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12 Apr 2004

Volume 84, Issue 15, pp. 2721-2955

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 2883 (2004); http://dx.doi.org/10.1063/1.1702137 (3 pages)

Pu Xian Gao and Zhong L. Wang
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Improvement of second-harmonic generation in quantum-cascade lasers with true phase matching

Oana Malis, Alexey Belyanin, Claire Gmachl, Deborah L. Sivco, Milton L. Peabody, A. Michael Sergent, and Alfred Y. Cho

Appl. Phys. Lett. 84, 2721 (2004); http://dx.doi.org/10.1063/1.1697644 (3 pages) | Cited 23 times

Online Publication Date: 7 April 2004

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About a 100-fold improvement of the second-harmonic generation in a quantum-cascade laser with integrated optical nonlinearity was obtained by including phase-matching considerations in the design of the deep-etched ridge waveguide. The waveguide layer structure was optimized to minimize the phase mismatch of the zero-order mode of the fundamental light with the second-order transverse mode of the second-harmonic light. Exact phase matching is made possible by the faster decrease of the modal refractive index of the fundamental light with decreasing ridge width relative to the refractive index of the second-harmonic light. Up to 240 μW of the second-harmonic power and a nonlinear power conversion efficiency of up to 36 mW/W2 were achieved. © 2004 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.55.Px Semiconductor lasers; laser diodes
42.82.Et Waveguides, couplers, and arrays

Ultraviolet amplified spontaneous emission from thin films of 4,4′-bis(9-carbazolyl)-2,2′-biphenyl and the derivatives

Yuichiro Kawamura, Hidetoshi Yamamoto, Kenichi Goushi, Hiroyuki Sasabe, Chihaya Adachi, and Hiroki Yoshizaki

Appl. Phys. Lett. 84, 2724 (2004); http://dx.doi.org/10.1063/1.1695091 (3 pages) | Cited 11 times

Online Publication Date: 7 April 2004

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We demonstrate 394 nm ultraviolet amplified spontaneous emission (ASE) with a low pumping power threshold of Eth = 1.3±0.2 μJ/cm2, from a thin film of an organic semiconductor 4,4′-bis(9-carbazolyl)-2,2′-biphenyl (CBP) under the pulse excitation of a N2 gas laser (337 nm). 3-methyl and 3,6-dimethyl substituted CBP derivatives also exhibited pronounced ASE in the deep-blue region of 401 and 406 nm and ASE thresholds of less than Eth = 2 μJ/cm2. We also examined the ASE characteristics of N,N′-di(m-tolyl)-N,N′-diphenylbenzidine (TPD), N,N,N′,N′-tetraphenylbenzidine (DPABP) and N,N′-di(α-naphtyl)-N,N′-diphenylbenzidine (α-NPD). While TPD and DPABP showed low ASE thresholds, α-NPD did not show any ASE. We show that the large radiative decay rate (kf) of DPABP and TPD, which is derived from their short fluorescence lifetime (τf) and large quantum efficiency (ηf), leads to a low ASE threshold. On the other hand, the lack of ASE from α-NPD is ascribable to the small kf of 0.8±0.1×108 s−1, which is due to the rather long τf of 3.5 ns and small ηf of 0.29±0.02. In addition, we observed that the ASE gain is closely correlated with kf. A larger kf resulted in a larger ASE gain. © 2004 American Institute of Physics.
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78.66.Li Other semiconductors
78.45.+h Stimulated emission
78.55.Kz Solid organic materials

Low-threshold amplified spontaneous emission and laser emission in a polyfluorene derivative

X. Liu, C. Py, Y. Tao, Y. Li, J. Ding, and M. Day

Appl. Phys. Lett. 84, 2727 (2004); http://dx.doi.org/10.1063/1.1699479 (3 pages) | Cited 13 times

Online Publication Date: 7 April 2004

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The amplified spontaneous emission (ASE) and lasing properties of a fluorene copolymer PF3Cz film waveguide were investigated under optical pumping. Low ASE and lasing threshold were observed at 59 W/cm2/pulse and 1.7 KW/cm2/pulse, respectively. The stimulated emission cross section of the PF3Cz film was estimated to be approximately 1.6×10−16 cm2 at the ASE peak of 448 nm. The absorption cross section was estimated to be 2.8×10−16 cm2 at the absorption peak λ = 370 nm. Gain and loss measurements at the ASE peak showed that the net gain coefficient reaches 26±1.7 cm−1 when pumped at 1.4 KW/cm2, and the loss coefficient of the waveguide was about 13±1.1 cm−1.
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78.45.+h Stimulated emission
78.55.Kz Solid organic materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Tunable terahertz emission from difference frequency in biased superlattices

Ren-Bao Liu and Bang-Fen Zhu

Appl. Phys. Lett. 84, 2730 (2004); http://dx.doi.org/10.1063/1.1703849 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2004

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The terahertz emission from difference frequency in biased superlattices is calculated with the excitonic effect included. Owing to the doubly resonant condition and the excitonic enhancement, the typical susceptibility is larger than 10−5 m/V. The doubly resonant condition can always be realized by adjusting the bias voltage and the laser frequencies, thus the in situ tunable emission is efficient in the range of 0.5–6 THz. Continuous wave operation with 1% quantum efficiency and microwatt output power is feasible while the signal absorption in undoped superlattices is negligible. © 2004 American Institute of Physics.
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73.21.Cd Superlattices
41.20.Jb Electromagnetic wave propagation; radiowave propagation
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.An Optical susceptibility, hyperpolarizability
78.66.Fd III-V semiconductors

Organic plastic laser in holographic materials by photopolymerization

Kokou D. Dorkenoo, Olivier Crégut, and Alain Fort

Appl. Phys. Lett. 84, 2733 (2004); http://dx.doi.org/10.1063/1.1689741 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2004

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We demonstrate how to excite a laser mode in a thin film of organic holographic material. By initiating a photopolymerization process with visible light, we generate a distributed feedback laser in such films. The technique fulfills two important aims. First, the construction of a tunable laser with the help of an interferometric system and, second, the fabrication of a corrugated surface without the help of any etching or photolithography process. In short, we demonstrate a full laser action in a plastic medium doped with rhodamine 6G, which acts as a lasing dye. Usually, a major problem with such lasers is the aging of the dye. In the approach we develop, this problem can be overcome by periodically cleaning the gain region and refilling it with fresh dye molecules. © 2004 American Institute of Physics.
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42.55.Mv Dye lasers
42.70.Hj Laser materials
42.60.By Design of specific laser systems
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.65.Cf Surface cleaning, etching, patterning
82.35.-x Polymers: properties; reactions; polymerization

Impact of spin blocking on the energy relaxation of electrons in quantum-dot lasers

C. Cao and D. G. Deppe

Appl. Phys. Lett. 84, 2736 (2004); http://dx.doi.org/10.1063/1.1705729 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2004

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The impact of the electron spin relaxation time on the electron distribution in quantum-dot lasers is analyzed. The results show that a relatively long spin relaxation time (∼300 ps) can create a nonequilibrium carrier distribution in quantum-dot lasers. It is shown that a mechanism we call “spin blocking” increases emission from the quantum-dot excited states and can lead to excited state lasing in quantum-dot lasers. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Rn Relaxation oscillations and long pulse operation

Microcavity lasing behavior of oriented hexagonal ZnO nanowhiskers grown by hydrothermal oxidation

Zhiren Qiu, K. S. Wong, Mingmei Wu, Wenjiao Lin, and Huifang Xu

Appl. Phys. Lett. 84, 2739 (2004); http://dx.doi.org/10.1063/1.1697633 (3 pages) | Cited 64 times

Online Publication Date: 7 April 2004

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The highly aligned ZnO whiskers, which are grown by hydrothermal oxidation of metallic zinc plate in the presence of ethylenediamine molecules, exhibit single and/or a few modes of supernarrow spectral emissions ( ∼ 0.7 nm) at near 378 nm and negligible deep level defects emissions. Time-integrated and time-resolved photoluminescence show that the supernarrow spectral peaks are due to the laser action with an excitation threshold about 70 μJ/cm2 and emission lifetime of <30 ps. The lasing emission is highly polarized along the excitation laser polarization direction. The low lasing threshold, stable and regular supernarrow longitudinal modes, and strong lasing polarization effects can be well explained by the model of microcavity laser where the two end facets of whisker form the microcavity. © 2004 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.55.Px Semiconductor lasers; laser diodes
78.55.Et II-VI semiconductors
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.65.Mq Oxidation
71.55.Gs II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Finite size effect of transmission property for metal hole arrays in subterahertz region

Fumiaki Miyamaru and Masanori Hangyo

Appl. Phys. Lett. 84, 2742 (2004); http://dx.doi.org/10.1063/1.1702125 (3 pages) | Cited 55 times

Online Publication Date: 7 April 2004

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The mechanism of the high band-pass transmission property of metal hole arrays (MHA), which is metal slabs perforated periodically with circular holes, in the subterahertz (sub-THz) wave region has been investigated. We measured the transmission spectra varying the number of holes using a THz time domain spectroscopy and observed that the peak transmittance normalized by the porosity of holes increases with increasing the number of holes. This finite size effect of the transmission characteristics of the MHA is attributed to the increase of the coupling efficiency between the incident THz wave and the surface mode excited on the MHA surface with increasing the number of holes. © 2004 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers

Role of free carriers from two-photon absorption in Raman amplification in silicon-on-insulator waveguides

T. K. Liang and H. K. Tsang

Appl. Phys. Lett. 84, 2745 (2004); http://dx.doi.org/10.1063/1.1702133 (3 pages) | Cited 58 times

Online Publication Date: 7 April 2004

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We show experimentally that free carriers generated by two-photon-absorption in silicon-on-insulator (SOI) waveguides can introduce large losses which limit the usable pump power for Raman amplification at telecommunication wavelengths. The measured pump loss agreed with a theoretical model of the free-carrier absorption arising from two-photon-induced free carrier generation inside the waveguide. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics
78.30.Hv Other nonmetallic inorganics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Blue GaN-based light-emitting diodes grown by molecular-beam epitaxy with external quantum efficiency greater than 1.5%

P. Waltereit, H. Sato, C. Poblenz, D. S. Green, J. S. Brown, M. McLaurin, T. Katona, S. P. DenBaars, J. S. Speck, J.-H. Liang, M. Kato, H. Tamura, S. Omori, and C. Funaoka

Appl. Phys. Lett. 84, 2748 (2004); http://dx.doi.org/10.1063/1.1705721 (3 pages) | Cited 19 times

Online Publication Date: 7 April 2004

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We have grown blue (480 nm) nitride semiconductor light emitting diodes (LEDs) by plasma-assisted molecular beam epitaxy (MBE) on GaN templates. Packaged devices exhibited output powers up to 0.87 mW at 20 mA forward current. The corresponding external quantum efficiency was 1.68%. Utilizing a combination of direct current (dc) and pulsed electroluminescence measurements it has been demonstrated that at low (<20 mA) dc conditions the emission from these devices is governed by the combined effects of bandfilling and screening of electrostatic fields. However, at larger currents device heating dominates the emission properties. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Temperature dependence and single-mode tuning behavior of second-harmonic generation in quantum cascade lasers

C. Gmachl, N. Owschimikow, A. Belyanin, A. M. Sergent, D. L. Sivco, M. L. Peabody, A. Y. Cho, and F. Capasso

Appl. Phys. Lett. 84, 2751 (2004); http://dx.doi.org/10.1063/1.1703850 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2004

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Second-harmonic generation (SHG) is reported in quantum cascade (QC) lasers with active regions that also support nonlinear cascades with large second order nonlinear susceptibility. SHG has been measured from 10 up to 250 K heat sink temperature, with about 1 μW of nonlinear power at 10 K and about 50 nW at 250 K. Single-mode and tunable SHG at 3.5 μm wavelength has been measured from single-mode QC distributed feedback lasers operating at the fundamental pump wavelength of 7.0 μm. Thermal tuning results in a tuning rate for the SHG emission of ∼ 0.2 nm/K for temperatures above ∼ 100 K. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking
42.65.An Optical susceptibility, hyperpolarizability

Reflection/transmission confocal microscopy characterization of single-crystal diamond microlens arrays

E. Gu, H. W. Choi, C. Liu, C. Griffin, J. M. Girkin, I. M. Watson, M. D. Dawson, G. McConnell, and A. M. Gurney

Appl. Phys. Lett. 84, 2754 (2004); http://dx.doi.org/10.1063/1.1695101 (3 pages) | Cited 22 times

Online Publication Date: 7 April 2004

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Using the method of photoresist reflow and inductively coupled plasma dry etching, we have fabricated microlens arrays in type-IIa natural single-crystal diamond, with diameters down to 10 μm. The surface profile of the microlenses was characterized by atomic force microscopy and was found to match well with a spherical shape, with a surface roughness of better than 1.2 nm. To characterize the optical properties of these diamond microlens arrays, a laser scanning reflection/transmission confocal microscopy technique has been developed. This technique enabled the surface profile of the microlenses to be measured simultaneously with optical parameters including focal length and spot size, opening up an application area for confocal microscopy. © 2004 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Performance enhancement of InGaN light-emitting diodes by laser lift-off and transfer from sapphire to copper substrate

Bee Sim Tan, Shu Yuan, and Xue Jun Kang

Appl. Phys. Lett. 84, 2757 (2004); http://dx.doi.org/10.1063/1.1704862 (3 pages) | Cited 27 times

Online Publication Date: 7 April 2004

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Laser lift-off technique was employed to carry out transfer of prefabricated InGaN multiple-quantum-well light-emitting diodes (LEDs) from sapphire onto Cu substrate. Silver epoxy was used as the bonding material. Characterization results showed tremendous device improvements in terms of maximum allowable current, light output power, and reliability from the use of conductive Cu substrate. LEDs on Cu could withstand a maximum current of 530 mA before breakdown while those on sapphire could only withstand 350 mA. At 40 mA, light output power of LEDs on sapphire and Cu was 0.74 and 0.95 mW, respectively. In addition, reliability test at constant current of 300 mA showed improvement in light output power for LEDs on Cu whereas LEDs on sapphire suffered deterioration with time. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
73.63.Hs Quantum wells
81.07.St Quantum wells
85.60.Jb Light-emitting devices

Activation mechanism of annealed Mg-doped GaN in air

Yow-Jon Lin

Appl. Phys. Lett. 84, 2760 (2004); http://dx.doi.org/10.1063/1.1704873 (3 pages) | Cited 10 times

Online Publication Date: 7 April 2004

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In this study, the activation mechanism of annealed Mg-doped GaN in air and the influence of ambient on activation of Mg-doped GaN were investigated. According to the experimental results, we found that the dissociation of MgGa–H, and the formation of hydrogenated gallium vacancies (VGaH2) and gallium vacancies occupied by interstitial Mg during the air-activation process, led to an increase in the hole concentration. In addition, from the observed photoluminescence results and the secondary ion mass spectroscopy measurements, it is suggested that the formation of VGaH2 will result in an enhancement of hydrogen desorption from the MgGa–H complexes. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals

Polarization switching induced by phase change in extremely short external cavity vertical-cavity surface-emitting lasers

Krassimir Panajotov, Mikel Arizaleta, Miren Camarena, Hugo Thienpont, Heiko J. Unold, Johannes Michael Ostermann, and Rainer Michalzik

Appl. Phys. Lett. 84, 2763 (2004); http://dx.doi.org/10.1063/1.1690468 (3 pages) | Cited 15 times

Online Publication Date: 7 April 2004

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We experimentally investigate the spectral and polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to polarization insensitive optical feedback from an extremely short external cavity (few microns) and find that the wavelength and the current at which the light polarization switches between the two linearly polarized fundamental modes of the VCSEL are periodically modulated with the length of the external cavity. High contrast polarization switching is demonstrated for a quarter-wavelength change of the external cavity length. To explain our experimental findings we suggest a two-mode rate equation VCSEL model that considers the feedback optical field as instantaneous and accounts for multiple roundtrips in the external cavity with different coupling efficiencies back into the laser. Our numerical results are in very good agreement with the experiments. © 2004 American Institute of Physics.
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42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.25.Ja Polarization
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