Nonselective and smooth etching of GaN/AlGaN heterostructures by $Cl2/Ar/BCl3$ inductively coupled plasmas

A systematic study of the nonselective and smooth etching of GaN/AlGaN heterostructures was performed using $Cl2/Ar/BCl3$ inductively coupled plasmas (ICPs). Nonselective etching can be realized by adjusting the $BCl3$ ratio in the $Cl2/Ar/BCl3$ mixture (20%–60%), increasing the ICP power, and decreasing the chamber pressure. Surface morphology of the etched heterostructures strongly depends on the gas chemistry and the chamber pressure, whereas selectivity and surface morphology show a slight dependence on the dc bias and total flow rate. Specifically, with the addition of 20% $BCl3$ to $Cl2/Ar$ (4:1) gas mixture, nonselective etching of $GaN/Al0.28Ga0.72N$ heterostructures at a high etch rate is maintained and the surface root-mean-square roughness is reduced from 10.6 nm to 0.5 nm, which is smoother than the as-grown sample. Auger electron spectroscopy analysis shows that the effective removal of residual oxygen from the surface of AlGaN during the etching process is crucial to the nonselective and smooth etching of GaN/AlGaN herterostructures at high etch rate.