Evidence for competing growth phases in ion-beam-deposited epitaxial silicon films

Epitaxial crystal growth using an energy- and mass-analysed ion beam can provide insights into the fundamental processes involved in thin-film growth. In these experiments layers of silicon were deposited onto (001) silicon substrates using 30 eV and 50 eV²⁸Si⁺ions. This Letter reports on the use of ultramicrotomy and high-resolution transmission electron microscopy to obtain lattice images of ion- beam-deposited epitaxial silicon films. The lattice images show that film growth proceeds via a competition between epitaxial and amorphous phases, similar to island (Volmer-Weber) growth. Electron energy loss and ion scattering measurements show that, although the film is epitaxial, it contains defect structures. The lattice images indicate that a sufficient amount of the native oxide layer could be removed simply using low-energy²⁸Si⁺bombardment to enable epitaxial growth. In the case of samples etched in situ by low-energy chlorine ions, initial epitaxial growth gave way to an amorphous growth phase after ͌7-5nm.