Graphene-Assisted Epitaxy of Nitrogen Lattice Polarity GaN Films on Non-Polar Sapphire Substrates for Green Light Emitting Diodes

Lattice polarity is a key point for hexagonal semiconductors such as GaN. Unfortunately, only Ga-polarity GaN have been achieved on graphene till now. Here, the epitaxy of high quality nitrogen-polarity GaN films on transferred graphene on non-polar sapphire substrates by molecular beam epitaxy is reported. This success is achieved through atomic nitrogen irradiation, where C-N bonds are formed in graphene and provide nucleation sites for GaN and leading to N-polarity GaN epitaxy. The N-polarity characteristics are confirmed by chemical etching and transmission electron microscopy measurement. Due to the higher growth temperature of InGaN at N-polarity than that at Ga-polarity, green light emitting diodes are fabricated on the graphene-assisted substrate, where a large redshift of emission wavelength is observed. These results open a new avenue for the polarity modulation of III-nitride films based on 2D materials, and also pave the way for potential application in longer wavelength light emitting devices.