Crystal-state–amorphous-state transition in low-temperature silicon homoepitaxy

Conventional molecular-beam epitaxy of Si(001) at low temperatures proceeds epitaxially up to a finite thickness followed by a crystalline-to-amorphous transition. Concurrent low-energy ${\mathrm{Ar}}^{+}$ ion irradiation during deposition results in an increase in epitaxial thickness. Surface smoothing is shown to be the primary effect of ${\mathrm{Ar}}^{+}$ ion irradiation. A possible pathway to the formation of amorphous silicon is the nucleation of twin boundaries on {111} planes. The intersection of a twin boundary with other {111} or {001} planes results in the formation of five- and seven-member rings which leads to the crystalline-to-amorphous transition.