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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Direct modulation of excited state quantum dot lasers

B. J. Stevens, D. T. D. Childs, H. Shahid, and R. A. Hogg

Appl. Phys. Lett. 95, 061101 (2009); http://dx.doi.org/10.1063/1.3193664 (3 pages) | Cited 8 times

Online Publication Date: 10 August 2009

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The use of the excited state quantum dot lasers for high speed direct modulation is proposed and demonstrated. A direct comparison of lasers utilizing the ground state and excited state from the same laser material reveals a factor of two increase in the K-factor limited bandwidth. This is attributed to an increase in the saturated gain and reduced carrier scattering time of the excited state compared to the ground state.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Complex emission dynamics of type-II GaSb/GaAs quantum dots

Kamil Gradkowski, Nicola Pavarelli, Tomasz J. Ochalski, David P. Williams, Jun Tatebayashi, Guillaume Huyet, Eoin P. O’Reilly, and Diana L. Huffaker

Appl. Phys. Lett. 95, 061102 (2009); http://dx.doi.org/10.1063/1.3202419 (3 pages) | Cited 7 times

Online Publication Date: 10 August 2009

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Optical properties of the GaSb/GaAs quantum dot system are investigated using a time-resolved photoluminescence technique. In this type-II heterostructure the carriers of different species are spatially separated and, as a consequence, a smooth evolution of both the emission wavelength and decay timescale is observed. A wavelength shift of 170 nm is measured simultaneously with the progressive timescale change from 100 ps to 23 ns. These phenomena are explained by the evolution of the carrier density, which brings a modification to the optical transition probability as well as the shift in the emission toward the higher energies.
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78.67.Hc Quantum dots
78.47.jd Time resolved luminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)

External cavity quantum cascade laser tunable from 7.6 to 11.4 μm

Andreas Hugi, Romain Terazzi, Yargo Bonetti, Andreas Wittmann, Milan Fischer, Mattias Beck, Jérôme Faist, and Emilio Gini

Appl. Phys. Lett. 95, 061103 (2009); http://dx.doi.org/10.1063/1.3193539 (3 pages) | Cited 41 times

Online Publication Date: 11 August 2009

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We present the development of a broad gain quantum cascade active region. By appropriate cascade design and using a symmetric active region arrangement, we engineer a flat gain and increase the total modal gain in the desired spectral range. Grating-coupled external cavity quantum cascade lasers using this symmetric active region are tunable from 7.6 to 11.4 μm with a peak optical output power of 1 W and an average output power of 15 mW at room-temperature. With a tuning of over 432 cm−1, this single source covers an emission range of over 39% around the center frequency.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems

Growths of staggered InGaN quantum wells light-emitting diodes emitting at 520–525 nm employing graded growth-temperature profile

Hongping Zhao, Guangyu Liu, Xiao-Hang Li, G. S. Huang, Jonathan D. Poplawsky, S. Tafon Penn, Volkmar Dierolf, and Nelson Tansu

Appl. Phys. Lett. 95, 061104 (2009); http://dx.doi.org/10.1063/1.3204446 (3 pages) | Cited 51 times

Online Publication Date: 12 August 2009

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Three-layer staggered InGaN quantum wells (QWs) light-emitting diodes (LEDs) emitting at 520–525 nm were grown by metal-organic chemical vapor deposition by employing graded growth-temperature profile. The use of staggered InGaN QW, with improved electron-hole wave functions overlap design, leads to an enhancement of its radiative recombination rate. Both cathodoluminescence and electroluminescence measurements of three-layer staggered InGaN QW LED exhibited enhancements by 1.8–2.8 and 2.0–3.5 times, respectively, over those of conventional InGaN QW LED.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
78.60.Fi Electroluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photonic crystal membrane waveguides with low insertion losses

Quynh Vy Tran, Sylvain Combrié, Pierre Colman, and Alfredo De Rossi

Appl. Phys. Lett. 95, 061105 (2009); http://dx.doi.org/10.1063/1.3205452 (3 pages) | Cited 20 times

Online Publication Date: 13 August 2009

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We demonstrate experimentally that the fiber to fiber total insertion loss into a single-mode waveguide in a suspended photonic crystal membrane can be reduced to less than 10 dB (input, output, and propagation) without introducing any supplementary processing step (e.g., polymer deposition and etching). This is achieved through a suitable design of the waveguide end-facets minimizing the impedance mismatch and thereby the residual reflectance at the waveguide ends.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Probing exciton-phonon interaction in AlN epilayers by photoluminescence

A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 95, 061106 (2009); http://dx.doi.org/10.1063/1.3206672 (3 pages) | Cited 4 times

Online Publication Date: 14 August 2009

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Deep ultraviolet (DUV) photoluminescence (PL) spectroscopy has been employed to investigate the exciton-phonon interaction in AlN. Longitudinal optical (LO) phonon replicas of free exciton recombination lines were observed in PL emission spectra, revealing the coupling of excitons with LO phonons. We have quantified such interaction by measuring Huang–Rhys factor based on polarization resolved DUV PL measurements. It was observed that the exciton-phonon coupling strength in AlN depends on the polarization configuration and is much larger in the direction with the electrical field (math) of the emitted light perpendicular to the wurtzite c-axis (math⊥math) than in the direction of math∥math. Furthermore, a larger coupling constant was also measured in AlN than in GaN. The large effective hole to electron mass ratio in AlN, especially in the math⊥math configuration, mainly accounts for the observed results.
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63.20.kk Phonon interactions with other quasiparticles
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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