Strain relaxation and optical properties of etched In_0.19Ga_0.81N nanorod arrays on the GaN template

InGaN/GaN epilayers, which are grown on sapphire substrates by metal-organic chemical-vapour deposition (MOCVD) method, are formed into nanorod arrays using inductively coupled plasma etching via self-assembled Ni nanomasks. The formation of nanorod arrays eliminates the tilt of the InGaN (0002) crystallographic plane with respect to its GaN bulk layer. Photoluminescence results show an apparent S-shaped dependence on temperature. The light extraction efficiency and intensity of photoluminescence emission at low temperature less than 30 K for the nanorod arrays are enhanced by the large surface area, which increases the quenching effect because of high density of surface states for the temperature above 30 K. Additionally, a red-shift for the InGaN/GaN nanorod arrays is observed due to the strain relaxation, which is confirmed by reciprocal space mapping measurements.