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16 Oct 2000

Volume 77, Issue 16, pp. 2437-2616

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GaAs/AlGaAs quantum-well photodetector for visible and middle infrared dual-band detection

H. C. Liu, C. Y. Song, A. Shen, M. Gao, Z. R. Wasilewski, and M. Buchanan

Appl. Phys. Lett. 77, 2437 (2000); http://dx.doi.org/10.1063/1.1318232 (3 pages) | Cited 18 times

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We present experimental results on quantum-well photodetectors for visible and infrared dual-band detection. Large band gap top contacts were used on a standard GaAs/AlGaAs quantum-well infrared photodetector so that visible light could reach the quantum-well region and be absorbed via interband transitions. Two designs were investigated, using a high Al fraction AlGaAs and a short period GaAs/AlAs superlattice contact layer. The dual-band response spectral regions are 0.55–0.7 and 7–10 μm. Measured responsivities are about 0.7 A/W at 8.3 μm and 0.1 A/W at 0.63 μm under −6 V bias voltage. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors

Strong modification of photoluminescence in erbium-doped porous silicon microcavities

Y. Zhou, P. A. Snow, and P. St. J. Russell

Appl. Phys. Lett. 77, 2440 (2000); http://dx.doi.org/10.1063/1.1318230 (3 pages) | Cited 4 times

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A microcavity composed of porous silicon multilayer mirrors was electrochemically etched and doped with erbium. Measurements of the reflectivity and photoluminescence spectra are presented. Thermal processing under a nitrogen atmosphere optically activated the erbium ions. Photopumping yielded room temperature emission around 1.54 μm from the erbium-doped samples with the emitted light strongly modified by the microcavity structure. Emission spectra with a peak at 1.536 μm had a full width at half maximum of ∼6 nm. © 2000 American Institute of Physics.
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78.55.Mb Porous materials
81.05.Rm Porous materials; granular materials
42.79.Bh Lenses, prisms and mirrors
78.55.Ap Elemental semiconductors
42.79.Wc Optical coatings
78.30.Am Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors

Photoluminescence from pendant dye molecules mediated by exciton transport on helical polysilane chains

Hiroaki Tachibana, Hideo Kishida, and Yoshinori Tokura

Appl. Phys. Lett. 77, 2443 (2000); http://dx.doi.org/10.1063/1.1318395 (3 pages) | Cited 5 times

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We have synthesized helical polysilanes on which the pendant groups are partly substituted by dye molecules. The introduction of a few percent of dye molecules into the substituents enhances the luminescent efficiency of the visible region, by behaving as luminescence centers. We have demonstrated that the excitation energy is transferred efficiently by free excitons on the Si backbones to reach the luminescence centers, where energy transfer occurs from the exciton to the dye molecule, and as a result sensitized luminescence occurs. The exciton transfer is found to occur over 50–100 monomer units on the polysilane backbone. This approach will open the way to fabricating a wavelength-tunable luminous device by utilizing the exciton transport on Si chains. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
71.35.-y Excitons and related phenomena
61.41.+e Polymers, elastomers, and plastics
71.55.Jv Disordered structures; amorphous and glassy solids

Luminescence enhancement from hydrogen-passivated self-assembled quantum dots

E. C. Le Ru, P. D. Siverns, and R. Murray

Appl. Phys. Lett. 77, 2446 (2000); http://dx.doi.org/10.1063/1.1318931 (3 pages) | Cited 23 times

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We have measured a large increase (by a factor of up to 50) in the room-temperature emission of InAs/GaAs self-assembled quantum dots subjected to a hydrogen-passivation treatment. Smaller enhancements were measured at low temperatures. We tentatively attribute the improved optical signal to passivation of defects within the GaAs matrix and wetting layer adjacent to the dots. Annealing studies show that these benefits are lost following annealing at temperatures above 600 °C for 5 min. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.55.Eq III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing

Amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers

J. M. Tang, P. S. Spencer, and K. A. Shore

Appl. Phys. Lett. 77, 2449 (2000); http://dx.doi.org/10.1063/1.1318932 (3 pages) | Cited 1 time

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A comprehensive theoretical model describing the amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers is developed, taking into account gain dispersion, short carrier relaxation time and ultrafast nonlinear refraction. It is shown that these factors are extremely important in determining the amplified optical pulse characteristics in both the time and frequency domains. The calculations also indicate that gain dispersion can be significantly enhanced by fast carrier relaxations, short pulse widths, and high pulse energies. © 2000 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.60.Fc Modulation, tuning, and mode locking

Electrical characterization of conducting polypyrrole by THz time-domain spectroscopy

Tae-In Jeon, D. Grischkowsky, A. K. Mukherjee, and Reghu Menon

Appl. Phys. Lett. 77, 2452 (2000); http://dx.doi.org/10.1063/1.1319188 (3 pages) | Cited 34 times

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Using an optoelectronic THz beam system for THz time-domain spectroscopy (THz TDS), we have measured the absorption and index of refraction of a conducting polypyrrole film from low frequencies to 2.5 THz. From these measurements, the dc conductivity of 215/(Ω cm) and the complex conductance were obtained over this frequency range. All of the results were well fit by Drude theory, which gives a carrier scattering time of only 12.6 fs, less than 1/10 that of the semiconductors, thereby illustrating the disorder and low mobility of the polymer. © 2000 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
78.70.Gq Microwave and radio-frequency interactions
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
77.22.Ch Permittivity (dielectric function)

Co2+:LiGa5O8 saturable absorber passive Q switch for 1.34 μm Nd3+:YAlO3 and 1.54 μm Er3+:glass lasers

I. A. Denisov, M. I. Demchuk, N. V. Kuleshov, and K. V. Yumashev

Appl. Phys. Lett. 77, 2455 (2000); http://dx.doi.org/10.1063/1.1319179 (3 pages) | Cited 21 times

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Passive Q switching of a Nd3+:YAlO3 laser at 1.34 μm and an Er3+: glass laser at 1.54 μm was demonstrated using a Co2+:LiGa5O8 crystal as a saturable absorber. Q-switched pulses at 1.34 μm of 13 mJ energy and 90 ns duration and at 1.54 μm of 8 mJ energy and 70 ns duration were obtained. The ground state absorption cross section of the Co2+:LiGa5O8 was estimated to be (2.6±0.4)×10−19 cm2 and (2.5±0.5)×10−19 cm2 at 1.34 and 1.54 μm, respectively. The 4T1(4F)→4A2 relaxation time of the Co2+ ion in the LiGa5O8 crystal was measured to be ∼130 ns. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Hj Laser materials

Color engineering by modified oligothiophene blends

M. Anni, G. Gigli, V. Paladini, R. Cingolani, G. Barbarella, L. Favaretto, G. Sotgiu, and M. Zambianchi

Appl. Phys. Lett. 77, 2458 (2000); http://dx.doi.org/10.1063/1.1314886 (3 pages) | Cited 31 times

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Fully tunable light emission is demonstrated with combinations of binary blends of modified oligothiophenes of high efficiency, covering the entire spectrum of colors according to the standards of the Commission International de l’Eclairage. The emission spectrum of each blend is determined by the Forster transfer when the energy separation between the highest occupied molecular orbital–lowest unoccupied molecular orbital gap of the constituent molecules is smaller than 0.56 eV. For larger energy separation, the blend emission is just given by the superposition of the emission spectra of the constituent molecules. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Enhanced photoinduced birefringence in polymer microcavities

Rozenn Piron, Eric Toussaere, Dominique Josse, and Joseph Zyss

Appl. Phys. Lett. 77, 2461 (2000); http://dx.doi.org/10.1063/1.1316072 (3 pages) | Cited 5 times

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We investigate photoinduced birefringence in functionalized polymer microcavities illuminated by a visible polarized cw laser beam. The cavity studied in this experiment consists of an assembly of two Bragg mirrors embedding a polymer film with tethered azobenzene dyes. Linearly polarized light induces orientationally selective excitation of the chromophore guests, resulting in optical anisotropy of the film. The mechanism of the phenomenon is based on random-to-axial statistical reorientation of the azochromophores following repetitive trans-cis-trans photoisomerization cycles. The resulting birefringence is inferred from analysis of the spectral shifts of the cavity Fabry–Pérot longitudinal modes as a result of illumination. A large value of the birefringence of the order of 10−2 is noted after currently unoptimized durations of the order of 30′ in the 1.3–1.5 μm range with possible applications in optical storage at WDM telecom-compatible wavelengths. © 2000 American Institute of Physics.
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78.20.Fm Birefringence
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.25.Lc Birefringence
42.55.Sa Microcavity and microdisk lasers
82.30.Qt Isomerization and rearrangement
82.50.-m Photochemistry
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