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1 Sep 2008

Volume 104, Issue 5, Articles (05xxxx)

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Nano-Ag on vanadium dioxide. I. Localized spectrum tailoring

Gang Xu, Chun-Ming Huang, Ping Jin, Masato Tazawa, and De-Ming Chen

J. Appl. Phys. 104, 053101 (2008); http://dx.doi.org/10.1063/1.2973340 (6 pages) | Cited 5 times

Online Publication Date: 2 September 2008

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We report on the utilization of localized surface plasmon resonance (LSPR) of Ag nanoparticles to tailor the optical properties of VO2 thin film. Interaction of nano-Ag with incident light yields a salient absorption band in the visible-near IR region and modifies the spectrum of VO2 locally. The wavelength of modification occurs in a limited spectral region rather than affects the full spectrum. The wavelength of modification shows a strong dependence on the metal nanoparticle size and shifts toward the red as the particle size or the mass thickness of nano-Ag increases. Also, we found that the wavelength can be shifted into the IR further by introducing a thin layer of TiO2 onto the nano-Ag. Interestingly, with the help of LSPR effects the VO2 film exhibits an anomalous thermochromic behavior in the modification wavelength region, which may be useful in optical switching applications.
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73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.30.Er Solid metals and alloys
68.55.aj Insulators

Nano-Ag on vanadium dioxide. II. Thermal tuning of surface plasmon resonance

Gang Xu, Chun-Ming Huang, Masato Tazawa, Ping Jin, and De-Ming Chen

J. Appl. Phys. 104, 053102 (2008); http://dx.doi.org/10.1063/1.2973341 (6 pages) | Cited 9 times

Online Publication Date: 2 September 2008

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Thermal tuning of the localized surface plasmon resonance (LSPR) of Ag nanoparticles on a thermochromic thin film of VO2 was studied experimentally. The tuning is strongly temperature dependent and thermally reversible. The LSPR wavelength λSPR shifts to the blue with increasing temperature from 30 to 80 °C, and shifts back to the red as temperature decreases. A smart tuning is achievable on condition that the temperature is controlled in a stepwise manner. The tunable wavelength range depends on the particle size or the mass thickness of the metal nanoparticle film. Further, the tunability was found to be enhanced significantly when a layer of TiO2 was introduced to overcoat the Ag nanoparticles, yielding a marked sensitivity factor ΔλSPR/Δn, of as large as 480 nm per refractive index unit (n) at the semiconductor phase of VO2.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.66.-w Optical properties of specific thin films

Role of oxygen atoms in CaF2 crystals doped with Eu atom

Suzuka Nishimura, Kazutaka Terashima, and Hiroshi Nagayoshi

J. Appl. Phys. 104, 053103 (2008); http://dx.doi.org/10.1063/1.2970155 (4 pages) | Cited 1 time

Online Publication Date: 2 September 2008

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The optical transparency in function of wavelength of CaF2 crystals doped with Eu (denoted by CaF2:Eu) has been measured. The optical absorption occurs below λ = 400 nm depending on the amount of Eu atoms doped. The short wavelength below 400 nm has been shifted to around λ = 425 nm. As a result, the 425 nm wavelength increased and the light below 400 nm was cut through CaF2:Eu crystals. This scintillating effect has been found much increased by adding oxygen atoms in crystals. This is due to the distortion of electrical and structural symmetry in crystals by adding oxygen atoms in the form of oxide materials.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.80.Sk Insulators
78.55.Hx Other solid inorganic materials
81.10.Fq Growth from melts; zone melting and refining

Spectral characteristics of continuous wave broadband from a fiber laser with a low dispersion fiber in the cavity

Deepa Venkitesh and R. Vijaya

J. Appl. Phys. 104, 053104 (2008); http://dx.doi.org/10.1063/1.2973458 (5 pages) | Cited 3 times

Online Publication Date: 3 September 2008

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The spectral width of the continuous wave broadband generated in an erbium doped fiber ring laser containing a dispersion shifted fiber (DSF) in a filterless cavity is found to be governed by the nature of the gain spectrum of the doped fiber, in addition to the nonlinear effects. This dependence is studied experimentally with different lengths of the doped fiber and the DSF. Spectral broadening is demonstrated in the conventional (C) and long wavelength (L) bands using pump powers less than 200 mW, with an appropriate choice of cavity parameters. The generated broadband is demultiplexed in the C-band to prove its utility in optical communication systems.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Growth and spectroscopic properties of Pr3+:NaLa(MoO4)2 crystal

Weijie Guo, Yanfu Lin, Xinghong Gong, Yujin Chen, Zundu Luo, and Yidong Huang

J. Appl. Phys. 104, 053105 (2008); http://dx.doi.org/10.1063/1.2973657 (8 pages) | Cited 3 times

Online Publication Date: 3 September 2008

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A Pr3+:NaLa(MoO4)2 (NLM) single crystal has been grown by the Czochralski method. Thermal expansion coefficients of the crystal were measured. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were recorded at room temperature. Detailed polarized spectroscopic analysis on the crystal has been carried out. The relationship between the Judd–Ofelt intensity parameters and the visible emissions from the 3P0-multiplet of Pr3+ ions has been discussed. The results of spectroscopic analysis imply that Pr3+:NLM crystal is a potential gain medium for visible laser and self-stimulated Raman scattering laser application.
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81.10.Fq Growth from melts; zone melting and refining
65.40.De Thermal expansion; thermomechanical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials

GaN-based microdisk light emitting diodes on (111)-oriented nanosilicon-on-insulator templates

S. Tripathy, T. E. Sale, A. Dadgar, V. K. X. Lin, K. Y. Zang, S. L. Teo, S. J. Chua, J. Bläsing, and A. Krost

J. Appl. Phys. 104, 053106 (2008); http://dx.doi.org/10.1063/1.2973684 (7 pages) | Cited 4 times

Online Publication Date: 3 September 2008

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InGaN/GaN microdisk light emitting diodes (LEDs) on (111)-oriented nanosilicon-on-insulator (nano-SOI) substrates are demonstrated. The (111)-oriented thin SOI substrates are prepared by separation by implantation of oxygen (SIMOX) method. The InGaN/GaN LED structures are grown on these SIMOX templates by metal-organic chemical vapor deposition. The circular mesa patterns are created by standard LED processing steps including photolithography, inductively coupled plasma etching, and contact metallization. Due to the reflectivity changes at the bottom Si/SiO2 interfaces beneath AlN buffer, an improved light extraction from these LEDs has been observed. The room-temperature electroluminescence (EL) spectrum of the microdisk LEDs on SOI shows multiple interference peaks due to the reflections at the Fabry-Pérot boundaries and such effect resulted in an increased integrated EL intensity. For a comparative analysis of light extraction with respect to similar LED structures grown on bulk Si(111), a detailed reflectivity analysis has been carried out to verify the LED structures and to model the EL lineshapes.
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85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Fi Electroluminescence

Truncated photonic crystal cavities with optimized mode confinement

Carl A. Bauer, Gregory R. Werner, and John R. Cary

J. Appl. Phys. 104, 053107 (2008); http://dx.doi.org/10.1063/1.2973669 (4 pages) | Cited 6 times

Online Publication Date: 4 September 2008

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Optimization of a truncated, dielectric photonic crystal cavity leads to configurations that are far from truncated crystal cavities, and which have significantly better radiation confinement. Starting from a two-dimensional truncated photonic crystal cavity with optimal Q-factor, moving the rods from the lattice positions can increase the Q-factor by orders of magnitude, e.g., from 130 to 11 000 for a cavity constructed from 18 rods. In the process, parity symmetry breaking occurs. Achieving the same Q-factor with a regular lattice requires 60 rods. Therefore, using optimized irregular structures for photonic cavities can greatly reduce material requirements and device size.
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42.70.Qs Photonic bandgap materials

Multiphoton absorption in CsLiB6O10 with femtosecond infrared laser pulses

J. N. Babu Reddy, V. B. Naik, Suja Elizabeth, H. L. Bhat, N. Venkatram, and D. Narayana Rao

J. Appl. Phys. 104, 053108 (2008); http://dx.doi.org/10.1063/1.2973680 (5 pages) | Cited 3 times

Online Publication Date: 4 September 2008

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Nonlinear absorption and refraction characteristics of cesium lithium borate (CsLiB6O10) crystal have been studied using Z-scan technique. Ti:sapphire laser with 110 fs pulse width operating at 800 nm wavelength and pulse repetition rate of 1 kHz is used as the source of photons. Intensity of the laser pulse is varied from 0.541 to 1.283 T W/cm2 to estimate the intensity dependence of multiphoton absorption coefficients. Using the theory of multiphoton absorption proposed by Sutherland [ Handbook of Nonlinear Optics, in 2nd ed., edited by D. G. McLean and S. Kirkpatrick, Dekker, New York (2003) ], found that open aperture Z-scan data fit well for the five-photon absorption (5PA) process. 5PA coefficients are obtained by fitting the expressions into the open aperture experimental data for various peak intensities (I00). The nonlinear refractive index n2 estimated from closed aperture Z-scan experiment is 1.075×10−4 cm2/T W at an input peak intensity of 0.723 T W/cm2. The above experiment when repeated with a 532 nm, 6 ns pulsed laser led to an irreversible damage of the sample resulting in an asymmetric open aperture Z-scan profile. This indicates that it is not possible to observe multiphoton absorption in this regime of pulse width using 532 nm laser.
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42.70.Mp Nonlinear optical crystals
72.20.Ht High-field and nonlinear effects
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Optical detection and characterization of graphene by broadband spectrophotometry

Alexander Gray, Mehdi Balooch, Stephane Allegret, Stefan De Gendt, and Wei-E Wang

J. Appl. Phys. 104, 053109 (2008); http://dx.doi.org/10.1063/1.2974096 (8 pages) | Cited 10 times

Online Publication Date: 4 September 2008

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The spectra of optical constants, index of refraction (n), and extinction coefficient (k) of graphene and graphite are obtained in the wavelength range of 190–1000 nm (6.53–1.24 eV) using broadband optical spectrophotometry in conjunction with the Forouhi–Bloomer dispersion relations for n and k. Measurement is made possible by the use of a multilayer substrate consisting of bulk Si and a 3000 Å SiO2 film. The effect of multiple internal reflections between the Si/SiO2 and SiO2/graphene interfaces amplifies the attenuating effect of the graphene layer, thereby improving the sensitivity of the reflectance measurement by a factor of 27 in the deep ultraviolet region of the spectrum. Maximum sensitivity is observed in the deep ultraviolet region of the spectrum, where a strong peak in the spectrum of the extinction coefficient of graphene is identified. The proposed method enables fast nondestructive angstrom-level thickness measurements of graphene and graphite. In this work, layers ranging in thickness between 3.8 Å (graphene) and 792.8 Å are detected, measured, and characterized. Reflectance spectra of graphene and graphite on Ni, Co, and Fe substrates are calculated. Differences of 1.1%–2.0% between the bare substrate and the graphene on the substrate are predicted in the deep ultraviolet region of the spectrum, which makes graphene detectable and measurable on these substrates.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
61.46.-w Structure of nanoscale materials

Determination of complex refractive index of thin metal films from terahertz time-domain spectroscopy

Da-xiang Zhou, E. P. J. Parrott, Douglas J. Paul, and J. Axel Zeitler

J. Appl. Phys. 104, 053110 (2008); http://dx.doi.org/10.1063/1.2970161 (9 pages) | Cited 1 time

Online Publication Date: 4 September 2008

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Thin metal films alone or incorporated in a multilayer stack structure with dielectric films are good candidates of terahertz absorbers necessary for achieving the maximum responsivity in microbolometer devices. However, the design and optimization of these absorber structures depend on the knowledge of the complex refractive index of metal films in the terahertz frequency range, which is not easy to measure or determine from experiment. This paper presents a novel method that allows fast and reliable extraction of the complex refractive index from terahertz time-domain spectroscopy. It starts with terahertz time-domain transmission measurements, followed by Fourier transforms to obtain the transmission spectrum in the frequency range of 0.1–3 THz, and finally an extraction process using the enhanced “on-the-downhill” algorithm. Some experimental examples are given, all of which show good agreement with theoretical calculations. This extraction method, combined with the scattering matrix model, can help design and optimize complicated absorber structures for terahertz microbolometers.
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78.66.Bz Metals and metallic alloys
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Light extraction enhancement of GaN-based light emitting diodes using MgF2/Al omnidirectional reflectors

Hyunsoo Kim, Sung-Nam Lee, Youngjo Park, Kyoung-Kook Kim, Joon Seop Kwak, and Tae-Yeon Seong

J. Appl. Phys. 104, 053111 (2008); http://dx.doi.org/10.1063/1.2973685 (4 pages) | Cited 3 times

Online Publication Date: 5 September 2008

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We report on the enhancement of the light extraction of GaN-based light emitting diodes (LEDs) by using MgF2/Al omnidirectional reflectors (ODRs). The ODRs consisting of a quarter-wavelength-thick MgF2 having a refractive index of 1.39 and Al metal produce a high-angle-integrated reflectivity of 96.6%. To optimize the electrical injection and light reflection, the MgF2/Al ODRs are combined with Pd/Ag metallic reflectors using mesh configuration. Compared to reference LEDs, LEDs fabricated with the MgF2/Al ODRs show an enhanced output power by 23% and a slight increase in the forward voltage by 0.18 V, leading to the improvement in power efficiency by 17%.
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71.55.Eq III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.Jb Light-emitting devices

Effect of polarity on the growth of InN films by metalorganic chemical vapor deposition

Abhishek Jain, Xiaojun Weng, Srinivasan Raghavan, Brenda L. VanMil, Thomas Myers, and Joan M. Redwing

J. Appl. Phys. 104, 053112 (2008); http://dx.doi.org/10.1063/1.2973681 (7 pages) | Cited 5 times

Online Publication Date: 8 September 2008

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The effect of surface polarity on InN growth on GaN by metalorganic chemical vapor deposition (MOCVD) was investigated. The polarity of the InN was found to follow that of the initial GaN template as determined by a comparison of experimental and simulated convergent beam electron diffraction patterns. Under identical MOCVD growth conditions, In-polar InN was observed to nucleate and grow on Ga-polar GaN as pyramidal-shaped islands with (10math1) as the stable surface facet. In contrast, enhanced lateral growth and reduced surface roughness were observed for N-polar InN grown on N-polar GaN. InN films grown on (0001) sapphire substrates using a thin AlN buffer under identical conditions to those used for growth on the GaN templates also exhibited reduced surface roughnesses and were determined to be N polar. A qualitative model based on the difference in surface terminations and crystal structures is proposed to explain the observed differences in the structural properties and growth modes of the In-polar and N-polar InN films.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.35.bg Semiconductors

Photoconductive response correction for detectors of terahertz radiation

E. Castro-Camus, L. Fu, J. Lloyd-Hughes, H. H. Tan, C. Jagadish, and M. B. Johnston

J. Appl. Phys. 104, 053113 (2008); http://dx.doi.org/10.1063/1.2969035 (7 pages) | Cited 3 times

Online Publication Date: 8 September 2008

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Photoconductive detectors are convenient devices for detecting pulsed terahertz radiation. We have optimized Fe+ ion-damaged InP materials for photoconductive detector signal to noise performance using dual-energy doses in the range from 2.5×1012 to 1.0×1016 cm−2. Ion implantation allowed the production of semiconducting materials with free-carrier lifetimes between 0.5 and 2.1 ps, which were measured by optical pump terahertz probe spectroscopy. The time resolved photoconductivity of the detector substrates was acquired as a function of time after excitation by 2 nJ pulses from a laser oscillator. These data, when combined with a deconvolution algorithm, provide an excellent spectral response correction to the raw photocurrent signal recorded by the photoconductive detectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.40.Ry Impurity doping, diffusion and ion implantation technology

Second-harmonic generation in sodium and niobium borophosphate glasses after poling under field-assisted silver ions anodic injection

Artem Malakho, Evelyne Fargin, Aurélien Delestre, Clément André, Thierry Cardinal, Michel Lahaye, Vincent Rodriguez, Michel Couzi, Frédéric Adamietz, Lionel Canioni, and Arnaud Royon

J. Appl. Phys. 104, 053114 (2008); http://dx.doi.org/10.1063/1.2973156 (4 pages) | Cited 1 time

Online Publication Date: 9 September 2008

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Monovalent silver ions, resulting from a thin silver layer initially deposited at the anode surface, have been introduced using the field-assisted ion-exchange technique in sodium niobium borophosphate glasses. A reproducible susceptibility χ(2) could be gained after this poling treatment, although a drop in the nonlinearity is observed due to the introduction of silver ions. From energy dispersive x-ray spectroscopy, it has been found that the nonlinear layer is characterized by a strong migration of sodium ions 4 μm deep inside the anode side, which have been partially replaced by silver ions. These results indicate a complex space-charge-migration process during the poling treatment, which is involved in the decrease in the mean second-harmonic generation signal.
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42.70.Ce Glasses, quartz
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Improvement in both giant magnetoresistance and exchange bias through hydrogen ion irradiation at low energy

Jaechul Shim, Yoonsung Han, Jinwon Lee, and Jongill Hong

J. Appl. Phys. 104, 053115 (2008); http://dx.doi.org/10.1063/1.2973396 (4 pages) | Cited 2 times

Online Publication Date: 9 September 2008

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Irradiation of IrMn-based spin valves with 550 eV hydrogen ions increased their giant magnetoresistance and exchange bias by 20% and 60%, respectively. This significant enhancement stems from the strong (111) texture and small mosaic spread of the IrMn antiferromagnet that resulted from the microstructural reconstruction caused by the energy transfer during the bombardment by hydrogen ions, as well as by the narrow dispersion in the exchange bias. Irradiation with the hydrogen ion at low energy can improve the properties of spin valves without resulting in undue degradation in the performance or the microstructure.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Ee Antiferromagnetics
61.80.Jh Ion radiation effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Polar orientation of a pendant anionic chromophore in thick layer-by-layer self-assembled polymeric films

Akhilesh Garg, Richey M. Davis, Cemil Durak, James R. Heflin, and Harry W. Gibson

J. Appl. Phys. 104, 053116 (2008); http://dx.doi.org/10.1063/1.2974094 (8 pages) | Cited 3 times

Online Publication Date: 9 September 2008

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Multilayer films with up to 600 bilayers and 740 nm thickness were fabricated using the alternating deposition of poly(allylamine hydrochloride) and poly{1-[p-(3′-carboxy-4′- hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl} on glass substrates. Linear relationships for absorbance, thickness, and the square root of the second harmonic intensity versus the number of bilayers demonstrates that the films have long range polar order and optical homogeneity. The deposition conditions (i.e., pH of the solutions, solvent quality, deposition and rinsing times) are critical variables in fabricating layer-by-layer thick films that exhibit long range polar orientation of chromophores. The ability to fabricate noncentrosymmetric films on the order of a micron thick with bulk second order nonlinear optical responses is crucial because it enables the development of nonlinear optical waveguide devices such as electro-optic modulators.
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81.16.Dn Self-assembly
68.55.am Polymers and organics
42.79.Wc Optical coatings
68.65.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Mean field theory with only a few transverse Fourier components of EM fields for low-frequency two-dimensional photonic bands

L. Chang, K.-C. Lee, and G. Y. Wu

J. Appl. Phys. 104, 053117 (2008); http://dx.doi.org/10.1063/1.2975354 (9 pages) | Cited 1 time

Online Publication Date: 9 September 2008

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We propose a mean field band structure theory for low-lying two-dimensional photonic states based on the principle of plane wave expansion. Our theory reduces the complexities of a two-dimensional problem into that of an effective one-dimensional crystal, which provides two key advantages: (a) simplification of dimensions assists in the ease of calculation and (b) delineation of the photonic state physics leads to a gain in its physical insights. Our method distinguishes itself from previous known mean field theories in its capability to include more than one Fourier component of EM fields decomposed along the direction perpendicular to propagation. Furthermore, the method applies to virtually any crystal structure and direction of propagation, and it was discovered to function well for both E-polarization and H-polarization modes of states. We also attempt to demonstrate a systematic improvement of the calculation with the increasing number of Fourier components. Satisfactory numerical accuracy is obtained particularly for the states of the two lowest bands.
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42.25.Bs Wave propagation, transmission and absorption
42.70.Qs Photonic bandgap materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Transverse laser-induced thermoelectric voltages in tilted La2−xSrxCuO4 thin films

F. Xiong, H. Zhang, Z. M. Jiang, and P. X. Zhang

J. Appl. Phys. 104, 053118 (2008); http://dx.doi.org/10.1063/1.2969719 (4 pages) | Cited 4 times

Online Publication Date: 9 September 2008

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The transverse laser-induced thermoelectric voltages in the tilted La2−xSrxCuO4 (LSCO) thin films are observed for the first time. The detected signals are demonstrated to originate from the anisotropy of thermoelectric power and depend on the Sr-doping level drastically. The largest voltage is observed in the LSCO films at x = 0.15 under the irradiation of different lasers with the wavelength in the spectrum range from infrared to ultraviolet. The dependence of the signals on Sr-doping content is associated with a two dimensional charge transport behavior in LSCO films near the optimum doping content.
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74.78.-w Superconducting films and low-dimensional structures
73.50.Lw Thermoelectric effects
74.25.F- Transport properties
74.72.-h Cuprate superconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Intersubband transitions in InGaAsN/GaAs quantum wells

W. Liu, D. H. Zhang, W. J. Fan, X. Y. Hou, and Z. M. Jiang

J. Appl. Phys. 104, 053119 (2008); http://dx.doi.org/10.1063/1.2976335 (8 pages) | Cited 4 times

Online Publication Date: 9 September 2008

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The dependences of intersubband transitions on well width and nitrogen (N) content in n-type In0.23Ga0.77As1−xNx/GaAs quantum wells (QWs) are investigated using a ten-band k⋅p model. The absorption peak energy is found to increase first with the well width starting from 2 nm. It becomes insensitive from about 2.5 to 4.5 nm although the absorption intensity increases and bandwidth decreases monotonically, and then keeps decreasing with the well width beyond 4.5 nm. The peak energy is much larger than that of the N-free structure for narrower wells, but the difference decreases quickly with increasing well width. In the case of wider wells, the absorption peak energy shows relatively slow monotonic increase with increasing N content up to 3% because of the N-band and conduction-band coupling. In the nearly lattice-matched GaAsN/AlGaAs QWs the absorption peak energy shows a redshift with increasing N content from 0% to 0.4% and then increases gradually. The theoretical results are consistent with the reported experimental data.
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78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.Fg Quantum wells
71.15.-m Methods of electronic structure calculations

Investigation of nanodefect properties in optical coatings by coupling measured and simulated laser damage statistics

Laurent Gallais, Jérémie Capoulade, Jean-Yves Natoli, and Mireille Commandré

J. Appl. Phys. 104, 053120 (2008); http://dx.doi.org/10.1063/1.2975179 (9 pages) | Cited 11 times

Online Publication Date: 10 September 2008

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We propose a model to link laser damage initiator properties (such as nature, size distribution, and density) to measured laser damage probabilities in optical materials. The model is based on the calculation of light absorption in nanoabsorbers and subsequent heating, coupled to laser damage statistics, and allows to obtain the laser damage probability as a function of laser fluence. Applications to the case of optical coatings irradiated in the nanosecond regime are presented. Laser damage probability curves are measured in hafnia single layer coatings made under different conditions: electron beam deposition and reactive low voltage ion plating. By studying the influence of the laser irradiation parameters (wavelength and beam size) and coating properties on the simulations, we show with our methodology that initiating defects (hafnium inclusions) can be identified. The implications of this approach for physical understanding and metrology applications are discussed.
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42.79.Wc Optical coatings
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Analysis of terahertz pulses from large-aperture biased semi-insulating and arsenic-ion-implanted GaAs antennas

Rone-Hwa Chou, Tze-An Liu, and Ci-Ling Pan

J. Appl. Phys. 104, 053121 (2008); http://dx.doi.org/10.1063/1.2967716 (7 pages) | Cited 4 times

Online Publication Date: 15 September 2008

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We investigate the characteristics of terahertz radiation pulses generated using biased semi-insulating and arsenic-ion-implanted GaAs photoconductive antennas with 1.5 cm aperture size under various pump fluences and bias fields. Compared with semi-insulating GaAs antenna, our arsenic-ion-implanted GaAs antenna exhibits larger bandwidth and better emission efficiency. Our simulation verifies that the superior characteristics for the latter can be partly attributed to larger optical absorption in the ion-implanted layer. For both types of antennas, we observe that the radiated peak terahertz amplitude displays an anomalous dependence on pump fluence, which deviates from the prediction given by the scaling rule. Analyzing the theoretical and simulation results, we infer that this behavior arises from band filling and two-photon absorption effects. At specific pump fluence, we find that the dependence of peak terahertz amplitude on bias field is distinct from the usual linear relationship predicted by the scaling rule.
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84.40.Ba Antennas: theory, components and accessories
42.25.Bs Wave propagation, transmission and absorption
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