Characterization of reactive ion etched surface of GaN using methane gas with chlorine plasma

Reactive ion etching of GaN has been carried out in two different plasma chemistries using ${\mathrm{10Cl}}_{\mathrm{2}}\mathrm{/10Ar}$ and ${\mathrm{1CH}}_{\mathrm{4}}{\mathrm{/9Cl}}_{\mathrm{2}}\mathrm{/10Ar}$ at various applied radio frequency (rf) power. We have addressed the postetch surface characteristics of GaN, and the effect of ${\mathrm{CH}}_4$ addition to chlorine plasma and the variation of rf power are discussed. Surface contamination, roughness, and stoichiometry have been determined from the results of secondary ion mass spectrometry. It is observed that in the case of plasma with 5% ${\mathrm{CH}}_{\mathrm{4}},$ above 125 W, contamination of carbon is minimal and roughness is similar to that of the as-grown sample. At rf power less than 125 W, the Ga/N ratio of the etched surface is almost unity, whereas at rf power more than 125 W, it is more than unity. When the GaN surface is etched with only chlorine plasma, the surface is Ga excess at all rf power applied. The intensity of the main band-to-band photoluminescence peak is found to decrease when ${\mathrm{10Cl}}_{\mathrm{2}}\mathrm{/10Ar}$ is used, and the intensity was a minimum at 200 W. When 5% ${\mathrm{CH}}_4$ is added to the plasma, the intensity at 200 W became almost the same as that of the as-grown sample, indicating minimal damage induced in the surface.