In this study we used RF plasma-assisted molecular beam epitaxy for the epitaxial growth of single-crystalline indium nitride (InN) thin films on aluminum nitride buffer layers/Si (111) substrates. We then used scratch techniques to study the influence of the c -axis orientation of the InN films and the beam interactions on the tribological performance of these samples. When grown at 440, 470, and 500 °C, the coefficients of friction were 0.18, 0.22, and 0.26, respectively, under a normal force ( F n ) of 2000 μN; 0.19, 0.23, and 0.27, respectively, under a value of F n of 4000 μN; and 0.21, 0.24, and 0.28, respectively, under a value of F n of 6000 μN. These measured values increased slightly upon increasing the growth temperature because of the resulting smaller sizes of the apertures and/or pores in the inner films. The sliding resistance of the ploughed area was observed. The contact sliding line became increasingly noticeable upon increasing the value of F n ; the plot of the friction with respect to the penetration depth revealed a significant relation in its adhesion properties presentation.