We experimentally investigated the density effect of Ag/SiO2 core–shell nanoparticles (CSNPs) on the carrier recombination rate and photoluminescence (PL) of the InGaN/GaN light-emitting diodes (LEDs). For the high-efficiency InGaN/GaN blue LEDs, there was an optimum Ag/SiO2 CSNP density of about 15 μm−2. From the numerical simulations, the fast carrier recombination rate and the enhanced PL intensity are related to the enhancement of the Purcell factor and the light extraction efficiency due to the localized surface plasmon (LSP) mode. However, this plasmonic enhancement was limited at high Ag/SiO2 CSNP densities by the LSP resonance shift and ohmic loss. We expect that these results could be useful for the practical design of LSP-assisted optoelectronic devices such as LEDs, organic light-emitting diodes, and photovoltaics.
Various types of nano-to-micron scale patterned structure have been employed into nitride light-emitting diodes
(LEDs) in order to investigate the optical performances of device. The patterned structure was formed on top of the LED
epitaxial structure or was embedded between epitaxial layers and sapphire substrate. The patterned structure affected to
the LED performances in terms of light distribution and anisotropic increase of light extraction as well as increase of
external quantum efficiency. The controllability of light extraction by forming a patterned structure with different index
material is applicable to flip chip devices or chips on board in which light is supposed to be extracted toward a certain
direction with the straight forward directionality. The index matched nano-patterned AlN template played such a role of
anisotropic directionality of light extraction in the device. Periodic (photonic band gap) and non-periodic (random hole)
patterned structure also showed different extraction efficiency and characteristics of light distribution. The experimental
result was well matched with the simulated estimation.
We investigated the surface plasmon coupling behavior in InGaN/GaN multiple quantum wells at 460 nm by
employing Ag nanostructures on the top of a roughened p-type GaN. After the growth of a blue light emitting diode
structure, the p-GaN layer was roughened by inductive coupled plasma etching and the Ag nanostructures were formed
on it. This structure showed a drastic enhancement in photoluminescence and electroluminescence intensity and the
degree of enhancement was found to depend on the morphology of Ag nanostructures. From the time-resolved
photoluminescence measurement a faster decay rate for the Ag-coated structure was observed. The calculated Purcell
enhancement factor indicated that the improved luminescence intensity was attributed to the energy transfer from
electron-hole pair recombination in the quantum well to electron vibrations of surface plasmon at the Ag-coated surface
of the roughened p-GaN.
Properties of GaN radiation detectors are analyzed. It is shown that present day epitaxial material is suitable for detection
of α-particles with the charge collection efficiency close to 100%. Such detectors can operate at temperatures of at least
60°C and withstand irradiation with reactor neutrons fluences higher than 1015 cm<sup>-2</sup>. They keep the collection efficiency
at 30% even after irradiation with 2×1016 cm<sup>-2</sup> neutron fluence. Registration of thermal neutrons with GaN detectors can
also be achieved by using <sup>10</sup>B converter and the efficiency of registration is determined by the <sup>10</sup>B conversion efficiency
from neutrons to low energy a-particles.
Conference Committee Involvement (1)
Quantum Sensing and Nanophotonic Devices VIII
23 January 2011 | San Francisco, California, United States