Periyayya Uthirakumar

Highly efficient degradation of dyes by carbon quantum dots/N-doped zinc oxide (CQD/N-ZnO) photocatalyst and its compatibility on three different commercial dyes under daylight

Eco-friendly carbon quantum dots/nitrogen-doped ZnO (CQD/N-ZnO) composites were successfully prepared by a facile one-step method. The various techniques were employed to characterize the phase structure, morphology and optical properties of CQD/N-ZnO composites. The nitrogen doping was confirmed by Raman and X-ray photoelectron spectroscopy. Three commercial dyes, such as malachite green, methylene blue and fluorescein dyes were chosen to investigate the photocatalytic performance of CQD/N-ZnO under daylight irradiation. It was found that the CQD/N-ZnO photocatalyst established a high compatibility to degrade all three commercial dyes within 30-45 min, under daylight irradiation. Also, it remains capable of reusing the CQD/N-ZnO photocatalyst for repeated photocatalytic performance due to anti-photocorrosion offered by CQDs. The synergetic effect of N-doping and CQDs is key to design a new class of photocatalyst for environmental remediation under naturally available daylight source.

Comparison of various surface textured layer in InGaN LEDs for high light extraction efficiency

The various surface texturing effects of InGaN light emitting diodes (LEDs) have been investigated by comparison of experimented data and simulated data. The single-layer and double-layer texturing were performed with the help of ITO nanospheres using wet etching, where the ITO ohmic contact layer and the p-GaN layer are textured using ITO nanospheres as an etch mask. In case of single-layer texturing, p-type GaN layer texturing was more effective than ITO ohmic contact layer texturing. The maximum enhancement of wall-plug efficiency of double-layered textured LEDs is 40% more than conventional LEDs, after packaging at an injected current of 20 mA. The increase of light scattering at the textured GaN surfaces is a major reason for increasing the light extraction efficiency of LEDs.

Impact of two-floor air prism arrays as an embedded reflector for enhancing the output power of InGaN/GaN light emitting diodes

This paper reports on the impact of two-floor air prism (TFAP) arrays InGaN/GaN light emitting diodes (LEDs) as an embedded reflector with low refractive indices. The reflectance spectra, measured over the entire visible spectral region, shows strong reflectance modulations due to the TFAP arrays in GaN. The light output powers of TFAP LEDs is seen to be 2.62 times higher than that of conventional LEDs, and 1.55 times higher than that of LEDs with one floor air prism arrays, respectively, at injection currents of 100 mA. This significant enhancement is attributable to a combined effect of effective shaping with 62° angled sidewalls and high refractive index difference between the embedded air prism and the GaN.

Improvement of Light Output Power in InGaN/GaN Light-Emitting Diodes with a Nanotextured GaN Surface Using Indium Tin Oxide Nanospheres

An etching process and indium tin oxide (ITO) nanospheres were used to fabricate nanotexturing on a GaN surface in InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) to improve the light output power. ITO nanospheres can be easily obtained by a simple wet etching process owing to the relatively weak binding energy at the grain boundary and at the interface between the ITO layer and the GaN surface. Inductively coupled plasma (ICP) treatment is carried out with the help of ITO nanospheres, used as a patterning mask, to nanotexture the GaN surface. A simple process is proposed for GaN-texturing on all possible sides, including the sidewall. The light extraction efficiency of InGaN/GaN LEDs is significantly improved owing to the possibility of a high level of light scattering at the textured surface. Thus, the light output power of the nanotextured LEDs was increased by 33% compared with that of conventional LEDs at an injection current of 20 mA.

Improved daylight-induced photocatalytic performance and suppressed photocorrosion of N-doped ZnO decorated with carbon quantum dots

Composites of N-doped ZnO decorated with carbon quantum dots were prepared as a promising strategy to enhance their photocatalytic performance in the degradation of aqueous malachite green dye. The carbon quantum dots enhanced the efficiency of the absorption of visible light and effectively separated the photogenerated electron–hole pairs, in addition to suppressing the photocorrosion of the ZnO crystals.

Enhanced air-cavity effect of periodically oriented embedded air protrusions for high-efficiency InGaN/GaN light-emitting diodes

We report on the development of periodically oriented embedded air protrusion (EAP) structures at the GaN-sapphire interface in InGaN/GaN LEDs. A specific SiO(2) mask pattern and a simple wet etching process were utilized for the fabrication of EAP structures. A strong coupling between closely proximate air cavities and the multiple quantum wells promoted spontaneous emission due to the high-index contrast at the GaN-air interface. As a result, the light output power of the EAP LED was 2.2 times higher than that of a conventional LED at an injection current of 20 mA.

Enhancement of Light Output Power in InGaN/GaN LEDs with Nanoroughed Hemispherical Indium Tin Oxide Transparent Ohmic Contacts

The light output power of light emitting diodes (LEDs) has been enhanced using nanoroughed hemispherical indium tin oxide (ITO) transparent ohmic contacts. The hemispherical shape is easily achieved by evaporating ITO film on an ITO nanosphere, and the aspect ratio of an individual hemispherical ITO is determined by the size of the ITO nanosphere. The diameter of the ITO nanospheres can be easily controlled by controlling the thickness of the ITO films. The light extraction efficiency of InGaN/GaN LEDs is significantly improved due to light incident at an angle of approximately 90° at the hemispherical nanoroughed prominence―air interface. Also, a high surface area of ITO prominences increases the light extraction efficiency. Thus, the light output power of the nanoroughed hemispherical LEDs is increased by 30% compared to conventional LEDs at an injection current of 20 mA.

Enhanced light output power of GaN-based light-emitting diodes by nano-rough indium tin oxide film using ZnO nanoparticles

We demonstrate the performance improvement of GaN-based light-emitting diodes (LEDs) using zinc oxide (ZnO) nanoparticles inserted between the p-GaN and the indium tin oxide (ITO) layers. Upon deposition of an ITO film over the dispersed ZnO nanoparticles, the ITO surface tends to attain a nano-rough morphology due to the presence of ZnO nanoparticles. The light output power of the fabricated LEDs with ZnO nanoparticles is 39% higher than that of conventional LEDs at an injection current of 20 mA. This is attributed to the improved light extraction favored by the light scattering tendency of ZnO nanoparticles and the nano-roughened ITO film. In addition, the intermediate refractive index (n ∼2) of ZnO materials between those of the p-GaN (n ∼2.5) and the ITO (n ∼1.9) results in a broader critical angle and a reduction of total internal reflection.

Enhanced Light Output Power of InGaN/GaN Light Emitting Diodes with Embedded Air Prisms

We report characteristics of the InGaN/GaN light emitting diodes (LEDs) grown by selective metallorganic chemical vapor deposition with embedded air prisms (EAPs) via a wet etching process. At first, aqueous KOH solution, an etchant, removed the SiO 2 mask pattern to facilitate a subsequent etching through N-face GaN to achieve crystallographically defined prism shapes. Well-aligned arrays of air prisms are formed and distributed throughout the entire device. The EAP―LED output power was increased 2.1 times compared with the conventional LED. The higher light extraction is attributed to the improvement in the scattering of photons at the EAP interface due to the large index difference between GaN and air prisms.

InGaN/GaN Light-Emitting Diodes with Overcut-Shaped Periodic Microstructures Formed by Wet Etching Process

In this article, overcut-shaped periodic microstructures (OSPMs), embedded InGaN/GaN light-emitting diodes (LEDs), are fabricated using a 2 M aqueous KOH solution wet etching process. Inclined overcut microstructures are formed as the GaN {1011} facets and GaN {1122} facets with angles of 57 and 62°. This can be attributed to the crystallographic properties of GaN by the difference in etch rates between the Ga face and the N face. The light extraction properties of OSPM-LEDs are effectively extracted upside of the LED device by entirely deflected photons from the inclined overcut microstructures.