High quality crack-free GaN film grown on si (1 1 1) substrate without AlN interlayer

•We studied the GaN layers growth on 2 inch Si (1 1 1) substrate without AlN interlayers.•We obtain crack free GaN layers by using two-step-pressure growth of the AlN buffer layer.•The two-step-pressure growth method can prolong the three-dimensional growth process of GaN.•The crystalline quality of the GaN film can be improved by the two-step-pressure growth method.

High quality crack-free GaN film has been grown on 2 in. n-type Si (1 1 1) 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 1.8 μm 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 0.62 GPa, which helps to reduce the possibility of cracking.