Volume 93, Issue 8, 25 August 2008
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Mimetization of biological structures aims to take advantage of their spatial features for the development of devices of tailored functionality. In this work, we replicated the wing of a butterfly at the micro- and nanoscales by implementing the conformal-evaporated-film-by-rotation (CEFR) technique. Chalcogenide glasses were used due to their good optical and mechanical properties. Morphological characterization and optical measurements indicate high-fidelity replication of the original biotemplate; furthermore, the optical properties of the butterfly wings have a structural origin. The CEFR technique might be useful for the fabrication of highly efficient, biomimetic optical devices.
- LASERS, OPTICS, AND OPTOELECTRONICS
93(2008); http://dx.doi.org/10.1063/1.2971206View Description Hide Description
We report on the realization of a molecule-based one-dimensional microcavity emitting in the near UV range at room temperature. The active material is a thin film of the two-dimensional perovskite, a molecular compound absorbing and emitting light around 3.6 eV. Angle-resolved reflectivity and photoluminescence measurements show that this microcavity works in the strong coupling regime. The emitting UVpolariton is a mixed state between the photon cavity mode and the exciton of the perovskite-type semiconductor.
93(2008); http://dx.doi.org/10.1063/1.2976124View Description Hide Description
We present a GaNAsSb/GaAs waveguidephotodetector operating in the wavelength range with enhanced photoresponsivity compared to a top-illuminated photodetectorfabricated using the same material system. The device consists of a strained GaNAsSb layer, with N and Sb contents of 3.5% and 18%, respectively, sandwiched between GaAs:Si (-type) and GaAs:C (-type) layers. X-rayreciprocal space map of the GaNAsSb layer before device fabrication showed that the film relaxation is . At , photoresponsivities of 0.25 and 0.29 A/W for devices with 6.5 and ridge width, respectively, was demonstrated.
93(2008); http://dx.doi.org/10.1063/1.2973152View Description Hide Description
A high performance liquid crystal display using combined fringe and in-plane horizontal electric fields is proposed. The strong electric fields cause more liquid crystals to reorient almost in plane above and between the pixel electrodes. As a result, the operation voltage is lower and transmittance is higher than those of fringe field switching and in-plane switching modes, while preserving a wide viewing angle. Such a high performance device is particularly attractive for large panelliquid crystal displays.
93(2008); http://dx.doi.org/10.1063/1.2973165View Description Hide Description
We analyze the extraordinary transmission effect in the periodic and random nanoaperture arrays in optically thick metalfilms. Experimental studies are combined with simulations to show that extraordinary transmission effect at midinfrared wavelengths is enhanced when the decaying waveguide mode of a single nanoaperture couples through the collective surface plasmon excitations created through periodicity. Transmission characteristics of the individual nanoapertures are investigated by randomizing the apertures. By comparing rectangular to coaxial rectangular nanoapertures, both of which support -like decaying waveguide modes, we study the effect of nanoaperture geometry on the efficiency of the transmission.
93(2008); http://dx.doi.org/10.1063/1.2961025View Description Hide Description
A ring-spiral coupled microcavity laser was fabricated. The ring resonator works as an oscillator and has a diameter that is slightly less than that of the spiral cavity. The spiral provides wavelength selective feedback and emits light out from the notch. As a result, the coupled cavity generates unidirectional single-frequency laser emission. Its lasing threshold is also significantly lower than a single spiral-shaped microcavity laser.
Photonic crystal fiber microtaper supporting two selective higher-order modes with high sensitivity to gas molecules93(2008); http://dx.doi.org/10.1063/1.2973641View Description Hide Description
A photonic crystal fiber consisting of three rings of air holes was tapered down to . The voids of the fiber were collapsed so a solid microtaper was formed. In this microtaper two selective higher-order modes propagate and interfere. This makes the transmission of the taper to exhibit a sinusoidal pattern with subnanometric width fringes. It was found that the device was highly sensitive to gas molecules. The latter is attributed to surfacerefractive index changes, number of molecules enveloping the taper, and high sensitivity of the modes participating in the interference.
93(2008); http://dx.doi.org/10.1063/1.2974795View Description Hide Description
Nanoscale epitaxial lateral overgrowth of GaN-based light-emitting diodes on a nanorod-array patterned sapphire template93(2008); http://dx.doi.org/10.1063/1.2969062View Description Hide Description
High efficiency GaN-based light-emitting diodes(LEDs) are demonstrated by a nanoscale epitaxial lateral overgrowth (NELO) method on a nanorod-array patternedsapphire substrate (NAPSS). The transmission electron microscopy images suggest that the voids between nanorods and the stacking faults introduced during the NELO of GaN can effectively suppress the threading dislocation density. The output power and external quantum efficiency of the fabricated LED were enhanced by 52% and 56%, respectively, compared to those of a conventional LED. The improvements originated from both the enhanced light extraction assisted by the NAPSS and the reduced dislocation densities using the NELO method.
High efficiency operation of butt joint line-defect-waveguide microlaser in two-dimensional photonic crystal slab93(2008); http://dx.doi.org/10.1063/1.2973207View Description Hide Description
Butt joint line-defect-waveguide microlasers are demonstrated on photonic crystal slabs with airholes in a triangular lattice. Such microlaser is designed to increase the output power from the waveguide edge directly. The output power is remarkably enhanced to 214 times higher by introducing chirped structure in the output waveguide. The lasing mode operates in the linear dispersion region of the output waveguide so that the absorption loss due to the band-edge effect is reduced. The laser resonance is illustrated theoretically using the finite difference time domain method. A practical high power efficiency of 20% is obtained in this microlaser.
Strain relaxation induced microphotoluminescence characteristics of a single InGaN-based nanopillar fabricated by focused ion beam milling93(2008); http://dx.doi.org/10.1063/1.2965461View Description Hide Description
A freestanding nanopillar with a diameter of and a height of is demonstrated by focused ion beammilling. The measuredmicrophotoluminescence from the embedded multiple quantum wells shows a blueshift of in energy with a broadened full width at half maximum, . Calculations based on the valence force field method suggest that the spatial variation of the strain tensors in the nanopillar results in the observed energy shift and spectrum broadening. Moreover, the power-dependent measurement suggests that the strain-relaxed emission region exhibits a higher radiative recombination rate than that of the strained region, indicating potential for realizing high-efficiency nanodevices in the UV/blue wavelength range.
93(2008); http://dx.doi.org/10.1063/1.2975165View Description Hide Description
Hybrid green light-emitting diodes(LEDs) comprised of multi-quantum-wells/ were grown on semi-insulating AlN/sapphire using pulsed laser deposition for the and metal organic chemical vapor deposition for the other layers. X-ray diffraction revealed that high crystallographic quality was preserved after the growth.LEDs showed a turn-on voltage of 2.5 V and a room temperature electroluminescence(EL) centered at 510 nm. A blueshift and narrowing of the EL peak with increasing current was attributed to bandgap renormalization. The results indicate that hybrid LED structures could hold the prospect for the development of green LEDs with superior performance.
93(2008); http://dx.doi.org/10.1063/1.2975170View Description Hide Description
Results of low temperature circularly polarized electroluminescence(EL) studies of InAs-based spin-light emitting diodes in magnetic fields up to 10 T are presented. Spin polarized electrons injected from cubic -(CdMn)Se recombine with unpolarized holes resulting in emission with a positive degree of optical polarization over this entire magnetic field range. Detailed rate equation modeling of the optical polarization degree (OPD) confirms a high spin injection efficiency (74%–95%) and a spin lifetime longer than the optical recombination time . Estimates of the temperature dependence of the ratio from the OPD are compared with the Elliot–Yafet and Dyakonov–Perel models.
93(2008); http://dx.doi.org/10.1063/1.2976123View Description Hide Description
We experimentally demonstrate all-optical wavelength conversions in a radius resonance-split silicon microring resonator based on free carrier dispersion effect. The split resonance is caused by the mutual coupling between the two countertraveling modes inside the ring resonator. Dense wavelength conversions are performed at data rates from 500 Mbytes/s to 5 Gbytes/s and a dual-channel wavelength multicasting is realized at a data rate of 1.25 Gbytes/s. The resonance splitting phenomenon opens up opportunities to convert more closely spaced wavelengths, thus effectively increasing the system capacity.
93(2008); http://dx.doi.org/10.1063/1.2976437View Description Hide Description
Photocathode for highly polarized electron emission has been developed, fabricated, and studied. The photocathode is based on short-period strained superlattice grown by molecular beam epitaxy. Deformation of AlInGaAs quantum well results in energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85% at room temperature.
93(2008); http://dx.doi.org/10.1063/1.2976135View Description Hide Description
This letter presents an experimental investigation into the effect of a surface-acoustic-wave (SAW) on the emission of a single InAsquantum dot. The SAW causes the energy of the transitions within the dot to oscillate at the frequency of the SAW, producing a characteristic broadening of the emission lines in their time-averaged spectra. This periodic tuning of the transition energy is used as a method to regulate the output of a device containing a single quantum dot and we study the system as a high-frequency periodic source of single photons.
93(2008); http://dx.doi.org/10.1063/1.2971027View Description Hide Description
ternary alloys with solid phase indium compositions between and 0.28 have been grown by metal organic chemical vapor deposition under indium rich conditions within the growth temperature range of . A thermally activated process with activation energy of is found to compete with indium incorporation. Smooth epitaxial layers with root mean-squares surface roughness of are obtained. (Al,In)N films lattice matched to GaN have been introduced into laser diodestructures for optical confinement. Optical gain is observed.
93(2008); http://dx.doi.org/10.1063/1.2977461View Description Hide Description
We report the realization of widely tunable single-mode emitting laser diodes on the (AlGaIn)/(AsSb) material system employing binary superimposed gratings. Through this specialized concept of multifrequency selective gratings, it is possible to generate a tunable laser emitting at several predetermined wavelengths. One major advantage of this approach is the simple fabrication process, which is similar to standard distributed feedback fabrication technologies, but with the result of one single laser emitting single mode at several discrete emission wavelengths.
High output power GaN-based light-emitting diodes using an electrically reverse-connected -Schottky diode and superlattice93(2008); http://dx.doi.org/10.1063/1.2977471View Description Hide Description
We demonstrate the high-performance and excellent reliability characteristics of InGaN–GaN light-emitting diodes(LEDs) using an electrically reverse-connected -Schottky diode and superlattice(SL). Measurements show that the LED with the Schottky diode and SL yields lower series resistance and higher output power compared to normal LEDs. In addition, the device degradation rate of the proposed LED is 33 times as low as that of the normal LED at high electrical stress of , indicating excellent reliability behavior. These results mean that the use of -Schottky diode and is very promising for the realization of high-performance GaN-based LEDs.
- PLASMAS AND ELECTRICAL DISCHARGES
93(2008); http://dx.doi.org/10.1063/1.2971235View Description Hide Description
Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum.
The role of the relative voltage and phase for frequency coupling in a dual-frequency capacitively coupled plasma93(2008); http://dx.doi.org/10.1063/1.2972117View Description Hide Description
Frequency coupling in multifrequency discharges is a complex nonlinear interaction of the different frequency components. An alpha-mode low pressure rf capacitively coupled plasma operated simultaneously with two frequencies is investigated and the coupling of the two frequencies is observed to greatly influence the excitation and ionization within the discharge. Through this, plasma production and sustainment are dictated by the corresponding electron dynamics and can be manipulated through the dual-frequency sheath. These mechanisms are influenced by the relative voltage and also the relative phase of the two frequencies.