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28 Sep 2009

Volume 95, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 95, 131107 (2009); http://dx.doi.org/10.1063/1.3236752 (3 pages)

Marcus Eichfelder, Wolfgang-Michael Schulz, Matthias Reischle, Michael Wiesner, Robert Roßbach, Michael Jetter, and Peter Michler
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Frequency response of large aperture oxide-confined 850 nm vertical cavity surface emitting lasers

A. Mutig, S. A. Blokhin, A. M. Nadtochiy, G. Fiol, J. A. Lott, V. A. Shchukin, N. N. Ledentsov, and D. Bimberg

Appl. Phys. Lett. 95, 131101 (2009); http://dx.doi.org/10.1063/1.3231446 (3 pages) | Cited 14 times

Online Publication Date: 28 September 2009

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Small and large signal modulation measurements are carried out for 850 nm vertical cavity surface emitting lasers (VCSELs). The resonance frequency, damping factor, parasitic frequency, and D-factor are extracted. Small signal modulation bandwidths larger than 20 GHz are measured. At larger currents the frequency response becomes partially limited by the parasitics and damping. Our results indicate that by increasing the parasitic frequency, the optical 3 dB bandwidth may be extended to ∼ 25 GHz. A decrease in the damping should enable VCSEL bandwidths of 30 GHz for current densities not exceeding ∼ 10 kA/cm2 and ultimately error-free optical links at up to 40 Gbit/s.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Photocurrent spectroscopy investigation of deep level defects in Mg-doped GaN and Mg-doped AlxGa1−xN (0.20<x<0.52)

P. Batoni, E. B. Stokes, S. F. LeBoeuf, and T. Nohava

Appl. Phys. Lett. 95, 131102 (2009); http://dx.doi.org/10.1063/1.3236776 (3 pages)

Online Publication Date: 28 September 2009

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Pulsed infrared photocurrent spectroscopy is used to investigate deep levels in highly resistive metal organic chemical vapor deposition-grown, magnesium-doped aluminum gallium nitride metal-semiconductor-metal test structures in the range of aluminum fraction from x = 0.0 to x = 0.52. Some background level of photocurrent is observed at all infrared pump wavelengths between 1.35 and 4.0 μm. The photocurrent decay time is a decreasing function of aluminum fraction. A peak photocurrent energy is observed for each aluminum fraction. With increasing aluminum fraction, the peak blueshifts and narrows.
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73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
73.40.Sx Metal-semiconductor-metal structures
73.50.Pz Photoconduction and photovoltaic effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

The importance of electron temperature in silicon-based terahertz quantum cascade lasers

L. Lever, A. Valavanis, C. A. Evans, Z. Ikonić, and R. W. Kelsall

Appl. Phys. Lett. 95, 131103 (2009); http://dx.doi.org/10.1063/1.3237177 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2009

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Quantum cascade lasers (QCLs) are compact sources of coherent terahertz radiation. Although all existing QCLs use III-V compound semiconductors, silicon-based devices are highly desirable due to the high thermal conductivity and mature processing technology. We use a semiclassical rate-equation model to show that Ge/SiGe THz QCL active region gain is strongly enhanced by reducing the electron temperature. We present a bound-to-continuum QCL design employing L-valley intersubband transitions, using high Ge fraction barriers to reduce interface roughness scattering, and a low electric field to reduce the electron temperature. We predict a gain of ∼ 50 cm−1, which exceeds the calculated waveguide losses.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Angular resolved effective optical properties of a Swiss cross metamaterial

C. Menzel, C. Helgert, J. Üpping, C. Rockstuhl, E.-B. Kley, R. B. Wehrspohn, T. Pertsch, and F. Lederer

Appl. Phys. Lett. 95, 131104 (2009); http://dx.doi.org/10.1063/1.3238554 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2009

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We both experimentally and theoretically study the effective optical properties of a Swiss cross metamaterial at oblique incidence and reveal their angular dependence. Almost perfect agreement between measured and calculated data is achieved. We show that the spectral and angular domains of negative refraction as well as its strength depend strongly on the light’s propagation direction and polarization state. Our results clearly indicate that a description of a Swiss cross metamaterial in terms of effective material parameters is impossible.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Modeling CO2 laser ablation impulse of polymers in vapor and plasma regimes

John E. Sinko (新光ジョンエリフ) and Claude R. Phipps

Appl. Phys. Lett. 95, 131105 (2009); http://dx.doi.org/10.1063/1.3234382 (3 pages) | Cited 10 times

Online Publication Date: 28 September 2009

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An improved model for CO2 laser ablation impulse in polyoxymethylene and similar polymers is presented that describes the transition effects from the onset of vaporization to the plasma regime in a continuous fashion. Several predictions are made for ablation behavior.
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52.38.Mf Laser ablation

High temperature excitonic lasing characteristics of randomly assembled SnO2 nanowires

H. Y. Yang, S. F. Yu, S. H. Tsang, T. P. Chen, J. Gao, and T. Wu

Appl. Phys. Lett. 95, 131106 (2009); http://dx.doi.org/10.1063/1.3240867 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2009

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The lasing characteristics of randomly assembled SnO2 nanowires, whose excitonic gain is attributed to the exciton states bounded to the surface defects, are studied from room temperature up to 500 K. It is found that the amount of excited carriers under the lasing conditions is well below the Mott density of SnO2 so that high pumping intensities have less influence on the radiative recombination mechanism and wavelength of the lasing peaks. Furthermore, the redshift of lasing peaks is mainly due to the reduction of bandgap energy of SnO2 with the increase of temperature.
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71.35.-y Excitons and related phenomena
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Room-temperature lasing of electrically pumped red-emitting InP/(Al0.20Ga0.80)0.51In0.49P quantum dots embedded in a vertical microcavity

Marcus Eichfelder, Wolfgang-Michael Schulz, Matthias Reischle, Michael Wiesner, Robert Roßbach, Michael Jetter, and Peter Michler

Appl. Phys. Lett. 95, 131107 (2009); http://dx.doi.org/10.1063/1.3236752 (3 pages) | Cited 7 times

Online Publication Date: 29 September 2009

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We demonstrate electrically pumped laser light emission in the visible (red) spectral range using self-assembled InP quantum dots embedded in a microcavity mesa realized by monolithically grown high-reflectivity AlGaAs distributed Bragg reflectors. We used common semiconductor laser processing steps to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical wave-guiding and electrical current constriction. Ultra-low threshold of around 10 A/cm2 and room temperature lasing were demonstrated. Additionally, the temperature independence of the threshold current, which was predicted in theory for quantum dot lasers, is displayed.
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42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High energy terahertz emission from two-color laser-induced filamentation in air with pump pulse duration control

Tie-Jun Wang, Yanping Chen, Claude Marceau, Francis Théberge, Marc Châteauneuf, Jacques Dubois, and See Leang Chin

Appl. Phys. Lett. 95, 131108 (2009); http://dx.doi.org/10.1063/1.3242024 (3 pages) | Cited 8 times

Online Publication Date: 30 September 2009

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Two-color laser-induced femtosecond filamentation was employed to generate high energy terahertz emission in air with high energy pump. By controlling the pump pulse duration, more than four times enhancement in terahertz pulse energy has been obtained when compared with a Fourier transform-limited pump. Multiple filaments’ dynamics might be responsible for the terahertz enhancement. Superbroadband terahertz pulse with energy up to 2 μJ was generated using loose focusing condition, while the maximum terahertz pulse energy in the frequency range below 5.5 THz was around 60 nJ.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Tunability of intersubband absorption from 4.5 to 5.3 μm in a GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition

N. Péré-Laperne, C. Bayram, L. Nguyen-Thê, R. McClintock, and M. Razeghi

Appl. Phys. Lett. 95, 131109 (2009); http://dx.doi.org/10.1063/1.3242027 (3 pages) | Cited 6 times

Online Publication Date: 30 September 2009

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Intersubband (ISB) absorption at wavelengths as long as 5.3 μm is realized in GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition. By employing low aluminum content Al0.2Ga0.8N barriers and varying the well width from 2.6 to 5.1 nm, ISB absorption has been tuned from 4.5 to 5.3 μm. Theoretical ISB absorption and interband emission models are developed and compared to the experimental results. The effects of band offsets and the piezoelectric fields on these superlattices are investigated.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.65.-j Piezoelectricity and electromechanical effects
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
68.65.Cd Superlattices

Compressive ghost imaging

Ori Katz, Yaron Bromberg, and Yaron Silberberg

Appl. Phys. Lett. 95, 131110 (2009); http://dx.doi.org/10.1063/1.3238296 (3 pages) | Cited 24 times

Online Publication Date: 30 September 2009

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We describe an advanced image reconstruction algorithm for pseudothermal ghost imaging, reducing the number of measurements required for image recovery by an order of magnitude. The algorithm is based on compressed sensing, a technique that enables the reconstruction of an N-pixel image from much less than N measurements. We demonstrate the algorithm using experimental data from a pseudothermal ghost-imaging setup. The algorithm can be applied to data taken from past pseudothermal ghost-imaging experiments, improving the reconstruction’s quality.
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89.20.Ff Computer science and technology

Low noise performance of passively mode locked quantum-dash-based lasers under external optical feedback

K. Merghem, R. Rosales, S. Azouigui, A. Akrout, A. Martinez, F. Lelarge, G.-H. Duan, G. Aubin, and A. Ramdane

Appl. Phys. Lett. 95, 131111 (2009); http://dx.doi.org/10.1063/1.3238324 (3 pages) | Cited 5 times

Online Publication Date: 30 September 2009

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We report on a systematic investigation of the effect of external optical feedback on 17 GHz passively mode-locked two-section lasers based on InAs/InP quantum dashes emitting at 1.58 μm. Narrowing of mode-beating linewidth down to a record value of ∼ 500 Hz is demonstrated over a large operating range.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Solution-processed cavity and slow-light quantum electrodynamics in near-infrared silicon photonic crystals

R. Bose, J. F. McMillan, J. Gao, and C. W. Wong

Appl. Phys. Lett. 95, 131112 (2009); http://dx.doi.org/10.1063/1.3238555 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2009

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We demonstrate enhanced emission of solution-processed sparse lead sulfide quantum dots (QDs) coupled to confined as well as propagating modes in silicon photonic crystals at near-infrared communications wavelengths. In the cavity case, by using cold-cavity characterization using on-board waveguides or cross-polarization techniques, we show that the coupled QD lineshape is identical to the cold-cavity spectra. For the photonic crystal waveguides (PhCWGs), we use transmission spectra for the PhCWG as well as three-dimensional finite difference time domain techniques to validate enhancements due to the propagating mode. The observation of room-temperature quantum electrodynamics using postfabrication QD integration techniques is promising for further studies.
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03.67.Hk Quantum communication
42.65.Wi Nonlinear waveguides
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.-m Integrated optics

Single-crystalline cubic MgZnO films and their application in deep-ultraviolet optoelectronic devices

L. K. Wang, Z. G. Ju, J. Y. Zhang, J. Zheng, D. Z. Shen, B. Yao, D. X. Zhao, Z. Z. Zhang, B. H. Li, and C. X. Shan

Appl. Phys. Lett. 95, 131113 (2009); http://dx.doi.org/10.1063/1.3238571 (3 pages) | Cited 11 times

Online Publication Date: 1 October 2009

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By employing a relatively low growth temperature and oxygen-rich conditions, single-crystalline cubic MgZnO films were prepared. A solar-blind deep ultraviolet (DUV) photodetector was finished on the MgZnO film. The maximum responsivity of the photodetector is 396 mA/W at 10 V bias, which is almost three orders of magnitude larger than the highest value ever reported in MgZnO-based solar-blind photodetectors. The dark current density is 1.5×10−11 A/cm2, comparable with the smallest value ever reported in solar-blind photodetectors. The improved performance reveals that the single-crystalline cubic MgZnO films have great potential applications in DUV optoelectronic devices.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects

Generation of extreme ultraviolet radiation with a Bessel–Gaussian beam

Lap Van Dao, Khuong Ba Dinh, and Peter Hannaford

Appl. Phys. Lett. 95, 131114 (2009); http://dx.doi.org/10.1063/1.3240404 (3 pages) | Cited 1 time

Online Publication Date: 1 October 2009

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The generation of few high-order harmonics in the extreme ultraviolet is enhanced by focusing the fundamental femtosecond laser beam with a combination of lens and axicon in an infinite gas cell. We show that this combination leads to an improvement in the phase-matched generation of harmonics in the cutoff region, with a higher photon flux and a better spatial beam profile. A high atom density through the use of a high gas pressure can be used and the absorption limit of the harmonic generation is obtained for an interaction length of a few millimeters.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Silver-copper alloy nanoparticles for metal enhanced luminescence

Sanchari Chowdhury, Venkat R. Bhethanabotla, and Rajan Sen

Appl. Phys. Lett. 95, 131115 (2009); http://dx.doi.org/10.1063/1.3242007 (3 pages) | Cited 8 times

Online Publication Date: 2 October 2009

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Large metal enhanced luminescence was realized at the vicinity of easily fabricated Ag–Cu alloy nanoparticles upon tuning of their surface plasmon resonance spectra by changing only one experimental variable—the annealing temperature, for maximum spectral overlap with the emission and excitation spectra of the luminophores. We observed strong emission enhancement of luminophores (141.48±19.20 times for Alexa Fluor 488 and 23.91±12.37 times for Alexa Fluor 594) at the vicinity of these Ag–Cu nanoparticles, which is significantly larger than for pure Ag nanoparticles. We present theoretical calculations to provide insights into these experimental findings.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.55.Hx Other solid inorganic materials
73.22.Lp Collective excitations
81.40.Gh Other heat and thermomechanical treatments

10 fs ultrafast all-optical switching in polystyrene nonlinear photonic crystals

Ye Liu, Fei Qin, Zhi-Yi Wei, Qing-Bo Meng, Dao-Zhong Zhang, and Zhi-Yuan Li

Appl. Phys. Lett. 95, 131116 (2009); http://dx.doi.org/10.1063/1.3242025 (3 pages) | Cited 22 times

Online Publication Date: 2 October 2009

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An ultrafast all-optical switching with the response time on the order of 10 fs is demonstrated in a three-dimensional opal polystyrene nonlinear photonic crystal by means of precise femtosecond pump-probe technique. The switching is realized by the shift in the photonic band gap under external optical pumping of 8 fs Ti:sapphire pulse laser with a peak pump power of 20.6 GW/cm2. The good performance of optical switching is attributed to the very strong and fast Kerr nonlinear optical response of the polystyrene material.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Double side electroluminescence from p-NiO/n-ZnO nanowire heterojunctions

Jen-Yi Wang, Chun-Yu Lee, Yung-Ting Chen, Chung-Tse Chen, Yung-Ling Chen, Ching-Fuh Lin, and Yang-Fang Chen

Appl. Phys. Lett. 95, 131117 (2009); http://dx.doi.org/10.1063/1.3232244 (3 pages) | Cited 16 times

Online Publication Date: 2 October 2009

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Double side light emission devices based on p-NiO/n-ZnO nanowire heterojunctions have been fabricated on indium tin oxide substrate by radio frequency magnetron sputtering combined with hydrothermal process. According to the energy band alignment, the detected broad visible and narrow ultraviolet electroluminescence arise from defect and band edge transitions in ZnO nanowires, respectively. The unique property of the double side emission is due to the nature of the large band gap of NiO film. It provides a good opportunity for the emission of a light emitting device with different colors on the top and back sides, simultaneously.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
71.20.Nr Semiconductor compounds
81.15.Cd Deposition by sputtering
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.Lt Quantum wires
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors

Photon-number resolving performance of the InGaAs/InP avalanche photodiode with short gates

Xiuliang Chen, E Wu, Lilin Xu, Yan Liang, Guang Wu, and Heping Zeng

Appl. Phys. Lett. 95, 131118 (2009); http://dx.doi.org/10.1063/1.3242380 (3 pages) | Cited 4 times

Online Publication Date: 2 October 2009

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By using a self-differencing circuit to achieve efficient spike cancellation for the near-infrared single-photon detector based on InGaAs/InP avalanche photodiode, we verified that shortening the gate duration enforced the detection efficiency to saturate at an increased voltage, while increasing the avalanche gain favored the discrimination of the avalanche signals caused by different photon-number states. Photon-number resolving detection was realized by measuring the weak current at the avalanche built-up. The photon-number resolving performance could be improved by shortening the gating pulse duration.
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85.60.Dw Photodiodes; phototransistors; photoresistors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Nonpolar GaN substrates grown by ammonothermal method

R. Kucharski, M. Rudziński, M. Zając, R. Doradziński, J. Garczyński, L. Sierzputowski, R. Kudrawiec, J. Serafińczuk, W. Strupiński, and R. Dwiliński

Appl. Phys. Lett. 95, 131119 (2009); http://dx.doi.org/10.1063/1.3227893 (3 pages) | Cited 12 times

Online Publication Date: 2 October 2009

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In this letter, the authors demonstrate large size m-plane GaN substrates grown by ammonothermal method. These substrates have excellent structural quality. The concentration of threading dislocation density is below 5×104 cm−2 and the full width at half maximum for the symmetrical and asymmetrical peaks equals 16 and 19 arc sec, respectively. Also good optical quality, the energy gap-related transition is clearly observed at room temperature in photoluminescence and contactless electroreflectance spectra. GaN epilayers deposited on these substrates exhibit intrinsic narrow exciton lines which are very sensitive to the optical selection rules typical for hexagonal symmetry, proving truly nonpolar character of the material.
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68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
68.35.bg Semiconductors
68.35.Dv Composition, segregation; defects and impurities
78.68.+m Optical properties of surfaces

Electrically pumped continuous-wave vertical-cavity surface-emitting lasers at ∼ 2.6 μm

Shamsul Arafin, Alexander Bachmann, Kaveh Kashani-Shirazi, and Markus-Christian Amann

Appl. Phys. Lett. 95, 131120 (2009); http://dx.doi.org/10.1063/1.3240406 (3 pages) | Cited 4 times

Online Publication Date: 2 October 2009

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In this paper, electrically pumped GaSb-based vertical-cavity surface-emitting lasers operating continuous wave at a record long emission wavelength of ∼ 2.6 μm are presented. Owing to the excellent thermal heat management, the devices exhibit single-mode operation up to a heat-sink temperature of 55 °C. Lateral current confinement and index guiding in the device are accomplished by utilizing the buried tunnel junction concept. Devices with aperture diameters of 6 μm show maximum output powers of 0.3 mW at room temperature with quantum efficiencies around 10%.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.-p Quantum optics
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