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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages)

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang
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Optofluidic ring resonator based dye laser

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang

Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages) | Cited 40 times

Online Publication Date: 29 May 2007

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The authors demonstrate a microfluidic dye laser using a liquid core optical ring resonator (LCORR). The LCORR is made of a fused silica capillary with a wall thickness of a few microns. The circular cross section of the capillary forms a ring resonator that supports whispering gallery modes (WGMs) and provides an optical feedback for lasers. Due to the high Q factor of the WGM (107), a low lasing threshold is achieved (1 μJ/mm2). In addition, they show that the laser can be coupled out via a tapered fiber in touch with the LCORR, thus providing a mechanism for easy laser delivery.
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42.55.Mv Dye lasers
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

In situ observation of Zn-induced etching during CdSe quantum dot formation using time-resolved ellipsometry

Carsten Kruse, Mariuca Gartner, Arne Gust, and Detlef Hommel

Appl. Phys. Lett. 90, 221102 (2007); http://dx.doi.org/10.1063/1.2742930 (3 pages) | Cited 4 times

Online Publication Date: 29 May 2007

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A combined segregation and desorption process has been observed in situ by ellipsometry in real-time during overgrowth of a CdSe layer by a ZnSe cap layer using migration enhanced epitaxy. This segregation enhanced etching of CdSe during Zn deposition is known to play an important role in the formation process of CdSe quantum dots. The time-resolved ellipsometry data can be fitted assuming a rapid thickness reduction of about 68% of the CdSe layer, consistent with results obtained by high-resolution x-ray diffraction after growth. Furthermore, a significant change in growth rate during deposition of CdSe has been observed.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.65.Cf Surface cleaning, etching, patterning
81.05.Dz II-VI semiconductors
64.75.-g Phase equilibria
78.47.-p Spectroscopy of solid state dynamics

Red light emission from controlled multilayer stack comprising of thin amorphous silicon and silicon nitride layers

W. K. Tan, M. B. Yu, Q. Chen, J. D. Ye, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 90, 221103 (2007); http://dx.doi.org/10.1063/1.2743743 (3 pages) | Cited 12 times

Online Publication Date: 29 May 2007

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The authors demonstrate photoluminescence from a multilayer stack comprising of thin amorphous silicon/silicon nitride multilayer stack. The peak emission wavelength is in the visible wavelength range (λ = 674–706 nm). The authors show that emission originates from the quantum confinement of the amorphous silicon layers. They demonstrate the tunability of the peak emission wavelength by controlling the amorphous silicon layer thickness. Postdeposition annealing was carried out to enhance the photoluminescence without recrystallization of the amorphous silicon layers as confirmed by transmission electron microscopy and Raman spectroscopy. Such multilayer structure should be advantageous for electrical injection of carriers due to the thin dielectric layers
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.-m Photoluminescence, properties and materials
61.72.Cc Kinetics of defect formation and annealing
78.30.-j Infrared and Raman spectra

Deviations from the reciprocity theory of McCumber at low temperature in Nd3+-doped glasses

R. M. Martin and R. S. Quimby

Appl. Phys. Lett. 90, 221104 (2007); http://dx.doi.org/10.1063/1.2743953 (3 pages) | Cited 1 time

Online Publication Date: 29 May 2007

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The reciprocity theory of McCumber [Phys. Rev. 136, A954 (1964)] , which relates optical absorption and emission spectra between two energy level manifolds, was tested at temperatures down to 130 K on the 4F3/2→4I9/2 transition in Nd-doped glass. Deviations between calculated and measured spectra were observed for temperatures below 230 K in Nd:silicate and below 170 K in Nd:fluorozirconate glass. Below these temperatures, the calculated absorption is skewed to shorter wavelength and the calculated emission is skewed to longer wavelength. The magnitude of the deviation depends on the ratio of inhomogeneous linewidth to thermal energy kBT.
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78.60.-b Other luminescence and radiative recombination
42.70.Ce Glasses, quartz

Growth and photoluminescence studies of a-plane AlN/AlxGa1−xN quantum wells

T. M. Al Tahtamouni, A. Sedhain, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 90, 221105 (2007); http://dx.doi.org/10.1063/1.2743956 (3 pages) | Cited 3 times

Online Publication Date: 29 May 2007

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Both a-plane and c-plane AlN/Al0.65Ga0.35N quantum wells (QWs) have been grown by metal organic chemical vapor deposition and their photoluminescence (PL) emission properties were studied and compared. It was found that the low temperature PL characteristics of a-plane QWs are primarily governed by the quantum size effect, whereas those of c-plane QWs are significantly affected by the polarization fields. The PL decay time was found to be only weakly dependent on the well width Lw for a-plane QWs, whereas a strong dependence of the PL decay time on Lw was observed for c-plane QWs. Moreover, Lw dependence studies also revealed that structures with Lw>2 nm and Lw ≈ 2 nm provide highest emission efficiency in a-plane and c-plane AlN/Al0.65Ga0.35N QWs, respectively.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.St Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
78.67.De Quantum wells

Contrast in transmission spectroscopy of a single quantum dot

B. D. Gerardot, S. Seidl, P. A. Dalgarno, R. J. Warburton, M. Kroner, K. Karrai, A. Badolato, and P. M. Petroff

Appl. Phys. Lett. 90, 221106 (2007); http://dx.doi.org/10.1063/1.2743750 (3 pages) | Cited 13 times

Online Publication Date: 30 May 2007

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The authors perform transmission spectroscopy on single quantum dots and examine the effects of a resident carrier’s spin, the incident laser spot size, polarization, and power on the experimental contrast. They demonstrate a factor of 5 improvement in the maximum contrast by using a solid immersion lens to decrease the spot area. This increase yields a maximum signal to noise ratio of ∼ 2000 Hz−1/2, which will allow for megahertz detection frequencies. The authors anticipate that this improvement will allow further investigation of spectral fluctuation and open up the feasibility for an all-optical readout of an electron spin in a quantum dot.
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78.67.Hc Quantum dots
73.21.La Quantum dots

Luminescence and absorption analysis of undoped organic materials

Stefan Odermatt, Nils Ketter, and Bernd Witzigmann

Appl. Phys. Lett. 90, 221107 (2007); http://dx.doi.org/10.1063/1.2743930 (3 pages) | Cited 2 times

Online Publication Date: 30 May 2007

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The authors model and analyze the electroluminescence and absorption properties of organic semiconductors using Alq3 as example. Instead of using a typical quasiparticle approach based on singlet and triplet excitons, they obtain the absorption and electroluminescence spectra by solving the equation of motion for the linear microscopic polarization in a hierarchical many-body framework. A special focus is put on Coulomb effects. The electronic structure input parameters for this model are obtained by molecular orbital calculations. In particular for Alq3, they find a (Coulomb) exciton binding energy of about 0.9 eV and discuss the impact of the strong carrier density induced Coulomb exchange shift on electroluminescence and absorption spectra.
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78.60.Fi Electroluminescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.20.Rv Polymers and organic compounds
71.15.Nc Total energy and cohesive energy calculations

40 J class laser oscillation of Nd-doped silica glass with high thermal shock parameter

Takahiro Sato, Yasushi Fujimoto, Hajime Okada, Hidetsugu Yoshida, Masahiro Nakatsuka, Tetsuji Ueda, and Akira Fujinoki

Appl. Phys. Lett. 90, 221108 (2007); http://dx.doi.org/10.1063/1.2744487 (3 pages) | Cited 6 times

Online Publication Date: 30 May 2007

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The authors demonstrated a 40 J class laser oscillation from a bulk-type Nd-doped silica glass with a high thermal shock parameter. A maximum output energy of 37.3 J was obtained from a laser oscillator that consisted of a 30% output coupler with a 30 mm diameter and 300 mm length laser medium. The thermal shock parameter, a figure of merit for the thermal toughness of the materials, was estimated to be 12.0 W/cm, which is 1.5 times larger than neodymium-doped yttrium aluminum garnet (7.9 W/cm). These results show that the Nd-doped silica glass has the potential to be installed in high-average-power or high-peak-power lasers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems

Air-suspended two-dimensional polymer photonic crystal slab waveguides fabricated by nanoimprint lithography

Choon-Gi Choi, Young-Tak Han, Jin Tae Kim, and Helmut Schift

Appl. Phys. Lett. 90, 221109 (2007); http://dx.doi.org/10.1063/1.2744482 (3 pages) | Cited 4 times

Online Publication Date: 30 May 2007

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Air-suspended membrane-type photonic crystals were fabricated in polystyrene. The two-dimensional photonic crystal slab nanostructures were replicated by a thermal nanoimprint process, and then air-suspended membrane structures were generated by a selective sacrificial layer etch process. The optical transmission showed clear band gap characteristics at 1550 nm wavelength, which is in good agreement with the theoretical calculations.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.70.Jk Polymers and organics
81.65.Cf Surface cleaning, etching, patterning

Field-induced and polymer-stabilized two-dimensional cholesteric liquid crystal gratings

Shin-Woong Kang and Liang-Chy Chien

Appl. Phys. Lett. 90, 221110 (2007); http://dx.doi.org/10.1063/1.2745198 (3 pages) | Cited 5 times

Online Publication Date: 31 May 2007

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The authors experimentally demonstrate an electrically switchable gratings based on polymer-stabilized, field-induced two-dimensional square-lattice pattern of a cholesteric liquid crystal. A dependence of the two-dimensional diffraction patterns with the magnitude of applied voltage is observed for before and after the polymer stabilization. The diffraction efficiency reaches 84% calculated for the zero order light intensity at the applied voltage of 0.23 V/μm for a 10 μm thick sample.
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42.79.Dj Gratings
42.79.Kr Display devices, liquid-crystal devices

Transflective liquid crystal display using commonly biased reflectors

Zhibing Ge, Xinyu Zhu, Robert Lu, Thomas X. Wu, and Shin-Tson Wu

Appl. Phys. Lett. 90, 221111 (2007); http://dx.doi.org/10.1063/1.2745206 (3 pages) | Cited 11 times

Online Publication Date: 31 May 2007

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A normally black single cell gap transflective liquid crystal display (LCD) using vertical alignment and commonly biased patterned reflectors is developed. In the transmissive region, continuous and uniform vertical electric fields are formed throughout the LC cell. On the other hand, in the reflective region, the electric fields are mainly confined near the substrate surfaces. As a result, the phase retardation in the transmissive region is approximately two times as that of the reflective region. Such a transflective LCD shows a high light efficiency (>90%) for both transmissive and reflective modes and well matched gray scales.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Contactless electroreflectance investigation of energy levels in a 1.3 μm emitting laser structure with the gain medium composed of InAsN quantum dots embedded in GaInNAs/GaAs quantum wells

M. Motyka, R. Kudrawiec, G. Sęk, J. Misiewicz, D. Bisping, B. Marquardt, A. Forchel, and M. Fischer

Appl. Phys. Lett. 90, 221112 (2007); http://dx.doi.org/10.1063/1.2743382 (3 pages) | Cited 6 times

Online Publication Date: 1 June 2007

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Laser structures designed for the emission at 1.3 μm and based on an active region containing InAsN quantum dots (QDs) embedded in GaInNAs/GaAs quantum wells (QWs) have been investigated by contactless electroreflectance. Optical transitions related to both the dots and the wells have been observed and the energies of the latter have been calculated using the effective mass approach. It has been shown that QW confines one electron, one light-hole, and three heavy-hole states only and the energy separation between the QD and QW ground state transitions is approximately 250 meV, which is ten times higher than the thermal energy at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Low threshold, high gain AlGaInAs quantum dot lasers

T. W. Schlereth, C. Schneider, W. Kaiser, S. Höfling, and A. Forchel

Appl. Phys. Lett. 90, 221113 (2007); http://dx.doi.org/10.1063/1.2745200 (3 pages) | Cited 9 times

Online Publication Date: 1 June 2007

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The properties of AlGaInAs quantum dot (QD) lasers are reported and compared to GaInAs QD lasers emitting at a similar wavelength ( ∼ 920 nm). It is found that Al0.15Ga0.23In0.62As QD lasers show an ∼ 2.1 times higher material gain and lower threshold current densities than Ga0.57In0.43As lasers (a factor of ∼ 1.4 for 1.0 mm long and 100 μm wide devices). Both laser samples display comparable high internal quantum efficiencies of 0.79 (AlGaInAs) and 0.83 (GaInAs). The AlGaInAs devices exhibit a high characteristic temperature of 174 K between 15 and 85 °C.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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