Jump to Content
View Cart
Top 20 Most Read Articles
April 2008
The 20 articles with the most full-text downloads during the month, in descending order.
 |
CW lasing of current injection blue GaN-based vertical cavity surface emitting laser Appl. Phys. Lett. 92, 141102 (2008); http://dx.doi.org/10.1063/1.2908034 (3 pages) Online Publication Date: 7 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Here, we report the cw laser operation of electrically pumped GaN-based vertical cavity surface emitting laser (VCSEL). The GaN-based VCSEL has a ten-pair InGaN/GaN multiple quantum well active layer embedded in a GaN hybrid microcavity of 5λ optical thickness with two high reflectivity mirrors provided by an epitaxially grown AlN/GaN distributed Bragg reflector (DBR) and a Ta2O5/SiO2 dielectric DBR. cw laser action was achieved at a threshold injection current of 1.4 mA at 77 K. The laser emitted a blue wavelength at 462 nm with a narrow linewidth of about 0.15 nm. The laser beam has a divergence angle of about 11.7° with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5×10−2 was measured.
|
|||
|
Show PACS
|
|||
|
|
Ordered n-type ZnO nanorod arrays Appl. Phys. Lett. 92, 132112 (2008); http://dx.doi.org/10.1063/1.2907197 (3 pages) Online Publication Date: 4 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type ZnO single crystal nanorods have been perpendicularly grown on p-GaN/Al2O3 substrates with a vapor phase transport growth method. The low temperature photoluminescence measurements of the n-ZnO nanorods show dominant In-related neutral donor bound exciton emission in the ultraviolet region. Electrical transport measurements performed on single n-ZnO nanorods yield resistances of about 50–200 kΩ and a typical specific resistivity of 2.0×10−2 Ω cm. The resistivity is one order of magnitude reduced by introducing In compared to the nominally undoped ZnO nanorods.
|
|||
|
Show PACS
|
|||
|
|
Spin transfer switching and low-field precession in exchange-biased spin valve nanopillars Appl. Phys. Lett. 92, 142501 (2008); http://dx.doi.org/10.1063/1.2905816 (3 pages) Online Publication Date: 7 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Using a three-dimensional focused ion beam lithography process, we have fabricated nanopillar devices that show spin transfer torque switching at zero external magnetic fields. Under a small in-plane external bias field, a field-dependent peak in the differential resistance versus current is observed similar to that reported in asymmetrical nanopillar devices. This is interpreted as evidence for the low-field excitation of spin waves, which in our case is attributed to a spin-scattering asymmetry enhanced by the IrMn exchange bias layer coupled to a relatively thin CoFe fixed layer.
|
|||
|
Show PACS
|
|||
|
|
ZnO nanorods for solar cells: Hydrothermal growth versus vapor deposition Appl. Phys. Lett. 92, 133507 (2008); http://dx.doi.org/10.1063/1.2906370 (3 pages) Online Publication Date: 2 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Performance of dye-sensitized solar cells (DSSCs) based on ZnO nanorods prepared by hydrothermal and vapor-deposition methods has been investigated. In spite of their inferior optical properties, DSSCs based on hydrothermally grown rods exhibit higher power conversion efficiency, which can be attributed to the higher dye adsorption. Hydrothermally grown and vapor deposited nanorods also exhibit different dependence of photovoltaic performance on the annealing conditions of the rods, indicating significant effect of the native defects on the achievable photocurrent and power conversion efficiency. Efficiency of 0.22% is obtained for both as grown hydrothermally grown nanorods and vapor deposited nanorods annealed in oxygen at 200 °C.
|
|||
|
Show PACS
|
|||
|
|
Appl. Phys. Lett. 92, 143101 (2008); http://dx.doi.org/10.1063/1.2905271 (3 pages) Online Publication Date: 7 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We report a high-bendability flexible dye-sensitized solar cell (DSSC) based on a ZnO-nanowire photoelectrode, which was fabricated on polyethylene terephtalate/indium tin oxide substrate by low-temperature hydrothermal growth. Nanowire morphology shows preferable in crack resistance due to its efficient release of bending stress. The ZnO-nanowire film can be bended to an extreme radius of 2 mm with no crack observed. Flexible DSSCs based on this kind of ZnO-nanowire photoelectrodes showed good bending stability. With a ZnO-nanoparticle modification on the nanowires, the flexible DSSC fabricated showed a much improved power conversion efficiency. Meanwhile, the good bendablility of this nanoparticle-modified nanowire electrode is maintained. The results demonstrate that high quality ZnO nanowires fabricated by the low-temperature method is promising for efficient and flexible plastic solar cells.
|
|||
|
Show PACS
|
|||
|
|
Low residual doping level in homoepitaxially grown ZnO layers Appl. Phys. Lett. 92, 141101 (2008); http://dx.doi.org/10.1063/1.2907562 (3 pages) Online Publication Date: 7 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
|||||||||||
|
Show Abstract
ZnO homoepitaxial growth is shown to change the luminescent properties of ZnO in a substantial way. Temperature dependent (4–300 K) photoluminescence properties of the films grown by metal organic vapor phase epitaxy or by liquid phase epitaxy are compared to those of the hydrothermal ZnO substrate used for the growth. The intensity ratio between the free exciton and the donor bound exciton strongly increases, following homoepitaxial growth. The activation energy of the band edge emission intensity also increases from 13 meV, which corresponds to the donor bound exciton localization energy, up to a value of 60 meV, which corresponds to the free exciton binding energy. This indicates that homoepitaxial growth favors free exciton emission instead of donor bound exciton emission.
|
||||||||||||
|
Show PACS
|
||||||||||||
|
|
Appl. Phys. Lett. 91, 233117 (2007); http://dx.doi.org/10.1063/1.2821113 (3 pages) Online Publication Date: 7 December 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
|||
|
Show Abstract
Silicon nanowire-based solar cells on metal foil are described. The key benefits of such devices are discussed, followed by optical reflectance, current-voltage, and external quantum efficiency data for a cell design employing a thin amorphous silicon layer deposited on the nanowire array to form the p-n junction. A promising current density of ∼ 1.6 mA/cm2 for 1.8 cm2 cells was obtained, and a broad external quantum efficiency was measured with a maximum value of ∼ 12% at 690 nm. The optical reflectance of the silicon nanowire solar cells is reduced by one to two orders of magnitude compared to planar cells.
|
||||
|
Show PACS
|
||||
|
|
Sb-doped p-ZnO/Ga-doped n-ZnO homojunction ultraviolet light emitting diodes Appl. Phys. Lett. 92, 152103 (2008); http://dx.doi.org/10.1063/1.2908968 (3 pages) Online Publication Date: 14 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
ZnO p-n homojunction light emitting diodes were fabricated based on p-type Sb-doped ZnO/n-type Ga-doped ZnO thin films. Low resistivity Au/NiO and Au/Ti contacts were formed on top of p-type and n-type ZnO layers, respectively. Au/NiO contacts on p-type ZnO exhibited a low specific resistivity of 7.4×10−4 Ω cm2. The light emitting diodes yielded strong near-band-edge emissions in temperature-dependent and injection current-dependent electroluminescence measurements.
|
|||
|
Show PACS
|
|||
|
|
Appl. Phys. Lett. 92, 131101 (2008); http://dx.doi.org/10.1063/1.2905260 (3 pages) Online Publication Date: 31 March 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
High efficiency diffractive grating structures to interface a single mode optical fiber and a nanophotonic integrated circuit fabricated on silicon-on-insulator are presented. The diffractive grating structures are designed to be inherently very directional by adding a silicon overlay before grating definition. 55% coupling efficiency at a wavelength of 1.53 μm is experimentally demonstrated on devices fabricated using standard complementary metal-oxide semiconductor technology. By optimizing the grating parameters, we theoretically show that 80% grating coupling efficiency can be obtained for a uniform grating structure.
|
|||
|
Show PACS
|
|||
|
|
Nonvolatile memory with molecule-engineered tunneling barriers Appl. Phys. Lett. 92, 153109 (2008); http://dx.doi.org/10.1063/1.2911741 (3 pages) Online Publication Date: 15 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We report a novel field-sensitive tunneling barrier by embedding C60 in SiO2 for nonvolatile memory applications. C60 is a better choice than ultrasmall nanocrystals due to its monodispersion. Moreover, C60 provides accessible energy levels to prompt resonant tunneling through SiO2 at high fields. However, this process is quenched at low fields due to highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap and large charging energy of C60. Furthermore, we demonstrate an improvement of more than an order of magnitude in retention to program/erase time ratio for a metal nanocrystal memory. This shows promise of engineering tunnel dielectrics by integrating molecules in the future hybrid molecular-silicon electronics.
|
|||
|
Show PACS
|
|||
|
|
Appl. Phys. Lett. 92, 141104 (2008); http://dx.doi.org/10.1063/1.2906632 (3 pages) Online Publication Date: 8 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
To improve light extraction from GaN-based light-emitting diodes (LEDs), we demonstrated an approach of modified laser lift-off (M-LLO) technique for patterning undoped GaN (u-GaN). The M-LLO consists in sequentially forming a two-dimensional triangular lattice pattern with a 4 μm period on a polymer layer over a sapphire substrate backplane by UV imprint and delivering the pattern onto u-GaN accompanied with the removal of the sapphire substrate. The enhancement of light extraction from GaN-based M-LLO LED with a reflective Ag film on the 120 nm deep u-GaN pattern was about 31% and 100% compared to that of a LLO-LED with a reflective film and a conventional LED with a sapphire substrate, respectively.
|
|||
|
Show PACS
|
|||
|
|
Highly efficient organic solar cells with printable low-cost transparent contacts Appl. Phys. Lett. 92, 143307 (2008); http://dx.doi.org/10.1063/1.2907564 (3 pages) Online Publication Date: 10 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Highly efficient organic solar cells with all-solution-processed low-cost transparent front contacts based on highly conductive formulations of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) are reported, demonstrating the feasibility of replacing the costly conventional vacuum-deposited indium-tin-oxide contacts by means of simple printing techniques. For small cell areas, the relatively high sheet resistances were found to be less detrimental to the photovoltaic performance than the deficiencies in the transparency of the contact layer.
|
|||
|
Show PACS
|
|||
|
|
Appl. Phys. Lett. 92, 141911 (2008); http://dx.doi.org/10.1063/1.2896642 (3 pages) Online Publication Date: 9 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Epitaxial ZnO thin films were grown on c-plane sapphire substrates by rf magnetron sputtering at room temperature followed by a rapid thermal annealing process. We found that crystallinity of the films was strongly affected by the partial oxygen pressure during deposition. Both x-ray diffraction and transmission electron microscopy studies revealed that the ZnO films grow epitaxially predominantly with aligned ZnO domains. An unresolved excitonic resonance was observed in the optical absorption spectrum. Nevertheless, refractive index and absorption edge of the ZnO films are similar to that of single crystal ZnO.
|
|||
|
Show PACS
|
|||
|
|
The surface engineering of top electrode in inverted polymer bulk-heterojunction solar cells Appl. Phys. Lett. 92, 133307 (2008); http://dx.doi.org/10.1063/1.2904967 (3 pages) Online Publication Date: 3 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We present surface engineering of the top electrode in organic solar cells through soft contact lamination. A polymer conductor and a self-assembled monolayer material are utilized for the surface engineering of gold electrode in a polymer bulk-heterojunction solar cell. Approximately a threefold increase in the overall power conversion efficiency is shown to be realized with the surface engineering, which is made possible by the lamination.
|
|||
|
Show PACS
|
|||
|
|
Choice of electrode geometry for accurate measurement of organic photovoltaic cell performance Appl. Phys. Lett. 92, 133301 (2008); http://dx.doi.org/10.1063/1.2895058 (3 pages) Online Publication Date: 31 March 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
The relationship between the performance and the electrode geometry of organic photovoltaic devices was investigated to establish the proper electrode geometry for reproducible and accurate performance measurement. Photovoltaic cells (ITO/PEDOT:PSS/P3HT+PCBM/LiF/Al) having crossbar-type and island-type electrode geometries were fabricated. The crossbar-type cells varied greatly in performance depending on the illuminated light beam size relative to the overlap area of the crossbar-type electrodes due to excess photocurrent generated from the cell region outside the overlapped electrode area, where PEDOT:PSS serves as anode. We systematically investigated the relationship between the conductivity of the PEDOT:PSS, the illumination area, and the amount of excess photocurrent generated.
|
|||
|
Show PACS
|
|||
|
|
Graded photonic crystals curve the flow of light: An experimental demonstration by the mirage effect Appl. Phys. Lett. 92, 133501 (2008); http://dx.doi.org/10.1063/1.2901684 (3 pages) Online Publication Date: 31 March 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We report the experimental demonstration of a beam curvature in graded photonic crystals via a spectacular mirage effect. A two-dimensional structure of metallic rods is constructed to produce this effect in the microwave domain near 10 GHz. Experimental results are in excellent agreement with theoretical predictions, thus, proving the versatility of graded photonic crystals in view of their integration in future photonic circuits.
|
|||
|
Show PACS
|
|||
|
|
Silicon nanowire array photoelectrochemical solar cells Appl. Phys. Lett. 92, 163103 (2008); http://dx.doi.org/10.1063/1.2909555 (3 pages) Online Publication Date: 22 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Silicon nanowires (SiNWs) arrays prepared by electroless etching show excellent optical antireflectivity over a wide spectral bandwidth from 300 to 1000 nm and surface defect-induced electrical conductivity. Both characteristics make the SiNWs a promising material for photovoltaic cell applications. Photoelectrochemical (PEC) measurements showed the electroless etching SiNWs are remarkably photoactive and effective in enhancing photovoltaic properties including photocurrent and photovoltage. Since electroless etching can enable simple, wafer-scale fabrication of SiNWs without the need of doping. SiNWs array thus prepared show great promise as low-cost and scalable photovoltaic-type PEC materials.
|
|||
|
Show PACS
|
|||
|
|
Hydrocarbon lithography on graphene membranes Appl. Phys. Lett. 92, 123110 (2008); http://dx.doi.org/10.1063/1.2901147 (3 pages) Online Publication Date: 28 March 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We present a simple and efficient way to obtain freestanding graphene membranes. On these membranes, we demonstrate that electron-beam induced deposition of carbon can be used to obtain arbitrary patterns with a nanometer-scale resolution. In the case of a periodic grating, we obtain a half-pitch of 2.5 nm. Electron-beam induced deposition on graphene might be used to create nanometer-scale doping patterns, diffraction gratings, or etch masks in this novel electronic material.
|
|||
|
Show PACS
|
|||
|
|
Enhanced light output of GaN-based light-emitting diodes with ZnO nanorod arrays Appl. Phys. Lett. 92, 121108 (2008); http://dx.doi.org/10.1063/1.2903153 (3 pages) Online Publication Date: 26 March 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
|||
|
Show Abstract
We report enhanced light output of GaN-based light-emitting diodes (LEDs) with vertically aligned ZnO nanorod arrays. The ZnO nanorod arrays were prepared on the top layer of GaN LEDs using catalyst-free metalorganic vapor phase epitaxy. Compared to conventional GaN LEDs, light output of GaN LEDs with the ZnO nanorod arrays increased up to 50% and 100% at applied currents of 20 and 50 mA, respectively. The source of the enhanced light output is also discussed.
|
||||
|
Show PACS
|
||||
|
|
Multiferroic properties of sputtered BiFeO3 thin films Appl. Phys. Lett. 92, 132908 (2008); http://dx.doi.org/10.1063/1.2901871 (3 pages) Online Publication Date: 2 April 2008
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
A cosputtering method was used to deposit BiFeO3 thin films on Pt/Ti/SiO2/Si substrates. It was confirmed as a polycrystalline film with a tetragonal crystal structure in the annealed state. Both Fe2+ and Fe3+ ions were found to coexist in the film. The leakage current density is as low as 10−3 A/cm2 at 120 kV/cm. This sputtered film shows multiferroic properties exhibiting a saturated ferroelectric loop with a large remnant polarization of 37 μC/cm2 and a saturated ferromagnetic loop with saturation magnetization of 21 emu/cm3 at room temperature.
|
|||
|
Show PACS
|
|||
This Publication
Scitation
Google Scholar
PubMed