  We present detailed Raman studies of graphene deposited on gallium nitride
nanowires with different variations in height. Our results show that different
density and height of nanowires being in contact with graphene impact graphene
properties like roughness, strain and carrier concentration as well as density
and type of induced defects. Detailed analysis of Raman spectra of graphene
deposited on different nanowire substrates shows that bigger differences in
nanowires height increase graphene strain, while higher number of nanowires in
contact with graphene locally reduce the strain. Moreover, the value of
graphene carrier concentration is found to be correlated with the density of
nanowires in contact with graphene. Analysis of intensity ratios of Raman G, D
and D' bands enable to trace how nanowire substrate impacts the defect
concentration and type. The lowest concentration of defects is observed for
graphene deposited on nanowires of the lowest density. Contact between graphene
and densely arranged nanowires leads to a large density of vacancies. On the
other hand, grain boundaries are the main type of defects in graphene on rarely
distributed nanowires. Our results also show modification of graphene carrier
concentration and strain by different types of defects present in graphene.
