Photonic crystals improve LED
We currently live
in a society where people are required to work more no matter it is a day or a night.
As more population tend to stay in their office or their factories for work, there
is an increase in the use of the light bulb. Some might think that damages
formed from increased usages in offices and factories do not apply or give impacts on our planet,
Earth. On the contrary, escalating use of inefficient light bulbs will result
damaging us not only financially but also other factors which can lead to serious
condition. As referring to Figure 1, the main portion of total lighting is
electricity and its usage is kept increasing.
Total Consumption of lighting from four factors in the UK (in
billion lumen-hours), “1700-2000 – Fouquet and Pearson (2007)” (Our World in
In this regard,
increasing the efficiency of electricity based light bulb is the only way to
diminish the tremendous financial lose that we currently experience with
inefficient light bulb.
Learning the way
to calculate the efficiency of the light bulb is the basic step for us to find the
methods to increase the efficiency. As the Figure 2 describes, we can calculate the efficiency by finding the values
for total electrical energy input, light energy output (useful), and heat
energy output (waste).
Figure 2. the
formula for efficiency (Passmyexams.co.uk, 2018)
To summarize the points, increasing the
light energy output and decreasing the heat energy output are our goals.
On the contrary,
there are some quantities that we first need to consider in order to improve
the efficiency. Those are the heat energy, poor internal quantum, and light-extraction
efficiency in the light bulbs. From these, we experience the loss in useful
light energy when heat energy increases and it results having descent
efficiency. And as most LEDs are not able to extract light efficiently due to
poor internal quantum, there would be total decrease in light bulb efficiency.
By far, the most
popular and commonly used light bulbs are the light emitting diode (LED). LEDs
dependent on the InGaN will be used more in the future with higher efficiency
and thus leading to the most cost-effective LEDs.
use the commonly available semi-conductor based LEDs. These LEDs are more beneficial
than those of incandescent, but less efficient than those of fluorescent. As I
have explained above, LEDs are
currently limited by poor internal quantum and light-extraction efficiency. On
the contrary, with the help from photonic crystals which gives the critical and
potential solutions, we will be able to solve both of the problems.
internal efficiency of InGaN LEDs can be enhanced from the effect called ‘Purcell
Effect’, which is an effect that more photons are created by placing the internal
Second way to
improve light energy is by upgrading in the extraction of the light from the semi-conductor
chip which has high-index. For typical or normal InGaN LEDs, a large portion of
the total energy is emitted into wave-guided modes to the semi-conductor. Light
generated inside the semi-conductor bounces around due to internal reflection,
and there is a high opportunity that the light particles will be absorbed
before it escapes from the semi-conductor. Referring to the Figure 3, a photonic crystal can improve its light
extraction by diffracting the modes out of the semi-conductor.
Figure 3. Placing a photonic crystal will result increasing both the internal
quantum efficiency and the whole amount of light extracted. (Spie.org, 2018)
On the contrary,
the limitations that can be made for the modifications are difficulty of
fabricating the photonic crystals in GaN. The process is quite complicated due
to difficulty of unique characteristics which are extremely hard and chemically
Discuss and evaluate:
in GaN will interact with economic factor as the crystals will increase the efficiency
of the LEDs in another term, reducing the total cost that we need to pay. According
to the document made from the Sandia, “they merged LEDs and photonic crystal
processing to make an electrically-injected InGaN LEDs.” (Spie.org, 2018) Figure 4. indicates
the emission patterns for both of photonic crystal and control LED.
The unique pattern
from the photonic crystal LEDs indicates a triangular symmetry due to the
extraction of wave-guided modes and showed approximately 60% increase of their
efficiency compared to the control variable.
Figure 4. two
photos taken from LEDs without photonic crystal and with the photonic crystal (Spie.org, 2018)
from the left and the right are each very distinct. For instance, the pattern
of photonic crystals shows a scattering of wave-guided modes out of the LEDs
chip, and has a diversely edited emission pattern.
Large portion of
InGaN LEDs performance improvements are still needed, including the increase in
their efficiencies. Photonic crystals have the potential capability to
dramatically increase efficiency of InGaN LEDs, “a big step towards producing
white-light at of approximately 200 lumens per watt.”
Some might insist
that the fabrication of photonic crystals in GaN is challenging and will
require a lot of efforts for producing the modified LEDs. However, the amount
of saving will be the most efficient economically in a long-term due to
dramatic increase in InGaN LEDs efficiency.
efficiency of a LEDs will be at its best state when photonic crystals enhance
the efficiency via Purcell effect and by improving the extraction of the light.
With the improvement in the efficiency, we will be able to save more money than
ever which will also result saving our planet, Earth.