Modulated ion beam studies of product formation and ejection in ion-induced etching of GaAs by Cl2

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Abstract
We have measured products’ identity and kinetic energy for ion-induced etching of GaAs by chlorine at room temperature. Modulated ion beams of 1-keV Ne+ are used to etch the surface in the presence of steady-state flux of Cl2 with a neutral/ion flux ratio of 0–100. The major product species observed are GaCl3 and AsCl3, and substantial amounts of elemental Ga and As. Subchlorides of Ga are observed for neutral/ion ratio <10. Kinetic energies were measured by analysis of time-of-flight waveforms. Sputtered Ga and As atoms, in the absence of surface chlorination have most probable kinetic energy of approximately 5 eV, in accord with the expected sputtering mechanism. GaCl3 and AsCl3 product species have most probable kinetic energies of 0.3–0.5 eV, and Ga and As atoms emitted from a chlorinated surface have most probable energy of 1–2 eV. No evidence for slow kinetic processes with substantial surface residence times was observed. These observations are discussed in light of other reports of product formation and ejection in plasma and ion-beam-assisted etching. The results suggest a mechanism involving synthesis and ejection of products during the collision cascade following ion impact.