Non-destructive method for strain imaging in an individual GaN nanorod by confocal Raman technique

GaN based layer structures on highly lattice mismatched substrates are widely used for electronic and optoelectronic devices. Top down etched, GaN based nanorod structures are mainly studied due to their more effective strain relaxation. The previous measurements on the strain state of these structures have been performed either on single detached nanorods or on ensembles of nanorods still on the substrate. Here we demonstrate a technique based on confocal Raman scattering spectroscopy to probe the strain state of a single GaN nanorod still on the original substrate non-destructively. Both lateral and depth resolved imaging is achieved close to the diffraction limit of light. We observe that a GaN nanorod on the substrate is compressively strained throughout. The strain decreases from the base of the nanorod towards the top surface, but the top surface is still compressively strained. The detached GaN nanorod is less compressively strained overall, and the strain relaxes from the center towards all the edges.