Diamond has the highest thermal conductivity among all materials and can be applied to overcome the heat dissipation problem in radio frequency devices based on the heterojunction of gallium nitride (GaN) and 4H silicon carbide (4H-SiC). However

growing high-quality diamond films on 4H-SiC substrates is quite difficult due to the very low nucleation density of diamond on their surfaces. In this study

the thermodynamic models of diamond nucleation on 4H-SiC substrates were carefully analyzed to investigate the effect of different surface states on diamond nucleation. The results indicated that although a 4H-SiC substrate with a smooth surface can significantly reduce the formation energy of diamond nucleation

it remains challenging for diamond to nucleate on the substrate. Fortunately

increasing the surface roughness can further decrease the formation energy of diamond nucleation and significantly increase the nucleation density on the 4H-SiC substrate

enabling the formation of a continuous high-quality film. Additionally

the rough surface of 4H-SiC substrates lapped by abrasives with small particle size contained numerous nanoscale defects and dense scratches

which serve as active sites for diamond nucleation. The smaller the particle size of the abrasives

the higher the nucleation density of diamond

which is also beneficial for the epitaxial growth of diamond on 4H-SiC substrates. Finally

crack-free diamond films on 4H-SiC substrates were successfully fabricated using an MPCVD system

and their properties were characterized by scanning electron microscopy (SEM)

Raman spectroscopy

and X-ray diffraction (XRD)

respectively.