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

Abstract

Bulk, single-crystal ZnO was etched in Cl2/Ar and CH4/H2/Ar inductively coupled plasmas as a function of ion impact energy. For CH4/H2/Ar, the etch rate (R) increases with ion energy (E) as predicted from a model of ion enhanced sputtering by a collision–cascade process, R∝(E0.5−ETH0.5), where the threshold energy, ETH, is ∼96 eV. Band edge photoluminescence intensity decreases with incident ion energy in both chemistries, with a 70% decrease even for low energies (∼116 eV). Surface roughness is also a function of ion energy with a minimum at ∼250 eV, where Auger electron spectroscopy shows there is no measurable change in near-surface stoichiometry from that of unetched control samples.