The mechanical response of the c- and m-planes GaN substrates with different texture sizes in the tip indentation process was investigated prior to the study on the entire scratching behaviour. The indentation directions for the c- and m-planes were [000–1] and [−1010], respectively. Fig. 2(a) and (b) show the variation of the indentation load with the penetration depth ranging from 0 nm to 2 nm given different groove widths (w values) of 0, 0.5, 1, 1.5, and 2 nm, and a groove depth (d value)
