Ahmed Fadil

Surface plasmon coupling dynamics in InGaN/GaN quantum-well structures and radiative efficiency improvement

Surface plasmonics from metal nanoparticles have been demonstrated as an effective way of improving the performance of low-efficiency light emitters. However, reducing the inherent losses of the metal nanoparticles remains a challenge. Here we study the enhancement properties by Ag nanoparticles for InGaN/GaN quantum-well structures. By using a thin SiN dielectric layer between Ag and GaN we manage to modify and improve surface plasmon coupling effects, and we attribute this to the improved scattering of the nanoparticles at the quantum-well emission wavelength. The results are interpreted using numerical simulations, where absorption and scattering cross-sections are studied for different sized particles on GaN and GaN/SiN substrates.

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm2, and a factor of 8.1 at 1 W/cm2. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.

Antireflective SiC Surface Fabricated by Scalable Self-Assembled Nanopatterning

An approach for fabricating sub-wavelength antireflective structures on SiC material is demonstrated. A time-efficient scalable nanopatterning method by rapid thermal annealing of thin metal film is applied followed by a dry etching process. Size-dependent optical properties of the antireflective SiC structures have been investigated. It is found that the surface reflection of SiC in the visible spectral range is significantly suppressed by applying the antireflective structures. Meanwhile, optical transmission and absorption could be tuned by modifying the feature size of the structure. It is believed that this effective fabrication method of antireflective structures could also be realized on other semiconductor materials or devices.

Experimental demonstration of phase sensitive parametric processes in a nano-engineered silicon waveguide

We demonstrate experimentally phase-sensitive processes in nano-engineered silicon waveguides for the first time. Furthermore, we highlight paths towards the optimization of the phase-sensitive extinction ratio under the impact of two-photon and free-carrier absorption.

Fabrication and improvement of nanopillar InGaN/GaN light-emitting diodes using nanosphere lithography

Abstract. Surface-patterning technologies have enabled the improvement of currently existing light-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency of green GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars on InGaN/GaN quantum-well LEDs. By etching through the active region, it is possible to improve both the light extraction efficiency and, in addition, the internal quantum efficiency through the effects of lattice strain relaxation. Nanopillars of different sizes are fabricated and analyzed using Raman spectroscopy. We have shown that nanopillar LEDs can be significantly improved by applying a combination of ion-damage curing techniques, including thermal and acidic treatment, and have analyzed their effects using x-ray photoelectron spectroscopy.

Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO2

Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation.

Photoluminescence Enhancement in Nanotextured Fluorescent SiC Passivated by Atomic Layer Deposited Al2O3 Films

The influence of thickness of atomic layer deposited Al2O3 films on nanotextured fluorescent 6H-SiC passivation is investigated. The passivation effect on the light emission has been characterized by photoluminescence and time-resolved photoluminescence at room temperature. The results show that 20nm thickness of Al2O3 layer is favorable to observe a large photoluminescence enhancement (25.9%) and long carrier lifetime (0.86ms). This is a strong indication for an interface hydrogenation that takes place during post-thermal annealing. These result show that an Al2O3 layer could serve as passivation in fluorescent SiC based white LEDs applications.

Localized surface plasmon on 6H SiC with Ag nanoparticles

Silver (Ag) nanoparticles (NPs) were deposited on the surface of bulk Nitrogen-Boron co-doped 6H silicon carbide (SiC), and the Ag NPs were observed to induce localized surface plasmons (LSP) resonances on the SiC substrate, which was expected to improve the internal quantum efficiency (IQE) of the emissions of the donor-acceptor pairs of the SiC substrate. Room-temperature measurements of photoluminescence (PL), transmittance and time-resolved photoluminescence (TRPL) were applied to characterize the LSP resonances. Through the finite-difference time-domain (FDTD) simulation of the LSP resonance of an Ag nanoparticle on the SiC substrate, it is predicted that when the diameter of the cross section on the xy plane of the Ag nanoparticle is greater than 225 nm, the LSP starts to enhance the PL intensity. With implementation of a 3rd order exponential decay fitting model to the TRPL results, it is found that the average minority carrier lifetime of the SiC substrate decreased.

Resonant Plasmonic Enhancement of InGaN/GaN LED using Periodically Structured Ag Nanodisks

Ag nanodisks are fabricated on GaN-based LED to enhance emission efficiency. Nanosphere lithography is used to obtain a periodic nano-structure, and a photoluminescence enhancement of 2.7 is reported with Ag nanodisk diameter of 330 nm.