High quality crack-free GaN film grown on si (111) substrate without AlN interlayer

High quality crack-free GaN film has been grown on 2in. n-type Si (111) substrate without AlN interlayers by metalorganic chemical vapor deposition (MOCVD). By using a two-step-pressure growth technique for the AlN buffer layer, we have obtained crack-free 1.8μm thick continuous GaN layer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results indicate that the two-step-pressure growth method can improve the crystalline quality of the GaN film by prolonging the three-dimensional (3D) growth process of the GaN layer, Raman spectrum analysis shows that tensile stress in the overlaying GaN layer can be reduced obviously to 0.62GPa, which helps to reduce the possibility of cracking.