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14 Jan 2002

Volume 80, Issue 2, pp. 165-338

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Polymer microring lasers with longitudinal optical pumping

S. X. Dou, E. Toussaere, T. Ben-Messaoud, A. Potter, D. Josse, G. Kranzelbinder, and J. Zyss

Appl. Phys. Lett. 80, 165 (2002); http://dx.doi.org/10.1063/1.1432759 (3 pages) | Cited 10 times

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We propose an optical pumping scheme for microring cavity lasers. The pump beam is end-fire coupled into the optical fiber that supports the microring cavity. When propagating along the fiber, the pump light is coupled into and excites the gain medium in the microring. We have demonstrated that this pumping geometry leads to an enhanced slope efficiency and significant reduction of the lasing threshold. In addition, as the excitation of the gain medium is uniform, certain effects that are prone to occur in the usual transversal pumping configuration because of nonuniform excitation can be avoided. © 2002 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.70.Jk Polymers and organics

Surface-induced photorefractive-like effect in pure liquid crystals

P. Pagliusi and G. Cipparrone

Appl. Phys. Lett. 80, 168 (2002); http://dx.doi.org/10.1063/1.1432765 (3 pages) | Cited 36 times

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We report a study of diffraction gratings observed in planar cells of nematic mixture (cyanobiphenyl and cyanotriphenyl derivatives, E7) made with different aligning substrates. Under the combined application of very low intensity laser beams (1.8 mW/cm2) and low dc voltage (4 V), highly sensitive gratings have been observed in degenerate four-wave-mixing experiments. Beam coupling measurements confirm the photorefractive-like nature of the gratings. Interesting results are obtained using two different liquid crystals, depending on the aligning substrates. The observed behavior suggests the fundamental role of the interfaces in the photoinduced processes. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Df Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Dj Gratings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.30.-v Liquid crystals

Bubble formation due to electrical stress in organic light emitting devices

Lin Ke, Soo-Jin Chua, Keran Zhang, and Peng Chen

Appl. Phys. Lett. 80, 171 (2002); http://dx.doi.org/10.1063/1.1435064 (3 pages) | Cited 7 times

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The degradation in electroluminescence of poly(p-phenylene vinylene)-based organic light-emitting devices is studied using optical microscopy, scanning electron microscopy, and secondary ion mass spectroscopy. “Bubbles” are formed at the polymer and indium tin oxide interface or in the polymer layer within the nonemissive area. This formation, which occurs during device electrical stress, is accompanied by a fluctuation of the device current. The bubbles are formed by the degraded polymer and/or the gas released from disintegration of the polymer. High local current density flowing near the dark spot center and the resultant heating, decomposes the polymer layer. The resultant carbonized area causes either local short circuit and/or open circuit leading to the final light-emitting device failure. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.60.Fi Electroluminescence
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

In situ growth monitoring of distributed GaN–AlGaN Bragg reflectors by metalorganic vapor phase epitaxy

H. P. D. Schenk, P. de Mierry, P. Vennéguès, O. Tottereau, M. Laügt, M. Vaille, E. Feltin, B. Beaumont, P. Gibart, S. Fernández, and F. Calle

Appl. Phys. Lett. 80, 174 (2002); http://dx.doi.org/10.1063/1.1430859 (3 pages) | Cited 14 times

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A series of distributed GaN-AlGaN Bragg reflectors (DBR) has been grown on Al2O3(0001) substrates by metalorganic vapor phase epitaxy. The growth of the GaN template as well as of the GaN–AlxGa1−xN quarter-wave stack has been monitored by laser reflectometry. The evolution of the in situ reflectivity as well as DBR reflection spectra are discussed as function of the AlxGa1−xN composition x. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Two-photon absorption spectroscopy of As2S3 glass

Keiji Tanaka

Appl. Phys. Lett. 80, 177 (2002); http://dx.doi.org/10.1063/1.1433908 (3 pages) | Cited 9 times

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Spectral dependence of two-photon absorption in a chalcogenide glass, As2S3, has been studied using a tunable light source. The result shows that two-photon and two-step absorptions occur, and the two-photon absorption spectrum appears to be exponential. These results and roles of nonlinear processes in photoinduced phenomena are discussed. © 2002 American Institute of Physics.
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42.65.-k Nonlinear optics
78.40.Pg Disordered solids

High carrier injection optical switch based on two-mode interference in SiGe alloy

Baojun Li and Soo-Jin Chua

Appl. Phys. Lett. 80, 180 (2002); http://dx.doi.org/10.1063/1.1432758 (3 pages) | Cited 4 times

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Based on the two-mode interference principle, the high carrier injection effect, and the free-carrier plasma dispersion effect, a directional coupling active optical switch in SiGe/Si alloy has been fabricated. Its insertion loss and crosstalk were measured to be 2.74 and −15.5 dB, respectively, at the wavelength of 1.3 μm and the total switching current of 110 mA. The fastest response time of the switch is up to 30 ns. © 2002 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers

Microlensed vertical-cavity surface-emitting laser for stable single fundamental mode operation

Si-Hyun Park, Yeonsang Park, Hyejin Kim, Heonsu Jeon, Seong Mo Hwang, Jeong Kwan Lee, Seung Ho Nam, Byeong Cheon Koh, J. Y. Sohn, and D. S. Kim

Appl. Phys. Lett. 80, 183 (2002); http://dx.doi.org/10.1063/1.1432744 (3 pages) | Cited 12 times

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We propose and demonstrate a vertical-cavity surface-emitting laser structure that operates predominantly in the single fundamental transverse mode over a wide operation current range. In this laser structure, a microlens is integrated on top of an otherwise ordinary surface-emitting laser so that a small portion of laser output is fed back into the cavity, forcing the lasing to occur in the fundamental mode. Model calculations reproduce the observed mode selection effect. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Frequency up-conversion as a temperature probe of organic opto-electronic devices

John M. Lupton

Appl. Phys. Lett. 80, 186 (2002); http://dx.doi.org/10.1063/1.1432766 (3 pages) | Cited 14 times

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Frequency up-conversion is demonstrated in a polyfluorene-based conjugated polymer. Up-converted emission is observed upon excitation to the red of the 0-0 luminescence band. The emission intensity depends strongly on temperature and provides an accurate probe of the operating temperature of organic light-emitting diodes. Temperature rises of up to 30 K are observed at standard operating current densities of 225 mA/cm2. Due to the low thermal conductivity and heat capacity of the polymer film, the temperature of the film is found to rise slowly on a time-scale of seconds. Upon termination of the current, the temperature decreases again on a time-scale of minutes. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
07.20.Dt Thermometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Jk Polymers and organics

Efficient organic light-emitting diodes with undoped active layers based on silole derivatives

Hideyuki Murata, Zakya H. Kafafi, and Manabu Uchida

Appl. Phys. Lett. 80, 189 (2002); http://dx.doi.org/10.1063/1.1432109 (3 pages) | Cited 72 times

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We report on efficient molecular organic light-emitting diodes (MOLEDs) composed of novel silole derivatives as an electron transporting layer and an emissive layer. The silole derivative, 2,5-bis(2′,2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene, used for the electron transport layer exhibits fast electron mobility of 2×10−4 cm2/V s at 0.64 MV/cm measured by the time-of-flight technique. Another silole derivative, 1,2-bis(1-methyl-2,3,4,5-tetraphenyl silacyclopentadienyl)ethane, used for an emissive layer exhibits blue-green fluorescence with an absolute quantum yield of 97±3% in the solid state. The devices using silole derivatives show a very low operating voltage, an external electroluminescence quantum efficiency (ηEL) of 4.8 %, and luminous power efficiency of 9 lm/W at a brightness of 100 cd/m2. This value of ηEL is the best efficiency achieved for MOLED using undoped emissive and carrier transport layers and is close to the theoretical limit for a device using a fluorescent emitter. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
78.55.Kz Solid organic materials

Light propagation in periodic microcavities

Hiromitsu Furukawa and Koji Tenjimbayashi

Appl. Phys. Lett. 80, 192 (2002); http://dx.doi.org/10.1063/1.1432752 (3 pages) | Cited 5 times

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We demonstrated light propagation in a type of optical waveguide, which consisted of periodically arrayed dielectric particles. Although the form is similar to a photonic crystal waveguide, our method used resonance frequencies instead of band-gap frequencies. Advantages provided by this waveguide are that dynamic optical interconnection can be realized and that a multichannel waveguide is easily formed. To fabricate the system of periodic microcavities, we used polystyrene-latex particles that have a uniform size of 15.6 μm. Some discrete frequencies of fluorescence were selected to agree with the phase matching condition and they were propagated through the microspheres. The assembled microspheres can be taken as a multichannel waveguide. © 2002 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.25.Bs Wave propagation, transmission and absorption
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.82.Et Waveguides, couplers, and arrays
82.35.Ej Nonlinear optics with polymers

Injection-seeded terahertz-wave parametric generator with wide tunability

Kodo Kawase, Hiroaki Minamide, Kazuhiro Imai, Jun-ichi Shikata, and Hiromasa Ito

Appl. Phys. Lett. 80, 195 (2002); http://dx.doi.org/10.1063/1.1429299 (3 pages) | Cited 6 times

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We report on the development of a widely tunable (frequency: 0.7–2.4 THz and wavelength: 125–430 μm), injection-seeded THz-wave parametric generator (IS-TPG), which operates at room temperature. The spectral resolution (<100 MHz and 0.003 cm−1) is the Fourier transform limit of the nanosecond THz-wave pulse. The continuous scanning and narrow spectral bandwidth of the IS-TPG were verified in the absorption spectrum of low-pressure water vapor. The high peak power (>200 mW) of the output wave and the small beam divergence are suited to a variety of applications. © 2002 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
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Comparative study of time-resolved K-shell spectra from aluminum plasmas generated by ultrashort laser pulses at 395 and 790 nm

U. Andiel, K. Eidmann, K. Witte, I. Uschmann, and E. Förster

Appl. Phys. Lett. 80, 198 (2002); http://dx.doi.org/10.1063/1.1432106 (3 pages) | Cited 17 times

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A comparative study of temporally and spectrally resolved K-shell emission from aluminum targets heated with 150 fs Ti:sapphire laser pulses at 790 and 395 nm is presented at an intensity of 5×1017 W/cm2. Whereas at 395 nm spectrally broad intense plasma lines and a weak Kα line with durations (full width at half maximum) of 1–2 ps are observed, the spectrum at 790 nm shows weak narrow plasma lines and an intense Kα line with durations of 3–5 ps. © 2002 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.La X-ray and γ-ray measurements
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Variable temperature study of the passivation of dangling bonds at Si(100)-2×1 reconstructed surfaces with H and D

M. C. Hersam, N. P. Guisinger, J. Lee, K. Cheng, and J. W. Lyding

Appl. Phys. Lett. 80, 201 (2002); http://dx.doi.org/10.1063/1.1431689 (3 pages) | Cited 13 times

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The passivation of the Si(100) surface with H and D is studied with scanning tunneling microscopy (STM). During the passivation process, the clean Si(100) surface is exposed to a gas phase mixture of atomic H and D. By directly observing the dramatic isotopic difference in STM-induced electron stimulated desorption rates, the relative surface concentrations of H and D is discerned with atomic resolution. The ratio of D to H on the Si(100) surface is found to vary by more than an order of magnitude following monolayer passivation at temperatures between 300 and 700 K. A statistical thermodynamics model attributes this behavior to the difference in the vibrational frequencies of H and D on silicon surfaces. © 2002 American Institute of Physics.
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81.65.Rv Passivation
68.35.Rh Phase transitions and critical phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

n-GaN surface treatments for metal contacts studied via x-ray photoemission spectroscopy

K. A. Rickert, A. B. Ellis, F. J. Himpsel, Jingxi Sun, and T. F. Kuech

Appl. Phys. Lett. 80, 204 (2002); http://dx.doi.org/10.1063/1.1430024 (3 pages) | Cited 22 times

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The surface chemistry and electronic properties of n-GaN surfaces were studied via x-ray photoemission spectroscopy before and after wet chemical treatments. Shifts of the surface Fermi level were measured with the change in position of the Ga 3d core level peak. HCl treatment of n-GaN led to a 0.9 eV shift of the surface Fermi level toward the conduction band minimum, while KOH treatment led to a 0.3 eV shift of the surface Fermi level toward the valance band maximum. These shifts lead to a reduction in the surface barrier for HCl-treated n-GaN and for KOH-treated p-GaN, potentially improving contact resistance. The changes in surface chemistry indicate that a N (or Ga) deficiency with HCl(KOH) treatment alters the surface state density through the formation of donor (acceptor)-like states. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
73.40.Cg Contact resistance, contact potential

Marked enhancement of 320–360 nm ultraviolet emission in quaternary InxAlyGa1−x−yN with In-segregation effect

Hideki Hirayama, Atsuhiro Kinoshita, Takayoshi Yamabi, Yasushi Enomoto, Akira Hirata, Tsutomu Araki, Yasushi Nanishi, and Yoshinobu Aoyagi

Appl. Phys. Lett. 80, 207 (2002); http://dx.doi.org/10.1063/1.1433162 (3 pages) | Cited 63 times

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We demonstrated room-temperature (RT) intense ultraviolet (UV) emission in the wavelength range of 315–370 nm from quaternary InxAlyGa1−x−yN alloys grown by metalorganic vapor-phase epitaxy. We found that the UV emission is considerably enhanced by the In-segregation effect upon introducing 2%–5% of In into AlGaN. The In incorporation in quaternary InxAlyGa1−x−yN is markedly enhanced with the increase of Al content when using a relatively high growth temperature (830–850 °C), resulting in efficient RT UV emission. Maximally efficient emission was obtained at around 330–360 nm from the fabricated quaternary InxAlyGa1−x−yN (x = 2.0%–4.8%,y = 12%–34%). The intensity of the 330 nm emission from quaternary In0.034Al0.12Ga0.85N was as strong as that of the 430 nm emission from In0.22Ga0.78N at RT. We clearly observed In segregation of submicron size from cathode luminescence images of quaternary InAlGaN films. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
64.75.-g Phase equilibria
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Behind the weak excitonic emission of ZnO quantum dots: ZnO/Zn(OH)2 core-shell structure

H. Zhou, H. Alves, D. M. Hofmann, W. Kriegseis, B. K. Meyer, G. Kaczmarczyk, and A. Hoffmann

Appl. Phys. Lett. 80, 210 (2002); http://dx.doi.org/10.1063/1.1432763 (3 pages) | Cited 114 times

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The structure of ZnO quantum dots prepared via the wet chemical method was studied. By introducing an annealing treatment (150 °C–500 °C), we also investigated the effect of the change in the structure of the dots on their luminescence properties. Our studies revealed that the surface of the as-prepared dots is passivated by a thin layer of Zn(OH)2, thus, the dots consist of a ZnO/Zn(OH)2 core-shell structure. We present evidence that the weak excitonic transition of ZnO quantum dots is strongly correlated with the presence of the surface shell of Zn(OH)2. When Zn(OH)2 is present, the excitonic transition is quenched. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Radiation sensitivity reduction in deuterium annealed Si–SiO2 structures

J. R. Chavez, R. A. B. Devine, and W. M. Shedd

Appl. Phys. Lett. 80, 213 (2002); http://dx.doi.org/10.1063/1.1428415 (3 pages)

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The x-ray radiation sensitivity of Si–SiO2–Si structures annealed at 420 °C in hydrogen containing forming gas and deuterium containing forming gas is compared. Irradiations carried out without electrical bias and with ±0.5 MV cm−1 up to doses ∼2M rad (SiO2) consistently indicate that positive fixed oxide charge is generated ∼1.5 times more efficiently in hydrogen-annealed oxides as compared to deuterium-annealed oxides. This result suggests that some radiation-induced positive charge creation involves defects passivated with hydrogen/deuterium during the forming gas anneal sequence. © 2002 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
81.65.Rv Passivation
61.80.Cb X-ray effects
73.40.Ty Semiconductor-insulator-semiconductor structures

Defect reduction with quantum dots in GaN grown on sapphire substrates by molecular beam epitaxy

D. Huang, M. A. Reshchikov, F. Yun, T. King, A. A. Baski, and H. Morkoç

Appl. Phys. Lett. 80, 216 (2002); http://dx.doi.org/10.1063/1.1432445 (3 pages) | Cited 8 times

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The GaN films grown on buffer layers containing quantum dots by molecular beam epitaxy on sapphire substrates were investigated. The density of the dislocations in the films was determined by wet chemical etching and atomic force microscopy. It was found that the insertion of a set of multiple GaN quantum-dot layers in the buffer layer effectively reduces the density of the dislocations in the epitaxial layers. As compared to the dislocation density of ∼ 1010 cm−2 in the typical GaN films grown on AlN buffer layer, a density of ∼ 3×107 cm−2 was demonstrated in the GaN films grown with quantum dot layers. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Polarized excimer laser-induced birefringence in silica

N. F. Borrelli, C. M. Smith, J. J. Price, and D. C. Allan

Appl. Phys. Lett. 80, 219 (2002); http://dx.doi.org/10.1063/1.1433902 (3 pages) | Cited 6 times

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We have used linearly polarized 193-nm-excimer laser irradiation to create polarization-induced birefringence in silica. We have observed the polarization-induced birefringence irrespective of whether the sample undergoes net compaction or expansion. The sign of the birefringence is dependent on whether the glass is expanding or compacting. It is suggested that the birefringence derives from an anisotropic density change effected by the linearly polarized exposure. This effect can be expressed formally as an optical frequency-induced dc electrostriction. © 2002 American Institute of Physics.
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78.20.Fm Birefringence
77.65.Bn Piezoelectric and electrostrictive constants

Growth of GaN free from cracks on a (111)Si substrate by selective metalorganic vapor-phase epitaxy

Y. Honda, Y. Kuroiwa, M. Yamaguchi, and N. Sawaki

Appl. Phys. Lett. 80, 222 (2002); http://dx.doi.org/10.1063/1.1432764 (3 pages) | Cited 33 times

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The selective metalorganic vapor-phase epitaxy of wurtzite GaN was performed on a (111) silicon substrate using SiO2 grid mask pattern. Within window regions of (0.2–0.5) mm×(0.2–0.5) mm, GaN films free from cracks were achieved. The full width at half maximum of the (0004) X-ray rocking curve was as narrow as 388 arcs and that of the band edge emission was 18.6 meV at 77 K. The band edge emission peak energy was redshifted. The redshift is reduced slightly in a sample grown on small windows. This suggests that the biaxial strain due to the thermal expansion coefficient mismatch is partly relaxed on small windows. © 2002 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
65.40.De Thermal expansion; thermomechanical effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Surface-modulation-controlled three-dimensional colloidal crystals

Dong Kee Yi, Eun-Mi Seo, and Dong-Yu Kim

Appl. Phys. Lett. 80, 225 (2002); http://dx.doi.org/10.1063/1.1434313 (3 pages) | Cited 15 times

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Significant effects of the modulation depth (h) on a three-dimensional (3D) colloidal self-assembly with symmetric and asymmetric two-dimensional (2D) templates are demonstrated. When the ratio h/D of the surface modulation (h) to the diameter of the bead (D) exceeded 0.35, then 3D square array patterns were obtained, and when the ratio h/D was from 0.28 to 0.35, pseudo-{110} structure resulted. When the ratio h/D was less than 0.28, the 3D crystallization of colloids was not observed but regular tetragonal or hexagonal clusters were formed in a 2D pattern.© 2000 American Institute of Physics.
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82.70.Dd Colloids
81.16.Dn Self-assembly
81.16.Rf Micro- and nanoscale pattern formation

Enhanced nitrogen diffusion in 4H-SiC

G. J. Phelps, N. G. Wright, E. G. Chester, C. M. Johnson, A. G. O’Neill, S. Ortolland, A. Horsfall, K. Vassilevski, R. M. Gwilliam, P. G. Coleman, and C. P. Burrows

Appl. Phys. Lett. 80, 228 (2002); http://dx.doi.org/10.1063/1.1432451 (3 pages) | Cited 4 times

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Experimental evidence is given for boron (B) enhanced diffusion of nitrogen (N) in ion-implanted 4H silicon carbide (4H-SiC), when a nitrogen implant is co-doped within an existing boron p-type well. The co-implanted nitrogen is shown to diffuse continuously with time when samples are annealed at 1600 °C—with little movement of the boron p-well implant profile. An effective nitrogen in boron diffusivity at 1600 °C is determined to be at least 60 times larger than that of a mono-doped nitrogen implant. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials

Strong localization in InGaN layers with high In content grown by molecular-beam epitaxy

F. B. Naranjo, M. A. Sánchez-García, F. Calle, E. Calleja, B. Jenichen, and K. H. Ploog

Appl. Phys. Lett. 80, 231 (2002); http://dx.doi.org/10.1063/1.1432751 (3 pages) | Cited 33 times

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The effect of the III/V ratio and growth temperature on the In incorporation has been studied in thick (>300 nm) InGaN layers, with In mole fractions from 19% to 37%, grown by molecular-beam epitaxy on sapphire and on GaN templates. Significant desorption of In occurs at growth temperatures above 550 °C. Symmetric and asymmetric reflections from high resolution X-ray diffraction reveals that the layers are not fully relaxed. A bowing parameter of 3.6 eV is calculated from optical absorption data, once corrected for strain-free band gap values. The increase of both, the absorption band-edge broadening and the photoluminescence full width at half maximum at room temperature with the In content, is discussed in terms of a strong In localization effect. This localization effect is further evidenced by the S-shaped temperature dependence of the emission energy. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors
78.55.Cr III-V semiconductors
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Optimization of white polychromatic semiconductor lamps

A. Žukauskas, R. Vaicekauskas, F. Ivanauskas, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 80, 234 (2002); http://dx.doi.org/10.1063/1.1432107 (3 pages) | Cited 37 times

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A stochastic method of optimization of a white-light source that relies on additive color mixing of the emissions from colored light-emitting diodes (LEDs) was developed. The method allows for finding the optimal wavelengths of LEDs in order to obtain the best possible trade off between luminous efficacy and the general color rendering index (CRI) of the white source for an arbitrary number of primary LEDs. Optimal solid-state lamps composed of two, three, four, and five different LEDs were analyzed. We show that a dichromatic LED lamp can only provide high efficacy with a general CRI close to zero, whereas trichromatic and quadrichromatic lamps are able to cover the entire range of reasonable general CRI values. The optimization of quintichromatic LED lamps and lamps with a higher number of primary color LEDs yields a negligible benefit in improving CRI but provides for quasicontinuous spectra that might be required for special lighting needs. © 2002 American Institute of Physics.
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42.72.Bj Visible and ultraviolet sources
85.60.Jb Light-emitting devices
02.60.Pn Numerical optimization

Anharmonicity of the C–H stretch mode in SiC: Unambiguous identification of hydrogen–silicon vacancy defect

A. Gali, B. Aradi, D. Heringer, W. J. Choyke, R. P. Devaty, and S. Bai

Appl. Phys. Lett. 80, 237 (2002); http://dx.doi.org/10.1063/1.1432757 (3 pages) | Cited 10 times

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Using first principles calculations, the vibronic properties of hydrogen in a silicon vacancy (VSi+H) are investigated in 3C–SiC. The calculations show that the neutral VSi+H complex, which can bind an exciton, is stable only in lightly p-type SiC. This result is consistent with the experimental findings. The calculations are able to account well for the observed anharmonicity of the C–H stretch vibrations, up to the third harmonic, and for the isotope effects. © 2002 American Institute of Physics.
Show PACS
63.20.Ry Anharmonic lattice modes
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
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