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1 Feb 2007

Volume 101, Issue 3, Articles (03xxxx)

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Wavelength switching dynamics in injected fiber ring lasers

Peter D. Dragic

J. Appl. Phys. 101, 033101 (2007); http://dx.doi.org/10.1063/1.2432308 (5 pages)

Online Publication Date: 1 February 2007

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We experimentally and theoretically investigate the wavelength switching dynamics of an injection-seeded Er doped fiber ring laser. The fiber ring laser is seeded by an external cavity laser diode that is amplitude modulated with a long period 50% duty cycle wave form so that the return to steady state can be investigated. It is found that the laser suffers from severe large-amplitude relaxation oscillations and slow decay times that limit the available wavelength switching speed.
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42.55.Wd Fiber lasers
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Efficient blue upconversion emission in Tm3+ via energy transfer from Yb3+ doped in lithium modified tellurite glass

Neeraj Kumar Giri, Anant Kumar Singh, and S. B. Rai

J. Appl. Phys. 101, 033102 (2007); http://dx.doi.org/10.1063/1.2432305 (4 pages) | Cited 12 times

Online Publication Date: 1 February 2007

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Intense blue and red upconversion emissions were obtained in Tm3+ doped tellurite glass when codoped with Yb3+ ions on pumping with 798 nm radiation. The highest intensity of the blue emission was found for glasses with 0.5 mol % Tm3+ and 6.0 mol % Yb3+. From a study of the dependence of the upconversion intensity on excitation intensity, it is concluded that emissions are due to Tm3+ ions and involve cooperative energy transfer as well as energy transfer from Yb3+ to Tm3+ ions. Lifetime of the Tm3+ level, which is responsible for the intense blue emission, has been measured for various concentrations of Yb3+.
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42.70.Ce Glasses, quartz
78.55.-m Photoluminescence, properties and materials

Efficient blue lasers based on gain structure optimizing of vertical-external-cavity surface-emitting laser with second harmonic generation

Jun-Youn Kim, Soohaeng Cho, Seong-Jin Lim, Jaeryung Yoo, Gi Bum Kim, Ki-Sung Kim, Junho Lee, Sang-Moon Lee, Taek Kim, and Yongjo Park

J. Appl. Phys. 101, 033103 (2007); http://dx.doi.org/10.1063/1.2432366 (4 pages) | Cited 5 times

Online Publication Date: 1 February 2007

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We report on the demonstration of highly efficient blue lasers based on intracavity frequency doubling vertical-external-cavity surface-emitting lasers (VECSELs). By optimizing the number of InGaAs quantum wells and employing Al0.3Ga0.7As carrier blocking layers in resonant periodic gain structures, we observed the pump-power-limited output power of 4.5 W at 920 nm for an InGaAs/GaAs quantum well VECSEL. With a frequency doubling LiB3O5 crystal inside the cavity, 1.9 W continuous-wave 460 nm blue output was demonstrated. Power conversion efficiencies ( = output power∕pump input power) of 22.5% and 9.5% are realized for λ ∼ 920 nm and λ ∼ 460 nm, respectively.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals

Improvements of external quantum efficiency of InGaN-based blue light-emitting diodes at high current density using GaN substrates

Katsushi Akita, Takashi Kyono, Yusuke Yoshizumi, Hiroyuki Kitabayashi, and Koji Katayama

J. Appl. Phys. 101, 033104 (2007); http://dx.doi.org/10.1063/1.2432307 (5 pages) | Cited 23 times

Online Publication Date: 1 February 2007

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InGaN-based blue light-emitting diodes (LEDs) with different quantum well (QW) thicknesses were grown on freestanding GaN substrates with low threading dislocation densities (TDDs) and on c-plane sapphire substrates. In the case of thin QWs of 3 nm in thickness, the external quantum efficiencies (EQEs) of LEDs on GaN substrates, as well as those on sapphire substrates, decreased with increasing forward current, indicating that carrier localization is in play on both types of substrates. For thicker 5-nm-thick QWs, the EQEs of LEDs grown on GaN substrates improved at high current densities, while those on sapphire substrates decreased even at low current densities. The LED with 5-nm-thick QWs on the GaN substrate mounted p-side down and molded with epoxy showed EQE as high as 26% at 125 A/cm2. Cathodoluminescence observations of the active layers on GaN substrates revealed that the expansion of nonradiative areas related to TDDs, which are responsible for the deterioration of the EQE of the LED on the sapphire substrate, had been suppressed.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Picosecond blue-light-induced infrared absorption in single-domain and periodically poled ferroelectrics

J. Hirohashi, V. Pasiskevicius, S. Wang, and F. Laurell

J. Appl. Phys. 101, 033105 (2007); http://dx.doi.org/10.1063/1.2434007 (5 pages) | Cited 10 times

Online Publication Date: 2 February 2007

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Picosecond blue-light-induced infrared absorption is investigated in bulk and periodically poled ferroelectrics known to have high photorefractive resistance (KTiOPO4, MgO-doped congruent LiNbO3, MgO-doped stoichiometric LiNbO3, MgO-doped stoichiometric LiTaO3, and KNbO3). KNbO3 and MgO-doped congruent and stoichiometric LiNbO3 show the lowest susceptibility to induced absorption. Periodic poling slightly increases the susceptibility to the induced absorption in all materials but most noticeably in KTiOPO4, MgO-doped stoichiometric LiTaO3, and KNbO3. Different dynamics of induced absorption are investigated. Relatively high thresholds for induced absorption were observed in MgO-doped stoichiometric LiTaO3 and KNbO3. By increasing the peak power intensity of blue light, the induced absorption for LiNbO3, KTiOPO4, and KNbO3 are saturated, while in MgO-doped stoichiometric LiTaO3, the induced absorption increases almost linearly with the blue peak intensity. The low susceptibility to induced absorption observed in KNbO3 corroborates well with the earlier proposed existence of very shallow traps close to the valence band.
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78.30.Hv Other nonmetallic inorganics
78.47.-p Spectroscopy of solid state dynamics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Analysis of plume following ultraviolet laser ablation of doped polymers: Dependence on polymer molecular weight

Esther Rebollar, Mohamed Oujja, Giannis Bounos, Andreas Kolloch, Savas Georgiou, and Marta Castillejo

J. Appl. Phys. 101, 033106 (2007); http://dx.doi.org/10.1063/1.2434013 (6 pages) | Cited 3 times

Online Publication Date: 5 February 2007

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This work investigates the effect of polymer molecular weight MW on the plume characteristics of poly(methyl methacrylate) (PMMA) and polystyrene (PS) films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI) following irradiation in vacuum at 248 nm. Laser-induced fluorescence probing of the plume reveals the presence of ArH products (NapH and PhenH from, respectively, NapI- and PhenI-doped films). While a bimodal translational distribution of these products is observed in all cases, on average, a slower translational distribution is observed in the low MW system. The extent of the observed dependence is reduced as the optical absorption coefficient of the film increases, i.e., in the sequence NapI∕PMMA, PhenI∕PMMA, and PS-doped films. Further confirmation of the bimodal translational distributions is provided by monitoring in situ the temporally resolved attenuation by the plume as it expands in vacuum of a continuous wave helium–neon laser propagating parallel to the substrate. Results are discussed in the framework of the bulk photothermal model, according to which ejection requires that a critical number of bonds are broken.
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78.55.Kz Solid organic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
78.66.Qn Polymers; organic compounds
81.40.Tv Optical and dielectric properties related to treatment conditions

Monte Carlo ray trace simulation for micro-ball-lens-integrated high-speed InGaAs p-i-n photodiodes

Chih-Chao Yang, Yun-Hsun Huang, Te-Chin Peng, Meng-Chyi Wu, Chong-Long Ho, Chao-Chi Hong, I-Ming Liu, and Yao-Tsong Tsai

J. Appl. Phys. 101, 033107 (2007); http://dx.doi.org/10.1063/1.2432484 (9 pages)

Online Publication Date: 5 February 2007

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To widen the alignment tolerance of a 10 Gbytes/s InGaAs p-i-n photodiode, which typically only has an optical coupling aperture of 30 μm in diameter, we have developed a self-positioning ball-lens-on-chip scheme for enlarging the effective coupling aperture. According to the measured results, the 4.5- and 5.3-fold improvements along the transverse and optical axes, respectively, in alignment tolerance have been demonstrated without sacrificing the diode efficiency as a commercially available ruby micro-ball-lens (MBL) with a 300 μm lens diameter integrated on the high-speed photodiode. To further explore the aperture enlargement capability and optimize the structural design, we have constructed a ray trace model based on the Monte Carlo method for the optical coupling system as well. Using this well-constructed simulation model, we further predict that, by integrating a 250 μm diametric ruby MBL on the photodiode with a 20 μm high lens socket, the alignment tolerance can have 7.1- and 10-fold improvements along the transverse and optical axes, respectively. Such a large alignment tolerance permits the usage of conventional passive scheme for photodiode package.
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85.60.Dw Photodiodes; phototransistors; photoresistors
42.82.Et Waveguides, couplers, and arrays
42.79.Bh Lenses, prisms and mirrors

1.84 μm emission of Tm3+ sensitized by Yb3+ ions in monoclinic KGd(WO4)2 single crystals

F. Güell, J. Massons, Jna. Gavaldà, M. C. Pujol, M. Aguiló, and F. Díaz

J. Appl. Phys. 101, 033108 (2007); http://dx.doi.org/10.1063/1.2433131 (6 pages) | Cited 3 times

Online Publication Date: 6 February 2007

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By exciting at 940 nm, we have characterized the 1.84 μm near infrared emission of trivalent thulium ions in Yb3+, Tm3+:KGd(WO4)2 single crystals as a function of the dopant concentration and temperature, from 10 K to room temperature. An overall 3H6 Stark splitting of ∼ 470 cm−1 for the Tm3+ ions in the Yb3+, Tm3+:KGd(WO4)2 was obtained. We also studied the blue emission at 476 nm (Tm3+) and the near infrared emissions at 1.48 μm (Tm3+) and 1 μm (Yb3+) as a function of the dopant concentration. Experimental decay times of the 1G4, 3H4, and 3F4 (Tm3+) and 2F5/2 (Yb3+) excited states have been measured as a function of Yb3+ and Tm3+ ion concentrations. For the 3F4→3H6 transition of Tm3+ ions, we used the reciprocity method to calculate the maximum emission cross section of 3.07×10−20 cm2 at 1.84 μm for the polarization parallel to the Nm principal optical direction.
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61.72.S- Impurities in crystals
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.-a Optical materials
78.55.Hx Other solid inorganic materials

Analytic determination of n, κ, and d of an absorbing film from polarimetric data in the thin-film limit

I. K. Kim and D. E. Aspnes

J. Appl. Phys. 101, 033109 (2007); http://dx.doi.org/10.1063/1.2434004 (11 pages) | Cited 4 times

Online Publication Date: 6 February 2007

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We obtain a solution of the three-phase model in the limit d/λ⪡1, where the complex refractive index math = n+iκ and thickness d of an isotropic film on an isotropic substrate are given analytically at any single wavelength λ from polarimetric data Δρ/ρ and ΔR/R, where ρ is the complex reflectance ratio and R is either the p- or s-polarized reflectance. We describe several procedures for extending the range of validity of the solution. Analysis of correlations shows that the uncertainty δ(ΔR/R) of ΔR/R is significantly more important than the δ(Δρ/ρ) of Δρ/ρ, which allows us to obtain an expression for the uncertainties δn, δκ, and δd of n, κ, and d, and to identify conditions that optimize the determination of the layer parameters. We find that the relative uncertainties δn/n and δd/d are not equal, as would be expected if they were determined by the optical thickness nd measured by ellipsometry, but that ΔR/R breaks the connection. We verify our results by measurements of H2O reversibly physisorbed on oxidized GaAs, finding, for example, that for our conditions δκ is determined more accurately than δn, and δn more accurately than δd. These data and model calculations show that fluctuations in parameters, particularly d, are asymmetric, leading in principle to inaccurate average values. However, we show that the importance of the ΔR/R data together with the remaining high correlation between n and d allows us to define a characteristic curve that can be used to correct the results for this nonlinearity. Finally, we extend our analysis to determine the orthogonal linear combinations of n, κ, and d that the data actually determine, which explains why the data fit the characteristic curve so well. Our results will be useful in various contexts for the analysis of films less than 1 nm thick, for example, in applications involving preparation of next-generation electronic and optoelectronic devices with complicated multilayer structures, real-time control of deposition, and the identification of physisorbed and chemisorbed layers on the monolayer scale.
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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)
82.80.-d Chemical analysis and related physical methods of analysis
68.43.Mn Adsorption kinetics
42.70.-a Optical materials

Self-assembled spontaneous structures induced by a pulsed laser on a surface of azobenzene polymer film

Naoto Tsutsumi and Arata Fujihara

J. Appl. Phys. 101, 033110 (2007); http://dx.doi.org/10.1063/1.2423083 (5 pages) | Cited 3 times

Online Publication Date: 7 February 2007

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The paper presents the self-assembled regularly patterned unique structures induced by the irradiation of pulsed laser beam on a surface of azobenzene polymer film. Self-assembled patterns depend on the polarization of laser beam. Linearly polarized beam gave rise to the ripple structures whose grating vector is perpendicular to the polarization of laser beam. Pitch of the ripple structures (Λ) was related to the wavelength (λ) of irradiated laser beam; Λ = λ/n. Λ = λ/1.05 for λ = 266 and 355 nm and Λ = λ/1.3 for λ = 420–540 nm were obtained. These results implied that the ripple structures were produced by the interference of the incident beam with the optical wave scattered in a surface (waveguide mode light). The difference of n value is explained by the wavelength dispersion of refractive indices in the azobenzene polymeric matrix. Circularly polarized beam gave rise to the concentric wavelike structure. Pitch of wavelike structure was analyzed using two dimensional Fourier transform imaging techniques. Pitch of wavelike structure increases with increasing the number of laser shots. Furthermore, with increasing irradiation time, well-defined honeycomblike structure was also developed.
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68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Resonant control of the characteristic temperatures T0 and T1 of AlInGaAs 0.8 μm semiconductor lasers with delta-doped tunneling quantum wells

D. Fekete

J. Appl. Phys. 101, 033111 (2007); http://dx.doi.org/10.1063/1.2433769 (6 pages) | Cited 1 time

Online Publication Date: 7 February 2007

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It is demonstrated experimentally that AlInGaAs/GaAs lasers with Te n-type δ-doped resonant tunneling quantum wells (QWs), tuned to operate at resonance at elevated temperature, exhibit higher external efficiency and improved temperature stability. These lasers were designed to ensure that the decrease in the band bending (which results from the increased current density at threshold due to the elevated temperature) would cause the ground-state levels in the two QWs to coincide, thus obtaining enhanced coupling between the QWs. The enhanced coupling increases the efficiency and reduces the transparency current which curbs the increase of the threshold current due to the elevated temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Broadband emission in Er–Tm codoped Al2O3 films: The role of energy transfer from Er to Tm

Zhisong Xiao, R. Serna, and C. N. Afonso

J. Appl. Phys. 101, 033112 (2007); http://dx.doi.org/10.1063/1.2433748 (6 pages) | Cited 11 times

Online Publication Date: 7 February 2007

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Er–Tm codoped a-Al2O3 thin films prepared by alternate pulsed laser deposition show a broad photoluminescence band with two characteristic peaks at 1540 and at 1640 nm, respectively, related to Er3+ and Tm3+ emissions. Two series of films have been prepared. For the first series, the Tm concentration [Tm] has been increased while keeping constant the Er concentration [Er]. The results show that the photoluminescence intensity at 1640 nm (I1640) to that at 1540 nm (I1540) decreases and that at 1640 nm (I1640) increases, i.e., the (I1640/I1540) ratio increases as [Tm] is increased. For [Tm]/[Er] = 3, a fairly flat emission spectrum (I1640/I1540 ∼ 1) with a full width at half maximum of 230 nm is achieved. For the second series both [Tm] and [Er] are increased while keeping the [Tm]/[Er] ratio constant. The I1640/I1540 ratio tends to be constant with a full width at half maximum of 150 nm. The lifetime values decrease in all cases as [Tm] increases. The evolution of the I1640/I1540 and lifetimes as a function of [Tm] as well as the analysis of the latter considering Er as a donor and Tm as an acceptor evidence that there is an efficient energy transfer from Er3+ to Tm3+. These results suggest that enhanced performance with a flat broadband emission useful for planar integrated devices is achievable by further dopant engineering in the nanoscale.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
42.70.Hj Laser materials

Fabry-Perot effects in InGaN/GaN heterostructures on Si-substrate

C. Hums, T. Finger, T. Hempel, J. Christen, A. Dadgar, A. Hoffmann, and A. Krost

J. Appl. Phys. 101, 033113 (2007); http://dx.doi.org/10.1063/1.2434010 (4 pages) | Cited 12 times

Online Publication Date: 8 February 2007

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A strong intensity modulation is found in spatially and angular resolved photoluminescence spectra of InGaN/GaN heterostructures and quantum wells epitaxially grown on Si(111) substrates. This Fabry-Perot effect results from the high refractive index contrasts at the GaN/Si and the Air/InGaN interfaces. It can be used for a wavelength stabilization of the sample upon temperature change and, e.g., in the case of light emitting diodes, to additionally reduce the blueshift at increasing injection currents. A simple geometric approach has been chosen to calculate the influence of layer thickness, absorption and refractive indices, as well as detection angle. The cavity can be described quantitatively by a simple three layer Fabry-Perot model. An analytical expression is derived for the external luminescence line shape. Microphotoluminescence measurements at samples with the silicon substrate locally removed corroborate the model.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Theoretical study of quantum well infrared photodetectors with asymmetric well and barrier structures for broadband photodetection

W. Liu, D. H. Zhang, Z. M. Huang, and W. J. Fan

J. Appl. Phys. 101, 033114 (2007); http://dx.doi.org/10.1063/1.2434938 (7 pages) | Cited 6 times

Online Publication Date: 8 February 2007

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The n-type InGaAs/AlxGa1−xAs quantum well infrared photodetector (QWIP) with asymmetric graded barriers for broadband detection has been investigated theoretically based on the eight-band k∙p model. It is found that the intersubband transitions from the ground state to all bound and continuum excited states contribute to the overall absorption and the bound-to-continuum (B-to-C) transitions dominate. The superposition of the bound-to-bound and B-to-C transitions results in a broad detection bandwidth, and both the detected wavelength and bandwidth can be tuned by the applied voltage. The analysis method is also applicable to the GaAs/InxGa1−xAs/InyGa1−yAs QWIP with step quantum wells. The calculated results are consistent with the reported experimental observations.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Third-order nonlinear optical properties of bismuth-borate glasses measured by conventional and thermally managed eclipse Z scan

A. S. L. Gomes, E. L. Falcão Filho, Cid B. de Araújo, Diego Rativa, R. E. de Araujo, Koichi Sakaguchi, Francesco P. Mezzapesa, Isabel C. S. Carvalho, and Peter G. Kazansky

J. Appl. Phys. 101, 033115 (2007); http://dx.doi.org/10.1063/1.2434940 (7 pages) | Cited 11 times

Online Publication Date: 8 February 2007

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Third-order nonlinearity one order of magnitude larger than silica is measured in bismuth-borate glasses presenting a fast response (<200 fs). The results for the sign and magnitude of the nonlinearity were obtained using a combination of the eclipse Z scan with thermal nonlinearity managed Z scan, whereas the Kerr shutter technique was employed to obtain the electronic time response of the nonlinearity, all performed with 76 MHz repetition rate 150 fs pulses at 800 nm. Conventional Z scans in the picosecond regime at 532 and 1064 nm were also independently performed, yielding the values of the third-order nonlinear susceptibilities at those wavelengths. The results obtained for the femtosecond response, enhanced third-order nonlinearity of this glass (with respect to silica), place this glass system as an important tool in the development of photonics devices. Electro-optical modulators, optical switches, and frequency converters are some of the applications using second-order nonlinear properties of the Bi-glass based on the rectification model.
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42.65.An Optical susceptibility, hyperpolarizability
42.70.Ce Glasses, quartz
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical limiting behavior of zinc phthalocyanines in polymeric matrix

R. Ostuni, M. C. Larciprete, G. Leahu, A. Belardini, C. Sibilia, and M. Bertolotti

J. Appl. Phys. 101, 033116 (2007); http://dx.doi.org/10.1063/1.2434941 (5 pages) | Cited 14 times

Online Publication Date: 9 February 2007

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Phthalocyanines are promising molecules which present very attractive properties for nonlinear optical applications of both second and third orders. Different solutions of zinc phthalocyanine in toluene at increasing concentration were investigated by spectroscopic analysis in order to get the best conditions for the realization of films in poly(methyl methacrylate). Some films of zinc phthalocyanine in polymeric matrix were realized and their nonlinear optical behavior was characterized. The ratio by weight of the compound to the host polymer was varied between 0.004% and 0.15%. In this range all samples show a low degree of aggregation. The nonlinear optical behavior of the films was evaluated by measuring nonlinear transmission. The measurements of nonlinear transmission were carried out at 532 nm using a nanosecond Nd:YAG laser followed by an optical parametric oscillator, and a nonlinear response was observed for the two highest concentrations (0.083% and 0.15%). Finally, the nonlinear absorption coefficient β was retrieved by fitting experimental data and found to be 29 and 43 cm/GW, respectively.
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42.70.Jk Polymers and organics
42.65.Yj Optical parametric oscillators and amplifiers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Broadband SiGe/Si quantum dot infrared photodetectors

C.-H. Lin, C.-Y. Yu, C.-Y. Peng, W. S. Ho, and C. W. Liu

J. Appl. Phys. 101, 033117 (2007); http://dx.doi.org/10.1063/1.2433768 (4 pages) | Cited 4 times

Online Publication Date: 12 February 2007

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The broadband absorption of metal-oxide-semiconductor SiGe/Si quantum dot infrared photodetectors is demonstrated using boron δ doping in the Si spacer. The peak at 3.7–6 μm results from the intersubband transition in the SiGe quantum dot layers. The other peak at 6–16 μm mainly comes from the intraband transition in the boron δ-doping wells in the Si spacers. Since the atmospheric transmission windows are located at 3–5.3 and 7.5–14 μm, broadband detection is feasible using this device. The δ doping in SiGe quantum dots and Si0.9Ge0.1 quantum wells is also investigated to identify the origin of the absorption.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.up Other materials

Microscopic electroabsorption line shape analysis for Ga(AsSb)/GaAs heterostructures

C. Bückers, G. Blume, A. Thränhardt, C. Schlichenmaier, P. J. Klar, G. Weiser, S. W. Koch, J. Hader, J. V. Moloney, T. J. C. Hosea, S. J. Sweeney, J.-B. Wang, S. R. Johnson, and Y.-H. Zhang

J. Appl. Phys. 101, 033118 (2007); http://dx.doi.org/10.1063/1.2433715 (8 pages) | Cited 8 times

Online Publication Date: 12 February 2007

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A series of Ga(AsSb)/GaAs/(AlGa)As samples with varying GaAs spacer width are studied by electric-field modulated absorption (EA) and reflectance spectroscopy and modeled using a microscopic theory. The analysis of the Franz–Keldysh oscillations of GaAs capping layer and of the quantum-confined Stark shift of the lowest quantum well (QW) transitions shows the strong inhomogeneity of the built-in electric field indicating that the field modulation due to an external bias voltage differs significantly for the various regions of the structures. The calculations demonstrate that the line shape of the EA spectra of these samples is extremely sensitive to the value of the small conduction band offset between GaAs and Ga(AsSb) as well as to the magnitude of the internal electric field changes caused by the external voltage modulation in the QW region. The EA spectra of the entire series of samples are modeled by the microscopic theory. The good agreement between experiment and theory allows us to extract the strength of the modulation of the built-in electric field in the QW region and to show that the band alignment between GaAs and Ga(AsSb) is of type II with a conduction band offset of approximately 40 meV.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects
73.21.Fg Quantum wells

Analysis of semiconductor laser dynamics under gigabit rate modulation

Moustafa Ahmed, Minoru Yamada, and Safwat W. Z. Mahmoud

J. Appl. Phys. 101, 033119 (2007); http://dx.doi.org/10.1063/1.2434803 (9 pages) | Cited 5 times

Online Publication Date: 12 February 2007

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A theoretical study of the dynamics of semiconductor lasers subjected to pseudorandom digital modulation at gigabit rates is presented. The eye diagram, turn-on jitter (TOJ), and power fluctuations in the modulated laser wave form are analyzed. The study is based on numerical large-signal analysis of the laser rate equations. Influences of the biasing and modulation currents on the eye diagram and TOJ are examined. The degree of eye opening is measured in terms of a Q factor of the laser signal analogous to the Q factor determining the bit-error rate in transmission systems. Influence of optimizing both the sampling and decision times on the signal Q factor is modeled. We show that the most eye opening corresponds to shortening the sampling time associated with lengthening the decision time. We also assess the relative contributions of the laser intrinsic noise and pseudorandom bit pattern to the TOJ. The results show that the bit pattern is the major contributor to the TOJ when the setting time of the relaxation oscillation is longer than the bit slot.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
02.50.-r Probability theory, stochastic processes, and statistics
42.60.Mi Dynamical laser instabilities; noisy laser behavior

Linearly polarized lasing in one-dimensional hybrid photonic crystal containing cholesteric liquid crystal

Yuko Matsuhisa, Ryotaro Ozaki, Yuuki Takao, and Masanori Ozaki

J. Appl. Phys. 101, 033120 (2007); http://dx.doi.org/10.1063/1.2434835 (4 pages) | Cited 6 times

Online Publication Date: 12 February 2007

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We have achieved single-mode laser action in a one-dimensional hybrid photonic crystal (HPC) containing cholesteric liquid crystal (CLC) as a defect and experimentally investigated the polarization characteristics of the laser light. The laser light emitted from the HPC containing the CLC was linearly polarized, which was different from that of the simple CLC, despite the CLC being contained in this structure. We have theoretically calculated the optical propagation to justify the experimental result. The calculated result was in good agreement with the experimental result and showed the difference in optical characteristics between the simple CLC and the HPC containing the CLC.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
42.70.Hj Laser materials

Modeling photoreflectance of quantum well heterostructures: A comprehensive approach

Laurel M. Mayhew, Deborah Lehr Trivedi, and Neal G. Anderson

J. Appl. Phys. 101, 033121 (2007); http://dx.doi.org/10.1063/1.2429728 (7 pages) | Cited 1 time

Online Publication Date: 12 February 2007

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We present a comprehensive approach to modeling the photoreflectance (PR) spectra of semiconductor quantum wells embedded in layered heterostructures. Near-gap PR spectra are obtained directly from the calculated variation of surface reflectance spectra induced by modulation of an internal electric field. The field-dependent reflectance spectra are themselves obtained from a transfer matrix model of a quantum well heterostructure (QWH) in which the quantum well layer is treated in detail using electric-field-dependent optical absorption calculations and all surrounding higher-gap layers are treated as lossless dielectric slabs. The model is described in detail and is applied to unstrained GaAs/AlGaAs and compressively strained InGaAs/GaAs single-well QWHs for which both experimental data and other calculations are available for comparison. This model can serve as a tool for interpretation of experimental PR spectra, and should be particularly useful for analysis of dense spectra with overlapping features that would be difficult to analyze using empirical fitting schemes. The approach can be used to model electroreflectance without modification.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects

Improvement of GaInNAs p‐i‐n photodetector responsivity by antimony incorporation

W. K. Loke, S. F. Yoon, K. H. Tan, S. Wicaksono, and W. J. Fan

J. Appl. Phys. 101, 033122 (2007); http://dx.doi.org/10.1063/1.2435990 (5 pages) | Cited 15 times

Online Publication Date: 13 February 2007

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Deep-level transient spectra (DLTS) and photoresponsivity were measured for Ga0.90In0.10N0.033As0.967/GaAs and Ga0.96In0.04N0.028As0.967Sb0.005/GaAs p‐i‐n photodetector structures. The GaInNAs and GaInNAsSb layers were grown closely lattice matched to GaAs substrate at 460 °C using molecular beam epitaxy. Two hole-trap levels were observed in the DLTS spectra of the GaInNAs sample with activation energies of 0.152 and 0.400 eV (labeled as H-1 and H-2 peak, respectively). The lower activation energy is believed to be associated with nitrogen-related defects and the higher activation energy is associated with arsenic antisite defects (AsGa). Following the incorporation of Sb into GaInNAs, the H-1 peak vanished from the DLTS spectra of the GaInNAsSb sample, and the AsGa defect-related DLTS signal was significantly reduced. Analysis of the DLTS data also showed that the trap concentration related to AsGa was reduced from 2.15×1015 to 2.58×1014 cm−3. The DLTS results are in good agreement with the photoresponsivity results, in which the GaInNAsSb sample showed 10× higher photoresponse compared to the GaInNAs sample. This indicates the incorporation of Sb into GaInNAs has effectively improved the p‐i‐n photodetector device performance.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Calculated optical properties of wurtzite InN

H. Jin, G. L. Zhao, and D. Bagayoko

J. Appl. Phys. 101, 033123 (2007); http://dx.doi.org/10.1063/1.2435802 (4 pages) | Cited 12 times

Online Publication Date: 14 February 2007

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We report ab initio, self-consistent calculations of the dielectric function of wurtzite indium nitride (w-InN). Our calculations employed a local density approximation (LDA) potential, a linear combination of atomic orbital basis set, and the Bagayoko-Zhao-Williams (BZW) method. Our findings agree very well with recent measurements up to photon energies of 6 eV. This excellent agreement shows the correct description, by the LDA-BZW method, of the relative separations between upper valence bands and low-lying conduction bands, in general, and corroborates our previous result of 0.88 eV for the intrinsic, fundamental band gap of w-InN, in particular. We also report results of simulations of the effect of high electron doping on the optical properties of InN.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
61.72.S- Impurities in crystals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Understanding the advantage of remote femtosecond laser-induced breakdown spectroscopy of metallic targets

H. L. Xu, J. Bernhardt, P. Mathieu, G. Roy, and S. L. Chin

J. Appl. Phys. 101, 033124 (2007); http://dx.doi.org/10.1063/1.2437580 (6 pages) | Cited 11 times

Online Publication Date: 14 February 2007

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We analyze the advantages of remotely sensing metallic targets using femtosecond laser-induced breakdown spectroscopy by studying the temperature and electron density of the plasma ejected from a lead target produced by femtosecond laser pulse filamentation in ambient air. The electron density of 8×1017 cm−3 and the plasma temperature of 6794 K were obtained for a 20 ns time delay with respect to the laser pulse arriving on the target. With these values the signal is high, while the continuum blackbody radiation is low. The continuum emission in the fluorescence spectra is mainly associated with the supercontinuum of the distorted pulse during filamentation (white light laser) in air and this can be controlled. Extrapolation of the single-shot detection limit shows that this technique of filament-induced breakdown spectroscopy could be extended up to the kilometer range, opening up potential applications in metallurgic industry for remote material analysis and process controls.
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42.62.Fi Laser spectroscopy
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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

rf magnetron sputter deposition of transparent conducting Nb-doped TiO2 films on SrTiO3

Meagen A. Gillispie, Maikel F. A. M. van Hest, Matthew S. Dabney, John D. Perkins, and David S. Ginley

J. Appl. Phys. 101, 033125 (2007); http://dx.doi.org/10.1063/1.2434005 (4 pages) | Cited 33 times

Online Publication Date: 14 February 2007

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rf magnetron sputtering, an established and scalable large area deposition process, is used to deposit Nb:TiO2 and Ta:TiO2 films onto (100) SrTiO3 substrates at temperatures TS ranging from room temperature to 400 °C. Optical, electrical, and structural properties similar to those reported for pulsed laser deposition grown films were obtained. In particular, the most conducting Ti0.85Nb0.15O2 films, grown at TS ≈ 375 °C, are epitaxially oriented anatase films with conductivity of 3000 S cm−1, carrier concentration of 2.4×1021 cm−3, Hall mobility of 7.6 cm2 V−1 s−1, and optical transparency T>80% from 400 to 900 nm. The conductivity is strongly correlated with the intensity of the anatase (004) x-ray diffraction peak.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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