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6 Aug 2001

Volume 79, Issue 6, pp. 705-888

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Picosecond superconducting single-photon optical detector

G. N. Gol’tsman, O. Okunev, G. Chulkova, A. Lipatov, A. Semenov, K. Smirnov, B. Voronov, A. Dzardanov, C. Williams, and Roman Sobolewski

Appl. Phys. Lett. 79, 705 (2001); http://dx.doi.org/10.1063/1.1388868 (3 pages) | Cited 250 times

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We experimentally demonstrate a supercurrent-assisted, hotspot-formation mechanism for ultrafast detection and counting of visible and infrared photons. A photon-induced hotspot leads to a temporary formation of a resistive barrier across the superconducting sensor strip and results in an easily measurable voltage pulse. Subsequent hotspot healing in ∼30 ps time frame, restores the superconductivity (zero-voltage state), and the detector is ready to register another photon. Our device consists of an ultrathin, very narrow NbN strip, maintained at 4.2 K and current-biased close to the critical current. It exhibits an experimentally measured quantum efficiency of ∼20% for 0.81 μm wavelength photons and negligible dark counts. © 2001 American Institute of Physics.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
06.60.Jn High-speed techniques (microsecond to femtosecond)
74.25.Gz Optical properties

Absorption bleaching of squarylium dye J aggregates via a two-photon excitation process

Makoto Furuki, Minquan Tian, Yasuhiro Sato, Lyong Sun Pu, Satoshi Tatsuura, and Shuji Abe

Appl. Phys. Lett. 79, 708 (2001); http://dx.doi.org/10.1063/1.1390322 (3 pages) | Cited 6 times

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Squarylium dye J aggregates exhibit ultrafast nonlinear optical response of absorption saturation at the resonant wavelength of 770 nm. We studied the two-photon excitation process of J aggregates. By fluorescence measurement, we found the two-photon absorption band at 1.3 μm, which was different from that of the dye solution at 1.2 μm. Absorption saturation at 770 nm via a two-photon excitation process was observed by two-photon resonant excitation at 1.3 μm and also by off-resonant excitation at 1.55 μm, suggesting the possibility of J aggregates for optical switching materials working at the wavelength used in optical communications. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.55.Bq Liquids
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Efficient and high-power AlGaN-based ultraviolet light-emitting diode grown on bulk GaN

Toshio Nishida, Hisao Saito, and Naoki Kobayashi

Appl. Phys. Lett. 79, 711 (2001); http://dx.doi.org/10.1063/1.1390485 (2 pages) | Cited 117 times

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By introducing thick bulk GaN as a substrate, we improved the performance of an AlGaN-based ultraviolet (UV) light-emitting diode (LED). The output power exceeds 3 mW at the injection current of 100 mA under a bare-chip geometry. Internal quantum efficiency is estimated as more than 80%, and the peak wavelength is 352 nm. The maximum power exceeds 10 mW at a large current injection of 400 mA, with an operation voltage of less than 6 V. These results indicate that an efficient UV LED is intrinsically possible by the combination of appropriate device design and the nitride substrate. By introducing packaging technology to enhance extraction efficiency, we will have a compact and efficient UV light source in the wide wavelength range of 200–360 nm, similar to conventional longer-wavelength LEDs. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors

Mechanism of terahertz lasing in SiGe/Si quantum wells

A. Blom, M. A. Odnoblyudov, H. H. Cheng, I. N. Yassievich, and K. A. Chao

Appl. Phys. Lett. 79, 713 (2001); http://dx.doi.org/10.1063/1.1389769 (3 pages) | Cited 15 times

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Intense terahertz (THz) stimulated emission from boron-doped SiGe/Si quantum well structures with internal strain has been observed recently. We present a theoretical calculation which shows the formation of resonant states, and explains the origin of the observed temperature dependence of the dc conductivity under low bias voltage. Thus, the mechanism of THz lasing is population inversion of the resonant state with respect to the localized impurity states. This is the same mechanism of lasing as in uniaxially stressed p-Ge THz lasers. © 2001 American Institute of Physics.
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78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.61.Le Other inorganic semiconductors
73.61.Cw Elemental semiconductors

Highly efficient mirrorless laser-like emission in an organic molecular salt

Achintya K. Bhowmik, Aditya Dharmadhikari, and Mrinal Thakur

Appl. Phys. Lett. 79, 716 (2001); http://dx.doi.org/10.1063/1.1388870 (3 pages) | Cited 5 times

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Unusually high conversion efficiency in laser-like emission has been observed in solutions of an organic molecular salt, styrylpyridinium cyanine dye, at a low threshold input pulse energy. Pumped with frequency-doubled 55 ps pulses from a Nd:YAG laser, a conversion efficiency as high as 40% was achieved without incorporating external mirrors. The spectrally narrowed output beam was observed to be polarized and having a low divergence. The exceptionally low threshold (<1 μJ with excitation area ∼5 mm2) and high conversion efficiency at a high molar concentration in spite of a very small photoluminescence quantum efficiency (<0.3%) can be attributed to the large dipole moments associated with the charge-transfer transitions of these molecules favoring strong cooperative emission. © 2001 American Institute of Physics.
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42.70.Hj Laser materials
42.55.Mv Dye lasers
78.55.Bq Liquids
42.70.Jk Polymers and organics

Optimum Er concentration for in situ doped GaN visible and infrared luminescence

D. S. Lee, J. Heikenfeld, A. J. Steckl, U. Hommerich, J. T. Seo, A. Braud, and J. Zavada

Appl. Phys. Lett. 79, 719 (2001); http://dx.doi.org/10.1063/1.1390480 (3 pages) | Cited 19 times

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GaN thin films have been doped with varying Er concentrations (0.01–10 at. %) during molecular-beam-epitaxy growth. As expected, the visible and infrared (IR) emissions, from photoluminescence (PL) and electroluminescence (EL), are a strong function of Er concentration. We report on the determination of an optimum Er doping level for PL and EL intensity. Secondary ion mass spectroscopy and Rutherford backscattering measurements showed that the Er concentration in GaN increased exponentially with Er cell temperature. PL and EL intensity of green emission at 537 and 558 nm, due to Er 4f–4f inner shell transitions, exhibited a maximum at ∼1 at. % Er. IR PL intensity at 1.54 μm, due to another Er transition, revealed the same maximum for ∼1 at. % Er concentration. PL lifetime measurements at 537 nm showed that samples with Er concentration <1 at. % had a lifetime of ∼5 μs. For Er concentration ⩾1 at. %, the lifetime decreased rapidly to values below 1 μs. This concentration quenching is believed to be due to a combination of Er cross relaxation and energy transfer to GaN defects, eventually followed by precipitation. This conclusion is supported by x-ray diffraction measurements. As a result, we have determined that the optimum Er doping concentration into GaN is ∼1 at. %. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.S- Impurities in crystals
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Temperature-dependent measurement of Auger recombination in self-organized In0.4Ga0.6As/GaAs quantum dots

S. Ghosh, P. Bhattacharya, E. Stoner, J. Singh, H. Jiang, S. Nuttinck, and J. Laskar

Appl. Phys. Lett. 79, 722 (2001); http://dx.doi.org/10.1063/1.1391401 (3 pages) | Cited 31 times

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We report experimental studies of temperature-dependent Auger recombination coefficients in self-assembled quantum dots. The results are based on a study of temperature-dependent large signal modulation experiments made on self-organized In0.4Ga0.6As/GaAs quantum dot lasers. The Auger coefficient decreases from ∼ 8×10−29 cm6/s at 100 K to ∼ 4×10−29 cm6/s at 300 K. This behavior, which is different from results in other higher-dimensional systems, is explained in terms of the temperature dependence of electron-hole scattering in the dots and contribution from higher lying states in the dot and adjoining layers. © 2001 American Institute of Physics.
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73.63.Kv Quantum dots
73.21.La Quantum dots
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Femtosecond laser interference technique with diffractive beam splitter for fabrication of three-dimensional photonic crystals

Toshiaki Kondo, Shigeki Matsuo, Saulius Juodkazis, and Hiroaki Misawa

Appl. Phys. Lett. 79, 725 (2001); http://dx.doi.org/10.1063/1.1391232 (3 pages) | Cited 106 times

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A simple optical interference method to fabricate microperiodic structures was demonstrated. Femtosecond laser pulse was split by a diffractive beam splitter and overlapped with two lenses. Temporal overlap of the split femtosecond pulses, which requires 10 μm order accuracy in optical path lengths, was automatically achieved by this optical setup. One-, two-, and three-dimensional periodic microstructures with micrometer-order periods were fabricated using this method. © 2001 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials
42.79.Fm Reflectors, beam splitters, and deflectors
42.25.Hz Interference
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Aperiodic optical superlattices engineered for optical frequency conversion

H. Liu, Y. Y. Zhu, S. N. Zhu, C. Zhang, and N. B. Ming

Appl. Phys. Lett. 79, 728 (2001); http://dx.doi.org/10.1063/1.1381569 (3 pages) | Cited 19 times

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An aperiodic optical superlattice is designed. The designing method is universal and can be applied to all frequency conversion processes by using the coupling of quasiphase matching, without any limitations to special materials and to given fundamental wavelengths. © 2001 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Wc Optical coatings
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.15.Eq Optical system design

Emission in a SnS2 inverted opaline photonic crystal

S. G. Romanov, T. Maka, C. M. Sotomayor Torres, M. Müller, and R. Zentel

Appl. Phys. Lett. 79, 731 (2001); http://dx.doi.org/10.1063/1.1389825 (3 pages) | Cited 26 times

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The photoluminescence of a dye embedded in the three-dimensional SnS2 inverted opal has been studied. Changes of the emission spectrum compared with the free-space dye emission was observed in the stop-band frequency range in accord with reflectance/transmission spectra of this photonic crystal. The angular-dependent component, due to the Bragg stop band, and the angular-independent component, which is, possibly, related to the minimum in the density of photon states, have been distinguished in the dye emission spectrum. © 2001 American Institute of Physics.
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78.55.-m Photoluminescence, properties and materials
42.70.Qs Photonic bandgap materials
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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Photoinduced optical absorption in Ca3Ga2Ge3O12:Mn garnet

V. V. Eremenko, S. L. Gnatchenko, I. S. Kachur, V. G. Piryatinskaya, M. B. Kosmyna, B. P. Nazarenko, and V. M. Puzikov

Appl. Phys. Lett. 79, 734 (2001); http://dx.doi.org/10.1063/1.1390489 (3 pages) | Cited 5 times

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Persistent photoinduced changes of optical absorption have been found in garnet Ca3Ga2Ge3O12 doped with manganese. Irradiation by a He–Ne laser of 633 nm wavelength results in a noticeable increase in the absorption coefficient of the crystal. The photoinduced changes are observed up to room temperature as distinct from concentrated manganese garnets in which the photoinduced absorption vanishes at much lower temperatures. The wide temperature range of the existence of the photoinduced effect together with a high transparency of the crystal makes it a promising material for optical recording. © 2001 American Institute of Physics.
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75.50.Gg Ferrimagnetics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics

Ellipsometric study of sinusoidally modulated ZnSeTe superlattices

Hosun Lee, S. Lee, and J. K. Furdyna

Appl. Phys. Lett. 79, 737 (2001); http://dx.doi.org/10.1063/1.1391235 (3 pages) | Cited 1 time

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We report an optical study of sinusoidally modulated ZnSeTe superlattices using spectroscopic ellipsometry. The pseudodielectric function 〈ϵ〉 = 〈ϵ1〉+i〈ϵ2〉 was determined for the photon energy range 1.5–6.5 eV and critical point parameters were obtained by fitting model line shapes to numerically calculated second energy derivatives of 〈ϵ〉. As the degree of the compositional modulation of the superlattice increased, the energies of E1−R1 and E1+Δ1−R1 either decreased or increased depending on the superlattice period. We explain this behavior in terms of an interlayer coupling and quantum-confinement effect characteristic, respectively, for the two geometries. © 2001 American Institute of Physics.
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68.65.Cd Superlattices
73.21.Cd Superlattices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Luminescent characteristics of blue-emitting Sr2B5O9Cl: Eu thin-film phosphors

Jianhua Hao and Michael Cocivera

Appl. Phys. Lett. 79, 740 (2001); http://dx.doi.org/10.1063/1.1391410 (3 pages) | Cited 25 times

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Thin films of Sr2B5O9Cl: Eu were deposited on glass plates using spray pyrolysis of aqueous solutions. Films exhibited blue cathodoluminescence and photoluminescence, indicating the films contained Eu2+ rather than Eu3+. A luminance of 76 cd/m2 at 5 kV was obtained for annealed films on glass substrates. The chromaticity coordinates were x = 0.162 and y = 0.035 with a dominant wavelength of 450 nm and a 95% color purity. © 2001 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
85.45.Fd Field emission displays (FEDs)
81.15.Rs Spray coating techniques

Evidence of eutectic crystallization and transient nucleation in Al89La6Ni5 amorphous alloy

Y. X. Zhuang, J. Z. Jiang, Z. G. Lin, M. Mezouar, W. Crichton, and A. Inoue

Appl. Phys. Lett. 79, 743 (2001); http://dx.doi.org/10.1063/1.1389506 (3 pages) | Cited 14 times

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The phase evolution with the temperature and time in the process of crystallization of Al89La6Ni5 amorphous alloy has been investigated by in situ high-temperature and high-pressure x-ray powder diffraction using synchrotron radiation. Two crystalline phases, fcc-Al and a metastable bcc-(AlNi)11La3-like phase, were identified after the first crystallization reaction, revealing a eutectic reaction instead of a primary reaction suggested in the literature. Time-dependent nucleation in the amorphous alloy is detected and the experimental data can be fitted by both the Zeldovich’s and Kashchiev’s transient nucleation models with transient nucleation times of 220 and 120 min, respectively. © 2001 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
62.50.-p High-pressure effects in solids and liquids

Role of adsorption kinetics in the low-temperature Si growth by gas-source molecular beam epitaxy: In situ observations and detailed modeling of the growth

Takeshi Murata, Hideki Nakazawa, Yoshikazu Tsukidate, and Maki Suemitsu

Appl. Phys. Lett. 79, 746 (2001); http://dx.doi.org/10.1063/1.1389768 (3 pages) | Cited 2 times

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The growth rate and surface hydrogen coverage during Si gas-source molecular beam epitaxy using disilane have been obtained as functions of both the growth temperature and the source-gas pressure. The activation energy of the low-temperature (<600 °C) growth rate was found to increase with the source-gas pressure, indicating a contribution by the adsorption process in these low-temperature growth kinetics. Several growth models have been constructed based on the results, among which the two-site/four-site-adsorption model [M. Suemitsu et al., Jpn. J. Appl. Phys., Part 2 36, L625 (1997)] showed the best fit to both the growth rate and the hydrogen coverage. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Mn Adsorption kinetics

White microbeam diffraction from distorted crystals

R. Barabash, G. E. Ice, B. C. Larson, G. M. Pharr, K.-S. Chung, and W. Yang

Appl. Phys. Lett. 79, 749 (2001); http://dx.doi.org/10.1063/1.1389321 (3 pages) | Cited 45 times

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We present a general description of white-beam (Laue) scattering from grains with dislocations. This approach is applied to examples with equal numbers of positive and negative Burger’s vectors (paired) and with unpaired dislocations of one sign (geometrically necessary). We find that streaking of the Laue reflections is sensitive to both long-range geometrical rotations introduced by unpaired edge dislocations and to local rotation fluctuations introduced by the total number of dislocations (paired and unpaired). We demonstrate the technique by analyzing the dislocation distribution in a nanoindented Cu single crystal. © 2001 American Institute of Physics.
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61.05.cc Theories of x-ray diffraction and scattering
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Effect of hydrogenation on Al-related photoluminescence in 6H–SiC

Yaroslav Koshka and Michael S. Mazzola

Appl. Phys. Lett. 79, 752 (2001); http://dx.doi.org/10.1063/1.1391403 (3 pages) | Cited 9 times

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Interaction of hydrogen with Al acceptors in SiC is investigated using low-temperature photoluminescence (PL) spectroscopy. Hydrogenation is performed in hydrogen plasma using a standard inductively coupled plasma etching system. Appearance of H-related PL peaks after hydrogenation is accompanied with a significant reduction in relative intensity of Al bound exciton (Al–BE) PL. A gradual quenching of the remaining Al–BE photoluminescence is observed in hydrogenated samples under excitation with above band gap light, resulting in a complete disappearance of Al–BE PL emission. High-temperature annealing completely restores the shape of the PL spectrum to its prehydrogenation form. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.05.Hd Other semiconductors

Low-temperature formation of an interfacial buffer layer using monomethylsilane for 3C–SiC/Si(100) heteroepitaxy

Hideki Nakazawa and Maki Suemitsu

Appl. Phys. Lett. 79, 755 (2001); http://dx.doi.org/10.1063/1.1390476 (3 pages) | Cited 16 times

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By using monomethylsilane (MMS:H3Si–CH3), we have formed a Si1−xCx interfacial buffer layer for 3C–SiC/Si(100) heteroepitaxy at substrate temperature Tf of as low as 450–650 °C, which is compared to the conventional carbonization temperature of 900 °C or higher. The buffer layer allows the subsequent growth of high-quality single-crystalline 3C–SiC films at 900 °C without formation of voids in the Si substrate at the interface. The grown 3C–SiC films degrade for Tf<450 or >650 °C. The low processing temperature as well as the suppressed Si outdiffusion can be related to the inclusion of both Si–H and Si–C bonds within the MMS molecule. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
68.35.Ct Interface structure and roughness

Change in electrical resistivity due to icosahedral phase precipitation in Zr70Pd20Ni10 and Zr65Al7.5Cu7.5Ni10Ag10 glasses

O. Haruyama, T. Miyazawa, J. Saida, and A. Inoue

Appl. Phys. Lett. 79, 758 (2001); http://dx.doi.org/10.1063/1.1394164 (3 pages) | Cited 5 times

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The glass-to-icosahedral phase transformation in Zr70Pd20Ni10 and Zr65Al7.5Cu7.5Ni10Ag10 glasses was examined by the electrical resistivity measurement performed with a heating rate of 0.67 K/s. The resistivity increased with the promotion of icosahedral precipitation in Zr70Pd20Ni10 glass. On the other hand, Zr65Al7.5Cu7.5Ni10Ag10 glass exhibited the decrement of the resistivity according to the evolution of icosahedral phase. The latter was qualitatively explained by the drop of the resistivity of supercooled liquid phase due to the transfer of oxide atoms into the icosahedral phase. Also, the low temperature resistivity experiment showed that the conductivity of glassy and icosahedral phases might obey the weak localization model of conduction electrons. © 2001 American Institute of Physics.
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61.44.Br Quasicrystals
61.43.Fs Glasses
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
64.75.-g Phase equilibria
71.55.Jv Disordered structures; amorphous and glassy solids
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Spatial variation of electrical properties in lateral epitaxially overgrown GaN

J. W. P. Hsu, M. J. Matthews, D. Abusch-Magder, R. N. Kleiman, D. V. Lang, S. Richter, S. L. Gu, and T. F. Kuech

Appl. Phys. Lett. 79, 761 (2001); http://dx.doi.org/10.1063/1.1388877 (3 pages) | Cited 11 times

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Using confocal Raman and scanning probe microscopies, we show that the electrical properties of lateral epitaxial overgrown GaN films vary at the submicron scale. Wing regions, which are located directly above the SiOx stripes, contain carrier densities ∼ 1020 cm−3, but possess a Fermi level deep in the band gap. This cannot be explained by having a high density of free electrons in the conduction band, but is consistent with high levels of compensation and impurity band transport. In the coalescence region, stripes of different electrical properties are evident, indicating the incorporation of impurities and defects being dictated by the growth dynamics. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
71.20.Nr Semiconductor compounds

Femtosecond response time in beryllium-doped low-temperature-grown GaAs/AlAs multiple quantum wells

Tsuyoshi Okuno, Yasuaki Masumoto, Yasushi Sakuma, Yuuichi Hayasaki, and Hiroshi Okamoto

Appl. Phys. Lett. 79, 764 (2001); http://dx.doi.org/10.1063/1.1390478 (3 pages) | Cited 8 times

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We have investigated optical nonlinearity in beryllium-doped low-temperature (LT) molecular-beam-epitaxy-grown GaAs/AlAs multiple quantum wells (MQWs). The response time of the nonlinearity is reduced by Be doping in the MQW. While the undoped LT MQW shows a 0.7–0.9 ps response, the response time of the Be-doped LT MQW is as short as 0.25 ps. The saturation density of the Be-doped MQW is almost the same as that of the undoped MQW, and is smaller than that of bulk GaAs. These results demonstrate that the Be-doped LT MQW exhibits a faster response than the undoped LT MQW, and a faster response as well as larger nonlinearity than LT bulk GaAs. © 2001 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Si/6H–SiC(0001): An unexpected cubic 4×3 Si phase overlayer

F. Amy, H. Enriquez, P. Soukiassian, C. Brylinski, A. Mayne, and G. Dujardin

Appl. Phys. Lett. 79, 767 (2001); http://dx.doi.org/10.1063/1.1389510 (3 pages) | Cited 9 times

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We investigate Si deposition on the 6H–SiC(0001) 3×3 surface reconstruction by atom-resolved scanning tunneling microscopy. Upon thermal annealing, the Si thin film forms an unexpected structure having dimer rows in a cubic 4×3 surface array. Such a 4×3 Si phase has a very open surface very likely being at the origin of the exceptionally high reactivity to oxygen of the Si/6H–SiC(0001) system. These findings are relevant in silicon carbide oxidation. © 2001 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing

Ultrafast impulsive excitation of coherent longitudinal acoustic phonon oscillations in highly photoexcited InSb

M. D. Cummings and A. Y. Elezzabi

Appl. Phys. Lett. 79, 770 (2001); http://dx.doi.org/10.1063/1.1389836 (3 pages) | Cited 8 times

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We report on the direct time-resolved measurement of high-frequency coherent longitudinal acoustic (LA) phonon oscillations in InSb. Two LA-phonon modes are impulsively generated in a highly photoexcited InSb sample and detected through reflectivity modulation with a temporal resolution of 15 fs. The measured frequencies, νLA(L1) = 4.34 THz and νLA(X3) = 3.75 THz, are in excellent agreement with those obtained through time-independent techniques. A frequency redshift in the LA(L1)-phonon frequency, as the energy fluence is increased beyond 10% of the damage threshold fluence, is attributed to an anisotropic impulsive softening of the InSb lattice. © 2001 American Institute of Physics.
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63.20.K- Phonon interactions
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors

Ultrasensitive Si phototransistors with a punchthrough base

Hailin Luo, Yuchun Chang, K. S. Wong, and Y. Wang

Appl. Phys. Lett. 79, 773 (2001); http://dx.doi.org/10.1063/1.1390477 (3 pages) | Cited 2 times

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Si phototransistors with a punchthrough base were fabricated with regular planar technology. Optical conversion gains larger than 15 000 were observed. In addition to very high gain, the unique structure of the device also resulted in a fast transient response as well as low output noise. The measured full width at half maximum of the device transient response is 1.6 ns and a −3 dB bandwidth of 300 MHz. The measured output noises at different currents can be well fitted by the relation math = 2qIC. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Oxygen exchange kinetics on a highly oriented La0.5Sr0.5CoO3−δ thin film prepared by pulsed-laser deposition

Yuemei L. Yang, A. J. Jacobson, C. L. Chen, G. P. Luo, K. D. Ross, and C. W. Chu

Appl. Phys. Lett. 79, 776 (2001); http://dx.doi.org/10.1063/1.1390316 (3 pages) | Cited 32 times

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Oxygen exchange at a highly oriented La0.5Sr0.5CoO3−δ thin film prepared on (100) surfaces of an yttria-stabilized zirconia single crystal by pulsed-laser deposition was studied with ac impedance spectroscopy under various temperatures and oxygen partial pressures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the electrolyte, oxide ion transfer across the electrode/electrolyte interface, and the oxygen exchange on the film surface. An equivalent circuit model was proposed to analyze the impedance results, from which the surface chemical exchange coefficients, kchem, were derived as a function of temperature and oxygen partial pressure. © 2001 American Institute of Physics.
Show PACS
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
66.30.H- Self-diffusion and ionic conduction in nonmetals
81.15.Fg Pulsed laser ablation deposition
82.45.Mp Thin layers, films, monolayers, membranes
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