Controlling the stress of growing GaN on 150-mm Si (111) in an AlN/GaN strained layer superlattice

The strain state in the AlN/GaN SLS was caused by the diffusion of Al from AlN into GaN in the SLS. The unintended AlGaN played a critical role in reducing the mismatch between the AlN and GaN layers, and efficiently accumulated stress without causing relaxation in the AlN/GaN SLS. •The interface of the 80-paired AlN/GaN SLS was periodical.•Adjusting the thickness of the GaN layer in the SLS controls stress of epilayer.•The compressive stress in the SLS exists during growth and after cool down.•Unintended AlGaN played a critical role in reducing the mismatch in SLS.•The AlGaN efficiently accumulated stress without causing relaxation in the SLS. For growing a thicker GaN epilayer on a Si substrate, generally, a larger wafer bowing with tensile stress caused by the mismatch of thermal expansion coefficients between GaN and Si easily generates a cracked surface during cool down. In this work, wafer bowing was investigated to control stress by changing the thickness of a GaN layer from 18.6 to 27.8nm in a 80-paired AlN/GaN strained layer superlattice (SLS) grown on a 150-mm Si (111) substrate. The results indicated that wafer bowing was inversely proportional to the total thickness of epilayer and the thickness of the GaN layer in the AlN/GaN SLS, since higher compressive stress caused by a thicker GaN layer during SLS growth could compensate for the tensile stress generated during cool down. After returning to room temperature, the stress of the AlN/GaN SLS was still compressive and strained in the a-axis. This is due to an unintended AlGaN grading layer was formed in the AlN/GaN SLS. This AlGaN layer reduced the lattice mismatch between AlN and GaN and efficiently accumulated stress without causing relaxation.