Photoluminescence characterisation of triangular lattices of holes and pillars etched in GaN epilayers

We report a low temperature and room temperature photoluminescence (PL) stu dy of a series of two-dimensional arrays of holes and pillars in a triangul ar lattice arrangement, fabricated in a 1.8 mu m thick GaN/sapphire epilaye r. The sample was patterned by electron beam lithography and reactive ion e tching in a CH4/H-2 plasma. Such structures with periodic variation of the dielectric constant may give rise to photonic crystals that can create a ra nge of forbidden frequencies called a photonic bandgap. We have used the PL peak to evaluate the damage introduced onto the semiconductor by the etchi ng procedure, and to determine the magnitude of the relaxation of the strai n in the GaN film. Theoretical computations predict the photonic bandgap po sitions for future experimental investigations.