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6 Mar 2000

Volume 76, Issue 10, pp. 1219-1345

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1.6 W continuous-wave coherent power from large-index-step (Δn ≈ 0.1) near-resonant, antiguided diode laser arrays

H. Yang, L. J. Mawst, and D. Botez

Appl. Phys. Lett. 76, 1219 (2000); http://dx.doi.org/10.1063/1.125990 (3 pages) | Cited 11 times

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Near-diffraction-limited-beam continuous-wave (cw) operation has been achieved to high powers from antiguided arrays with a large effective-index step between element and interelement regions. InGaAs/InGa(As)P/GaAs 40-element arrays (λ = 0.985 μm) emit in beams 2×diffraction-limit (0.67°) at 1.6 W and 9×threshold in cw operation. 1 W of the coherent cw power resides in the central lobe. The external differential quantum efficiency and the threshold current are 40% and 0.4 A, respectively, for 1-mm-long devices of 191 μm emitting aperture. The overall electrical to optical power conversion efficiency at 1.6 W output power is 23%. Modeling of the thermal effects in cw operation on the array modes reveals that for high-index-step (∼0.1) near-resonant antiguided arrays thermal lensing hardly affects high-order modes, and as a consequence, 2×diffraction-limited beams can be maintained to watt-range cw powers. © 2000 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Dynamic response of 1.3-μm-wavelength InGaAs/GaAs quantum dots

L. Zhang, Thomas F. Boggess, D. G. Deppe, D. L. Huffaker, O. B. Shchekin, and C. Cao

Appl. Phys. Lett. 76, 1222 (2000); http://dx.doi.org/10.1063/1.125991 (3 pages) | Cited 40 times

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The temperature-dependent dynamic response of 1.3-μm-InGaAs/GaAs quantum dots is investigated using time-resolved photoluminescence upconversion with subpicosecond temporal resolution for excitation in either the GaAs bulk region surrounding the dots or within the wetting layer. Relaxation to the quantum-dot ground state occurs on a time scale as short as 1 ps, while radiative lifetimes as short as 400 ps are measured. The influence of nonradiative recombination is observed only for temperatures above 250 K. At temperatures below 77 K, an increase in the relaxation time and lifetime is observed when carriers are injected into the bulk GaAs region versus excitation into the wetting layer, which suggests that diffusion in the bulk GaAs region influences both the relaxation rate and the recombination rate. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics

Continuous wave simultaneous multi-self-frequency conversion in Nd3+-doped aperiodically poled bulk lithium niobate

J. Capmany, V. Bermúdez, D. Callejo, J. García Solé, and E. Diéguez

Appl. Phys. Lett. 76, 1225 (2000); http://dx.doi.org/10.1063/1.125897 (3 pages) | Cited 11 times

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We report simultaneous participation of the fundamental laser wave in self-frequency doubling and self-sum-frequency mixing with pump radiation in Nd3+-doped bulk aperiodically poled lithium niobate structures. A green continuous wave visible laser output power of 1.5 mW generated by self-frequency doubling and 0.5 mW of blue generated by self-sum-frequency mixing have been obtained simultaneously from 30 mW of laser output power available in the fundamental. Stable and efficient infrared laser action at room temperature is obtained in both 4F3/2→4I11/2 and 4F3/2→4I13/2 laser channels of Nd3+ ion without oxide codoping, although some residual photorefractive damage for the visible outputs is observed. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.By Design of specific laser systems

Photoinduced layer alignment control in ferroelectric liquid crystal with N∗–C∗ phase transition doped with photochromic dye

Tatsunosuke Matsui, Keizo Nakayama, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 76, 1228 (2000); http://dx.doi.org/10.1063/1.125992 (3 pages) | Cited 7 times

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Photoinduced layer alignment control has been proposed in an azo-dye-doped ferroelectric liquid crystal with a chiral nematic (N∗)–chiral smectic C (SmC∗) phase sequence. This layer alignment control is based on the N∗–SmC∗ phase transition induced by the photoisomerization of the azo-dye. Trans-cis photoisomerization of the azo-dye upon UV irradiation in the SmC∗ phase induces the N∗ phase, and an opposite isomerization process upon sequentially stopping the UV irradiation induces the SmC∗ phase again. The photoinduced SmC∗–N∗–SmC∗ phase transition under an appropriate electric field allows us to control the smectic layer alignment. This photoassisted layer switching can be applied to the fabrication of the designed multidomain structure in electro-optic elements such as display, optical memory, and optical grating. © 2000 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
82.30.Qt Isomerization and rearrangement
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
78.20.Jq Electro-optical effects

Efficient high-speed near-infrared Ge photodetectors integrated on Si substrates

L. Colace, G. Masini, G. Assanto, Hsin-Chiao Luan, K. Wada, and L. C. Kimerling

Appl. Phys. Lett. 76, 1231 (2000); http://dx.doi.org/10.1063/1.125993 (3 pages) | Cited 68 times

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We have fabricated Ge/Si heterojunction photodetectors with high responsivities of 550 mA/W at 1.32 μm and 250 mA/W at 1.55 μm and time responses shorter than 850 ps. High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition followed by cyclic thermal annealing. The beneficial effect of the post-growth thermal annealing on the electrical properties of Ge epilayers, due to the reduction of threading-dislocation densities, is confirmed by the dramatic enhancement of the performance of the photodetectors. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm

J. Alnis, U. Gustafsson, G. Somesfalean, and S. Svanberg

Appl. Phys. Lett. 76, 1234 (2000); http://dx.doi.org/10.1063/1.125994 (3 pages) | Cited 16 times

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Blue diode lasers emitting 5 mW continuous-wave power around 400 nm have recently become available. We report on the use of a blue diode laser together with a 30 mW red diode laser for sum-frequency generation around 254 nm. The ultraviolet power is estimated to be 0.9 nW, and 35 GHz mode-hop-free tuning range is achieved. This is enough to perform high-resolution ultraviolet spectroscopy of mercury isotopes. The possibility to use frequency modulation in the ultraviolet is demonstrated; however, at present the ultraviolet power is too low to give advantages over direct absorption monitoring. Mercury detection at atmospheric pressure is also considered which is of great interest for environmental monitoring. © 2000 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.62.Fi Laser spectroscopy
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.88.+y Instruments for environmental pollution measurements

Molecular orientation in laser-induced periodic microstructure on polyimide surface

Qing-hua Lu, Zong-guang Wang, Jie Yin, Zi-kang Zhu, and H. Hiraoka

Appl. Phys. Lett. 76, 1237 (2000); http://dx.doi.org/10.1063/1.125995 (3 pages) | Cited 8 times

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The dichroism of the laser-induced periodic microstructure on a polyimide surface was studied with polarized reflectance infrared spectroscopy. The experimental results show that the polar C�O groups in the polyimide exhibit a greater tendency of orienting in the direction parallel to the microlines while the nonpolar C–C–C linkages between the two benzene rings in the diamine moiety tend to orient in a direction perpendicular to the nanolines. This result indicates that the polyimide molecule chains tend to orient in a direction perpendicular to the nanolines. © 2000 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.20.Fm Birefringence
78.30.Jw Organic compounds, polymers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Ultrahigh-resolution liquid crystal display with gray scale

Bing Wen, Milind P. Mahajan, and Charles Rosenblatt

Appl. Phys. Lett. 76, 1240 (2000); http://dx.doi.org/10.1063/1.125996 (3 pages) | Cited 38 times

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An atomic force microscope was used to write planar alignment patterns on a polyimide-coated glass substrate. Paired with a substrate treated for homeotropic alignment, the resulting hybrid liquid crystal cell produced fixed gray scale images with pixel sizes of order 1 μm. The physics and efficacy of this architecture are compared to a cell having planar alignment at both substrates. © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.30.Va Image forming and processing
07.79.Lh Atomic force microscopes

Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium

Takashi Yamasaki, Kazuhiro Sumioka, and Tetsuo Tsutsui

Appl. Phys. Lett. 76, 1243 (2000); http://dx.doi.org/10.1063/1.125997 (3 pages) | Cited 90 times

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Periodic dielectric structures, consisting of hexagonally closed-packed arrays of silica microspheres with the diameter of 550 nm, were incorporated into organic light-emitting devices with a conventional two-layer structure made with vacuum-sublimation. The arrays acted as a two-dimensional diffraction lattice which behaved as a light scattering medium for the light propagated in waveguiding modes within the device. Strongly scattered light emission through the front surface of the devices was observed. An increase in the device coupling-out factor for electroluminescent efficiency by using the scattering structure is demonstrated. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
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Electron energy control in an inductively coupled plasma at low pressures

Haruo Shindo, Takuya Urayama, Takashi Fujii, Yasuhiro Horiike, and Syuitsu Fujii

Appl. Phys. Lett. 76, 1246 (2000); http://dx.doi.org/10.1063/1.125998 (3 pages) | Cited 5 times

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A method of electron energy control was studied in an inductively coupled plasma that employed a multimode antenna, for high performance in device fabrication plasma processes. The electron energy was reduced by changing the azimuthal mode of a one-turn antenna from m = 0 to 2 with no notable change in electron density. Langmuir probe measurements showed that the electron energy reduction was more pronounced in the higher modes and at lower pressures. The antenna size was also a critical parameter. These results were confirmed by optical emission spectroscopy. It was found to be essential for the energy control that the distance between the induction-field reverse points is shorter than the electron free path. © 2000 American Institute of Physics.
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52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Hot-electron flux observation in large-area microwave sustained plasmas

Jozef Kudela, Tibor Terebessy, and Masashi Kando

Appl. Phys. Lett. 76, 1249 (2000); http://dx.doi.org/10.1063/1.125999 (3 pages) | Cited 17 times

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Flux of hot electrons directed away from the waveguiding plasma-dielectric interface was experimentally observed in large-area microwave discharges. The energy of these electrons attains values of some 60 eV, and they are believed to be originating from the resonantly-enhanced electric field region localized near the dielectric. The phenomenon appears to play a significant role in discharge heating mechanism, which is demonstrated by plasma parameter profiles. © 2000 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.50.Gj Plasma heating by particle beams
52.50.Dg Plasma sources
52.40.Hf Plasma-material interactions; boundary layer effects
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Time-resolved photoluminescence studies of AlxGa1−xN alloys

H. S. Kim, R. A. Mair, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 76, 1252 (2000); http://dx.doi.org/10.1063/1.126000 (3 pages) | Cited 58 times

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The optical properties of AlxGa1−xN alloys with x varied from 0 to 0.35 have been investigated by picosecond time-resolved photoluminescence (PL) spectroscopy. Our results revealed that while the PL intensity decreases with an increase of Al content, the low-temperature PL decay lifetime increases with Al content. These results can be understood in terms of the effects of tail states in the density of states due to alloy fluctuation in the AlxGa1−xN alloys. The Al-content dependence of the energy-tail-state distribution parameter E0, which is an important parameter for determining optical and electrical properties of the AlGaN alloys, has been obtained experimentally. The PL decay lifetime increases with the localization energy and, consequently, increases with Al content. The implications of our findings to III-nitride optoelectronic device applications are also discussed. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Catalytically active nickel {110} surfaces in growth of carbon tubular structures

M. H. Kuang, Z. L. Wang, X. D. Bai, J. D. Guo, and E. G. Wang

Appl. Phys. Lett. 76, 1255 (2000); http://dx.doi.org/10.1063/1.126001 (3 pages) | Cited 30 times

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Recent interest in the growth of aligned carbon nanotube films using transition metal catalysts has led to questions concerning the growth mechanism involved. In our experiment carbon tubules grown using Ni catalysts exhibit a preferred orientation relative to the catalytically active surfaces of Ni. The axial directions of the tubular structure are mainly parallel to the 〈110〉 and 〈042〉 directions of Ni. The faceted shape of the Ni particles determines the intrinsic structure of the tubules. A mechanism involving spiral growth is proposed to explain the nucleation and growth of such tubules. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology

Dephasing of coherent phonons by lattice defects in bismuth films

Muneaki Hase, Kunie Ishioka, Masahiro Kitajima, Kiminori Ushida, and Shunichi Hishita

Appl. Phys. Lett. 76, 1258 (2000); http://dx.doi.org/10.1063/1.126002 (3 pages) | Cited 19 times

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We have studied the effect of point defects on coherent optical phonons in ion-implanted bismuth polycrystalline films. Ultrafast dynamics of coherent phonons and photogenerated carriers in the femtosecond time domain have been investigated by means of pump-probe reflectivity measurements. The dephasing rate of the A1g phonon increases linearly with increasing ion dose, which is explained by the additional dephasing process of the coherent phonon originated from scattering of phonons by the defects. Carrier dynamics are also found to be affected by additional scattering process mediated by point defects. © 2000 American Institute of Physics.
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63.20.kp Phonon-defect interactions
68.60.Wm Other nonelectronic physical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.At Metal and metallic alloys
61.72.J- Point defects and defect clusters
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
78.66.Bz Metals and metallic alloys

Direct wafer bonding and transfer of 10-μm-thick magnetic garnet films onto semiconductor surfaces

T. Izuhara, M. Levy, and R. M. Osgood

Appl. Phys. Lett. 76, 1261 (2000); http://dx.doi.org/10.1063/1.126003 (3 pages) | Cited 8 times

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Bonding between liquid-phase-epitaxy-grown yttrium iron garnet films and various semiconductors is realized by direct wafer bonding. The semiconductor substrates can serve as a platform for integration or as a “handle” platform for the transfer of mesoscopic garnet films. To effect film transfer, a sacrificial layer is formed in the garnet by deep ion implantation prior to bonding. Shear stress at the garnet/semiconductor interface can be controlled by temperature tuning during the bonding process. A debonding temperature threshold of ∼400 °C is found and related to the interfacial thermal stress due to difference in thermal expansion coefficients of the bonded materials. Film separation is realized by the application of thermally induced stress at the sacrificial layer. © 2000 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
85.30.-z Semiconductor devices
68.60.Wm Other nonelectronic physical properties

Transplanted Si films on arbitrary substrates using GaN underlayers

Supratik Guha, Arunava Gupta, Nestor A. Bojarczuk, and Joseph Karasinski

Appl. Phys. Lett. 76, 1264 (2000); http://dx.doi.org/10.1063/1.126004 (3 pages) | Cited 1 time

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We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred onto host substrates by using the technique of laser-induced metallization of GaN at the GaN/sapphire interface via the reaction GaN=Ga+1/2N2. This may allow the grafting of films of Si onto substrates such as glass or plastic for microelectronic applications. We examine the debonding mechanism and propose that it occurs due to pressures of the order of a few thousand atmospheres generated with the release of nitrogen from the GaN metallization reaction. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology

Effects of nitrogen on the band structure of GaNxP1−x alloys

H. P. Xin, C. W. Tu, Yong Zhang, and A. Mascarenhas

Appl. Phys. Lett. 76, 1267 (2000); http://dx.doi.org/10.1063/1.126005 (3 pages) | Cited 67 times

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We report that the incorporation of N in GaNxP1−x alloys (x ≥ 0.43%) leads to a direct band-gap behavior of GaNP. For N concentration lower than 0.43%, a series of sharp emission lines from the various N pair centers are observed for GaNP bulk layers. With increasing N concentration higher than 0.43%, a strong photoluminescence (PL) emission from GaNP bulk layers is observed at room temperature. While the PL peak redshifts with increasing N concentration to 3.1%, the PL intensity remains as intense. Absorption measurements show a direct band-gap behavior of GaNP alloys. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

In situ transmission electron microscopy observation of thin solid aluminum film thermal flow into submicron-sized periodic grooves fabricated on a silicon oxide substrate

Hidehiro Yasuda, Jun-ichi Wada, and Kazuo Furuya

Appl. Phys. Lett. 76, 1270 (2000); http://dx.doi.org/10.1063/1.125899 (3 pages)

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Thin solid aluminum film thermal flow into submicron-sized periodic grooves fabricated on a silicon oxide substrate has been studied in situ by transmission electron microscopy (TEM). Preparation of an aluminum film on the substrate was carried out using an evaporator installed in the specimen chamber of a TEM. The aluminum film was then gradually heated in situ in the microscope. At temperatures around 878 K, the polycrystalline aluminum film on the surface of the substrate started to flow into the grooves, and eventually the grooves were filled with polycrystalline aluminum. At 933 K, the aluminum in the grooves melted. It was confirmed that thin-film thermal flow into the grooves took place in the solid state. It is suggested that a creep deformation of the film driven by surface tension is responsible for this flow. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.Hg Creep
85.40.Ls Metallization, contacts, interconnects; device isolation

Interfacial conduction in silica gels containing nanocrystalline copper oxide

D. Das and D. Chakravorty

Appl. Phys. Lett. 76, 1273 (2000); http://dx.doi.org/10.1063/1.126006 (3 pages) | Cited 19 times

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Nanometer-sized copper particles have been grown within a gel derived glass in the system 60 CuO, 40 SiO2 (mole %). By heat treatment at temperatures in the range of 450–850 °C, copper oxide shells of thickness varying from 1.1 to 1.7 nm have been produced. DC resistivity measurements carried out over the temperature range of 30–300 °C show a drastically reduced activation energy as compared to that of a reference sample with the above composition. This is ascribed to the presence of an interfacial amorphous phase generated by the assembly of nanosized copper oxide particles. © 2000 American Institute of Physics.
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72.80.Tm Composite materials
82.70.Gg Gels and sols
73.63.-b Electronic transport in nanoscale materials and structures
61.46.-w Structure of nanoscale materials

Improved brightness, efficiency, and stability of sputter deposited alternating current thin film electroluminescent ZnS:Mn by codoping with potassium chloride

Karen E. Waldrip, J. S. Lewis, Q. Zhai, M. R. Davidson, P. H. Holloway, and S. S. Sun

Appl. Phys. Lett. 76, 1276 (2000); http://dx.doi.org/10.1063/1.126007 (3 pages) | Cited 11 times

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Electroluminescent ZnS:Mn thin films have been codoped with KCl via an ex situ deposition and diffusion process. The brightness, efficiency, and stability of sputter deposited ZnS:Mn alternating current thin film electroluminescent devices have been greatly improved over untreated devices. Potassium chloride doping is shown to have a modest fluxing effect on the grain size of ZnS:Mn films, particularly in the region of the film where nucleation occurs. However, improved electroluminescence is postulated to be strongly influenced by doping control of electric fields and injected charge. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Pg Display systems
78.66.Hf II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering

Interband optical absorption in free standing layer of Ga0.96In0.04As0.99N0.01

Piotr Perlin, Przemek Wiśniewski, Czesław Skierbiszewski, Tadeusz Suski, Eliana Kamińska, Sudhir G. Subramanya, Eicke R. Weber, Dan E. Mars, and Wladek Walukiewicz

Appl. Phys. Lett. 76, 1279 (2000); http://dx.doi.org/10.1063/1.126008 (3 pages) | Cited 45 times

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We have measured the interband optical absorption of a free-standing sample of Ga0.96In0.04As0.99N0.01 in a wide energy range from 1 to 2.5 eV. We found that the fundamental absorption edge is shifted by 150 meV towards lower energies, and the absorption coefficient measured at higher energies exhibits substantial reduction comparing to that of GaAs. By removing the GaAs substrate, we were able to get an experimental insight into the interband optical transitions and the density of state in this material. The changes can be understood within the band anticrossing model predicting the conduction band splitting. New absorption edges associated with optical transitions from the spin-orbit split off band to the lower conduction subband (1.55 eV) and from the top of the valence band to the upper subband (1.85 eV) are observed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Determination of pore-size distribution in low-dielectric thin films

D. W. Gidley, W. E. Frieze, T. L. Dull, J. Sun, A. F. Yee, C. V. Nguyen, and D. Y. Yoon

Appl. Phys. Lett. 76, 1282 (2000); http://dx.doi.org/10.1063/1.126009 (3 pages) | Cited 79 times

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Positronium annihilation lifetime spectroscopy is used to determine the pore-size distribution in low-dielectric thin films of mesoporous methylsilsesquioxane. A physical model of positronium trapping and annihilating in isolated pores is presented. The systematic dependence of the deduced pore-size distribution on pore shape/dimensionality and sample temperature is predicted using a simple quantum mechanical calculation of positronium annihilation in a rectangular pore. A comparison with an electron microscope image is presented. © 2000 American Institute of Physics.
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61.43.Gt Powders, porous materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Temperature dependence of band gap energies of GaAsN alloys

Katsuhiro Uesugi, Ikuo Suemune, Tatsuo Hasegawa, Tomoyuki Akutagawa, and Takayoshi Nakamura

Appl. Phys. Lett. 76, 1285 (2000); http://dx.doi.org/10.1063/1.126010 (3 pages) | Cited 56 times

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The temperature dependence of band gap energies of GaAsN alloys was studied with absorption measurements. As the N concentration in GaAsN increased, the temperature dependence of the band gap energy was clearly reduced in comparison with that of GaAs. The redshift of the absorption edge in GaAsN for the temperature increase from 25 to 297 K was reduced to 60% of that of GaAs for the N concentration larger than ∼1%. The differential temperature coefficient of the energy gap at room temperature was also reduced to 70% of that of GaAs. The main factor for this reduced temperature dependence in GaAsN was attributed to the transition from band-like states to nitrogen-related localized states with detailed studies of the temperature-induced shift of the absorption edge. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
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A femtosecond, polarization-sensitive optically addressed modulator based on virtual exciton effects in an anisotropically strained multiple quantum well

M. Wraback and H. Shen

Appl. Phys. Lett. 76, 1288 (2000); http://dx.doi.org/10.1063/1.126011 (3 pages) | Cited 8 times

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High contrast and femtosecond speed have been achieved in an optically addressed anisotropically strained multiple quantum well modulator by exploiting polarization-sensitive optical nonlinearities associated with the interaction of resonantly excited excitons with a population of nonresonantly created excitons that adiabatically follows the temporal intensity profile of the excitation pulse. The resultant modulation is characterized by a contrast ratio of 380:1, corresponding to a dynamic polarization rotation of 18°, and a pulse-width-limited full width at half maximum of 165 fs. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.79.Hp Optical processors, correlators, and modulators
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes

Effect of Sb composition on lateral oxidation rates in AlAs1−xSbx

P. Chavarkar, U. K. Mishra, S. K. Mathis, and J. S. Speck

Appl. Phys. Lett. 76, 1291 (2000); http://dx.doi.org/10.1063/1.126012 (3 pages) | Cited 4 times

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We demonstrate the effect of antimony (Sb) composition on the oxidation mechanism of AlAs1−xSbx (x<0.21) layers on GaAs substrates. It has been demonstrated that addition of a group-III element like Ga to AlAs slows the rate of oxidation. In contrast, addition of a group-V element like Sb to AlAs changes the oxidation mechanism in more than one way. The oxidation rate increases with Sb addition, and the oxidation reaction changes from a diffusion-limited mechanism to a reaction-rate-limited mechanism at higher oxidation temperatures. This is attributed to the increase in the permeability of the oxide. Nonuniform segregation of Sb is observed upon oxidation. The activation energy of the oxidation reaction-rate constant initially decreases with the Sb composition upto 10%, further Sb addition increases the activation energy. © 2000 American Institute of Physics.
Show PACS
81.05.Ea III-V semiconductors
81.65.Mq Oxidation
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
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