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23 Jun 2008

Volume 92, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 254102 (2008); http://dx.doi.org/10.1063/1.2945893 (3 pages)

M. Trinker, S. Groth, S. Haslinger, S. Manz, T. Betz, S. Schneider, I. Bar-Joseph, T. Schumm, and J. Schmiedmayer
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A micromachined optical double well for thermo-optic switching via resonant tunneling effect

W. M. Zhu, X. M. Zhang, A. Q. Liu, H. Cai, T. Jonathan, and T. Bourouina

Appl. Phys. Lett. 92, 251101 (2008); http://dx.doi.org/10.1063/1.2951621 (3 pages) | Cited 4 times

Online Publication Date: 23 June 2008

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This letter presents the thermo-optic switching characteristics of an optical double-well structure, which has a high-low-high-low-high refractive index construct formed by micromachined silicon prisms and air gaps. Analysis shows such structure features full transmission (i.e., on state) and requires low refractive index change for switching function. The device is fabricated on silicon-on-isolator wafer using deep etching process. In experiment, it measures a switching speed of 1 μs and an extinction ratio of 30 dB. Compared with the other micromachined switches, this device utilizes different physical principle and processes various merits such as fast switching speed and low power consumption.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

High-performance 4H-SiC based metal-semiconductor-metal ultraviolet photodetectors with Al2O3/SiO2 films

Feng Zhang, Weifeng Yang, Huolin Huang, Xiaping Chen, Zhengyun Wu, Huili Zhu, Hongji Qi, Jianke Yao, Zhengxiu Fan, and Jianda Shao

Appl. Phys. Lett. 92, 251102 (2008); http://dx.doi.org/10.1063/1.2949318 (3 pages) | Cited 10 times

Online Publication Date: 23 June 2008

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4H-silicon carbide (SiC) metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with Al2O3/SiO2 (A/S) films employed as antireflection/passivation layers have been demonstrated. The devices showed a peak responsivity of 0.12 A/W at 290 nm and maximum external quantum efficiency of 50% at 280 nm under 20 V electrical bias, which were much larger than conventional MSM detectors. The redshift of peak responsivity and response restriction effect were found and analyzed. The A/S/4H-SiC MSM photodetectors were also shown to possess outstanding features including high UV to visible rejection ratio, large photocurrent, etc. These results demonstrate A/S/4H-SiC photodetectors as a promising candidate for OEIC applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Influence of tip-sample interaction in a time-domain terahertz scattering near field scanning microscope

A. Thoma and T. Dekorsy

Appl. Phys. Lett. 92, 251103 (2008); http://dx.doi.org/10.1063/1.2949858 (3 pages) | Cited 3 times

Online Publication Date: 23 June 2008

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Apertureless near field measurements with a metallic tip are performed in the terahertz frequency range. Lateral scans are recorded for different time delays within a terahertz pulse. The forward scattered terahertz signal strongly depends on the time delay. At larger time delays, the tip-sample interaction leads to additional structures in the scan that do not correspond to a change in topography or dielectric function.
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07.79.Fc Near-field scanning optical microscopes
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Silicon resonant cavity enhanced photodetector based on the internal photoemission effect at 1.55 μm: Fabrication and characterization

M. Casalino, L. Sirleto, L. Moretti, M. Gioffrè, G. Coppola, and Ivo Rendina

Appl. Phys. Lett. 92, 251104 (2008); http://dx.doi.org/10.1063/1.2952193 (3 pages) | Cited 14 times

Online Publication Date: 24 June 2008

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In this paper, the realization and the characterization of a resonant cavity enhanced (RCE) photodetector, completely silicon compatible and working at 1.55 μm, are reported. The detector is a RCE structure incorporating a Schottky diode and its working principle is based on the internal photoemission effect. Taking advantage of a Cu/Si Schottky diode fed on a high reflectivity Bragg mirror, an improvement in responsivity at 1.55 μm is experimentally demonstrated.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Kk Junction diodes

An analysis of 1.55 μm InAs/InP quantum dash lasers

S. C. Heck, S. B. Healy, S. Osborne, E. P. O’Reilly, F. Lelarge, F. Poingt, A. Accard, F. Pommereau, O. Le Gouezigou, and B. Dagens

Appl. Phys. Lett. 92, 251105 (2008); http://dx.doi.org/10.1063/1.2952194 (3 pages) | Cited 4 times

Online Publication Date: 24 June 2008

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Calculations show that electron states are not confined in the dashes in 1.55 μm InAs/InP quantum dash-in-a-well laser structures. The combination of strain and three-dimensional confinement reduces the calculated density of states (DOS) near the valence band maximum, with the conduction and valence DOS then almost equal close to the band edges. Calculations and photoabsorption measurements show strongly polarized spontaneous emission and gain spectra. Experimental analysis shows the room temperature threshold current is dominated by nonradiative current paths.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
73.21.La Quantum dots
78.30.Fs III-V and II-VI semiconductors

Intensity-dependent enhancement of saturable absorption in PbS–Au4 nanohybrid composites: Evidence for resonant energy transfer by Auger recombination

Hendry I. Elim, Wei Ji, Jian Yang, and Jim Yang Lee

Appl. Phys. Lett. 92, 251106 (2008); http://dx.doi.org/10.1063/1.2952273 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2008

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Intensity-dependent enhancement of saturable absorption in a film of PbS–Au4 nanohybrid composites has been observed by femtosecond time-resolved transient absorption measurement at 780 nm. The nonlinear absorption coefficient (α2) of saturable absorption in PbS–Au4 nanohybrid composites is found to be dependent on excitation irradiance and it is determined to be −2.9 cm/GW at 78 GW/cm2, an enhancement of nearly fourfold in comparison with that of pure PbS quantum dots (QDs). The enhancement is attributed to the excitation of surface plasmon by resonant energy transfer between PbS QDs and Au nanoparticles through Auger recombination.
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78.66.Sq Composite materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics
79.60.Dp Adsorbed layers and thin films

Fast photorefractive response and high sensitivity of Zr and Fe codoped LiNbO3 crystals

Yongfa Kong, Shengqing Wu, Shiguo Liu, Shaolin Chen, and Jingjun Xu

Appl. Phys. Lett. 92, 251107 (2008); http://dx.doi.org/10.1063/1.2952275 (3 pages) | Cited 13 times

Online Publication Date: 24 June 2008

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A series of Zr and Fe codoped LiNbO3 crystals was grown and their photorefractive properties have been investigated. Compared with LiNbO3:Fe,Hf, the concentration of Fe2+ ions is strongly increased in LiNbO3:Fe,Zr. As a result, the photorefractive response speed of these as-grown LiNbO3:Fe,Zr crystals is only 2 s and the sensitivity is larger than 12 cm/J while the saturation diffraction efficiency still remains at a high level. These findings prove that LiNbO3:Fe,Zr is an excellent choice for volume holographic storage.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ln Holographic recording materials; optical storage media

Multilayer white polymer light-emitting diodes with deoxyribonucleic acid-cetyltrimetylammonium complex as a hole-transporting/electron-blocking layer

Qingjiang Sun, Dong Wook Chang, Liming Dai, James Grote, and Rajesh Naik

Appl. Phys. Lett. 92, 251108 (2008); http://dx.doi.org/10.1063/1.2948864 (3 pages) | Cited 14 times

Online Publication Date: 24 June 2008

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Using a thin film of deoxyribonucleic acid-cetyltrimetylammonium (DNA-CTMA) complex as a hole-transporting/electron-blocking layer, we have developed a sequential solution-processing approach for constructing multilayer (up to five layers) white polymer light-emitting diodes, incorporating the poly(9,9-dioctylfluorene-2,7-diyl)/poly[2-methoxy-5(2′-ethyl-hexyloxy)-1, 4-phenylene vinylene] emissive layer. These devices were demonstrated to show a low turn-on voltage ( ∼ 5 V), high efficiency (10.0 cd/A), and high brightness (10500 cd/m2) with an improved white-color stability.
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85.60.Jb Light-emitting devices

Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes

Jack Ng and C. T. Chan

Appl. Phys. Lett. 92, 251109 (2008); http://dx.doi.org/10.1063/1.2951599 (3 pages) | Cited 14 times

Online Publication Date: 26 June 2008

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We show that when a microsphere is illuminated by an evanescent wave, the optical forces on- and off-whispering gallery mode (WGM) resonance can differ by several orders of magnitude. Such size-selective force allows one to selectively manipulate the resonating particles, while leaving those particles at off-resonance untouched. As WGM resonances have very high-Q’s, this kind of force could be deployed for size-selective manipulation with a very high accuracy ( ∼ 1/Q), as well as simultaneous particle-sorting according to their size or resonant frequency.
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42.50.-p Quantum optics

Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal

Min-Ki Kwon, Ja-Yeon Kim, Il-Kyu Park, Ki Seok Kim, Gun-Young Jung, Seong-Ju Park, Je Won Kim, and Yong Chun Kim

Appl. Phys. Lett. 92, 251110 (2008); http://dx.doi.org/10.1063/1.2948851 (3 pages) | Cited 25 times

Online Publication Date: 26 June 2008

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A photonic crystal (PC) structure of periodic SiO2 pillar cubic array is embedded in n-GaN layer of InGaN/GaN multiple quantum well (MQW) blue (480 nm) light-emitting diode (LED). The diameter, period, and depth of SiO2 pillar are 124±6, 230±10, and 130±10 nm, respectively. The increments of 70% for external quantum efficiency, 17% for internal quantum efficiency, and 45% for light extraction efficiency from photoluminescence measurement, and 33% for optical output power at 20 mA are observed for LEDs with an embedded PC layer. This improvement can be attributed to the increased extraction efficiency by PC effect as well as increased internal quantum efficiency due to the decrease of dislocation density in n-GaN layer because of an epitaxial lateral over-growth process.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Pockel’s effect and optical rectification in (111)-cut near-intrinsic silicon crystals

Zhanguo Chen, Jianxun Zhao, Yuhong Zhang, Gang Jia, Xiuhuan Liu, Ce Ren, Wenqing Wu, Jianbo Sun, Kun Cao, Shuang Wang, and Bao Shi

Appl. Phys. Lett. 92, 251111 (2008); http://dx.doi.org/10.1063/1.2952462 (3 pages) | Cited 6 times

Online Publication Date: 26 June 2008

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Pockel’s effect and optical rectification are demonstrated in the charge space region of a (111)-cut near-intrinsic silicon crystal by the use of a planar metal-insulator-semiconductor structure. The results show that both Pockel’s effect and optical rectification are so considerable that these effects should be taken into account for designing silicon-based photonic devices. The anisotropy of optical rectification is measured too, and experimental results are in good accordance with the theoretical analysis. These effects can also be used as a tool to investigate the properties of the charge space region of silicon devices in future.
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78.20.Jq Electro-optical effects
78.66.Db Elemental semiconductors and insulators

Tamm plasmon polaritons: Slow and spatially compact light

M. E. Sasin, R. P. Seisyan, M. A. Kalitteevski, S. Brand, R. A. Abram, J. M. Chamberlain, A. Yu. Egorov, A. P. Vasil’ev, V. S. Mikhrin, and A. V. Kavokin

Appl. Phys. Lett. 92, 251112 (2008); http://dx.doi.org/10.1063/1.2952486 (3 pages) | Cited 32 times

Online Publication Date: 26 June 2008

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We report on the first experimental observation of Tamm plasmon polaritons (TPPs) formed at the interface between a metal and a dielectric Bragg reflector (DBR). In contrast to conventional surface plasmons, TPPs have an in-plane wavevector less than the wavevector of light in vacuum, which allows for their direct optical excitation. The angular resolved reflectivity and transmission spectra of a GaAs/AlAs DBR covered by Au films of various thicknesses show the resonances associated with the TPP at low temperatures and room temperature. The in-plane dispersion of TTPs is parabolic with an effective mass of 4×10−5 of the free electron mass.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.79.Bh Lenses, prisms and mirrors

Tunneling-injection of electrons and holes into quantum dots: A tool for high-power lasing

Dae-Seob Han and Levon V. Asryan

Appl. Phys. Lett. 92, 251113 (2008); http://dx.doi.org/10.1063/1.2952488 (3 pages) | Cited 4 times

Online Publication Date: 26 June 2008

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We study the optical output power of a semiconductor laser, which exploits tunneling-injection of electrons and holes into quantum dots (QDs) from two separate quantum wells. Even if there is out-tunneling leakage of carriers from QDs, the intensity of parasitic recombination outside QDs remains restricted with increasing injection current. As a result, the light-current characteristic becomes increasingly linear, and the slope efficiency grows closer to unity at high injection currents—a fascinating feature favoring the use of tunneling-injection of both electrons and holes into QDs for high-power lasing.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Electric-field switching of exciton spin splitting in coupled quantum dots

Xiaojing Li and Kai Chang

Appl. Phys. Lett. 92, 251114 (2008); http://dx.doi.org/10.1063/1.2952509 (3 pages) | Cited 1 time

Online Publication Date: 26 June 2008

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We investigate theoretically the spin splitting of the exciton states in semiconductor coupled quantum dots (CQDs) containing a single magnetic ion. We find that the spin splitting can be switched on/off in the CQDs via the sp-d exchange interaction using the electric field. An interesting bright-to-dark exciton transition can be found and it significantly affects the photoluminescence spectrum. This phenomenon is induced by the transition of the ground exciton state, arising from the hole mixing effect, between the bonding and antibonding states.
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71.35.Aa Frenkel excitons and self-trapped excitons
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions

Experimental demonstration of phase locking of a two-dimensional fiber laser array using a self-imaging resonator

Bing He, Qihong Lou, Wei Wang, Jun Zhou, Yinghui Zheng, Jingxing Dong, Yunrong Wei, and Weibiao Chen

Appl. Phys. Lett. 92, 251115 (2008); http://dx.doi.org/10.1063/1.2952508 (3 pages) | Cited 12 times

Online Publication Date: 27 June 2008

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Phase locking of a two-dimensional fiber laser array is experimentally demonstrated by using a self-imaging resonator and a spatial filter. The stable beam profiles of in-phase mode and out-of-phase mode are observed by controlling the position of spatial filter. The phase locking fiber array with in-phase mode has produced 26 W coherent output. An antisymmetric eigenmode is also observed in our experiments. The phase locking is not sensitive to power variations among the pump beams and the configuration has the ability to repair a missing element.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers

Tunable surface plasmons for emission enhancement of silicon nanocrystals using Ag-poor cermet layer

Xuan Tang, Yidong Huang, Yuxuan Wang, Wei Zhang, and Jiangde Peng

Appl. Phys. Lett. 92, 251116 (2008); http://dx.doi.org/10.1063/1.2953085 (3 pages) | Cited 4 times

Online Publication Date: 27 June 2008

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To improve the quantum efficiency from silicon nanocrystals, a structure with Ag/Ag-poor cermet layers is proposed. Due to large permittivity of Ag-poor cermet and its dispersion characteristic, density of states can be enhanced at the energy much lower than the plasmon energy of Ag. By properly choosing the component of the Ag-poor cermet, the dispersion of surface plasmons can be engineered to increase radiative emission rate significantly at the emission energy of silicon nanocrystals. Effective enhancement is theoretically demonstrated using Ag, which was generally recognized as nonideal material for emission enhancement in silicon nanocrystals due to its high plasmon energy.
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78.66.Db Elemental semiconductors and insulators
78.68.+m Optical properties of surfaces
77.22.Ch Permittivity (dielectric function)

Analysis of negative refraction from anomalous phase in transmission spectrum

A. Mandatori, C. Sibilia, M. Bertolotti, and J. W. Haus

Appl. Phys. Lett. 92, 251117 (2008); http://dx.doi.org/10.1063/1.2950322 (3 pages) | Cited 2 times

Online Publication Date: 27 June 2008

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The dependence of the negative refraction of a simple Fabry–Perot system as a function of the sign of material permittivity and permeability is analyzed. It is shown that negative refraction is possible every time the transmission phase of the system shows an anomalous behavior. However if the permittivity or the permeability are complex the anomalous phase is no longer univocally related to the presence of a negative refractive index.
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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
77.22.Ch Permittivity (dielectric function)
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Efficient 13.5 nm extreme ultraviolet emission from Sn plasma irradiated by a long CO2 laser pulse

Y. Tao, M. S. Tillack, K. L. Sequoia, R. A. Burdt, S. Yuspeh, and F. Najmabadi

Appl. Phys. Lett. 92, 251501 (2008); http://dx.doi.org/10.1063/1.2951595 (3 pages) | Cited 21 times

Online Publication Date: 23 June 2008

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The effect of pulse duration on in-band (2% bandwidth) conversion efficiency (CE) from a CO2 laser to 13.5 nm extreme ultraviolet (EUV) light was investigated for Sn plasma. It was found that high in-band CE, 2.6%, is consistently obtained using a CO2 laser with pulse durations from 25 to 110 ns. Employing a long pulse, for example, 110 ns, in a CO2 laser system used in an EUV lithography source could make the system significantly more efficient, simpler, and cheaper as compared to that using a short pulse of 25 ns or shorter.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.72.Bj Visible and ultraviolet sources
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Hard x-ray generation by low energy, tightly focused laser pulses

K. Takano, K. Nemoto, T. Nayuki, Y. Oishi, T. Fujii, A. Zhidkov, E. Hotta, M. Todoriki, and S. Hasegawa

Appl. Phys. Lett. 92, 251502 (2008); http://dx.doi.org/10.1063/1.2945283 (3 pages) | Cited 2 times

Online Publication Date: 24 June 2008

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The interaction of λ2 laser pulses with plasma is studied to scale the high-field physics from high power laser systems to low-energy, high-repetition-rate lasers. For this purpose, 20 mJ, 40 fs Ti:sapphire laser pulses were focused in a spot of 2.2×2.3 μm2 with a maximum intensity of I ∼ 1019 W/cm2. Efficient generations of energetic electrons ( ∼ 1 MeV) and hard x-rays with energies of over 100 keV were obtained by irradiating the low-energy, tightly focused laser pulses on a massive Cu target.
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52.38.Ph X-ray, γ-ray, and particle generation
52.38.Kd Laser-plasma acceleration of electrons and ions

Pulsed corona discharge for oxidation of gaseous elemental mercury

Kyung Bo Ko, Youngchul Byun, Moohyun Cho, Won Namkung, Ian P. Hamilton, Dong Nam Shin, Dong Jun Koh, and Kyoung Tae Kim

Appl. Phys. Lett. 92, 251503 (2008); http://dx.doi.org/10.1063/1.2952496 (3 pages) | Cited 4 times

Online Publication Date: 27 June 2008

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Positive pulsed corona discharge has been applied for the oxidation of gaseous elemental mercury (Hg0) from a simulated flue gas. The oxidation of Hg0 to HgO and HgCl2 can significantly enhance the mercury removal from flue gas. At a gas condition of O2 (10%), H2O (3%), and N2 (balance), Hg0 oxidation efficiency of 84% was achieved at an input energy density of 45 J/l. The presence of NO, however, hinders Hg0 oxidation due to the preferential reaction of NO with O and O3. On the contrary, SO2 shows little effect on Hg0 oxidation due to its preferential reaction with OH. It has been also observed that the HCl in gas stream can be dissociated to Cl and Cl2 and can induce additional Hg0 oxidation to HgCl2.
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52.80.Hc Glow; corona
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Anisotropic damping of longitudinal optical phonon-plasmon coupling modes of InN films

Yoshihiro Ishitani, Masayuki Fujiwara, Xinqiang Wang, Song-Bek Che, and Akihiko Yoshikawa

Appl. Phys. Lett. 92, 251901 (2008); http://dx.doi.org/10.1063/1.2951614 (3 pages) | Cited 7 times

Online Publication Date: 23 June 2008

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The energy broadenings of the higher energy branch of the longitudinal optical (LO) phonon-plasmon coupling modes for E1(LO) and A1(LO) are analyzed for InN films by infrared reflectance and spectroscopic ellipsometry. Larger broadening for the vibration parallel to c of A1(LO)-plasmon coupling is found with the decrease in electron density. This phenomenon is caused by the plasmon lifetime anisotropy, and is attributed to the reduction in crystal defects causing isotropic carrier scattering and the remaining of defects along the c axis such as threading dislocations and columnar grain boundaries.
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63.20.kk Phonon interactions with other quasiparticles
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.Mm Grain and twin boundaries

Three-dimensional morphology of nanoporous gold

Takeshi Fujita, Li-Hua Qian, Koji Inoke, Jonah Erlebacher, and Ming-Wei Chen

Appl. Phys. Lett. 92, 251902 (2008); http://dx.doi.org/10.1063/1.2948902 (3 pages) | Cited 50 times

Online Publication Date: 23 June 2008

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We report transmission electron tomography of nanoporous gold fabricated by chemically dealloying Au35Ag65 films. A number of algorithms were employed to quantitatively characterize the complex three-dimensional nanoporous structure. It was found that gold ligaments and nanopore channels are topologically and morphologically equivalent, i.e., they are inverses of each other in three-dimensional space. Statistical analysis reveals that this bicontinuous nanostructured material is actually quasiperiodic and has, on average, a near zero surface curvature. These quantitative measurements will help in understanding the structural stability of nanoporous gold and in modeling its physical and chemical performances.
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61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials

Mechanical behavior of ultralow-dielectric-constant mesoporous amorphous silica

M. Rauf Gungor, James J. Watkins, and Dimitrios Maroudas

Appl. Phys. Lett. 92, 251903 (2008); http://dx.doi.org/10.1063/1.2949556 (3 pages) | Cited 2 times

Online Publication Date: 23 June 2008

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Using molecular-dynamics simulations, we examine the mechanical behavior of mesoporous amorphous silicas that are considered as ultralow-dielectric-constant materials in microelectronics. We study structures with a regular array of spherical pores and densities between 88% and 72% of the amorphous silica normal density. We find that the Young modulus depends on density according to a sublinear power-law scaling relationship and decreases with decreasing mesopore size. Upon uniaxial compression, an elastic instability is triggered in structures with less-than-critical density or mesopore size.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
77.22.Ch Permittivity (dielectric function)
61.43.Gt Powders, porous materials

Thermally tunable polymer microlenses

Xian Huang, Chao-Min Cheng, Li Wang, Bin Wang, Chih-Chuan Su, Mon-Shu Ho, Philip R. LeDuc, and Qiao Lin

Appl. Phys. Lett. 92, 251904 (2008); http://dx.doi.org/10.1063/1.2945646 (3 pages) | Cited 9 times

Online Publication Date: 23 June 2008

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Polymer microlenses capable of using heat to control its focal length are presented. The microlenses are created by exposing droplets of the polymer SU-8 to UV light. By altering the temperature of the microlenses via on-chip heating, their curvature and focal length are actively controlled without mechanical movements. By directly and indirectly measuring temperature-dependent changes of the focal length, we test the ability of the microlenses as a tunable imaging component. The microlenses have potential use in applications such as laser systems, functional biomimetics, and endoscopy.
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42.79.Bh Lenses, prisms and mirrors

Carrier lifetimes in type-II InAs quantum dots capped with a GaAsSb strain reducing layer

Y. D. Jang, T. J. Badcock, D. J. Mowbray, M. S. Skolnick, J. Park, D. Lee, H. Y. Liu, M. J. Steer, and M. Hopkinson

Appl. Phys. Lett. 92, 251905 (2008); http://dx.doi.org/10.1063/1.2949741 (3 pages) | Cited 15 times

Online Publication Date: 23 June 2008

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Carrier lifetimes have been measured for long-wavelength emitting InAs quantum dots (QDs) capped with a thin GaAsSb layer. Above a critical Sb composition, a type-II system is formed, resulting in an increase in the carrier lifetime. The carrier lifetime in a strongly type-II structure is increased by a factor ∼ 54 in comparison to the lifetime in a type-I structure. In addition, the type-II carrier lifetime varies across the inhomogeneously broadened ground-state emission, while the type-I QD lifetime is invariant.
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73.63.Kv Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.La Quantum dots
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