emitting diodes (LEDs) are emerging as a future market leader for indoor
and outdoor lighting because
it has higher energy
efficiency, longer lifetime, more compact size and more flexible spectral design,
compared to the conventional incandescent lamp and fluorescent light tubes. In order to fully explore the
potential of this
light sources, huge amount of effort has been made to enhance the light extraction
efficiency, which is usually very low due to the large
index difference between
and the air, thus is very crucial in order to imp
rove the overall efficiency of the LEDs. In this paper
have developed various methods for two important semiconductors: silicon carbide (SiC) and gallium
nitride (GaN), and demonstrated enormous extraction
SiC is an important
bstrate for LED devices. It has refractive index of 2.6, and only a few percent of light could escape from it.
We have developed periodic nanocone structures
by using electron
beam lithography, periodic nanodome
structures by using nanosphere lithography,
random nanostructures by using self
nanoparticles, and random nanostructures by directly using the self
masking effect of thin Al films, as shown
in Fig.1. All these nanostructures have shown increased transmittance or reduced reflectance c
the bare surface. Fluorescent SiC samples show tremendous photoluminescence enhancement
(up to 210%)
after the surface nanostructuring.
As active material for LEDs, GaN also has high refractive index of 2.
. So, it
is also very important to ext
ract more light out by roughening the surface.
method was applied. The same transmittance enhancement
is demonstrated, similar to SiC. In
addition to SiC and GaN, these developed methods could be applied to other semicon
ductors such as Si, etc.
Furthermore, all optoelectronic devices having an optical interface such as solar cells, photo
benefit from these developed methods for opto
electronic performance improvement.
|Conference||3rd international symposium on disperse systems for electronic applications|
|Period||11/09/2014 → 12/09/2014|
Invited talk at 3rd international symposium on disperse systems for electronic applications, Erlangen, Germany, September 11-12, 2014