Volume 83, Issue 25, 22 December 2003
- lasers, optics, and optoelectronics
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- interdisciplinary and general physics
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
83(2003); http://dx.doi.org/10.1063/1.1634373View Description Hide Description
Wavelength-selective operation of an optical filter (add/drop) based on a contra-directional photonic crystal waveguide coupler is demonstrated. The waveguides are defined as line defects in a two-dimensional triangular photonic crystalfabricated in an InP/GaInAsP heterostructure. The device is characterized using the end-fire method for the drop functionality. The experimental data are in good agreement with the theoretical results predicted by finite-difference time-domain simulations.
Observation of three-dimensional optical stacking of microparticles using a single Laguerre–Gaussian beam83(2003); http://dx.doi.org/10.1063/1.1635079View Description Hide Description
Optical stacking of microparticles has been demonstrated earlier using a single focused Gaussian beam, multiple beams from Laguerre–Gaussian (LG) interference patterns, and Bessel beams. In this letter, we demonstrate that a single focused LG beam has the ability to optically stack multiple high-index microparticles around the intensity annular rings of the LG beam, and thus form a three-dimensional structure. Due to the symmetrically circular shape of the LG, we have been able to stack particles in a circular manner. Hence we propose that this technique of stacking can be extended to optical fields of designed shaped such that the stacking microparticles will be organized according to the shaped of the beam intensity. This is an alternative method to obtain a desired three-dimensional crystalline structure, where shaping the optical vortices beam is used instead of using multiple beams.
83(2003); http://dx.doi.org/10.1063/1.1635076View Description Hide Description
A high-reflectivity bottom anode is essential for high-performance top-emitting organic light-emitting devices(OLEDs).Ag has the highest reflectivity for visible light among all metals, yet its electronic properties are not ideal for anodes of OLEDs. In this letter, we report that by inducing a thin silver oxide at the surface of Ag, hole injection from Aganodes into OLEDs is largely enhanced yet with rather high reflectivity retained. Top-emitting devices using such surface-modified Aganode show device characteristics competitive with those of a bottom-emitting device using the indiumtin oxide anode.
83(2003); http://dx.doi.org/10.1063/1.1635981View Description Hide Description
We demonstrate a voltage tunable two-color quantum-well infrared photodetector (QWIP) that consists of multiple periods of two distinct AlGaAs/GaAs superlattices separated by AlGaAs blocking barriers on one side and heavily doped GaAs layers on the other side. The detection peak switches from 9.5 μm under large positive bias to 6 μm under negative bias. The background-limited temperature is 55 K for 9.5 μm detection and 80 K for 6 μm detection. We also demonstrate that the corrugated-QWIP geometry is suitable for coupling normally incident light into the detector.
Continuous wave optically pumped lead-salt mid-infrared quantum-well vertical-cavity surface-emitting lasers83(2003); http://dx.doi.org/10.1063/1.1636246View Description Hide Description
Continuous wave optically pumped mid-infrared lead-salt quantum-well vertical-cavity surface-emitting lasers with an eleven-period PbSe/PbSrSe quantum-well active region are demonstrated. The cw emissions are observed up to 230 K at the emission wavelengths around 4.03 μm. The lowest threshold pump density of 2.6 kW/cm2 appears at 190 K, 65 °C lower than that of the pulsed measurements. This indicates the temperature difference between the active region and the heat sink of the episide-up mounted on-wafer testing under cw pumping.
Cavity-length effects of high-temperature high-power continuous-wave characteristics in quantum-cascade lasers83(2003); http://dx.doi.org/10.1063/1.1634689View Description Hide Description
We report the cavity-length dependent high-temperature high-power cw characteristics in λ=6 μm quantum-cascade lasers with a thick electroplated Au top contact layer. For a high-reflectivity (HR) coated 15 μm wide and 3 mm long laser, the cw operation is achieved up to 313 K (40 °C) with an output power of 17 mW. At 298 K, a very high cw output power of 213 mW is obtained for a HR coated 15 μm wide and 4 mm long laser. Thermal resistance is analyzed at temperatures above 283 K for HR coated lasers with different cavities.
Realization of waveguiding epitaxial GaN layers on Si by low-pressure metalorganic vapor phase epitaxy83(2003); http://dx.doi.org/10.1063/1.1635075View Description Hide Description
Waveguiding GaN epitaxial layers have been grown by low-pressure metalorganic vapor phase epitaxy on Si(111) substrates using AlN/GaN short period-superlattice (SPS) buffer layer systems. The AlN/GaN SPS has been studied by x-ray diffraction where it appears as pseudoternary alloy. Using elastictheory an effective Al content of 44% is calculated. This value is confirmed by the average Al content calculated from the AlN:GaN layer thickness ratio measured in cross-section transmission electron microscopy. The GaN waveguiding properties have been assessed using the prism coupling method. They sensibly improve with the total thickness of the underlying AlN/GaN superlattice as well as if an additional AlN/GaN SPS is grown atop the GaN waveguiding layer.
83(2003); http://dx.doi.org/10.1063/1.1635657View Description Hide Description
We report operation of a terahertz quantum-cascade laser at 3.8 THz up to a heat-sink temperature of 137 K. A resonant phonon depopulation design was used with a low-loss metal–metal waveguide, which provided a confinement factor of nearly unity. A threshold current density of was obtained in pulsed mode at 5 K. Devices fabricated using a conventional semi-insulating surface-plasmon waveguide lased up to 92 K with a threshold current density of at 5 K.
Surface-relief diffraction gratings based on selective etching of periodically poled lithium niobate83(2003); http://dx.doi.org/10.1063/1.1636535View Description Hide Description
This work reports the use of selective etching in a periodically poled crystal of to engineer a surface-relief diffraction grating. A 35.1%–64.9% fill factor (domain duty cycle) grating with a 6.86 μm domain period is presented. The diffraction grating created provides a simple tool for accurate characterization of domain size and structure homogeneity. Following a similar process, arbitrary surface-relief two-level binary diffractive optical elements can be patterned in domain-engineered lithium niobate crystals.
83(2003); http://dx.doi.org/10.1063/1.1636266View Description Hide Description
We report polarization switching in a monolithic dual-resonator vertical-cavity laser. The light output from the top ion-implanted cavity under forward bias above threshold is partitioned into two orthogonal polarizations of the fundamental transverse mode. A reverse bias of sufficient magnitude applied to the bottom oxide-confined cavity causes the abrupt suppression of the dominant polarization and simultaneous emergence of the orthogonal polarization. We find that the electro-optic birefringence of the two polarizations increases with increasing reverse bias. We show that the mechanism of the polarization switch is consistent with wavelength-dependent loss from electroabsorption in the reverse-biased quantum wells of the oxide-confined cavity.
83(2003); http://dx.doi.org/10.1063/1.1636518View Description Hide Description
We report infrared light modulation based on direct free-carrier absorption induced by visible light irradiation in silicon-on-insulator waveguides. An amplitude modulation depth of 96% and 89% was measured for waveguide light carrier at a wavelength of 1.55 and 1.32 μm. The frequency dependence of the modulation effect was measured as well.
83(2003); http://dx.doi.org/10.1063/1.1635982View Description Hide Description
A four-electrode liquid crystal cell, featuring a double-side fringe-field switching, has been designed with two-layer electrodes on both glass substrates. The two-layer electrode is the same as that used in fringe-field switching liquid crystal displays. Using a negative dielectric liquid crystal, a homogeneous cell has been fabricated with top and bottom stripe electrodes perpendicular to each other. The fringe fields near top and bottom surfaces drive the homogeneous liquid crystal layer to a twisted structure. The distributions of electric field and molecular director are obtained by theoretical analysis. The double-side fringe-field switching cell shows a much faster response and wider viewing cone compared to traditional fringe-field switching one. The improved electro-optical properties are due to the wider and more symmetric director distribution with respect to the midplane of the liquid crystal cell.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
83(2003); http://dx.doi.org/10.1063/1.1635077View Description Hide Description
During molecular-beam epitaxy of InN films on GaN(0001) surface, three-dimensional (3D) islands are observed following an initial wetting layer formation. Depending on deposition condition, the 3D islands take different shapes. Pyramidal islands form when excess nitrogen fluxes are used, whereas pillar-shaped islands are obtained when excess indium fluxes are employed. The pillar-shaped islands are identified to represent the equilibrium shape, whereas the pyramidal ones are limited by kinetics. As the size of islands increases, their aspect ratio shows a decreasing trend, which is attributed to a gradual relaxation of strain in the layer by defects.
Near-equilibrium strain relaxation and misfit dislocation interactions in PbTe on PbSe (001) heteroepitaxy83(2003); http://dx.doi.org/10.1063/1.1633675View Description Hide Description
Strain relaxation of PbTe layers on PbSe (001) by misfit dislocation formation is shown to take place near equilibrium without kinetic barriers. A comparison of the experimental data with different strain relaxation models shows that mutual dislocation interactions are of crucial importance for the strain relaxation process. This results in faster relaxation than predicted by the models for noninteracting dislocation arrays.
83(2003); http://dx.doi.org/10.1063/1.1633965View Description Hide Description
With a recently developed unique deep ultraviolet picoseconds time-resolvedphotoluminescence(PL)spectroscopy system and improved growth technique, we are able to determine the detailed band structure near the Γ point of wurtzite (WZ) AlN with a direct band gap of 6.12 eV. Combined with first-principles band structure calculations we show that the fundamental optical properties of AlN differ drastically from that of GaN and other WZ semiconductors. The discrepancy in energy band gap values of AlN obtained previously by different methods is explained in terms of the optical selection rules in AlN and is confirmed by measurement of the polarization dependence of the excitonic PL spectra.
83(2003); http://dx.doi.org/10.1063/1.1633968View Description Hide Description
We investigate hydrogenated and deuterated amorphous Si and solar cell material, prepared under conditions of high hydrogen and deuterium dilution, respectively. Using cross-sectional transmission electron microscopy, we provide direct observation of the microstructure of these materials. We observe that the high hydrogen dilution results in homogeneous material with no evidence of microvoids. In contrast, the replacement of hydrogen with deuterium produces a heterogeneous mixture of amorphous and microcrystalline material. The amorphous phase contains significant numbers of microvoids or low-density deuterium-rich domains. The observed heterogeneity is related to the effect of the substitution of hydrogen with deuterium on the microstructure of the Si film.
83(2003); http://dx.doi.org/10.1063/1.1632544View Description Hide Description
Large third-order optical nonlinearities were observed in epitaxialthin films of grown on substrates. Using 140 fs laser pulses at 900 nm, a negative nonlinear refractive index and a nonlinear absorption coefficient for are measured at room temperature. Large electric-field-induced enhancement of three to four orders of magnitude in the second-harmonic response at 450 nm is observed with effective nonlinear coefficients of at 300 (473) K under applied fields of ∼707 (177) V/mm, respectively, from a 110 nm multivariant thin film.
83(2003); http://dx.doi.org/10.1063/1.1635664View Description Hide Description
Several three-dimensional dielectric network structures possessing large photonic band gaps are presented. Two of these photonic crystals show gaps as large as 26% of the midgap frequency for a refractive index contrast 3.6:1. Four of the proposed structures consist of three-connected networks and a fifth structure has a mixture of three- and four-connected nodes. The realization of these structures using block polymerself-assembly, interference lithography and layer-by-layer lithography is briefly discussed.
83(2003); http://dx.doi.org/10.1063/1.1635072View Description Hide Description
The limit of the Rayleigh scattering and total losses in silica fiber was determined from the results of the Rayleigh scattering and structural relaxation measurements.Annealing condition during fiber drawing was optimized, and much potential to reduce the Rayleigh scattering loss has been verified. Total loss can be reduced below 0.15 dB/km at 1.55 μm, for example, even when annealing time is 0.1 s. Total loss below 0.14 dB/km can be realized by increasing the annealing time.
83(2003); http://dx.doi.org/10.1063/1.1635661View Description Hide Description
We investigate the composition profile of -plane multiple quantum well structures by both high-resolution x-raydiffractometry and secondary ion mass spectrometry. The results reveal significant In surface segregation, resulting in a reduced In content and much wider wells than intended. The resulting In content of is lower than that obtained for corresponding -plane structures grown under identical conditions, suggesting a lower In incorporation efficiency on the plane compared to the (0001) plane. Finally, the dependence of the transition energies on the well thickness of these -plane quantum wells evidences the absence of internal electrostatic fields along the growth direction.