Role of boron and (√3 × √3)‐B surface defects on the growth mode of Si on Si(111): A photoemission and electron diffraction study

Abstract

AbstractThe influence of boron on Si molecular beam epitaxy was investigated as function of coverage and temperature by reflection high‐energy electron diffraction (RHEED). The development of the boron‐covered Si surface was studied additionally by ultraviolet photo electron spectroscopy (UPS) as function of boron coverage (cB) and annealing condition. We found a direct correlation between the appearance of surface states in UPS and the transient growth behaviour observed in RHEED. For cB > 0.4 monolayer (ML) regular RHEED oscillations occur with a period typically for two bilayers (BLs), whereas for lower cB a transient behaviour with irregular intensity oscillations was observed in the initial growth stages. The appearance of this transient behaviour is discussed in terms of an initial surface defect‐induced nucleation of BL‐high Si islands and the formation of two BLs‐high Si islands on top of the van der Waals‐like perfect boron‐covered surface, respectively. The occurrence of surface defects for cB < 0.6 ML is clearly established in UPS measurements, where an intensity peak slightly below the Fermi level (−0.4 eV) was visible. We suggest that this surface defect level is related to Si adatom dangling bonds acting also as preferential nucleation centres in epitaxy. Furthermore, surface defects results in a significant Fermi level pinning.