Structural modifications in InP nanostructures prepared by Ar+-ion irradiation

The evolution of nanopatterned InP surfaces by low-energy Ar+-ion irradiation and their dependence on incidence angle were investigated by field emission scanning electron microscopy, atomic force microscopy, and Raman scattering. Ordered surface nanodots of high aspect ratio were created. At large ion incidence angle the dot density decreases and the size varies in the range of 65-130 nm with height of around 25-30 nm. Rapid thermal annealing of the patterned surface shows cluster formation at annealing temperatures of 400 deg. C and above, with some micro-cracks at ion incidence angle of 45 deg. C . With increasing ion incidence angle, the optical phonon Raman modes display systematic downward shift and large asymmetric broadening associated with increased contribution of disorder activated LO and TO modes from the patterned surface. The lowering of phonon frequencies, induced by the phonon wave function confinement, signifies the presence of embedded nanocrystallites in the large sized nanodot patterned surface. The surface damage recovery is achieved by rapid thermal annealing of the samples as reflected in the increased optical phonon frequencies and reduced line shape broadening with annealing temperature. For large ion incident angle, the strain relaxation in the irradiated surface region leads to micro-crack formation in the patterned surface and further hardening of the phonon frequencies