An electrically pumped 239  nm AlGaN nanowire laser operating at room temperature
In this work, we report on the demonstration of an electrically injectedAlGaNnanowire laser operating at 239  nm at roomtemperature. Vertically aligned Al-richAlGaNnanowires are grown on Si substrate by plasma-assisted molecular beam epitaxy. It is observed that the randomly distributedAlGaNnanowires can strongly confinephotons in the deepultraviolet wavelength range, due to the recurrent multiple scattering of light and the inversely taperednanowire geometry. The laser exhibits a very low thresholdcurrent of 0.35  mA at roomtemperature. From the detailed rate equation analysis, thespontaneous emission coupling factor ...
Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: S. Zhao, X. Liu, Y. Wu and Z. Mi Source Type: research
Design of p-type cladding layers for tunnel-injected UV-A light emitting diodes
We discuss the engineering of p-AlGaNcladding layers for achieving efficient tunnel-injected III-Nitrideultraviolet light emittingdiodes(UVLEDs) in the UV-A spectral range. We show that the capacitance-voltage measurements can be used to estimate the compensation anddoping in the p-AlGaN layers located between the multi-quantum well region and thetunnel junction layer. By increasing the p-typedoping concentration to overcome the background compensation, on-wafer external quantum efficiency and wall-plug efficiency of 3.37% and 1.62%, respectively, were achieved for the tunnel-injectedUVLEDs emitting at 325  nm. We also s...
Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: Yuewei Zhang, Sriram Krishnamoorthy, Fatih Akyol, Andrew A. Allerman, Michael W. Moseley, Andrew M. Armstrong and Siddharth Rajan Source Type: research
Silver free III-nitride flip chip light-emitting-diode with wall plug efficiency over 70% utilizing a GaN tunnel junction
Amolecular beam epitaxy regrowth technique was demonstrated on standard industrial patterned sapphire substratelight-emitting diode(LED) epitaxial wafers emitting at 455  nm to form a GaNtunnel junction. By using an HF pretreatment on the wafers before regrowth, a voltage of 3.08  V at 20 A/cm2 was achieved on small area devices. A high extraction package was developed for comparison withflip chip devices which utilize anLED floating in silicone over a BaSO4coated header and produced a peak external quantum efficiency (EQE) of 78%. A highreflectivitymirror was designed using a seven-layerdielectriccoating backed byal...
Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: B. P. Yonkee, E. C. Young, S. P. DenBaars, S. Nakamura and J. S. Speck Source Type: research
High power telecommunication-compatible photoconductive terahertz emitters based on plasmonic nano-antenna arrays
We present a high-power and broadband photoconductive terahertz emitter operating attelecommunication optical wavelengths, at which compact and high-performance fiber lasers are commercially available. The presented terahertz emitter utilizes an ErAs:InGaAs substrate to achieve highresistivity and shortcarrier lifetime characteristics required for robust operation attelecommunication optical wavelengths. It also uses a two-dimensional array ofplasmonic nano-antennas to offer significantly higher optical-to-terahertz conversion efficiencies compared to the conventional photoconductive emitters, while maintaining broad opera...
Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: Nezih Tolga Yardimci, Hong Lu and Mona Jarrahi Source Type: research
Subwavelength far-field ultrasound drug-delivery
The theoreticaldiffraction-limit of resolution forultrasound imaging has recently been bypassedin-vitro andin-vivo. However, in the context ofultrasound therapy, the precision oftherapeutic beams remains bound to the half-wavelength limit. By combining acoustic vaporization of compositedroplets and rapidultrasound monitoring, we demonstrate that theultrasound drug-delivery can be restricted to a subwavelength zone. Moreover, two release zones closer than the wavelength/4 can be distinguished both optically and through ultrafastultrasound localizationmicroscopy. This proof-of-concept let us envision the possibility to treat...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Vincent Hingot, Marine B ézagu, Claudia Errico, Yann Desailly, Romain Bocheux, Mickael Tanter and Olivier Couture Source Type: research
Transmissive concentrator multijunction solar cells with over 47% in-band power conversion efficiency
Transmissive concentrator multijunction (TCMJ) solar cells with over 47% in-band power conversion efficiency (PCE) have been designed and realized. These TCMJ solar cells have been characterized under 1 sun and concentrated 500 sun solarspectra, showing that the PCE for in-band light(photon energies above the cell's lowestbandgap) can reach up to 47.6% (29.5% for the full solarspectrum).Temperature coefficients of electrical parameters (Voc, Jsc, fill factor) have been derived frommeasurements within thetemperature range of 20  °C–130 °C, showing linear variations versustemperature change. Opticalmeasurements demon...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Qi Xu, Yaping Ji, Dimitri D. Krut, Jim H. Ermer and Matthew D. Escarra Source Type: research
Enhanced energy density with a wide thermal stability in epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin films
High-qualityepitaxialPb0.92La0.08Zr0.52Ti0.48O3 (PLZT)films of thickness of ∼880 nm were fabricated using pulsed laser deposition on (001) Nb doped SrTiO3 (Nb:STO) substrates. Besides a confirmation of theepitaxial relationship [100]PLZT//[100]Nb:STO and (001)PLZT//(001)Nb:STO using X-ray diffraction, a transmission electron microscopy study has revealed a columnarstructure across thefilm thickness. The recoverableenergy density (Wrec) of theepitaxial PLZTthin film capacitors increases linearly with the appliedelectric field and the best value of ∼31 J/cm3 observed at 2.27 MV/cm is considerably higher by 41% than t...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Guangliang Hu, Chunrui Ma, Wei Wei, Zixiong Sun, Lu Lu, Shao-Bo Mi, Ming Liu, Beihai Ma, Judy Wu and Chun-lin Jia Source Type: research
Circular photogalvanic effect in organometal halide perovskite CH3NH3PbI3
We study the circular photogalvanic effect in the organometal halideperovskite solar cell absorber CH3NH3PbI3. The calculatedphotocurrent density for a system with broken inversion symmetry is about 10−9 A/W, comparable to the previously studiedquantum well and bulk Rashba systems. The circular photogalvanic effect relies on inversion symmetry breaking, so that by tuning the optical penetration depth, the degree of inversion symmetry breaking can be probed at different depths from the sample surface. We propose that measurements of this effect may clarify the presence or absence of inversion symmetry, which remains a con...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Junwen Li and Paul M. Haney Source Type: research
Aerodynamic modification to a circular cylinder to enhance the piezoelectric wind energy harvesting
This study aims to expand the aeroelastic unstable range of a circular cylinder for improving the efficiency of a vortex-induced vibration (VIV)-basedwind energy harvester. The kineticenergy of the harvester is provided by flow-induced vibration of a circular cylinder. Two small-diameter cylindrical rods were attached on two sides of the circular cylinder parallel to the cylinder axis and symmetrical to the stagnation line at a series of circumferential locations. This was inspired by rain-wind-induced vibrations of stay-cables of cable-stayed bridges. It was found that attaching two small-diameter cylindrical rods at the ...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Gang Hu, K. T. Tse, K. C. S. Kwok, Jie Song and Yuan Lyu Source Type: research
Optical projection angiography
We propose the optical projection angiography(OPA) based on lateral dynamicscattering light forvisualizing a three-dimensional(3D) blood-flow network. InOPA, apulsed laser source illuminates a live biological sample for eliminating digitalcamera integration effects. The 2Dflowimage can be obtained by separating the dynamic and staticscattering light signal of eachcamera pixel in the frequency domain.Flowimages at a different angle are combined toreconstruct the3D volume of the sample to realizeOPA. Moreover, as our experiment retains the bright-field optical projection tomography (OPT) setup, theOPAimage for the circulator...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Riwei Liao, Mingyi Wang, Fuli Zhang, Dingan Han, Ruikang K. Wang, Guojian Yang and Yaguang Zeng Source Type: research
Hemorheological alterations of red blood cells induced by non-thermal dielectric barrier discharge plasma
In this study, we investigated the effects of non-thermalplasma on rheological characteristics of red bloodcells (RBC). We experimentally measured the extent of hemolysis, deformability, andaggregation of red bloodcells (RBC) with respect to exposure times of non-thermalplasma. RBC morphology was also examined using field-emissionscanning electron microscopy. The absorbance of hemoglobin released from the RBCs increased with increasing exposure time of the non-thermalplasma. Values of the elongation index andaggregation index were shown to decrease significantly with increasingplasma exposure times. Therefore, hemorheologi...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Jeongho Kim, Jae Hyung Kim, Boksoon Chang, Eun Ha Choi and Hun-Kuk Park Source Type: research
Improved interfacial and electrical properties of HfLaON gate dielectric Ge MOS capacitor by NbON/Si dual passivation layer and fluorine incorporation
Gemetal-oxide-semiconductor(MOS) capacitor with HfLaON/(NbON/Si) stacked gatedielectric and fluorine-plasma treatment is fabricated, and its interfacial andelectrical properties are compared with its counterparts without the Sipassivation layer or the fluorine-plasma treatment. The experimental results show that the HfLaON/(NbON/Si)GeMOS device treated by fluorine plasma exhibits excellent performance: low interface-state density (4.3  × 1011 cm−2 eV−1), small flatband voltage (0.22  V), good capacitance-voltage behavior, small frequency dispersion and low gate leakage current (4.18 × 10−5 A/cm2 at Vgâ€...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Yong Huang, Jing-Ping Xu, Lu Liu, Pui-To Lai and Wing-Man Tang Source Type: research
Characterization of channel temperature in Ga2O3 metal-oxide-semiconductor field-effect transistors by electrical measurements and thermal modeling
The channeltemperature (Tch) and thermal resistance (Rth) of Ga2O3metal-oxide-semiconductor field-effect transistors were investigated through electricalmeasurements complemented by electrothermal device simulations that incorporated experimental Ga2O3 thermal parameters. The analysis technique was based on a comparison between DC and pulsed drain currents (IDS) at known applied biases, where negligible self-heating under pulsed conditions enabled approximation ofTch to the ambienttemperature (Tamb) and hence correlation ofIDS toTch. Validation of the devicemodel was achieved throughcalibration against the DC data. The exp...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Man Hoi Wong, Yoji Morikawa, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi and Masataka Higashiwaki Source Type: research
Enhanced efficiency of organic light-emitting devices with corrugated nanostructures based on soft nano-imprinting lithography
An enhanced efficiency organic light-emitting device(OLED) with corrugatednanostructures on a small-molecule organicfilm has been demonstrated. Bypatterning the hole transport layer via soft nano-imprinting lithography and coating with Ag, a nanostructured cathode is introduced to enhance the light extraction of theOLED without affecting the flatness and conductivity of the indium-tin-oxidefilm. Both luminance and current efficiency are improved compared with those of conventional planar devices. The observable improvement in luminance and current efficiency can be ascribed to thesurface plasmonic and scattering effects ca...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: Yue-Feng Liu, Ming-Hui An, Xu-Lin Zhang, Yan-Gang Bi, Da Yin, Yi-Fan Zhang, Jing Feng and Hong-Bo Sun Source Type: research
Site-selection of Si1 −xGex quantum dots on patterned Si(001) substrates
We investigate theheteroepitaxial Si0.5Ge0.5quantum dot site-selection on apatterned Si(001) substrate by continuously varying the underlying substratepattern morphology from pit-in-terrace to quasi-sinusoidal. The pit-in-terrace morphology leads to well-orderedquantum dots centered in the pits over a wide range ofpattern wavelengths. However, for quasi-sinusoidal morphology, when thepattern wavelength is twice the intrinsic lengthscale,quantum dots suddenly bifurcate and shift to form in every saddle point, with high uniformity in size and site occupancy. We compare our results with existingmodels ofquantum dot formation ...
Source: Applied Physics Letters - November 8, 2016 Category: Physics Authors: J. M. Amatya and J. A. Floro Source Type: research
