Electrically pumped GaN-based microdisk laser – MILAGAN

MILAGaN aims at developing electrically pumped microdisk-lasers covering the UV-visible range based on group III-nitrides (Al,Ga,In)-N. Several applications are envisioned as a result of this project: water/air purification/disinfection, environmental sensing, and fabrication of ever more efficient white light sources. MILAGaN will focus his attention on solid state lighting because it is likely one of the most challenging issues of the century. Solid state lighting is rapidly expanding due to its better energetic efficiency compared to other technologies, and the huge energy savings that are expected. The only remaining limitation to its massive adoption is the price of light emitting diodes (LEDs). One solution is to reduce the number of LEDs in the lamp, and drive them under a larger current. Unfortunately, GaN-based LED have a reduced efficiency at larger currents, and then loose part of their energetic bonus and interest. While this effect is believed to be intrinsic, it is related to spontaneous emission and can be largely suppressed in stimulated emission sources, i.e. in lasers. Among the various laser geometries, the microdisk laser is well-suited for this application. Based on the consortium know-how on GaN-on-Si, we will develop electrical µdisk lasers emitting in the UV/blue, and pumping phosphors, as in conventional white LEDs, to emit white light. Microdisks will be fabricated in arrays and driven in parallel in order to achieve a high optical power. First prototypes will then help to assess very important issues such as cost of devices, thermal management, losses, lifetime and robustness of this new technology. But of course the main challenge is first to fabricate the electrical devices. Microdisks have been developed in nitrides for a long time for optical pumping, large resonance quality (Q) factors have been demonstrated and laser action has been achieved. The difficulty is to reproduce the same features with electrical pumping, which is completely novel and challenging. Our consortium gathers four partners with complementary expertise in France, and one partner in Hong Kong. French partners have been collaborating for a while on nanophotonics and have a good track record in producing state of the art photonic crystals, µdisks, and planar cavities in nitrides, with record Q factors, strong coupling and polariton lasers. However, they lack experience in electrically injected µdisks and white light sources, and for this reason, the help of a Hong Kong partner has been sought in the frame of a PRCI project. The University of Hong Kong has experience in µdisks, implementation of phosphors for white light sources and in electrically injected nanodevices. This complementarity allows one proposing a complete process from epitaxy to phosphor deposition, with state of the art players.
The objective is to assess the potential of µdisks lasers for solid state lighting and identify problems and limitations. Obtaining high performance white sources based on µdisks competing with existing white LEDs, which have experienced 2 decades of optimization by large industrial companies, is obviously outside the scope of an ANR project. The impact of the project will be reinforced by the international nature of the project, and also by having all partners being members of GaNeX, which already supports MILAGaN’s objective. Also, the company Aledia and the startup EasyGaN, a young spin-off from CRHEA, both developing nitride-based technologies on silicon for optoelectronics, are interested in the project.