Volume 92, Issue 10, 10 March 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:
We report the synthesis of hierarchically branched semiconducting nanowire on metallic Sb-doped nanowires by the sequential seeding of multiple nanowire generations with Aunanoparticles as catalysts. Such semiconducting nanowire/metallic backbone complex structures increase the potential functionality of nanowires. Branched nanowirefilms are used as sensing materials for high-performance ethanol sensor fabrication. The nanowire sensors show sub-ppm sensitivity and fast response and recovery times at . A linear equation relationship between sensitivity and the ethanol vapor concentration was observed.
- LASERS, OPTICS, AND OPTOELECTRONICS
High performance of GaN thin films grown on sapphire substrates coated with a silica-submicron-sphere monolayer film92(2008); http://dx.doi.org/10.1063/1.2891067View Description Hide Description
A high-performance, GaN-based light emitting diode(LED) was prepared using a metal organic chemical vapor deposition method on a silica-sphere, monolayer-coated sapphire substrate. Various surface coverage ratios of the silica submicron spheres with diameters ranging from were deposited on the sapphire substrate using a spin-coating method. The LED output power was increased 2.5-fold compared with the LED constructed without silica spheres and uniform light distribution was achieved. In addition, LED output power was dependent on silica-sphere size and surface coverage of the substrates.
92(2008); http://dx.doi.org/10.1063/1.2892678View Description Hide Description
A technique for evanescent broadside coupling to surface plasmons is described and demonstrated. The technique makes use of a polarization maintaining optical fiber cleaved at a steep angle and positioned near the structure to be excited such that the slow mode of the fiber couples evanescently to the surface plasmon propagating thereon. The technique is applied to excite long-range surface plasmons on a metal stripe supported by a freestanding dielectric membrane. The technique should be useful for coupling to other plasmonic or dielectric waveguides, and for optical wafer probing.
92(2008); http://dx.doi.org/10.1063/1.2892634View Description Hide Description
We demonstrated the long wavelength lasing of InGaNlaser diodes under continuous wave condition at room temperature over . Two InGaN laser structures were adapted with different indium composition for InGaN optical confinement layers (OCLs) below quantum wells. The blue shift of electroluminescence(EL) was reduced in InGaNlaser diodesgrown on 3% In concentration in InGaN OCL compared with 1.5% In concentration in InGaN OCL. The EL peak for laser diode with 3% In concentration in InGaN OCL occurs at longer wavelength for all current levels compared to the laser with 1.5% In concentration in InGaN OCL. In addition, the laterally nonuniform InGaN wells grown on 1.5% In concentration in InGaN OCL was verified by the cross-sectional view of InGaNactive layer using high-resolution transmission electron microscopy.
92(2008); http://dx.doi.org/10.1063/1.2830023View Description Hide Description
Nonpolar -plane GaNfilms have been grown by metal-organic vapor deposition on -plane sapphire. Lateral growth is favored using a low V:III ratio resulting in films with a smooth surface, while pitted films are grown at a high V:III ratio indicating preferential on-axis growth. High-resolution x-ray diffraction analysis of both film types showed a strong anisotropy in the peak width of the symmetric omega rocking curve with respect to the in-plane orientation, phi. In-plane isotropic behavior of crystallinity with overall reduced omega full width at half maximum values was achieved when the growth was initiated at a high V:III ratio before reducing the V:III ratio for film coalescence. An improvement of crystal quality through initial surface roughening was equally realized by the incorporation of partial-coverage interlayers.
92(2008); http://dx.doi.org/10.1063/1.2894569View Description Hide Description
We demonstrate quantum cascade lasers at an emitting wavelength of , which are capable of room temperature, high power continuous wave (cw) operation. Buried ridge geometry with a width of was utilized. A device with a cavity length that was epilayer-down bonded on a diamond submount exhibited a maximum output power of at room temperature in cw operation. The maximum output power at was measured to be , with a wall plug efficiency of 27%.
Optical property and spectroscopy studies on the explosive 2,4,6-trinitro-1,3,5-trihydroxybenzene in the terahertz range92(2008); http://dx.doi.org/10.1063/1.2895638View Description Hide Description
Using the terahertz time-domain spectroscopy, the complex refraction index and dielectric function of the pure 2,4,6-trinitro-1,3,5-trihydroxybenzene (TNPG) are calculated with the obtained parameters of the pure polyethylene (PE) and a mixture of TNPG and PE based on the Bruggeman effective medium theory. The theoretical investigation consistent with the experimental data in the vibration spectra of TNPG is presented in the range of . The results reveal that the two absorption features identified as the fingerprint of TNPG in our studied range are mainly dominated by the intramolecular collective vibration modes.
Experimental study of the output dynamics of intracavity frequency doubled optically pumped semiconductor disk lasers92(2008); http://dx.doi.org/10.1063/1.2895642View Description Hide Description
The dynamic behavior of the continuous wave output of an intracavity frequency doubled optically pumped semiconductor disk laser is described. These lasers typically exhibit stable emission. The reasons are found to be the tendency to single-mode operation and the high gain coupling of different modes due to an extremely short gain medium and the resonant periodic gain structure. A dependence of the fluctuation amplitude on gain decoupling of different fundamental modes is demonstrated. With the presented laser setup, more than 80% of conversion efficiency with respect to the available fundamental power has been achieved.
92(2008); http://dx.doi.org/10.1063/1.2883978View Description Hide Description
We demonstrated transverse-magnetic (TM)-mode dominated gain at the wavelength in semiconductor optical amplifiers (SOAs) with columnar quantum dots(QDs). We show that we can control the polarization dependence of optical gain in QD-SOAs by changing the height and tensile-strained barrier of columnar QDs. The TM mode gain is and a gain of over was attained over a wide wavelength range of . The saturation output power is at .
92(2008); http://dx.doi.org/10.1063/1.2892656View Description Hide Description
We present a technique that involves tailoring the angular spectrum in optical microscopy of siliconintegrated circuits, with a solid immersion lens. Spatial light modulation to select only supercritical light at the substrate/dielectric interface yields only evanescent and scattered light in the interconnect layers. We demonstrated the technique in optical excitation microscopy of silicon-on-insulator circuits, which enabled localization of a fault during microprocessor development. Acquiring images with and without angular spectrum tailoring allowed longitudinal localization of the electrical response to optical excitation. Lateral registration of electrical response and confocal reflection images to the circuit layout was also significantly improved.
92(2008); http://dx.doi.org/10.1063/1.2892677View Description Hide Description
A submicron siliconwaveguide optical switch driven by a microelectromechanical actuator is fabricated. The switch is composed of single-mode silicon input and output waveguides and a movable waveguide suspended by silicon springs. Switching occurs when the air gap between input and output waveguides is closed by displacing the movable waveguide by an electrostatic comb actuator. The switch, fabricated on a silicon-on-insulator wafer, is monolithic, and active switching region is as small as about . An extinction ratio of is experimentally obtained between switch off and on states at wavelength.
92(2008); http://dx.doi.org/10.1063/1.2894193View Description Hide Description
We report the observation of power law dynamics on nanosecond to microsecond timescales in the fluorescence decay from semiconductornanocrystals and draw a comparison between this behavior and power law fluorescence blinking from single nanocrystals. The link is supported by comparison of blinking and lifetime data measured simultaneously from the same nanocrystal. Our results reveal that the power law coefficient changes little over the nine decades in time from , in contrast with the predictions of some diffusion based models of power law behavior.
92(2008); http://dx.doi.org/10.1063/1.2894508View Description Hide Description
Due to their large optical phonon energies, nitride semiconductors are promising for the development of terahertz quantum cascade lasers with dramatically improved high-temperature performance relative to existing GaAs devices. Here, we present a rigorous Monte Carlo study of carrier dynamics in two structures based on the same design scheme for emission at , consisting of or quantum wells. The population inversion and hence the gain coefficient of the nitride device are found to exhibit a much weaker (by a factor of over 3) temperature dependence and to remain large enough for laser action even without cryogenic cooling.
Control of quantum-confined Stark effect in multiple quantum well active region by -type layer for III-nitride-based visible light emitting diodes92(2008); http://dx.doi.org/10.1063/1.2894514View Description Hide Description
We demonstrate the control of the quantum-confined Stark effect in quantum wells(QWs),grown along the  direction as part of the active region of visible light emitting diodes(LEDs). The effect can be altered by modifying the strain applied to the active region by the hole injection and contact layers. The optical characteristics and electrostatic potentials of the active region of the visible LEDs with different -type layers are compared. LEDs with on top of the active region show a reduced blueshift in the peak wavelength with increasing injection current and a lower potential difference across the QW than those with layers. The electrostatic potentials across the QW have estimated average values of and for the active region of LEDs of current study with and layers, respectively.
92(2008); http://dx.doi.org/10.1063/1.2894521View Description Hide Description
An electrically tunable optical vortex was generated in an antiparallel liquid crystal cell, where one electrode was patterned by a photomask, which is achieved by transferring a computer-generated hologram onto a transparency with a resolution of about . When a voltage was applied on the cell, an index modulation was induced due to the realignment of liquid crystal molecules, and then an optical vortex beam was produced. The diffraction efficiency measured was about 27.5%. The device also showed a reasonably fast response time.
92(2008); http://dx.doi.org/10.1063/1.2896297View Description Hide Description
The vacuum ultraviolet excitation and ultraviolet-visible emission spectra are reported for the laser and upconverter material. The low-phonon energies of the host lattice enable, in addition to the ten luminescent states of in the visible and infrared spectral regions at room temperature, the observation of a further two luminescent multiplet terms in the ultraviolet spectral region at . A careful distinction is made between transitions and the band to band and transitions.
92(2008); http://dx.doi.org/10.1063/1.2894585View Description Hide Description
We measured the time dependence of the local lattice temperature in terahertz quantum cascade lasers with surface plasmon waveguides. The time constants for heat extraction from the active region are approximately ten times shorter than those associated with heat extraction from the substrate, thereby showing the dominant role of the substrate-heat sink coupling. Thermal diffusivities and thermal diffusion lengths in the active region (substrate) have been extracted by fitting the solution of the heat transport equation to the experimental data.
High spatial resolution fiber-optic Fizeau interferometric strain sensor based on an in-fiber spherical microcavity92(2008); http://dx.doi.org/10.1063/1.2895637View Description Hide Description
We present a fiber-optic Fizeau interferometric strain sensor consisting of an in-fiber spherical microcavity of in diameter. The spherical microcavity was formed by splicing a normal single-mode fiber with a hollow-core photonic crystal fiber. We demonstrate that strain sensing can be realized by using the interference between the light signals reflected by the front and rear surfaces of the sphere. Experiments have shown that the strain sensor has a strain sensitivity of and a temperature sensitivity of .
92(2008); http://dx.doi.org/10.1063/1.2896648View Description Hide Description
We report on nearly lattice-matched grown InGaN based photodiodes detecting in the range with tunable peak responsivity tailored by the -layer properties. The growth of lattice matched - and layer leads to improvement in the device performance. This approach produced photodiodes with zero-bias responsivities up to at , corresponding to 15.5% internal quantum efficiency. The peak responsivity wavelength ranged between 416 and , the longest reported for III-N photodiodes. The effects of InN content and -layer thickness on photodiode properties and performance are discussed.
Combined nonlinear-optical electric and magnetic field response in a cadmium manganese telluride crystal92(2008); http://dx.doi.org/10.1063/1.2896651View Description Hide Description
Utilizing experimental results, which demonstrate the presence of both Faraday rotation and electric-field-induced linear birefringence in a diluted-magnetic-semiconductor crystal of cadmium manganese telluride (CMT), a single probe that is capable of sensing both electric and magnetic fields independently has been developed. A higher field sensitivity and greater accuracy are observed for the CMT crystal when compared to a lithium tantalate electro-optic crystal and terbium gallium garnet magneto-optic crystal. The linear electro-optic coefficient for CMT has been calculated from electric-field measurements to be .
92(2008); http://dx.doi.org/10.1063/1.2897039View Description Hide Description
The performance of back-illuminated avalanche photodiodes with separate absorption and multiplication regions is presented. Devices with an active area of show a maximum multiplication gain of 41 200. The calculation of the noise equivalent power yields a minimum value of at a gain of 3000, increasing to at a gain of 41 200. The broadening of the response edge has been analyzed as a function of bias.