Growth Orientation Dependent Hardness for Epitaxial Wurtzite InN Films

We report the hardness of wurtzite InN thin film grown with different crystalline orientations of heteroepitaxial s-plane (1 (1) under bar 01) and a-plane (11 (2) under bar0) on r-plane (1 (1) under bar 02) Al2O3, and homoepitaxial film on c-plane (0001) Al2O3. Hardness values along with elastic properties are studied using nanoindentation technique. Maximum hardness is reported for c-plane (similar to 8 GPa), which is followed by s-plane (similar to 5.5 GPa) and then a-plane (similar to 4 GPa) oriented InN Films. Peierls force in the slip system of different crystalline orientations for wurtzite sample is calculated for explaining the systematic variations in hardness values of these films grown with different crystalline orientations.