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28 Jan 2002

Volume 80, Issue 4, pp. 535-701

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InAs/GaAs quantum dot lasers with InGaP cladding layer grown by solid-source molecular-beam epitaxy

Nien-Tze Yeh, Wei-Sheng Liu, Shu-Han Chen, Pe-Chin Chiu, and Jen-Inn Chyi

Appl. Phys. Lett. 80, 535 (2002); http://dx.doi.org/10.1063/1.1445269 (3 pages) | Cited 7 times

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This letter presents the lasing properties of InAs/GaAs quantum dot lasers with InGaP cladding layers grown by solid-source molecular-beam epitaxy. These Al-free lasers exhibit a threshold current density of 138 A/cm2, an internal loss of 1.35 cm−1, and an internal quantum efficiency of 31% at room temperature. At a low temperature, a very high characteristic temperature of 425 K and very low threshold current density of 30 A/cm2 are measured. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

Towards a voltage tunable two-color quantum-well infrared photodetector

Amlan Majumdar, K. K. Choi, L. P. Rokhinson, and D. C. Tsui

Appl. Phys. Lett. 80, 538 (2002); http://dx.doi.org/10.1063/1.1436529 (3 pages) | Cited 5 times

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Two-color quantum-well infrared photodetectors (QWIPs), based on electron transfer between coupled QWs, suffer from the presence of the shorter wavelength peak at all bias voltages Vb. We investigate this problem by studying the bias dependence of absorption coefficient α and photoconductive gain g as a function of wavelength at 10 K. We fabricate such a detector with a peak wavelength of 8 μm for both bias polarities but a voltage tunable cutoff wavelength (9 μm for Vb>0 and 11 μm for Vb<0). We use corrugated QWIPs with different corrugation periods to extract α and g for different values of Vb. We find α ≈ 0.1 μm−1 in the 6–12 μm range with small peaks at 8 and 9.8 μm for Vb>0 and 10 μm for Vb<0. g has a pronounced peak at 7.8 μm for both bias polarities and determines the line shape of the QWIP spectral responsivity. These results are attributed to insufficient electron transfer between the coupled QWs and to low tunneling probability of the longer wavelength photoelectrons. A modified QWIP structure has been proposed for complete switching of spectral responsivity peak when the bias voltage polarity is reversed. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Coherent x-ray pulse generation in the sub-Ångström regime

C. H. Keitel and S. X. Hu

Appl. Phys. Lett. 80, 541 (2002); http://dx.doi.org/10.1063/1.1436277 (3 pages) | Cited 17 times

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A mechanism is proposed to generate femtosecond coherent light pulses with a wavelength shorter than the dimension of a single atom. X rays of such short wavelength and high energy are shown to arise from the relativistic interaction of multiply charged ions with short and intense near-optical laser pulses. The generated x-ray pulses have thus potential to be useful in investigating the dynamics of chemical and biological systems with a subatomic resolution. © 2002 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
32.80.-t Photoionization and excitation

Emission gain narrowing from single crystals of a thiophene/phenylene co-oligomer

Michifumi Nagawa, Ryota Hibino, Shu Hotta, Hisao Yanagi, Musubu Ichikawa, Toshiki Koyama, and Yoshio Taniguchi

Appl. Phys. Lett. 80, 544 (2002); http://dx.doi.org/10.1063/1.1435797 (3 pages) | Cited 54 times

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Emission gain narrowing has been observed for single crystals of a thiophene/phenylene co-oligomer. The hexagon flake crystals were placed on a quartz substrate with the crystals’ face in close contact with the substrate plane. These crystals were irradiated with a N2 laser with a 337.1 nm wavelength at a repetition rate 10 Hz that tuned its intensity to 100–1150 μJ/cm2. The emission gain narrowing takes place at 21490 (465.4 nm) and 20220 cm−1 (494.5 nm) with increased intensities, with their half width at half maxima reaching ∼ 50 cm−1. On the basis of the nonlinear relationship between the emission peak intensities and the laser light intensity, the gain narrowing has been attributed to the amplified spontaneous emission. © 2002 American Institute of Physics.
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78.55.Kz Solid organic materials
78.45.+h Stimulated emission

Photonic-crystal ultrashort bends with improved transmission and low reflection at 1.55 μm

A. Talneau, L. Le Gouezigou, N. Bouadma, M. Kafesaki, C. M. Soukoulis, and M. Agio

Appl. Phys. Lett. 80, 547 (2002); http://dx.doi.org/10.1063/1.1445270 (3 pages) | Cited 60 times

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We propose and demonstrate improved designs in order to increase the transmission level through double 60°-bend photonic-crystal-based waveguides. These bends are defined in a two-dimensional photonic crystal (PC) patterned into a GaInAsP slab on InP substrate. Transmission spectra calculated using a two-dimensional finite difference time domain method that accounts for radiation losses, as well as measurements, demonstrate enhancement of the transmission when moving holes in the corner. As expected a drop in reflection is obtained. The sensitivity to the PC guide width is also evidenced. © 2002 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
78.66.Fd III-V semiconductors
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
02.70.Bf Finite-difference methods

Low Stokes shift in thick and homogeneous InGaN epilayers

S. Srinivasan, F. Bertram, A. Bell, F. A. Ponce, S. Tanaka, H. Omiya, and Y. Nakagawa

Appl. Phys. Lett. 80, 550 (2002); http://dx.doi.org/10.1063/1.1436531 (3 pages) | Cited 27 times

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The optical properties of thick InxGa1−xN layers have been studied using optical absorption and cathodoluminescence techniques. The indium composition x of the layers ranged from 0.03 to 0.17 as determined by Rutherford backscattering measurements. The difference between the band gap and the peak emission energy (Stokes shift) was found to be considerably smaller than reported in the past for these alloys. Monochromatic images show that light emission from most of the film is homogeneous and is associated with a low Stokes shift. A second emission band at longer wavelengths is observed for x ≥ 0.08. This band originates from indium-rich regions in the vicinity of extended defects, and exhibits a larger Stokes shift. Our observations indicate that it is possible to grow InGaN epilayers with high indium composition, high homogeneity, and lower Stokes shift. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
78.60.Hk Cathodoluminescence, ionoluminescence
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultraviolet photoresponse of porous ZnO thin films prepared by unbalanced magnetron sputtering

Parmanand Sharma, Abhai Mansingh, and K. Sreenivas

Appl. Phys. Lett. 80, 553 (2002); http://dx.doi.org/10.1063/1.1445480 (3 pages) | Cited 35 times

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Fast ultraviolet photoresponse is observed in ZnO thin films prepared by unbalanced magnetron sputtering. Films with a porous microstructure and a mixed (100), (002) and (101) crystallographic orientation exhibit photoresponse with good linearity and minimal aging effects. A fast rise time of 792 ms and a fall time of 805 ms are observed under low intensity (9.5 mW/cm2, λ = 365 nm) ultraviolet light. © 2002 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Hf II-VI semiconductors
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