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29 Dec 1997

Volume 71, Issue 26, pp. 3749-3909

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Blueshifting of InGaAsP/InP laser diodes by low-energy ion implantation

M. Paquette, J. Beauvais, J. Beerens, P. J. Poole, S. Charbonneau, C. J. Miner, and C. Blaauw

Appl. Phys. Lett. 71, 3749 (1997); http://dx.doi.org/10.1063/1.120407 (3 pages) | Cited 16 times

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A new method based on low-energy implantation is presented for the fabrication of laser diodes with shifted emission wavelength. The laser diodes are based on InGaAsP/InGaAs/InP material, with compressively strained active layers. Low-energy implantation (18 keV As+) is used to generate vacancies near the surface of an incomplete laser structure, for which the epitaxial growth was interrupted 45 nm above the active layers of the device. The vacancies are subsequently diffused through the quantum wells by rapid thermal annealing. This diffusion causes a local intermixing of atoms at the interfaces of the active layers, which induces an increase of the band gap energy. The implantation/anneal process can be repeated several times to increase the amount of intermixing, thereby further shifting the emission wavelength. Once this process is completed, the upper optical confinement layer of the structure is overgrown using chemical beam epitaxy. Operational lasers with blueshifts as large as 35 nm were obtained. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.35.Fx Diffusion; interface formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.55.Eq III-V semiconductors

Epitaxially stacked lasers with Esaki junctions: A bipolar cascade laser

J. Ch. Garcia, E. Rosencher, Ph. Collot, N. Laurent, J. L. Guyaux, B. Vinter, and J. Nagle

Appl. Phys. Lett. 71, 3752 (1997); http://dx.doi.org/10.1063/1.120408 (3 pages) | Cited 33 times

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We present a two-color (956 and 985 nm) InGaAs/AlGaAs laser structure epitaxially stacked through a low-resistance (10−5–10−4 Ω cm2) Esaki junction, exhibiting two threshold characteristics. It is shown that this structure can be considered as a bipolar cascade laser. © 1997 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
73.40.Gk Tunneling

Decay kinetics and thermoluminescence of PbWO4: La3+

M. Nikl, P. Bohäcek, K. Nitsch, E. Mihoková, M. Martini, A. Vedda, S. Croci, G. P. Pazzi, P. Fabeni, S. Baccaro, B. Borgia, I. Dafinei, M. Diemoz, G. Organtini, E. Auffray, et al.

Appl. Phys. Lett. 71, 3755 (1997); http://dx.doi.org/10.1063/1.120409 (3 pages) | Cited 52 times

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Correlated measurements of emission spectra, photoluminescence and scintillation decays, thermoluminescence, and light yield were performed on a selected set of undoped and La-doped PbWO4 single crystals. The samples were grown from 5N purity raw powders and show the blue emission component only. Distinct influence of La doping was found in the decays, thermoluminescence and light yield characteristics. It is discussed in the light of the direct influence of La doping on suppressing the creation of point defect centers in the PbWO4 lattice, which are involved in the energy transfer and storage processes in this material. © 1997 American Institute of Physics.
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78.60.Kn Thermoluminescence
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

High-performance GaInAsSb thermophotovoltaic devices with an AlGaAsSb window

H. K. Choi, C. A. Wang, G. W. Turner, M. J. Manfra, D. L. Spears, G. W. Charache, L. R. Danielson, and D. M. Depoy

Appl. Phys. Lett. 71, 3758 (1997); http://dx.doi.org/10.1063/1.120497 (3 pages) | Cited 24 times

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A large increase in the quantum efficiency (QE) and open-circuit voltage Voc of GaInAsSb thermophotovoltaic (TPV) devices is obtained by the use of an AlGaAsSb window layer compared with devices without a window layer. The TPV structure, grown on GaSb substrates by organometallic vapor phase epitaxy or molecular beam epitaxy, consists of a 1-μm-thick n-GaInAsSb base layer, a 3-μm-thick p-GaInAsSb emitter layer, a 100-nm-thick AlGaAsSb window layer, and a 25-nm-thick GaSb contacting layer. The band-gap energy of the lattice-matched GaInAsSb is 0.53–0.55 eV. The peak internal QE of the TPV cells with the window is >90%, compared with less than 60% for those without the window. At a short-circuit current density of ∼ 1000 mA/cm2, Voc of ∼ 300 meV is obtained for cells with the window layer, compared with less than 220 meV without the window layer. These increases are attributed to a substantial decrease in the surface recombination velocity with the window layer. Based on a standard calculation, the electron diffusion length in the p-GaInAsSb layer is at least 5 μm. © 1997 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.50.Lw Thermoelectric effects
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Influence of carrier relaxation on the dynamics of stimulated emission in microcavity lasers

M. Hilpert, H. Klann, M. Hofmann, C. Ellmers, M. Oestreich, H. C. Schneider, F. Jahnke, S. W. Koch, W. W. Rühle, H. D. Wolf, D. Bernklau, and H. Riechert

Appl. Phys. Lett. 71, 3761 (1997); http://dx.doi.org/10.1063/1.120498 (3 pages) | Cited 8 times

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The influence of carrier relaxation on the emission dynamics of a semiconductor microcavity laser is investigated using femtosecond optical excitation. For moderate excitation intensities, the dynamics of the output laser pulse becomes significantly slower when the photon energy of the pump laser is tuned from the quantum well band-gap energy towards higher energies. Theoretical calculations reproduce this trend only if the interaction-induced dephasing of the polarization driven by the pump pulse, the formation, and relaxation of the nonequilibrium carrier distribution as well as the chirp of the excitation pulse are taken into account. Additionally, band-structure effects such as excitation of light holes influence the thermalization dynamics and lead to discontinuities in the general trend. © 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
78.47.-p Spectroscopy of solid state dynamics
78.45.+h Stimulated emission

III-V interband 5.2 μm laser operating at 185 K

Michael E. Flatté, T. C. Hasenberg, J. T. Olesberg, S. A. Anson, Thomas F. Boggess, Chi Yan, and D. L. McDaniel

Appl. Phys. Lett. 71, 3764 (1997); http://dx.doi.org/10.1063/1.120499 (3 pages) | Cited 21 times

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We report the operation of a III-V interband laser at a wavelength beyond 5 μm and temperatures above 90 K. The active region consists of a strain compensated broken gap four layer superlattice of InAs/Ga0.6In0.4Sb/InAs/Al0.3Ga0.42In0.28As0.5Sb0.5 grown by molecular beam epitaxy. The maximum operating temperature under 2.01 μm pulsed optical excitation was 185 K at a wavelength of 5.2 μm. The peak pump intensity at the 80 K threshold was 62 kW/cm2, and the characteristic temperature (T0) of the threshold intensity was 37 K. This T0 is comparable to the best observed values for 3–4.5 μm lasers based on the InAs/GaInSb material system. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Observation of wavelength-dependent generation efficiency of laser-induced ultrasonic surface acoustic waves on ceramic materials

C. M. Flannery, P. V. Kelly, J. T. Beechinor, and G. M. Crean

Appl. Phys. Lett. 71, 3767 (1997); http://dx.doi.org/10.1063/1.120500 (3 pages) | Cited 3 times

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In this work, the efficiency of laser generation of surface acoustic waves (SAWs) in ceramic materials is reported to be wavelength dependent. A pulsed Nd:YAG laser operating at wavelengths of 1064 or 532 nm was used to generate SAWs on ceramic (silicon nitride and silicon carbide) and metal substrates. It was observed that 1064 nm radiation is more efficient than 532 nm radiation for SAW generation on ceramics, whereas the opposite is the case for metals. While the wavelength dependence of SAW generation efficiency in metals is due to stronger optical absorption at the shorter wavelength, the dependence for the ceramics is attributed to a longer absorption length at the longer wavelength. © 1997 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
62.65.+k Acoustical properties of solids
43.35.Pt Surface waves in solids and liquids
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Free-standing ZnSe/ZnS quantum wires with high luminescence efficiency

R. Rinaldi, C. Turco, N. Lovergine, R. Cingolani, L. Vasanelli, E. DiFabrizio, L. Grella, M. Gentili, L. DeCaro, and L. Tapfer

Appl. Phys. Lett. 71, 3770 (1997); http://dx.doi.org/10.1063/1.120501 (3 pages) | Cited 3 times

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We have fabricated ZnSe/ZnS quantum wires emitting at the shortest wavelength ever reported for a one-dimensional system. We show that inhomogeneous strain relaxation and Stark effect due to the internal piezoelectric field influence the ground level energy of the wires and overcome the quantum size effect. © 1997 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
42.55.Px Semiconductor lasers; laser diodes
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Imaging the irradiance distribution in the optical near field

J. Aizenberg, J. A. Rogers, K. E. Paul, and G. M. Whitesides

Appl. Phys. Lett. 71, 3773 (1997); http://dx.doi.org/10.1063/1.120502 (3 pages) | Cited 29 times

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This letter describes the use of a sensitive photoresist for direct imaging of optical intensity profiles in near-field photolithographic experiments. A comparison between experimental patterns in exposed, developed photoresist and calculated profiles of intensity shows that this procedure provides a reliable semiquantitative image of the irradiance distribution in the near field; experiment and theory correlate adequately. A potential use of the superficial diffraction contrast recorded in photoresist as the basis for a new method of the fabrication of nanostructures is discussed. © 1997 American Institute of Physics.  
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85.40.Hp Lithography, masks and pattern transfer

Lasing and radiation-mode dynamics in a Van de Graaff accelerator–free-electron laser with an internal cavity

A. Abramovich, A. Arensburg, D. Chairman, A. Eichenbaum, M. Draznin, A. Gover, H. Kleinman, I. Merhasin, Y. Pinhasi, J. S. Sokolowski, Y. M. Yakover, M. Cohen, L. A. Levin, O. Shahal, A. Rosenberg, et al.

Appl. Phys. Lett. 71, 3776 (1997); http://dx.doi.org/10.1063/1.120503 (3 pages) | Cited 3 times

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The lasing of a Van de Graaff electrostatic accelerator–free-electron laser (EA–FEL) with an internal cavity is reported. An EA–FEL employing an internal cavity is a FEL configuration that has a potential to operate at high average power, high frequency, and possibly in a continuous wave (cw) mode. The initial lasing provided a pulsed radiation power of 1 kW at 100.5 GHz frequency. The FEL operated with a 1.4 A, 1.4 MeV electron beam in a recirculation (depressed collector) configuration. It utilizes a high quality (Q ≈ 30 000) Talbot effect resonator and a Halbach-type wiggler placed internally in the center of the accelerator tank. Nonlinear features of the oscillation power buildup and decay near saturation and mode hopping were observed and are interpreted. © 1997 American Institute of Physics.
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41.60.Cr Free-electron lasers
29.20.-c Accelerators
29.27.Fh Beam characteristics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High performance electro-optic polymer waveguide device

Hyang-Mok Lee, Wol-Yon Hwang, Min-Cheol Oh, Heuk Park, Taehyoung Zyung, and Jang-Joo Kim

Appl. Phys. Lett. 71, 3779 (1997); http://dx.doi.org/10.1063/1.120541 (3 pages) | Cited 15 times

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A high performance electro-optic polymer modulator is fabricated by utilizing a thermally curable cladding polymer. Half-wave modulation voltage as low as 3.7 and 4.8 V under 500 Hz operation is obtained with a 1.5 cm long electrode at wavelengths of 1.3 and 1.55 μm, respectively. The modulator also shows stable dc bias voltage to be traceable and low poling-induced optical loss. This work implies that proper selection of a cladding material is as important as the electro-optic materials in the electro-optic waveguide devices. © 1997 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.86.+b Optical workshop techniques

High power KrF laser with a phase-unifying unstable cavity

G. De Nunzio, M. R. Perrone, C. Panzera, D. Flori, A. Piegari, and S. Scaglione

Appl. Phys. Lett. 71, 3782 (1997); http://dx.doi.org/10.1063/1.120504 (3 pages) | Cited 2 times

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The performance of a 0.45 J KrF excimer laser with an unstable cavity using a phase-unifying mirror as an output coupler is described. The output beam having a cross section of 2.4×1.2 cm2 exhibits a smooth far field profile with 86.5% of the total near field energy contained within a far-field full angle θ ⩽ 0.05 mrad. The measurements for determining the beam quality factor M2 and the beam angular stability are also reported. © 1997 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Reflection of surface acoustic waves by localized wetting liquids

M. I. Newton, G. McHale, and M. K. Banerjee

Appl. Phys. Lett. 71, 3785 (1997); http://dx.doi.org/10.1063/1.120505 (2 pages) | Cited 3 times

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Rayleigh wave propagation on unloaded solid surfaces becomes severely damped when the surface is covered by a liquid. Our experimental results show that, when the liquid is localized on the surface, reflections of the wave may occur. Moreover, if the liquid shape dynamically evolves, these reflections display a distinct series of maxima and minima. © 1997 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
68.08.Bc Wetting

Generation of pulse-modulated induction thermal plasma at atmospheric pressure

Takamasa Ishigaki, Xiaobao Fan, Tadahiro Sakuta, Toshiyuki Banjo, and Yukihito Shibuya

Appl. Phys. Lett. 71, 3787 (1997); http://dx.doi.org/10.1063/1.120506 (3 pages) | Cited 34 times

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The radio frequency induction thermal plasma of sufficiently high electric power for materials processing has been successfully generated with a pulsemodulated operating condition. A solid-state amplifier, which supplies the electric power with a nominal frequency of 1 MHz, was employed for the pulsing plasma generation. The Ar–H2 plasma was generated at a high power level of 17 kW at atmospheric pressure. Typically, the plasma remained stable until the pulse duty factor went down to 30%, when the period of the high power level was 5 ms and the low power level was about 6 kW. © 1997 American Institute of Physics.
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52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Some qualitative features of the Couette flow of monodisperse, smooth, inelastic spherical particles

Piroz Zamankhan, Ali Mazouchi, and Pertti Sarkomaa

Appl. Phys. Lett. 71, 3790 (1997); http://dx.doi.org/10.1063/1.120507 (3 pages) | Cited 12 times

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Computer simulations have been performed to examine the occurrence of power-law correlations for the stresses exerted on the confining walls by the particles in the three dimensional Couette flow of hard, smooth, dissipative spherical particles of uniform size. At high particle concentrations, the wavelet analysis of the wall shear stress has revealed the existence of anomalous, long-ranged temporal correlations. Based on the results obtained, there are indications that the dense Couette flow of monodisperse, smooth, inelastic, spherical particles is a system which may be characterized by continuous distributions of the physical measures of its particles, such as size. © 1997 American Institute of Physics.
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47.15.-x Laminar flows
47.11.-j Computational methods in fluid dynamics
47.55.Kf Particle-laden flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
81.05.Rm Porous materials; granular materials

Is ball lightning “Anderson Localization”?: Localized and enhanced fields in a corridor with irregular-shaped metal walls

Kazuo Tanaka and Masahiro Tanaka

Appl. Phys. Lett. 71, 3793 (1997); http://dx.doi.org/10.1063/1.120508 (3 pages) | Cited 4 times

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We propose that “Anderson Localization” is a possible explanation for ball lightning on the basis of computer simulation of electromagnetic wave propagation in a corridor with irregular-shaped metal walls. It was found that the electromagnetic wave could be strongly localized and its strength could be strongly enhanced in small regions in the corridor under specific conditions. Similar effects may create electric fields strong enough to cause electrical breakdown conditions in the open atmosphere, and this phenomenon may be observed as ball lightning. © 1997 American Institute of Physics.
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92.60.Pw Atmospheric electricity, lightning
92.60.Ta Electromagnetic wave propagation
52.80.-s Electric discharges

Quenching of the 750.4 nm argon actinometry line by H2 and several hydrocarbon molecules

A. Francis, U. Czarnetzki, H. F. Döbele, and N. Sadeghi

Appl. Phys. Lett. 71, 3796 (1997); http://dx.doi.org/10.1063/1.120555 (3 pages) | Cited 12 times

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The quenching rate of the 750.4 nm actinometer line in argon by H2 and several hydrocarbons (CH4, C2H2, C2H4, C2H6) has been determined. Argon atoms at room temperature are excited by two-photon excitation at 184 nm to the 4p′[1/2]0 state, and the decay time of the fluorescence emission at 750.4 nm is measured. The quenching rates are inferred from the change of the decay time with the pressure of the quenching gas. For hydrocarbons, the quenching rates are of the order of 10−9 cm3 s−1. The radiative lifetime of the 4p′[1/2]0 is found to be 24 ns. © 1997 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules
07.60.Dq Photometers, radiometers, and colorimeters

Low-temperature, chemically driven atomic-layer epitaxy: In situ monitored growth of CdS/ZnSe(100)

Yi Luo, David Slater, Ming Han, Joseph Moryl, and R. M. Osgood

Appl. Phys. Lett. 71, 3799 (1997); http://dx.doi.org/10.1063/1.120509 (3 pages) | Cited 10 times

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A chemical reaction scheme for room-temperature atomic-layer epitaxial growth of II–VI semiconductors is described and demonstrated. Growth is accomplished by dosing in an ultra-high-vacuum chamber, and the surface structure and composition is probed in situ by a variety of electron and ion probes. © 1997 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)

The effects of oxidation temperature on the capacitance–voltage characteristics of oxidized AlN films on Si

J. Kolodzey, E. A. Chowdhury, G. Qui, J. Olowolafe, C. P. Swann, K. M. Unruh, J. Suehle, R. G. Wilson, and J. M. Zavada

Appl. Phys. Lett. 71, 3802 (1997); http://dx.doi.org/10.1063/1.120510 (3 pages) | Cited 19 times

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The thermal oxidation of AlN thin films produces a high quality insulator which exhibits the gate voltage-controlled charge regimes of accumulation, depletion, and inversion on Si surfaces. The temperature dependence of oxidation is important for device processing. We report on the composition, structure, and electrical properties of the AlN versus the oxidization temperature. AlN layers 500 nm thick were deposited by rf sputtering on p-type Si (100) substrates, followed by oxidation in a furnace at temperatures from 800 to 1100 °C with O2 flow. An oxidation time of 1 h produced layers of Al2O3 with small amounts of N having a thickness of 33 nm at 800 °C, and 524 nm at 1000 °C. Electrical measurements of metal-oxide-semiconductor capacitors indicated that the dielectric constant of the oxidized AlN was near 12. The best layer had a flatband voltage near zero with a net oxide trapped charge density less than 1011 cm−2. These results show that oxidized AlN has device-grade characteristics for the gate regions of field effect transistors, and for optoelectronic applications. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Mq Oxidation
85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)
81.05.Ea III-V semiconductors

Scanning probe nanostructuring of YBa2Cu3O7: A corrosion induced abrasion

J. Boneberg, M. Böhmisch, M. Ochmann, and P. Leiderer

Appl. Phys. Lett. 71, 3805 (1997); http://dx.doi.org/10.1063/1.120511 (3 pages) | Cited 11 times

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Nanostructuring experiments were performed on a YBa2Cu3O7 thin film surface with an atomic force microscope (AFM) with a conductive tip. Measurements of the local conductivity with the AFM tip show that corrosion towards a nonconducting surface occurs on a timescale of hours under ambient conditions. The corroded surface can easily be abraded, whereas the clean YBa2Cu3O7 surface is comparably resistive against mechanical forces. The corrosion is promoted by an electric current at positive sample bias. Thus it can be concluded that the nanostructuring process performed in former experiments with the scanning tunneling microscope consists of two steps: corrosion and succeeding abrasion. © 1997 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
74.72.-h Cuprate superconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
73.25.+i Surface conductivity and carrier phenomena

Bulk metallic glass matrix composites

H. Choi-Yim and W. L. Johnson

Appl. Phys. Lett. 71, 3808 (1997); http://dx.doi.org/10.1063/1.120512 (3 pages) | Cited 175 times

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Composites with a bulk metallic glass matrix were synthesized and characterized. This was made possible by the recent development of bulk metallic glasses that exhibit high resistance to crystallization in the undercooled liquid state. In this letter, experimental methods for processing metallic glass composites are introduced. Three different bulk metallic glass forming alloys were used as the matrix materials. Both ceramics and metals were introduced as reinforcement into the metallic glass. The metallic glass matrix remained amorphous after adding up to a 30 vol% fraction of particles or short wires. X-ray diffraction patterns of the composites show only peaks from the second phase particles superimposed on the broad diffuse maxima from the amorphous phase. Optical micrographs reveal uniformly distributed particles in the matrix. The glass transition of the amorphous matrix and the crystallization behavior of the composites were studied by calorimetric methods. © 1997 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.05.Pj Glass-based composites, vitroceramics
64.70.K- Solid-solid transitions
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Quenching with rapid decompression—a new method for rapid solidification

D. W. He, F. X. Zhang, M. Zhang, R. P. Liu, Z. C. Qin, Y. F. Xu, and W. K. Wang

Appl. Phys. Lett. 71, 3811 (1997); http://dx.doi.org/10.1063/1.120542 (3 pages) | Cited 10 times

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We report that a rapid drop of pressure applied to a melt whose crystallization point is a decreasing function of the pressure may, if the temperature, the initial pressure, and the final pressure are appropriately chosen, be equivalent to a rapid thermal quenching. In particular, it may lead to the formation of metastable crystalline or glassy phases bulk materials. The method might be useful to simulate adiabatic decompressions subsequent to shocks such as meteorite impacts. The relation between the undercooling rate (νc) obtained by rapid decompression and the rate of pressure release (νp) is given by νc = kνp, where k is the drop rate of the melting point with pressure. This method is evaluated for the Al–Ge system. The solidification products are either stable or metastable crystalline compounds, depending on the rate at which the pressure is released. Our experimental results indicate that quenching with rapid decompression is an effective method to generate high undercooling rates exceeding 105 Ks−1. © 1997 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
81.30.Fb Solidification
81.05.Kf Glasses (including metallic glasses)
81.10.Fq Growth from melts; zone melting and refining

The influence of atomic nitrogen flux on the composition of carbon nitride thin films

P. Mérel, M. Chaker, M. Tabbal, and M. Moisan

Appl. Phys. Lett. 71, 3814 (1997); http://dx.doi.org/10.1063/1.120513 (3 pages) | Cited 16 times

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Carbon nitride (CNx) thin films have been deposited using a hybrid system combining pulsed laser deposition of graphite with the surface-wave discharge atomic nitrogen source (3% N2 in Ar). Using this system, an experiment is designed to study the influence of the atomic nitrogen flux on the composition of the CNx thin films at various laser intensities. The nitrogen percentage in the thin films is positively correlated with the N atom flux impinging on the substrate surface but it is counter-productive to use excessively high values of laser intensities on the graphite target. For a laser intensity of 6×108 W/cm2, the nitrogen percentage increases with the N atom flux and saturates at only about 16 at. %. On the other hand, a maximum nitrogen percentage of 30 at. % is obtained at the much lower laser intensity of 5×107 W/cm2. © 1997 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Fg Pulsed laser ablation deposition
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.66.Bi Elemental solids
61.66.Dk Alloys

Piezoresistive effect in GaN–AlN–GaN structures

R. Gaska, J. W. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminskii, and S. Soloviov

Appl. Phys. Lett. 71, 3817 (1997); http://dx.doi.org/10.1063/1.120514 (3 pages)

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We report on a high sensitivity of GaN–AlN–GaN semiconductor–insulator–semiconductor structures grown on sapphire to an applied strain. The measured static gauge factor (GF) is almost twice as large as the GF for n-type SiC films. We link the observed magnitude and sign of the gauge factor to the crystalline structure of the GaN and AlN films and to their piezoelectric constants. We show that even higher sensitivity can be achieved if the material and interface quality is improved. © 1997 American Institute of Physics.
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73.40.Ty Semiconductor-insulator-semiconductor structures
72.20.Fr Low-field transport and mobility; piezoresistance

Thick stress-free amorphous-tetrahedral carbon films with hardness near that of diamond

T. A. Friedmann, J. P. Sullivan, J. A. Knapp, D. R. Tallant, D. M. Follstaedt, D. L. Medlin, and P. B. Mirkarimi

Appl. Phys. Lett. 71, 3820 (1997); http://dx.doi.org/10.1063/1.120515 (3 pages) | Cited 50 times

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We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon (a-tC) films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thin a-tC films (0.1–0.2 μm) were deposited at room temperature. The intrinsic stress in these films (6–8 GPa) was relieved by a short (2 min) anneal at 600 °C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 μm thick have been grown that are adherent to the substrate and have low residual compressive stress (<0.2 GPa). The values of hardness and modulus determined directly from an Oliver–Pharr analysis of nanoindentation experimental data were 80.2 and 552 GPa, respectively. We used finite-element modeling of the experimental nanoindentation curves to separate the “intrinsic” film response from the measured substrate/film response. We found a hardness of 88 GPa and Young’s modulus of 1100 GPa. From these fits, a lower bound on the compressive yield stress of diamond ( ∼ 100 GPa) was determined. © 1997 American Institute of Physics.
Show PACS
68.60.Bs Mechanical and acoustical properties
81.15.Fg Pulsed laser ablation deposition
61.43.Er Other amorphous solids
78.66.Db Elemental semiconductors and insulators
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
79.20.Kz Other electron-impact emission phenomena
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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