Hi,

one challenging issue for GaN on substrate epitaxy is the lack of a suitable substrate. GaN growth is done on SiC or sapphire substrates, which are not lattice-matched to GaN. Because of this lattice-mismatch a lot of defects (e.g. dislocations) are created in the GaN layer. The van de Waals epitaxy of GaN on graphene is a viable route to obtain GaN layer with high quality as described by Jeehwan Kim et al. in Nature Communications 5,

4836. I hope my comment was helpful.

http://www.nature.com/ncomms/2014/140911/ncomms5836/full/ncomms5836.html

Dear Nouman, Pure GaN is used in laser LEDs. Since the GaN has wide band gap semiconductor, which holds promise for high-density optical data-storage applications. On the other side Graphene is conductor, semiconductor and insulator depending upon the chirality of Graphene. Deposition of GaN on Graphene can open new doors of optoelectronics and nanoelectronics applications. You can modify the band gap of GaN depending upon the concentration of Graphene. You may face one big hurdle that is the lattice parameters should approximately match so that you have least strain and good hetrostructures. Hope this will help you.

Regards, 

GaN emission edge nearly 364 nm basically UV-A line edge; c-c bond in graphene  might be adjustable to in plane lattice match as a result  better defect free growth as well as graphene conductive as well as transparent (might be)  properties are highly desirable for GaN integration in optoelectronic field. Because currently GaN grown on transparent insulating sapphire is highly defective and improper for integration.