Strain modification in epitaxial 2H-AlN layers on 3C-SiC/Si(111) pseudo-substrates

Optical measurements are used to investigate the crystalline quality and the stress in thin AlN layers; these thin films are grown on cubic silicon carbide layers which are in turn grown on silicon (111) substrates. Different Ge amounts were deposited at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers is derived from the phonon frequency shifts of the E₁(TO) phonon mode. The crystalline quality of AlN films is investigated by considering the intensity of E₁(TO) mode of the 2H-AlN and its full width of the half maximum (FWHM). Ge deposition at low temperature 325 °C, before the carbonization process leads to an improved crystalline quality and a reduced residual stress in the AlN/SiC/Si heterostructures. The best crystalline quality and the lowest stress value are found in the case where 1ML Ge amount was predeposited. The E₁(TO) mode, phonon frequency shifts-down by 3 cm^? 1/GPa with respect to an unstrained layer. The obtained values for the phonon deformation are in reasonable agreement with theoretical calculations.