A polycrystalline GaN layer is grown on {HEAD ~ the bulk GaN layer} to form {TAIL ~ a GaN/substrate bi layer} 
to form
A polycrystalline GaN layer is grown on { HEAD ~ the bulk GaN layer } to form { TAIL ~ a GaN / substrate bi layer }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL