The effect of sub-band gap photon illumination on the properties of GaN layers grown on Si(111) by MBE

Nanostructured GaN layers are fabricated by laser-induced etching processes based on heterostructure of n-type GaN/AlN/Si grown on n-type Si(111) substrate. The effect of varying laser power density on the morphology of GaN nanostructure layer is observed. The formation of pores over the structure varies in size and shape. The etched samples exhibit dramatic increase in photoluminescence intensity compared to the as-grown samples. The Raman spectra also display strong band at 522 cm⁻¹ for the Si(111) substrate and a small band at 301 cm⁻¹ because of the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 and 568 cm⁻¹ due to E2 (low) and E2 (high), respectively. Surface morphology and structural properties of nanostructures are characterized using scanning electron microscopy and X-ray diffraction. Photoluminance measurement is also taken at room temperature by using He–Cd laser (λ = 325 nm). Raman scattering is investigated using Ar⁺ Laser (λ = 514 nm).