High quality of N-polar GaN film fabricated by layer transfer technology using high selective material removal rate of CMP

Abstract

A new method has been proposed for layer transfer technology to fabricate N-polar GaN film, which is extremely promising to be applied in the preparation of related devices. In our study, after wafer bonding and original Si substrate removal process, the N-polar GaN was exposed by chemical mechanical polishing (CMP) within a short time due to the high selective material removal rate (MRR) ratio of about 35:1 between N-polar AlxGa1-xN (0.33≤x≤1, 1400 nm/min) and N-polar GaN (40 nm/min). The high selective MRR can be attributed to the different corrosion resistance. Hexagonal hillock structure and corrosion pits were appeared quickly on the AlN surface when immersing the N-polar AlN and N-polar GaN in the same CMP slurry, but was not observed on the GaN surface. Meanwhile, the quality of the fabricated N-polar GaN film has been characterized by atomic force microscope (AFM) and Photoluminescence (PL) spectroscopy. Comparing with the N-polar GaN processed through inductive coupled plasma (ICP) etching, the N-polar GaN fabricated by CMP has smaller surface roughness (Rq=0.307 nm) and stronger band-edge PL intensity indicating fewer surface damage. These results can provide guidance on the fabrication of N-polar GaN related devices.