–V semiconductor laser to date has been realized employing a quantum cascade configuration for the active material. It operates at λ ∼ 19 μm on interminiband transitions in graded superlattices. The waveguide is based on surface plasmon modes confined at a metal–semiconductor interface. The devices emit peak output powers of 14 mW per facet at 10 K and laser action is achieved up to the maximum temperature of 145 K. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Optical characterization of CdS nanocrystals in Al2O3 matrices fabricated by ion-beam synthesis

D. Matsuura, Y. Kanemitsu, T. Kushida, C. W. White, J. D. Budai, and A. Meldrum

Appl. Phys. Lett. 77, 2289 (2000); http://dx.doi.org/10.1063/1.1316777 (3 pages) | Cited 31 times

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We have studied optical properties of CdS nanocrystals formed by sequential Cd+ and S+ ion implantation into Al2O3 matrices. Two bands related to free excitons in the wurtzite CdS are clearly observed in the absorption spectrum at low temperatures. Efficient photoluminescence (PL) appears near the absorption edge. At high temperatures, the band edge PL band consists of two components. One is the free-exciton emission with a short lifetime (several hundreds of picoseconds), while the other is the bound exciton emission at shallow localized states with a long lifetime (several nanoseconds). The temperature dependence of the band gap energy has been determined for wurtzite CdS nanocrystals. Spectroscopic analysis shows that high-quality compound semiconductor nanocrystals are fabricated by the ion-beam synthesis technique. © 2000 American Institute of Physics.
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78.66.Vs Fine-particle systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.22.-f Electronic structure of nanoscale materials and related systems
61.72.up Other materials
78.40.Fy Semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.35.Gg Exciton-mediated interactions
78.47.-p Spectroscopy of solid state dynamics

Stabilization of the response time in photorefractive polymers

J. A. Herlocker, C. Fuentes-Hernandez, K. B. Ferrio, E. Hendrickx, P.-A. Blanche, N. Peyghambarian, B. Kippelen, Y. Zhang, J. F. Wang, and S. R. Marder

Appl. Phys. Lett. 77, 2292 (2000); http://dx.doi.org/10.1063/1.1316077 (3 pages) | Cited 12 times

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The optical and photoconductive fatigue of fast photorefractive polymers have been studied in a family of C60-sensitized polymer composites containing styrene-based chromophores with varying ionization potential. Changes in response time and in photoconductivity were studied for exposures up to 104 J/cm2. Increasing the chromophore ionization potential beyond that of the polyvinylcarbazole host was found to stabilize the response time. Studies of the electric-field dependence of the steady-state diffraction efficiency in various samples confirm the role of C60 anions as possible traps. © 2000 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.70.Gi Light-sensitive materials
72.40.+w Photoconduction and photovoltaic effects
72.80.Rj Fullerenes and related materials
78.20.Jq Electro-optical effects
72.80.Le Polymers; organic compounds (including organic semiconductors)
78.20.-e Optical properties of bulk materials and thin films

Optimization of the emission characteristics of light emitting diodes by surface plasmons and surface waveguide modes

S. Gianordoli, R. Hainberger, A. Köck, N. Finger, E. Gornik, C. Hanke, and L. Korte

Appl. Phys. Lett. 77, 2295 (2000); http://dx.doi.org/10.1063/1.1317538 (3 pages) | Cited 14 times

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In this letter, the influence of metal films and dielectric waveguides on the radiation characteristics of light emitting diodes (LEDs) is investigated. Cross and hexagonal surface grating structures are used to excite surface plasmons and waveguide modes in these media. A beam divergence as small as 17° is achieved for a hexagonal grating coated with a 40 nm Ag film. The maximum quantum efficiency is found for a hexagonal grating with a 10-nm-thick Au film and a 250-nm-thick dielectric layer. The optical power emitted by this LED into the solid angle from −30° to 30° is 10% higher than that of an LED without metal film and dielectric layer. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.82.Et Waveguides, couplers, and arrays
42.79.Dj Gratings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Type-II InAsSb/InAs strained quantum-well laser diodes emitting at 3.5 μm

A. Wilk, M. El Gazouli, M. El Skouri, P. Christol, P. Grech, A. N. Baranov, and A. Joullié

Appl. Phys. Lett. 77, 2298 (2000); http://dx.doi.org/10.1063/1.1317537 (3 pages) | Cited 9 times

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Mid-infrared laser diodes with compressively strained InAsSb/InAs type-II slightly coupled quantum wells are reported. These lasers, grown on InAs by molecular-beam epitaxy, have emission wavelength near 3.5 μm. They exhibit pulsed operation up to 220 K, with at 90 K threshold current density of 150 A/cm2. Ridge lasers continuous wave (cw) operated up to 130 K with cw output power of 40 mW/A/facet and a characteristic temperature T0 = 40 K. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High-temperature optical gain of 980 nm InGaAs/AlGaAs quantum-well lasers

Federico Beffa, Heinz Jäckel, Martin Achtenhagen, Christoph Harder, and Daniel Erni

Appl. Phys. Lett. 77, 2301 (2000); http://dx.doi.org/10.1063/1.1317541 (3 pages) | Cited 6 times

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The optical modal gain of ridge-waveguide single-quantum-well InGaAs/AlGaAs diode lasers with an emission wavelength of 980 nm were measured up to a temperature of 250 °C. Comparisons of the obtained gain curves with a simple semiclassical model based on the single-band envelope function theory allows straightforward curve fitting of the gain as it is used, e.g., in numeric models. As a result a simple temperature dependence of the line shape function has been deduced. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Dynamics of GaAs/AlGaAs microdisk lasers

K. J. Luo, J. Y. Xu, H. Cao, Y. Ma, S. H. Chang, S. T. Ho, and G. S. Solomon

Appl. Phys. Lett. 77, 2304 (2000); http://dx.doi.org/10.1063/1.1317544 (3 pages) | Cited 14 times

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Dynamic response of a GaAs/AlGaAs microdisk laser has been experimentally investigated using femtosecond optical pumping. Below the lasing threshold, the delay time of the emission pulse from the microdisk hardly changes with the pump power. Above the lasing threshold, the delay time is shortened dramatically, and it decreases with increasing the pump power. The theoretical simulation based on the rate equations reproduces the experimental observation after the effect of carrier diffusion is taken into account. The simulation result illustrates that the speed of a microdisk laser is limited mainly by the carrier diffusion in the disk plane. © 2000 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Two-dimensional phase-locked antiguided vertical-cavity surface-emitting laser arrays

D. Zhou and L. J. Mawst

Appl. Phys. Lett. 77, 2307 (2000); http://dx.doi.org/10.1063/1.1317545 (3 pages) | Cited 16 times

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4×4 antiguided phase-locked vertical-cavity surface-emitting laser (VCSEL) arrays have been fabricated by a selective etching process and metalorganic chemical vapor deposition regrowth. Stable, diffraction-limited output is observed corresponding to either in-phase or out-of-phase mode operation, depending on the interelement spacing width. Calculations indicate resonant leaky-wave coupling occurs for interelement spacings corresponding to an integral number of half-waves of the radiation leakage from each VCSEL region, and the use of interelement loss is effective in suppressing nonresonant modes. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
81.65.Cf Surface cleaning, etching, patterning
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

A nearly diffraction limited surface emitting conjugated polymer laser utilizing a two-dimensional photonic band structure

S. Riechel, C. Kallinger, U. Lemmer, J. Feldmann, A. Gombert, V. Wittwer, and U. Scherf

Appl. Phys. Lett. 77, 2310 (2000); http://dx.doi.org/10.1063/1.1310207 (3 pages) | Cited 87 times

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We have fabricated a mechanically flexible conjugated polymer laser utilizing distributed feedback due to a two-dimensional photonic band structure. An ultraviolet-embossing process is used for nanopatterning a plastic substrate. On top we spin-coat a ladder-type poly(p-phenylene) as the active laser medium. Upon optical pumping, we observe a low threshold and nearly diffraction limited monomode laser emission perpendicular to the surface. Our results are explained within a Laue formulation for the feedback mechanism in the two-dimensional organic photonic crystal. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Jk Polymers and organics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Evidence of a two-dimensional nucleation and growth mechanism for metastable nanocrystals embedded in Pd40.5Ni40.5P19 glass

K. F. Yao and H. W. Kui

Appl. Phys. Lett. 77, 2313 (2000); http://dx.doi.org/10.1063/1.1316067 (3 pages) | Cited 4 times

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Nanocrystals, with a body-centered-cubic crystal structure of lattice parameter 18.2525 Å , were found in amorphous Pd40.5Ni40.5P19 specimens that had been annealed at 628 K for 30 min. The crystal surfaces are smooth and dislocations are absent, suggesting that the growth of these nanocrystals is through a two-dimensional nucleation and growth mechanism (formation of surface nuclei of critical size and their subsequent growth). © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Bx Metals, semimetals, and alloys
64.60.Q- Nucleation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.66.Dk Alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Anisotropic polarization memory in thermally oxidized porous silicon

Hideki Koyama and Philippe M. Fauchet

Appl. Phys. Lett. 77, 2316 (2000); http://dx.doi.org/10.1063/1.1316068 (3 pages) | Cited 5 times

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Visible photoluminescence (PL) from thermally oxidized porous silicon (PSi) has been investigated in terms of polarization memory (PM). The PSi samples were prepared by anodization of (100)p+-Si wafers in a HF/ethanol solution, followed by thermal oxidation at 700–1000 °C. These oxidized PSi samples show significantly anisotropic PM which depends largely on the polarization direction of the excitation light with respect to their crystallographic axes. In addition, the anisotropic PM from samples oxidized at 800 and 900 °C shows an anomalous emission-energy dependence. It is also observed that thermal oxidation at 1000 °C results in a significant decrease in the degree of PM, although it increases with increasing oxidation temperatures for ⩽900 °C. These experimental results suggest that the PL from oxidized PSi cannot be explained as a simple extension of the PL from as-anodized PSi and should be attributed to several different origins. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
81.65.Mq Oxidation
81.05.Rm Porous materials; granular materials
81.05.Cy Elemental semiconductors

Investigation of the thermal conductivity of the mixed pentatellurides Hf1−xZrxTe5

B. M. Zawilski, R. T. Littleton, and Terry M. Tritt

Appl. Phys. Lett. 77, 2319 (2000); http://dx.doi.org/10.1063/1.1316065 (3 pages) | Cited 5 times

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Transition-metal pentatellurides (HfTe5 and ZrTe5) exhibit a promising power factor (electronic properties) for possible use as a thermoelectric material. For complete characterization of these crystals, thermal conductivity measurements are necessary. In this letter, we report measurements of the thermal conductivity for this group of materials using the parallel thermal conductance technique which is well adapted for needle-like samples. Thermal conductivity is presented as a function of temperature and composition of the pentatelluride solid solution HfxZr1−xTe5 with 0 ⩽ x ⩽ 1 in which the magnitude of the room temperature thermal conductivity varies from 5 to 8 W/(m K). Dependence on the cross-sectional area and possible size effects (or sample quality) is also presented and discussed. These results also indicate the importance of sample quality on the low-temperature thermal conductance maximum λmax. © 2000 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.Hd Other semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
07.20.-n Thermal instruments and apparatus
72.80.Ga Transition-metal compounds

Excitonic gain and stimulated ultraviolet emission in nanocrystalline zinc-oxide powder

Y. Sun, J. B. Ketterson, and G. K. L. Wong

Appl. Phys. Lett. 77, 2322 (2000); http://dx.doi.org/10.1063/1.1316069 (3 pages) | Cited 45 times

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We have studied ultraviolet photoluminescence from high-purity zinc-oxide powder over a wide temperature range (2–293 K). At low temperatures, the spontaneous emission is due to radiative recombination of excitons bound to donors and acceptors. At high temperature (>90 K), it mainly consists of recombination of free excitons, with exciton–exciton collision-induced recombination dominating the spectrum at higher pumping intensities. Emission from the exciton–exciton collision process shows clear stimulated-emission behavior. At sufficiently high pumping intensity, the stimulated emission band shifts abruptly to a longer wavelength due to the formation of an electron–hole plasma. Sharp emission peaks are observed in the stimulated emission bands. The possible origins of these sharp peaks are discussed. © 2000 American Institute of Physics.
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78.45.+h Stimulated emission
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
42.50.-p Quantum optics
71.35.Ee Electron-hole drops and electron-hole plasma
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.30.+q High-frequency effects; plasma effects

Mechanism for rapid thermal annealing improvements in undoped GaNxAs1−x/GaAs structures grown by molecular beam epitaxy

I. A. Buyanova, G. Pozina, P. N. Hai, N. Q. Thinh, J. P. Bergman, W. M. Chen, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 77, 2325 (2000); http://dx.doi.org/10.1063/1.1315632 (3 pages) | Cited 51 times

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A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1−x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1−x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies. © 2000 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.82.Fk Semiconductors
76.70.Hb Optically detected magnetic resonance (ODMR)
78.47.-p Spectroscopy of solid state dynamics
61.72.-y Defects and impurities in crystals; microstructure
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Structural transition of Ge dots induced by submonolayer carbon on Ge wetting layer

Yutaka Wakayama, Gerhard Gerth, Peter Werner, Ulrich Gösele, and Leonid V. Sokolov

Appl. Phys. Lett. 77, 2328 (2000); http://dx.doi.org/10.1063/1.1316778 (3 pages) | Cited 8 times

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We have investigated the influence of carbon on Ge dot growth on Si(100) substrates. To modify the Ge dot structure, submonolayers of carbon were deposited on Ge wetting layers. The Ge deposited on the carbon-covered wetting layer tends to form dome structures instead of hut structures even at a substrate temperature of 500 °C. The main effect of C is to enhance a structural transition from huts to domes by influencing the configurational energy of the Ge dots. The dominant factor to determine the dot size is the substrate temperature. Accordingly, small domes with 10–20 nm in diameter were formed by combining techniques of the submonolayer C on the Ge wetting layer and low-temperature deposition. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Cy Elemental semiconductors
68.08.Bc Wetting
68.35.Rh Phase transitions and critical phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)

Scanning second-harmonic/third-harmonic generation microscopy of gallium nitride

Chi-Kuang Sun, Shih-Wei Chu, Shi-Peng Tai, Stacia Keller, Umesh K. Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 77, 2331 (2000); http://dx.doi.org/10.1063/1.1316776 (3 pages) | Cited 21 times

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Scanning second-harmonic generation and third-harmonic generation microscopy of a gallium nitride (GaN) sample was demonstrated using a femtosecond Cr:forsterite laser. Taking advantage of the electric-field enhanced second-harmonic generation effect and bandtail state resonance effect, the obtained second-harmonic and third-harmonic generation microscopic images revealed the piezoelectric field and bandtail state distributions in a GaN sample. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
71.20.Nr Semiconductor compounds
77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Spectroscopic imaging of nanoparticles in laser ablation plume by redecomposition and laser-induced fluorescence detection

Junichi Muramoto, Takahiro Inmaru, Yoshiki Nakata, Tatsuo Okada, and Mitsuo Maeda

Appl. Phys. Lett. 77, 2334 (2000); http://dx.doi.org/10.1063/1.1316780 (3 pages) | Cited 12 times

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We propose and demonstrate an imaging technique to observe clusters formed in a laser ablation plume, which are difficult to be detected by conventional laser-induced fluorescence (LIF) and ultraviolet Rayleigh scattering techniques. The clusters were decomposed by the irradiation of another laser beam, and the disintegrated atoms were visualized by a two-dimensional LIF technique. This technique was applied to visualize the formation process of clusters in a laser ablation plume. Based on this imaging diagnostics, the onset time of the clustering in the plume is discussed. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Solid–liquid interface velocity and diffusivity in laser-melt amorphous silicon

Luigi Brambilla, Luciano Colombo, Vittorio Rosato, and Fabrizio Cleri

Appl. Phys. Lett. 77, 2337 (2000); http://dx.doi.org/10.1063/1.1317535 (3 pages) | Cited 17 times

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We studied the microscopic kinetics of the amorphous-liquid interface in supercooled laser-melt silicon by means of molecular dynamics computer simulations. The interface velocity was obtained as a function of temperature by direct simulation of the interface motion in an amorphous-liquid model system. The temperature dependence of the kinetic prefactor was extracted from the interface velocity function and compared to the values of self-diffusivity obtained from independent molecular dynamics simulations of bulk amorphous Si. The kinetic prefactor for interfacial diffusion shows a distinctly non-Arrhenius behavior which is attributed to Fulcher–Vogel kinetics in the supercooled liquid. © 2000 American Institute of Physics.
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64.70.D- Solid-liquid transitions
61.43.Dq Amorphous semiconductors, metals, and alloys
68.35.Fx Diffusion; interface formation
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.20.Ja Computer simulation of liquid structure

Heat capacity of hydrogenated diamond-like carbon films

M. Hakovirta, J. E. Vuorinen, X. M. He, M. Nastasi, and R. B. Schwarz

Appl. Phys. Lett. 77, 2340 (2000); http://dx.doi.org/10.1063/1.1290387 (3 pages) | Cited 8 times

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We have used differential scanning calorimetry to measure the heat capacity of diamond-like carbon (DLC) film prepared by a plasma immersion ion processing method. The same calorimeter was used to measure the heat capacity of single crystal natural diamond and of high purity graphite. The amount of atomic hydrogen trapped in the DLC films was determined by elastic-recoil-detection spectrometry. The present data and literature values were used to deduce an expression for the specific heat that factors out the contribution from the sp3/sp2 bonding and from the atomic hydrogen trapped in the carbon. The data shows that the hydrogen contribution to the specific heat of carbon is independent of the sp3/sp2 bonding and amounts to about 0.63kB per hydrogen atom. We propose a simple method to determine the sp3/sp2 bonding ratio in hydrogenated DLC films based on measuring the specific heat and the hydrogen content of the sample. © 2000 American Institute of Physics.
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65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.43.Dq Amorphous semiconductors, metals, and alloys
68.60.Dv Thermal stability; thermal effects
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Vertically faceted lateral overgrowth of GaN on SiC with conducting buffer layers using pulsed metalorganic chemical vapor deposition

R. S. Qhalid Fareed, J. W. Yang, Jianping Zhang, Vinod Adivarahan, Vinamra Chaturvedi, and M. Asif Khan

Appl. Phys. Lett. 77, 2343 (2000); http://dx.doi.org/10.1063/1.1316063 (3 pages) | Cited 26 times

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A “pulsed metalorganic chemical vapor deposition” technique has been developed for lateral overgrowth of GaN thin films on SiC with conducting buffer layers for vertically conducting devices. Growth was carried out at temperatures as low as 950 °C keeping a constant gallium flux while pulsing NH3. We demonstrate that, by varying the NH3 pulse duration, growth morphology can be gradually changed from triangular to rectangular for the lateral overgrowth. Even at a V/III ratio as low as 550, high quality smooth layers with (1100) vertical facets were successfully grown with a lateral to vertical growth rate ratio as high as 4:1. Atomic force microscopic measurements show the root-mean-square roughness of the laterally overgrown layers to be 7.0 Å. Scanning thermal microscopy was used to measure a thermal conductivity of 1.7 and 1.5 W/cm K, respectively, for the laterally overgrown film and the GaN deposition in the window region. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.35.B- Structure of clean surfaces (and surface reconstruction)
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