Temperature dependence of Raman scattering in defect-free AlN nanorods grown on multilayer graphene by van der Waals epitaxy

The crystalline quality of traditional epitaxy is hampered by the lattice and thermal mismatch of epilayer and substrate. Van der Waals epitaxy (vdWE) allows the epilayer to show no excessive strain and results in low defects density. Here, the multilayer graphene as a substrate for c-axis-oriented growth of vertically aligned AlN nanorods by vdWE have been presented. Defect-free of the AlN nanorods was evidenced through transmission electron microscopy (TEM). The strain of AlN nanorods was reduced with the exponential of height, which was characterized by micro-Raman spectroscopy. Moreover, the temperature dependence of Raman scattering of AlN has been further studied for clarifying the relationship of optical phonons and temperature. This temperature dependence was well matched by an empirical relationship which has proved to be applicable for other III-Nitride (such as GaN, InN) semiconductors.