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

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Abstract
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 eV 28Si+ 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-energy 28Si+ 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 ≈ 7·5 nm.