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13 Sep 2004

Volume 85, Issue 11, pp. 1871-2145

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1895 (2004); http://dx.doi.org/10.1063/1.1792802 (3 pages)

Markus Deubel, Martin Wegener, Artan Kaso, and Sajeev John
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Arrays of microlenses of complex shapes prepared by reaction-diffusion in thin films of ionically doped gels

Christopher J. Campbell, Eric Baker, Marcin Fialkowski, and Bartosz A. Grzybowski

Appl. Phys. Lett. 85, 1871 (2004); http://dx.doi.org/10.1063/1.1787595 (3 pages) | Cited 8 times

Online Publication Date: 17 September 2004

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This letter describes a wet-stamping technique for the fabrication of highly regular arrays of microlenses through reaction-diffusion-swelling processes occurring in a thin film of ionically doped gelatin. Geometrical parameters of the lenses depend on and can be controlled by the geometries of the stamped features and the concentrations of chemicals diffusing and reacting in the gelatin matrix. Surface topographies of the lenses are studied experimentally, and are reproduced by a lattice gas reaction-diffusion model.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Bh Lenses, prisms and mirrors
82.20.-w Chemical kinetics and dynamics
82.70.Gg Gels and sols
82.33.Ln Reactions in sol gels, aerogels, porous media

InGaSb photodetectors using an InGaSb substrate for 2 μm applications

Tamer F. Refaat, M. Nurul Abedin, Vinay Bhagwat, Ishwara B. Bhat, Partha S. Dutta, and Upendra N. Singh

Appl. Phys. Lett. 85, 1874 (2004); http://dx.doi.org/10.1063/1.1787893 (3 pages) | Cited 8 times

Online Publication Date: 17 September 2004

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Detectors operating at 2 μm are important for several applications including optical communication and atmospheric remote sensing. In this letter, fabrication of 2 μm photodetectors using an InGaSb substrate is reported. The ternary substrates were grown using vertical Bridgmann technique and Zn diffusion was used to fabricate p–n junction diodes and photodiodes. Dark current measurement reveals that the breakdown voltage is in the 0.75 to 1 V range. Spectral response measurements indicated a 2 μm responsivity of 0.56 A∕W corresponding to 35% quantum efficiency. Photodiode performance was compared to similar devices fabricated on binary substrates.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
81.10.Fq Growth from melts; zone melting and refining
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Video-rate compatible photorefractive polymers with stable dynamic properties under continuous operation

Canek Fuentes-Hernandez, Jayan Thomas, Roberto Termine, Gerald Meredith, Nasser Peyghambarian, Bernard Kippelen, Steve Barlow, Gregory Walker, Seth R. Marder, Michiharu Yamamoto, Kevin Cammack, and Kenji Matsumoto

Appl. Phys. Lett. 85, 1877 (2004); http://dx.doi.org/10.1063/1.1787956 (3 pages) | Cited 7 times

Online Publication Date: 17 September 2004

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We report on photorefractive polymer composites that exhibit stable dynamic properties under continuous operation. These materials are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential. The evolution of the response time for exposures up to 4 kJ∕cm2 was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites. In the composites, operational stability is combined with video-rate compatible dynamics, large dynamic range at moderate fields, and long shelf lifetimes.
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42.70.Jk Polymers and organics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrafast dynamics of the third-order nonlinear response in a two-dimensional InP-based photonic crystal

F. Raineri, Crina Cojocaru, P. Monnier, A. Levenson, R. Raj, C. Seassal, X. Letartre, and P. Viktorovitch

Appl. Phys. Lett. 85, 1880 (2004); http://dx.doi.org/10.1063/1.1788884 (3 pages) | Cited 30 times

Online Publication Date: 17 September 2004

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We report experimental demonstration of very fast nonlinear response around 1.5 μm in an InP-based two-dimensional photonic crystal. The nonlinearity produced by low pump powers via carrier induced nonlinear refractive index, leads to an efficient wavelength shift of a photonic crystal resonance observed in reflectivity. Thus we show that it is possible to obtain round the clock (rise and recovery) switching times shorter than 10 ps with contrast ratio higher than 80%.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Highly efficient second-harmonic generation in doubly resonant planar microcavities

Marco Liscidini and Lucio Claudio Andreani

Appl. Phys. Lett. 85, 1883 (2004); http://dx.doi.org/10.1063/1.1786657 (3 pages) | Cited 17 times

Online Publication Date: 17 September 2004

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A theoretical study of second-harmonic generation in planar microcavities with periodic dielectric mirrors is made. Strong enhancement of the nonlinear conversion is predicted when double resonance for the pump and harmonic fields, as well as phase matching, are achieved. For a given structure design, the finite angle of incidence is used as a tuning parameter and the splitting between cavity modes with different polarizations is used to compensate the material dispersion. Examples are given for GaAs cavities with AlGaAs∕Alox dielectric mirrors.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Ultrawide tuning range in doped organic solid-state lasers

D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, M. Kröger, E. Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, and P. Hinze

Appl. Phys. Lett. 85, 1886 (2004); http://dx.doi.org/10.1063/1.1791742 (3 pages) | Cited 33 times

Online Publication Date: 17 September 2004

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We report on the tunability of 4-(Dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2)-doped guest-host organic lasers. As host materials Tris-(8-hydroxy-quinoline)aluminum (Alq3), 4,4′‐N,N′-dicarbazole-bipheny1 (CBP), and N′N-di(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPD) are used. The largest tuning range was observed in the Alq3:DCM2 film with 115.3 nm between 597.8 and 713.1 nm. In CBP:DCM2, a tuning range of 85 nm was measured, whereas in NPD:DCM2 only one laser wavelength at 624.4 nm could be observed. When comparing the pump energies, we observed considerably lower threshold energy densities in Alq3:DCM2 and CBP:DCM2 compared to NPD:DCM2.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Rz Doped-insulator lasers and other solid state lasers

Vertical-cavity semiconductor devices for generation and detection of fluorescence emission on a single chip

P. A. Porta and H. D. Summers

Appl. Phys. Lett. 85, 1889 (2004); http://dx.doi.org/10.1063/1.1787153 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2004

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In this letter, we describe the realization and the characterization of vertical-cavity semiconductor devices with monolithically integrated detectors for the excitation and detection of fluorescence emission from a fluorophore. These devices can act as excitation sources in forward bias and as detectors in reverse bias mode. Photonic microstructuring is used to control the optical field within the device. Detection is made possible at wavelengths longer than that of emission, with minimum attenuation of the output signal. These characteristics make these devices suitable for fluorescence spectroscopy as they are able to provide an excitation signal and detect the redshifted dye fluorescence.
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85.60.Jb Light-emitting devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Directional emission from asymmetric microlaser resonators of π-conjugated polymers

R. C. Polson and Z. V. Vardeny

Appl. Phys. Lett. 85, 1892 (2004); http://dx.doi.org/10.1063/1.1753064 (3 pages) | Cited 8 times

Online Publication Date: 17 September 2004

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A π-conjugated polymer film was fabricated into an asymmetric microlaser resonator having a quadrapole deformation with irregular boundaries and a Q factor of 600. At high excitation intensities above the threshold for lasing, we observed multimode laser emission spectra and directional emission at four different angles. Chaotic ray dynamics explains the observed emission pattern. © 2004 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
78.66.Qn Polymers; organic compounds

Direct laser writing and characterization of “Slanted Pore” Photonic Crystals

Markus Deubel, Martin Wegener, Artan Kaso, and Sajeev John

Appl. Phys. Lett. 85, 1895 (2004); http://dx.doi.org/10.1063/1.1792802 (3 pages) | Cited 35 times

Online Publication Date: 17 September 2004

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We report the fabrication and characterization of the recently proposed Slanted Pore Photonic Crystals. The Photonic Crystals fabricated via direct laser writing by multiphoton polymerization are characterized by electron microscopy as well as by optical spectroscopy. The latter is compared with band structure calculations. We show that this Slanted Pore geometry allows for controlling the surface termination of the Photonic Crystal.
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42.70.Qs Photonic bandgap materials
42.62.-b Laser applications
82.35.-x Polymers: properties; reactions; polymerization

Absorption, emission spectrum properties, and efficient laser performances of Yb:Y3ScAl4O12 ceramics

J. Saikawa, Y. Sato, T. Taira, and A. Ikesue

Appl. Phys. Lett. 85, 1898 (2004); http://dx.doi.org/10.1063/1.1791339 (3 pages) | Cited 22 times

Online Publication Date: 17 September 2004

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We report on the continuous-wave laser performances of Yb3+-doped disordered Y3Al5O12∕Y3Sc2Al4O12 (YAG∕YSAG) ceramics fabricated by sintering method. These materials exhibit relatively low minimum pump intensity (Imin) and broad emission bandwidth even in the yttrium aluminum garnet systems. The value of Imin in the Yb:Y3ScAl4O12 ceramics was found to be 2∕3 compared with the Yb:YAG single crystal under 970 nm zero-line pumping. Efficient laser oscillation of 72% slope efficiency was obtained for input pump power. These materials attract great interest for high power femtosecond microchip lasers and amplifier applications.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.62.-b Laser applications

Lasing action and photodegradation of disperse Orange 11 dye in liquid solution

Brent F. Howell and Mark G. Kuzyk

Appl. Phys. Lett. 85, 1901 (2004); http://dx.doi.org/10.1063/1.1791323 (3 pages) | Cited 12 times

Online Publication Date: 17 September 2004

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We report optically pumped lasing action near 650 nm of 1-amino-2-methylanthraquinone (known as Disperse Orange 11 or DO11) in the common laser dye solvents dimethylformamide and dimethylsulfoxide. Amplified spontaneous emission (ASE) was studied under second-harmonic Nd:YAG laser excitation in a transverse pumping configuration. ASE conversion efficiency is found to be comparable to other laser dyes. Photodegradation of dye solution in a micro-cuvette was investigated. While DO11 in poly(methyl methacrylate) polymer shows reversible photodegradation, in liquid solution, degradation is permanent.
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42.55.Mv Dye lasers
42.70.Hj Laser materials
78.45.+h Stimulated emission

Optical properties of InP∕GaInP quantum-dot laser structures

G. M. Lewis, J. Lutti, P. M. Smowton, P. Blood, A. B. Krysa, and S. L. Liew

Appl. Phys. Lett. 85, 1904 (2004); http://dx.doi.org/10.1063/1.1794379 (3 pages) | Cited 4 times

Online Publication Date: 17 September 2004

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We have grown InP quantum dots with different rates and on substrates with different orientations. The growth conditions have a major influence on the form of the gain spectrum. Using a high growth rate on a 10° off (100) substrate we obtain a broad gain spectrum due to contributions from a bimodal dot size distribution whereas a sample containing mostly small dots, produced using (211)B substrates, has a narrower gain spectrum centered at a shorter wavelength of ∼700–710 nm. The modal gain saturates at a magnitude significantly smaller than the modal absorption, nevertheless the measured values of modal gain are sufficient to sustain laser action, and structures grown at high growth rate on 10° off (100) substrates are capable of providing laser devices operating in the region of 750 nm.
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42.55.Px Semiconductor lasers; laser diodes
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Front-coupling of a prefocused x-ray beam into a monomodal planar waveguide

Christian Fuhse, Ansgar Jarre, Christoph Ollinger, Jens Seeger, Tim Salditt, and Remi Tucoulou

Appl. Phys. Lett. 85, 1907 (2004); http://dx.doi.org/10.1063/1.1791736 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2004

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A hard x-ray beam of photon energy E=12.5 keV has been focused by a Kirkpatrick–Baez mirror system and coupled into the front side of a single-mode x-ray waveguide. The beam dimensions of 3.8×2.5 μm2 in the focus of the mirror system have thus been reduced in one direction to 32 nm, corresponding to the guiding layer thickness of the waveguide. At the same time the waveguide acts as a coherence filter and leads to a well-defined intensity distribution with steep tails in the near- and far-field regions. The total flux transmitted by the waveguide exceeded 108 photons/s while no significant contributions of radiation transmitted through the absorbing waveguide cladding have been observed.
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41.50.+h X-ray beams and x-ray optics

High-quantum-efficiency erbium-doped optical fiber and the effective deactivator

B. Peng, X. M. Qiu, L. Jiang, Z. C. Fan, and W. Huang

Appl. Phys. Lett. 85, 1910 (2004); http://dx.doi.org/10.1063/1.1791743 (3 pages) | Cited 10 times

Online Publication Date: 17 September 2004

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The optical properties of erbium-doped bismuth-based oxide glasses were studied in this letter. By adding a proper amount of hydroxyl group as the deactivator, the excited state absorption and upconversion of erbium were restrained. The mechanism is explained and some amplifiers with good properties are produced.
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42.81.Dp Propagation, scattering, and losses; solitons
78.55.Qr Amorphous materials; glasses and other disordered solids

High external efficiency in a monomode full-photonic-crystal laser under continuous wave electrical injection

A. Talneau, L. LeGratiet, J. L. Gentner, A. Berrier, M. Mulot, S. Anand, and S. Olivier

Appl. Phys. Lett. 85, 1913 (2004); http://dx.doi.org/10.1063/1.1789573 (3 pages) | Cited 7 times

Online Publication Date: 17 September 2004

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We demonstrate continuous wave with an external efficiency over 0.15 W∕A and monomode operation of a full photonic crystal (PhC) laser. The optical confinement and a wavelength selectivity better than 25 dB are all ensured by a unique PhC. We take advantage of the feedback on the fundamental mode which exists within the photonic gap for some specific designs of the PhC guide. These designs are calculated using the plane wave expansion method.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
68.65.Fg Quantum wells
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Pulsed electron beam generation in a simple discharge device

M. J. Rhee and M. Strikovski

Appl. Phys. Lett. 85, 1916 (2004); http://dx.doi.org/10.1063/1.1784540 (3 pages)

Online Publication Date: 17 September 2004

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We report a phenomenon of pulsed electron beam generation in a low-pressure gas discharge device. The cathode of the device is of simple geometry without a hollow cavity that is employed in the transient hollow cathode discharge (THCD) devices. The discharge and beam characteristics are measured and found to be similar to that of THCDs such as pseudospark and channelspark.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.77.-j Plasma applications

Monochromatic imaging and angular distribution measurements of extreme ultraviolet light from laser-produced Sn and SnO2 plasmas

Y. Tao, F. Sohbatzadeh, H. Nishimura, R. Matsui, T. Hibino, T. Okuno, S. Fujioka, K. Nagai, T. Norimatsu, K. Nishihara, N. Miyanaga, Y. Izawa, A. Sunahara, and T. Kawamura

Appl. Phys. Lett. 85, 1919 (2004); http://dx.doi.org/10.1063/1.1788878 (3 pages) | Cited 20 times

Online Publication Date: 17 September 2004

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Properties of extreme ultraviolet (EUV) emission from laser-produced Sn and SnO2 plasmas were investigated. EUV emission images were taken with a monochromatic imager for 13.5 nm with 4% bandwidth. It was found that the EUV emitting plasma is not formed symmetrically with respect to the target surface normal but extends toward laser incident axis. This result is consistent with the angular distribution of EUV emission peaked toward the direction nearly perpendicular to the laser axis. The asymmetric plasma can be attributed to the interaction of a long laser pulse with expanding plasma along the path of laser incidence.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Relation between the CF2 radical and plasma density measured using LIF and cutoff probe in a CF4 inductively coupled plasma

Jung-Hyung Kim, Yong-Hyeon Shin, Kwang-Hwa Chung, and Yong-Shim Yoo

Appl. Phys. Lett. 85, 1922 (2004); http://dx.doi.org/10.1063/1.1788880 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2004

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The behavior of the CF2 radical was studied in a CF4 inductively coupled plasma. The CF2 radical was measured using a laser-induced fluorescence method. Absolute electron density was measured using a cutoff probe and the electron temperature was measured using a double probe to study the relationship between these electron properties and the CF2 radical. To examine the relationship between them, the CF2 radical and electron density were measured as a function of the rf power, which is a major external parameter influencing the electron density. As the rf power was increased, the CF2 radical density increased in the range of low electron density, and then decreased beyond a critical electron density. The dependence of the CF2 radical density on the electron density was theoretically analyzed with rate equations. The theoretical result was in good agreement with experiment.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
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Light-induced metastability in hydrogenated nanocrystalline silicon solar cells

Baojie Yan, Guozhen Yue, Jessica M. Owens, Jeffrey Yang , and Subhendu Guha

Appl. Phys. Lett. 85, 1925 (2004); http://dx.doi.org/10.1063/1.1790072 (3 pages) | Cited 33 times

Online Publication Date: 17 September 2004

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Light-induced metastability in hydrogenated nanocrystalline silicon (nc-Si:H) single-junction solar cells has been studied under different light spectra. The nc-Si:H studied contains a certain fraction of hydrogenated amorphous silicon (a-Si:H). We observe no light-induced degradation when the photon energy used is lower than the bandgap of a-Si:H, while degradation occurs when the photon energy is higher than the bandgap. We conclude that the light-induced defect generation occurs mainly in the amorphous phase. Light soaking experiments on a-Si:H∕a-SiGe:H∕nc-Si:H triple-junction solar cells show no light-induced degradation in the bottom cell, because the a-Si:H top and a a-SiGe:H middle cells absorb most of the high-energy photons.
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84.60.Jt Photoelectric conversion
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Heteroepitaxy of high-quality Ge on Si by nanoscale Ge seeds grown through a thin layer of SiO2

Qiming Li, Ying-Bing Jiang, Huifang Xu, Stephen Hersee, and Sang M. Han

Appl. Phys. Lett. 85, 1928 (2004); http://dx.doi.org/10.1063/1.1790027 (3 pages) | Cited 14 times

Online Publication Date: 17 September 2004

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We demonstrate that high-quality Ge can be grown on Si covered with a thin layer of chemical SiO2. When the oxidized Si substrate is exposed to Ge molecular beam, 7-nm-wide seed pads form in the oxide layer and “touchdown” on the underlying Si. Upon continued exposure, Ge selectively grows on the seed pads rather than on SiO2, and the seeds coalesce to form an epitaxial lateral overgrowth (ELO) layer. The Ge ELO layer is characterized by transmission electron microscopy and etch-pit density (EPD). The Ge ELO layer is free of dislocation network, but stacking faults exist near the Ge-SiO2 interface. A fraction of these stacking faults propagate to the surface, resulting in EPD less than 2×106 cm−2. The high quality Ge ELO layer is attributed to a high density of nanoscale Ge seed pads interspaced by 2–12-nm-wide SiO2 patches.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Below band gap photoreflectance transitions in epitaxial GaN

Phil W. Yu, Jerry D. Clark, David C. Look, C. Q. Chen, Jinwei Yang, Edmundas Koutstis, M. Asif Khan, Denis V. Tsvertkov, and Vladimir A. Dmitriev

Appl. Phys. Lett. 85, 1931 (2004); http://dx.doi.org/10.1063/1.1780602 (3 pages) | Cited 4 times

Online Publication Date: 17 September 2004

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A photoreflectance (PR) and photoluminescence (PL) study has been performed on a Si-doped epitaxial GaN layer that contains impurity or defect related below band gap features in its PR spectrum. In the 300 K PR spectrum, these features appear at energies of 3.26 and 3.33 eV, respectively, but below 180 K they can no longer be seen. The 3.26 eV line evidently corresponds to a donor acceptor pair transition, also seen in PL. The origin of the 3.33 eV line is uncertain, but may correspond to a transition involving the nitrogen vacancy.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Laser-induced wavy pattern formation in metal thin films

Ke Xiao, Zi Sheng Guan, Guo Jie Wang, Lei Jiang, Dao Ben Zhu, and Yu Ren Wang

Appl. Phys. Lett. 85, 1934 (2004); http://dx.doi.org/10.1063/1.1787891 (3 pages) | Cited 10 times

Online Publication Date: 17 September 2004

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Laser-induced well-ordered and controllable wavy patterns are constructed in the deposited metal thin film. The micrometer-sized structure and orientation of the wavy patterns can be controlled via scanning a different size of rectangle laser spot on the films. Ordered patterns such as aligned, crossed, and whirled wave structures were designed over large areas. This patterning technique may find applications in both exploring the reliability and mechanical properties of thin films, and fabricating microfluidic devices.
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42.62.-b Laser applications
68.55.-a Thin film structure and morphology
61.82.Bg Metals and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Indirect optical absorption of single crystalline β-FeSi2

Haruhiko Udono, Isao Kikuma, Tsuyoshi Okuno, Yasuaki Masumoto, and Hiroyuki Tajima

Appl. Phys. Lett. 85, 1937 (2004); http://dx.doi.org/10.1063/1.1790590 (3 pages) | Cited 20 times

Online Publication Date: 17 September 2004

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We investigated optical absorption spectra near the fundamental absorption edge of β-FeSi2 single crystals by transmission measurements. The phonon structure corresponding to the emission and absorption component was clearly observed in the low-temperature absorption spectra. Assuming exciton state in the indirect allowed transition, we determined a phonon energy of 0.031±0.004 eV. A value of 0.814 eV was obtained for the exciton transition energy at 4 K.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Role of N ions in the optical and morphological properties of InGaAsN quantum wells for 1.3–1.5 μm applications

J. Miguel-Sánchez, A. Guzmán, and E. Muñoz

Appl. Phys. Lett. 85, 1940 (2004); http://dx.doi.org/10.1063/1.1790591 (3 pages) | Cited 11 times

Online Publication Date: 17 September 2004

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In this work, we show the effects of N ions coming from a nitrogen plasma source on the optical and structural properties of InGaAsN quantum wells. The presence of ions in the growth chamber was measured by a modified Langmuir probe method at the substrate position. A magnetic field was applied to deflect charged species from the growing surface, producing a lower concentration of ions in the growth surface that led to an improvement of the optical and structural properties of the InGaAsN layers. The samples grown with an applied magnetic field showed a more intense and narrower photoluminescence emission, as well as a lower surface roughness. Additionally, postgrowth annealing has a smaller impact on the photoluminescence emission when a magnetic field is used, and a much lower blueshift is observed.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Anharmonic decay of phonons in strain-free wurtzite AlN

J. G. Tischler and J. A. Freitas

Appl. Phys. Lett. 85, 1943 (2004); http://dx.doi.org/10.1063/1.1787957 (3 pages) | Cited 10 times

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We present Raman scattering measurements on high-quality freestanding AlN single crystals. Polarization studies provide clear identification of all allowed phonons. We report the smallest phonon linewidths observed in AlN, which provide a direct measurement of the anharmonic decay of phonons in this material. Also from the Raman mode frequencies and reported index of refraction values we estimated the ordinary and extraordinary dielectric constant values. The calculated values are considerably different from previously reported values of the dielectric constant of AlN.
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63.20.Ry Anharmonic lattice modes
77.22.Ej Polarization and depolarization
78.30.Fs III-V and II-VI semiconductors
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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