RESUMO
High quality GaN epilayers were obtained by using a magnesium nitride (MgxNy) inter-layer. X-ray photoelectron spectroscopy (XPS) reveals Mg 2p core-level spectra from the MgxNy inter-layers. The roughness of the MgxNy layers increased with the growth time, though a prolonged processing time resulted in a decrease in the roughness. A high-resolution X-ray diffraction ω-scan rocking curve was used to reveal that the screw dislocation density (TDD) of GaN with an MgxNy inter-layer was reduced and the crystalline quality of the GaN epitaxial layer was enhanced. Furthermore, the luminous efficiency of an LED with the MgxNy layers was increased by 20% relative to a reference LED.
RESUMO
A lithographically aligned palladium nano-ribbon (Pd-NRB) array with gaps of less than 40 nm is fabricated on a poly(ethylene terephthalate) substrate using the direct metal transfer method. The 200 µm Pd-NRB hydrogen gas sensor exhibits an unprecedented sensitivity of 10(9) % after bending treatment, along with fast sensing behavior (80% response time of 3.6 s and 80% recovery time of 8.7 s) at room temperature.
RESUMO
Polymer residue-free graphene nanoribbons (GNRs) of 200 nm width at 1 µm pitch were periodically generated in an area of 1 cm(2) via laser interference lithography using a chromium interlayer prior to photoresist coating. High-quality GNRs were evidenced by atomic force microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy measurements. Palladium nanoparticles were then deposited on the GNRs as catalysts for sensing hydrogen gases, and the GNR array was utilized as an electrically conductive path with less electrical noise. The palladium-decorated GNR array exhibited a rectangular sensing curve with unprecedented rapid response and recovery properties: 90% response within 60 s at 1000 ppm and 80% recovery within 90 s in nitrogen ambient. In addition, reliable and repeatable sensing behaviors were revealed when the array was exposed to various gas concentrations even at 30 ppm.
RESUMO
We textured the surface of a silicone encapsulant to increase the extraction efficiency of white light-emitting diodes (LEDs) by using a plasma treatment. Here, the surface morphology could be controlled by changing the plasma condition and texturing morphology of the silicone encapsulant were proportion to the increased ratio of white LEDs. The luminous efficacy of the surface textured LEDs were increased 9.70% relative to the reference LED. Furthermore, the Fourier transform infrared spectroscopy spectrum showed that the chemical bonds of the silicone encapsulant were not changed by the argon-nitrogen plasma treatment, thereby reducing degradation of the optical characteristics and improving the reliability of LEDs.
RESUMO
All-solution-processed transparent thin film transistors (TTFTs) are demonstrated with silver grid source/drain electrodes, which are fabricated by printing and subsequent silver nanoparticles solution coating, which allows continuous processing without using high vacuum systems. The silver grid electrode shows a reasonable transmittance in visible range, moderate electrical conductance and mechanical strength. The TTFTs are employed to drive liquid crystal cells and demonstrate a successful switching operation.
RESUMO
We describe the fabrication of corrugated inorganic oxide surface via direct single step conformal nanoimprinting to achieve enhanced light extraction in light emitting diodes (LEDs). Nanoscale zinc oxide (ZnO) and indium tin oxide (ITO) corrugated layer were created on a nonplanar GaN LED surface including metal electrode using ultraviolet (UV) assisted conformal nanoimprinting and subsequent inductively coupled plasma reactive ion etching (ICP-RIE) treatment. The total output powers of the surface corrugated LEDs increased by 45.6% for the patterned sapphire substrate LED and 41.9% for the flat c-plane substrate LED without any degradation of the electrical characteristics. The role of the nanoscale corrugations on the light extraction efficiency enhancement was examined using 3-dimensional finite-difference time-domain (FDTD) analysis. It was found that light scattering by subwavelength scale surface corrugation plays important role to redirect the trapped light into radiative modes. This straightforward inorganic oxide imprint method with inherent flexibility provides an efficient way to generate nanoscale surface textures for the production of high power LEDs and optoelectronic devices.
RESUMO
We investigated high-brightness light emitting diodes (LEDs) appropriate for general lighting applications in terms of their temperature dependent photoluminescence characteristics and device performance according to the change of quantum well pairs (QWs). As the number of QWs was increased from 2 to 35 pairs, radiative recombination efficiency and device performances significantly improved, due to the suppression of carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from barrier to well. At a further increase in the number of QWs to 50 pairs, however, the optical and device performances started to degrade because of the increase in internal loss in the active region, such as the well volume itself acting as light absorbing layer and due to the aluminum oxide complexes in the barrier.
RESUMO
Nanopatterned aluminum nitride (NP-AlN) templates were used to enhance the light extraction efficiency of the light-emitting diodes (LEDs). Here, the NP-AlN interlayer between the sapphire substrate and GaN-based LED was used as an effective light outcoupling layer at the direction of bottom side and as a buffer layer for growth of GaN LEDs. The cross-sectional transmission electron microscopy (TEM) analysis showed that the formation of stacking faults and voids could help reduce the threading dislocations. Micro Raman spectra also revealed that the GaN-based epilayer grown on the NP-AlN template had smaller residual stress than that grown on a planar sapphire substrate. The normalized electroluminescence (EL) spectra at the top and bottom sides of device revealed that the enhancement of the bottom side emission of the LED with the NP-AlN interlayer was more notable than a planar sapphire substrate due to the graded-refractive-index (GRIN) effect of the NP-AlN.
RESUMO
Nanosphere lithography is proposed as a new technique for the fabrication of nanoscale pillars on p-GaN layer. This technique is an easy and simple process using a self-assembled monolayer of spheres, which act as etching masks to form pillars on a Si3N4 substrate, that could be utilized as a stamp for UV-based imprint lithography. We can apply the UV-based imprint technique in the field of solid-state lighting in order to extract more lights to out-world by texturing the outer surface of the light emitting diodes (LED) structure. Photoluminescence intensity from the pillar patterned GaN layer was higher than that from the unpatterned GaN layer by 2.5 times.
RESUMO
Improvement in light extraction efficiency of Ultra Violet-Light Emitting Diode (UV-LED) is achieved by nano-scale roughening of p-type Gallium Nitride (p-GaN) surface. The process of surface roughening is carried out by using self assembled gold (Au) nano-clusters with support of nano-size silicon-oxide (SiO2) pillars on p-GaN surface as a dry etching mask and by p-GaN regrowth in the regions not covered by the mask after dry etching. Au nano-clusters are formed by rapid thermal annealing (RTA) process carried out at 600 degrees C for 1 min using 15 nm thick Au layer on top of SiO2. The p-GaN roughness is controlled by p-GaN regrowth time. Four different time values of 15 sec, 30 sec, 60 sec and 120 sec are considered for p-GaN regrowth. Among the four different p-GaN regrowth time values 30 sec regrown p-GaN sample has the optimum roughness to increase the electroluminescence (EL) intensity to a value approximately 60% higher than the EL intensity of a conventional LED.
