A GaN wafer looks like a disc of clear glass. However, the
top and bottom of the GaN crystal are fundamentally different. GaN grows
normally in Ga-polar orientation, i.e. one side is strongly preferred. If done correctly,
one can invert the orientation and with it the internal electric field. N-polar
GaN and AlN enable better high-speed transistors, operating at higher voltages
as well as deep ultra-violet light sensors.
This research is currently undertaken by a Marie-Curie outgoing Fellowship
together with Tyndall University, Ireland.
The crystal structure of GaN is not symmetrical. Instead of
inverting like for N-polar, one can also tilt the GaN crystal into so-called
semi-polar orientations. The weaker polarization of semi-polar GaN can increase
the efficiency of LEDs, especially at high current densities as in virtual
reality display applications. But despite worldwide efforts for more than 15
years, semi-polar LEDs have been worse than standard commercial Ga-polar (0001)
LEDs.
Recently our group demonstrated better semi-polar LEDs than the commercial ones.
The secret was the use of a special orientation, (10-13). In this orientation,
the polarisation field has the right sign.
We are still improving our cheap process to obtain semi-polar (10-13) GaN on sapphire
and evaluate these LEDs for display applications.
µLEDs are light emitting diodes than are less than 20µm across. Such small µLEDS are sought after for virtual reality displays, where million of pixels are needed with high brightness and high efficiency to project 3D images into your eyes.
However, as the dimension shrink, the efficiency reduces as well.The main suspect is surface recombination at the sidewalls.
The project looks at the fundamental properties of the LED emmission process, and thries from that to understand the physical mechanism and devise ways to reduce this effect.
AlPN is a new III-Nitride semiconductor, combining Al with a mixture of phosphorous and nitrogen. It was first realised worldwide in our group in 2020. The material can enable high speed or high power transistors for electric cars with longer range or the next generation wireless networks. We work together with many groups to make this a reality.
This research is currently funded by a Kakenhi-Grant and a international grant together with Germany.
We are looking for a Postdoc/Research Assistent Professor.