Light Enhanced Ion-Acoustic Signal Generation in Si and GaAs

Abstract

Modulated beams of Ar⁺ ions have been used as acoustic sources for studies of ion-specimen interactions [1–3]. The technique is analogous to Scanning Electron Acoustic Microscopy (SEAM) [4] in using electrostatic beam blanking and piezoelectric detection. However, the ion-beam-specimen interactions differ from electron beams in causing surface erosion, ion implantation and,for reactive ion species, chemical reactions. This paper presents some preliminary information on the role of surface oxygen in elastic generation by rare gas ions on silicon and GaAs. Illumination of the specimens with unmodulated light above the semiconductor band gap changes the acoustic signal. The dependence of the acoustic signal on light wavelength, modulation frequency of the source, energy of the primary ion beam, and the electrical characteristics of the specimen are presented. A tentative model of the interactions which produce these effects in silicon is suggested. The model may be applicable to GaAs in revised form.