Structural and chemical characteristics of atomically smooth GaN surfaces prepared by abrasive-free polishing with Pt catalyst

This paper reports the structural and chemical characteristics of atomically flat gallium nitride (GaN) surfaces prepared by abrasive-free polishing with platinum (Pt) catalyst. Atomic force microscopy revealed regularly alternating wide and narrow terraces with a step height equivalent to that of a single bilayer on the flattened GaN surfaces, which originate from the differences in etching rate of two neighboring terraces. The material removal characteristics of the method for GaN surfaces were investigated in detail. We confirmed that an atomically smooth GaN surface with an extremely small number of surface defects, including pits and scratches, can be achieved, regardless of the growth method, surface polarity, and doping concentration. X-ray photoelectron spectroscopy showed that the flattening method produces clean GaN surfaces with only trace impurities such as Ga oxide and metallic Ga. Contamination with the Pt catalyst was also evaluated using total-reflection X-ray fluorescence analysis. A wet cleaning method with aqua regia is proposed, which markedly eliminates this Pt contamination without affecting the surface morphology.

► Atomically smooth GaN surfaces with highly ordered steps were achieved.
► Alternating wide and narrow terraces were formed on the flattened HVPE GaN surface.
► Chemically clean GaN surfaces with only traces of impurities were confirmed by XPS.
► Pt contaminations were eliminated by aqua regia treatment from GaN surface.