Nanowires on graphene
CrayoNano has developed a novel technique that enables growth of positioned and vertically aligned nanowires on graphene.
By growing AlGaN (aluminium gallium nitride) nanowires on graphene, graphene will be used both as a substrate and as a UV transparent electrode in order to achieve a high external efficiency.
CrayoNano’s unique device structure thus leads to reduced heat loss, and in addition reduced material consumption.
Nanowires enables improved internal quantum efficiency, operating lifetime, and reliability.
The result is a flexible and extremely thin and lightweight epiwafer able to emit large amounts of light from a small area.
Graphene is experiencing tremendous attention worldwide. Semiconductor nanowires on graphene are expected to become the basis for new types of device systems, and ultimately change the semiconductor industry.
DUV LED Challenges and CrayoNano’s Solution
While traditional planar design has more issues with lattice mismatch that affects the crystal quality and efficiency,
AlGaN nanowires on graphene have high crystal quality (<2% lattice mismatch) and can accommodate strain without the formation of dislocations.
Today’s UV LED solutions
Transparent electrode and substrate issues
- Traditional transparent top contacts like ITO cannot be used (absorbs light from around 350 nm). DUV LED suppliers are therefore emitting light through AlN or sapphire substrates.
- AlN is very expensive, and needs extra process to thin the substrate.
- Sapphire starts to absorb in UVC (T=75% at 250 nm) and needs thick conductive GaN buffer.
Graphene as combined substrate and electrode
- CrayoNano’s devices will be based on a unique method of growing AlGaN nanowires on graphene, where graphene will be used both as a substrate and a DUV transparent electrode in order to achieve a high external efficiency.
- Graphene is transparent to all wavelengths, has a very low absorption (T=97%) and record high electrical and thermal conductivity that enable a high external efficiency.
Planar layered design
- Traditional planar design has more issues with lattice mismatch that affects the crystal quality and efficiency.
Wall plug efficiency is therefore today only around 1-5%.
Nanowire based design
- AlGaN nanowires on graphene have good crystal quality (<2% lattice mismatch) and can accommodate strain without the formation of dislocations.
- Nanowires enables improved internal quantum efficiency, operating lifetime and reliability.
Wall plug efficiency similar to near UV LEDs can therefore be achieved (approx. 40–50%).
The technology uses existing wafer fabrication processes and tools, enabling production of DUV LED chips
with 10 times higher efficiency at less than 10 % of the cost of existing DUV LEDs.
Higher output - lower cost
Nanowires on graphene enables UV LEDs with 10 times higher efficiency
at less than 10 % of the cost of existing deep UV LEDs.
State-of-the-art UV solutions
CrayoNano’s graphene DUV solution
Wall plug efficiency (WPE) =1–5 %
Wall plug efficiency (WPE) = 10–50 %
100 mW UV output power needs about 10 W of electricity (biasing the LED at 1 A and 10 V). 9.9 W is converted to heat.
100 mW UV output power needs <1 W of electricity (= a 10x increase in WPE). Less than 0.9 W is converted to heat.
UVC LED companies are using expensive aluminum nitride (AlN) substrates or thick buffer layers.
Graphene is already <10x the cost of AlN. Additionally less heat will allow simpler and cheaper module design.
What is it with Graphene?
Graphene has several outstanding properties:
- High transparency: Graphene is transparent to all wavelengths of light (T=97 %).
- Record high conductivity: Graphene has record high electrical & thermal conductivity that enables high external efficiency.
- Thinnest and strongest material ever
- Semiconductor substrate: Can be used as a substrate for growth of semiconductor nanowires
Graphene is not a semiconductor…
… but due to these unique properties, graphene is a new and novel semiconductor substrate that will enable radical new devices and applications.
CrayoNano has patented the use of graphene as a semiconductor substrate.