Atomic scale flattening of gallium nitride substrate grown by Na flux method applying catalyst-referred etching

In this study, a gallium nitride (GaN) substrate produced by the Na flux method was planarized using catalyst-referred etching (CARE). To improve the removal rate, the GaN substrate was processed using CARE-assisted photoelectrochemical (PEC) reaction (PEC CARE); the removal rate was 45 nm/h. However, the shape was embossed because of subsurface scratches introduced during preprocessing. These scratches were removed when the PEC CARE process was conducted under an applied potential of 2.5 V. In addition, a smooth surface of surface roughness 0.4 nm rms was obtained. A surface with step-terrace structures on the entire substrate was subsequently obtained when the CARE process was performed using a platinum (Pt) catalyst and deionized water; in this case, the surface roughness was 0.11 nm rms and the removal rate was 5 nm/h.