Effect of high-density plasma etching on the optical properties and surface stoichiometry of ZnO

Bulk, single-crystal ZnO was etched in Cl-2/Ar and CH4/H-2/Ar inductively coupled plasmas as a function of ion impact energy. For CH4/H-2/Ar, the etch rate (R) increases with ion energy (E) as predicted from a model of ion enhanced sputtering by a collision-cascade process, Rproportional to(E-0.5-E-TH(0.5)), where the threshold energy, E-TH, is similar to96 eV. Band edge photoluminescence intensity decreases with incident ion energy in both chemistries, with a 70% decrease even for low energies (similar to116 eV). Surface roughness is also a function of ion energy with a minimum at similar to250 eV, where Auger electron spectroscopy shows there is no measurable change in near-surface stoichiometry from that of unetched control samples. (C) 2002 American Institute of Physics.