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20 Sep 2004

Volume 85, Issue 12, pp. 2157-2437

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2390 (2004); http://dx.doi.org/10.1063/1.1796520 (3 pages)

Stas Polonsky and Alan Weger
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Guided-wave acousto-optic diffraction in AlxGa1−xN epitaxial layers

G. Bu, M. S. Shur, D. Čiplys, R. Rimeika, R. Gaska, and Q. Fareed

Appl. Phys. Lett. 85, 2157 (2004); http://dx.doi.org/10.1063/1.1792796 (3 pages) | Cited 6 times

Online Publication Date: 24 September 2004

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The acousto-optic (AO) diffraction of guided optical waves from surface acoustic waves in AlxGa1−xN layers grown on sapphire substrates by Migration Enhanced Metalorganic Chemical Vapor Deposition (MEMGCVD™) technique was studied at the optical wavelengths of 442 and 633 nm and acoustic wavelength of 16 μm. In the near-to-Bragg diffraction regime, the diffraction efficiency from 90% to 95% was attained at SAW powers of 0.28 and 0.72 W for the blue and red light, respectively. The simulation using photo-elastic and electro-optic constants reported in literature revealed the prevailing contribution of the photo-elastic effect to the AO diffraction. The calculated SAW power required to attain the diffraction maximum was about seven times larger than the measured values. This discrepancy implies that the photo-elastic constants of AlN and GaN available from literature are underestimated. The increase in the diffraction efficiency with the decreasing optical wavelength is in a good agreement with the theoretical prediction. This feature makes AlGaN very promising for AO applications in the deep UV region.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
78.66.Fd III-V semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.65.+k Acoustical properties of solids
68.35.Iv Acoustical properties
62.20.D- Elasticity
78.40.Fy Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Silicon-containing organic matrices as hosts for highly photostable solid-state dye lasers

A. Costela, I. García-Moreno, D. del Agua, O. García, and R. Sastre

Appl. Phys. Lett. 85, 2160 (2004); http://dx.doi.org/10.1063/1.1793336 (3 pages) | Cited 24 times

Online Publication Date: 24 September 2004

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Modified polymeric matrices incorporating silicon atoms in their structure and doped with lasing dyes have been synthesized and demonstrated to render improved laser performance. When transversely pumped at 532 nm, highly stable laser operation with reasonable, not-optimized efficiencies was obtained. Materials were prepared where dyes pyrromethene 567 and pyrromethene 597 emitted laser radiation with no sign of degradation in the laser output, albeit with some oscillations, after 100 000 pump pulses in the same position of the sample at 10 Hz repetition rate.
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42.55.Mv Dye lasers
42.55.Rz Doped-insulator lasers and other solid state lasers

Junction–temperature measurement in GaN ultraviolet light-emitting diodes using diode forward voltage method

Y. Xi and E. F. Schubert

Appl. Phys. Lett. 85, 2163 (2004); http://dx.doi.org/10.1063/1.1795351 (3 pages) | Cited 39 times

Online Publication Date: 24 September 2004

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A theoretical model for the dependence of the diode forward voltage (Vf) on junction temperature (Tj) is developed. An expression for dVf∕dT is derived that takes into account all relevant contributions to the temperature dependence of the forward voltage including the intrinsic carrier concentration, the band-gap energy, and the effective density of states. Experimental results on the junction temperature of GaN ultraviolet light-emitting diodes are presented. Excellent agreement between the theoretical and experimental temperature coefficient of the forward voltage (dVf∕dT) is found. A linear relation between the junction temperature and the forward voltage is found.
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85.60.Jb Light-emitting devices
73.20.At Surface states, band structure, electron density of states
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.De Semiconductor-device characterization, design, and modeling

Continuous-wave operation of λ∼4.8 μm quantum-cascade lasers at room temperature

A. Evans, J. S. Yu, S. Slivken, and M. Razeghi

Appl. Phys. Lett. 85, 2166 (2004); http://dx.doi.org/10.1063/1.1793340 (3 pages) | Cited 57 times

Online Publication Date: 24 September 2004

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Continuous-wave (cw) operation of quantum-cascade lasers emitting at λ∼4.8 μm is reported up to a temperature of 323 K. Accurate control of layer thickness and strain-balanced material composition is demonstrated using x-ray diffraction. cw output power is reported to be in excess of 370 mW per facet at 293 K, and 38 mW per facet at 323 K. Room-temperature average power measurements are demonstrated with over 600 mW per facet at 50% duty cycle with over 300 mW still observed at 100% (cw) duty cycle.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

All-epitaxial mode-confined vertical-cavity surface-emitting laser

D. Lu, J. Ahn, H. Huang, and D. G. Deppe

Appl. Phys. Lett. 85, 2169 (2004); http://dx.doi.org/10.1063/1.1795982 (3 pages) | Cited 6 times

Online Publication Date: 24 September 2004

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A type of AlGaAs∕GaAs-based vertical-cavity surface-emitting laser is demonstrated that creates a strongly-confined optical mode in an all-epitaxial heterostructure. The mode-confining region in this monolithic device is due to a lithographically defined intracavity phase-shifting layer. Analysis shows that the optical loss in the device can be less than for oxide-confinement.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

White electroluminescence from polyfluorene chemically doped with 1,8-napthalimide moieties

Guoli Tu, Quanguo Zhou, Yanxiang Cheng, Lixiang Wang, Dongge Ma, Xiabin Jing, and Fosong Wang

Appl. Phys. Lett. 85, 2172 (2004); http://dx.doi.org/10.1063/1.1793356 (3 pages) | Cited 95 times

Online Publication Date: 24 September 2004

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An efficient white light-emitting polymer was developed with blue polyfluorene (PFO) chemically doped with orange fluorescent 1, 8-naphthalimide moieties. The emission spectrum can be easily tuned by varying the content of 1, 8-naphthalimide moieties. A white polymeric light-emitting diode (WPLED) with a structure of indium tin oxide (ITO)/the complex of (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT)/polymer∕Ca∕Al showed a current efficiency of 5.3 cd∕A and a power efficiency of 2.8 Lm∕W at 6 V with the Commission Internationale de L'Eclairage (CIE) coordinates at (0.25,0.35). Moreover, the WPLED from the copolymer showed a very stable white light emission at different driving voltage and brightness. The CIE coordinates of the WPLED were (0.25, 0.35), (0.26, O.36), and (0.26, 0.36) under driving voltages of 6, 8, and 10 V, corresponding to the brightness of 82, 3555, and 7530 cd∕m2, respectively. This approach for realization of white light emission is promising over the polymer blending system in terms of both efficiency and color stability.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
85.60.Jb Light-emitting devices

250 nm AlGaN light-emitting diodes

V. Adivarahan, W. H. Sun, A. Chitnis, M. Shatalov, S. Wu, H. P. Maruska, and M. Asif Khan

Appl. Phys. Lett. 85, 2175 (2004); http://dx.doi.org/10.1063/1.1796525 (3 pages) | Cited 83 times

Online Publication Date: 24 September 2004

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We report AlGaN deep ultraviolet light-emitting diodes (LEDs) at 250 and 255 nm that have short emission wavelengths. For an unpackaged 200×200 μm square geometry LED emitting at 255 nm, we measured a peak power of 0.57 mW at 1000 mA of pulsed pump current. For a similar device emitting at 250 nm the peak output power of 0.16 mW was measured at 300 mA of pulsed pump current. Progress is based on the development of high quality AlGaN cladding layers with an Al content up to 72%, which were grown over AlGaN∕AlN superlattice buffer layers on sapphire substrates. These n-Al0.72Ga0.28N layers were doped with Si up to about 1×1018 cm−3 and electron mobilities up to 50 cm2∕V⋅s were estimated. High resolution x-ray diffraction studies gave a narrow (002) rocking curve with full width at half maximum of only 133 arc sec.
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85.60.Jb Light-emitting devices
72.20.Fr Low-field transport and mobility; piezoresistance
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.60.Fi Electroluminescence

Three-dimensional wavelength-scale confinement in quantum dot microcavity light-emitting diodes

C. Zinoni, B. Alloing, C. Paranthoën, and A. Fiore

Appl. Phys. Lett. 85, 2178 (2004); http://dx.doi.org/10.1063/1.1791341 (3 pages) | Cited 19 times

Online Publication Date: 24 September 2004

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We introduce a microcavity light-emitting diode (LED) structure that uses submicrometer oxide aperture and a quantum dot active region to achieve strong three-dimensional confinement of both the carrier distribution and the optical field. Light–current curves show optical emission for devices as small as 400 nm in diameter. Spectroscopy on electrically pumped LEDs, with apertures ranging from 2.5 down to 0.7 μm, show several spectral lines corresponding to cavity modes. A strong blueshift of the resonant modes for smaller apertures demonstrates the role of the oxide aperture in confining laterally the optical wave in a volume comparable to (λ∕n)3. Due to the high quality factors and low mode volumes, the devices could be good candidates for the demonstration of the Purcell effect under electrical pumping.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence

Electrically tunable liquid-crystal photonic crystal fiber

Fang Du, Yan-Qing Lu, and Shin-Tson Wu

Appl. Phys. Lett. 85, 2181 (2004); http://dx.doi.org/10.1063/1.1796533 (3 pages) | Cited 86 times

Online Publication Date: 24 September 2004

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Tunable light switch using a photonic crystal fiber filled with nematic liquid crystal is demonstrated. The original band-gap-guiding fiber structure was transformed to a total internal reflection-guiding photonic crystal fiber by filling liquid crystal into the air core and cladding air holes. By applying external voltage to the liquid-crystal-filled fiber, we have demonstrated an electrically tunable fiber-optical switch with over 30 dB attenuation at 60 Vrms for a He-Ne laser beam. This liquid-crystal-filled photonic crystal fiber will find useful applications in fiber-optic communication systems.
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42.70.Df Liquid crystals
42.81.Wg Other fiber-optical devices
42.70.Qs Photonic bandgap materials
42.81.Gs Birefringence, polarization

Self-aligned, buried heterostructure AlInGaAs laser diodes by micro-selective-area epitaxy

D. Bour, S. Corzine, W. Perez, J. Zhu, A. Tandon, R. Ranganath, C. Lin, R. Twist, L. Martinez, G. Höfler, and M. Tan

Appl. Phys. Lett. 85, 2184 (2004); http://dx.doi.org/10.1063/1.1794382 (3 pages) | Cited 1 time

Online Publication Date: 24 September 2004

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We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quantum well lasers deposited by micro-selective-area growth. The lateral waveguide is defined by metalorganic vapor-phase epitaxy in narrow stripe openings; and the natural tendency to form smooth, no-growth {111} sidewall planes produces a low-loss, single-mode waveguide. By proper adjustment of the growth conditions after the waveguide formation, the waveguide may be buried in p-type InP. A buried heterostructure (BH) laser is there formed in a single growth step, eliminating the deterioration associated with air exposure and etch damage, especially for AlInGaAs active regions. The AlInGaAs BH lasers formed in this simple manner exhibit good performance characteristics, with room-temperature threshold current of 4 mA.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Intracavity coherent addition of Gaussian beam distributions using a planar interferometric coupler

A. A. Ishaaya, N. Davidson, L. Shimshi, and A. A. Friesem

Appl. Phys. Lett. 85, 2187 (2004); http://dx.doi.org/10.1063/1.1791330 (3 pages) | Cited 19 times

Online Publication Date: 24 September 2004

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We present a compact and practical combined laser resonator configuration in which several Gaussian beam distributions are efficiently combined. It is based on intracavity coherent addition of pairs of Gaussian beam distributions with a planar interferometric coupler. The principle, configuration, and experimental results using pulsed Nd:YAG laser beams are presented. The results reveal more than 92% combining efficiency with a nearly Gaussian output beam, in free running and Q-switched operation.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Gn Optical waveguides and couplers
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.25.Kb Coherence
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Action of co-dopant in electron-trapping materials: The case of Sm3+ in Mn2+-activated zinc borosilicate glasses

Chengyu Li and Qiang Su

Appl. Phys. Lett. 85, 2190 (2004); http://dx.doi.org/10.1063/1.1797562 (3 pages) | Cited 6 times

Online Publication Date: 24 September 2004

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The action of electron-trapping materials (ETMs) consists of three sequential steps, i.e., the storage, the transfer, and the release of energy. It is generally considered that the co-dopant acts as a trapping center to enhance the storage ability of ETMs, which focus on the first step. In this letter, by the abnormal phosphorescence of Sm3+ in zinc borosilicate glasses doped with samarium and manganese (ZSBMS), we suggest that the co-dopant is able to change the energy transfer in the material.
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81.05.Kf Glasses (including metallic glasses)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Qr Amorphous materials; glasses and other disordered solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Screening-photovoltaic bright solitons in lithium niobate and associated single-mode waveguides

E. Fazio, F. Renzi, R. Rinaldi, M. Bertolotti, M. Chauvet, W. Ramadan, A. Petris, and V. I. Vlad

Appl. Phys. Lett. 85, 2193 (2004); http://dx.doi.org/10.1063/1.1794854 (3 pages) | Cited 68 times

Online Publication Date: 24 September 2004

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Photorefractive screening-photovoltaic solitons are observed in lithium niobate. Two-dimensional bright circular solitons are formed thanks to a strong static bias field, externally applied, opposite to the photovoltaic internal field. The dynamics of the soliton formation is monitored and compared to a time-dependent numerical model allowing determination of the photovoltaic field. Efficient single mode waveguides are shown to be memorized by the soliton beam for a long time.
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42.65.Tg Optical solitons; nonlinear guided waves
42.81.Dp Propagation, scattering, and losses; solitons
72.40.+w Photoconduction and photovoltaic effects
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials

Raman gain and nonlinear optical absorption measurements in a low-loss silicon waveguide

Haisheng Rong, Ansheng Liu, Remus Nicolaescu, Mario Paniccia, Oded Cohen, and Dani Hak

Appl. Phys. Lett. 85, 2196 (2004); http://dx.doi.org/10.1063/1.1794862 (3 pages) | Cited 44 times

Online Publication Date: 24 September 2004

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We fabricated a low-loss (∼0.22 dB∕cm) rib waveguide (WG) in silicon-on-insulator with a small effective core area of ∼1.57 μm2 and measured the stimulated Raman scattering gain in the WG. We obtained 2.3 dB Raman gain in a 4.8-cm-long S-shaped WG using a 1455 nm pump laser with a cw power of 0.9 W measured before the WG. In addition, we observed nonlinear dependence of Raman gain and optical propagation loss as a function of the pump power. Our study shows that this mainly is due to two-photon absorption (TPA) induced free carrier absorption in the silicon WG. We experimentally determined the TPA induced free carrier lifetime of 25 ns, which agrees well with our modeling.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Es Stimulated Brillouin and Rayleigh scattering
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