MOLECULAR-BEAM EPITAXIAL-GROWTH OF THIN CAF2 FILMS ON VICINAL SI(111)SURFACES

The growth of CaF2 on Si(111) 7 x 7 surface at similar to 77 degrees C and similar to 250 degrees C on both similar to 2 degrees and similar to 0.5 degrees off-normal, vicinal substrates (titled towards the [11 -2] arimuth) has been studied using RHEED, AFM and SEM. For growth at similar to 770 degrees C an both substrates, the CaF2 grows in a layer -by-layer fashion for the first two monolayers which gives rise to RHE ED intensity oscillations. Beyond two monolayers, relatively thick CaF 2 islands nucleate at the Si step edges (which are bunched into step b ands) and grow laterally with constant height (similar to 5 nm for sim ilar to 2 degrees and similar to 2 nm for similar to 0.5 degrees miscu t substrates) along the Si step edges and eventually form a flat overl ayer. The height of the CaF2 islands appears to be determined by the h eight of the Si step bunches which, in turn, is determined by the subs trate miscut angle. For growth at similar to 250 degrees C, the integr al diffraction spot RHEED intensity decreases exponentially for the fi rst similar to 2 monolayers of growth and then oscillates for similar to 6 periods, In addition, the non-integral diffraction spots, corresp onding to the Si(111) 7 x 7 pattern, are not fully removed until the i ntegral diffraction spot intensity starts to oscillate at similar to 3 monolayers. These results indicate that the CaF2 initially grows by n ucleation and coalescence of 2D islands which are 2 to 3 monolayers hi gh, followed by a multilayer-by-multilayer mode which leads to a featu reless, flat surface morphology.