Formation and silicon overgrowth of √3 × √3-R30° boron surface phases on Si(111)

It is well known that boron (B) forms surface phases if deposited on Si surfaces. One interesting phase is the so called √3 × √3-R30° boron surface phase (BSP) on Si(111). This surface phase is different from all other √3 × √3-R30° surface reconstructions formed by group III atoms because B alone is able to induce this reconstruction in two different configurations. Few facts are known about the step by step formation of this √3 × √3-R30° BSP and its Si overgrowth, although this is particularly important for the incorporation of BSPs into novel electronic devices. Therefore, the formation of the surface phase by in situ scanning tunnelling microscopy (STM) has been investigated. Examination showed that deposition of B led to the breakdown of the 7 × 7 reconstruction and to the formation of a Si surface with a BSP located on T₄ lattice sites (B-T₄). Thermal annealing of the structure causes the B atoms to migrate from T₄ to S₅ positions. The two phases exhibit completely different properties as a result of their different chemical binding. A technique has also been developed to distinguish both surface phases and to visualise the phase transition from B-T₄ to B-S₅. This has been achieved using work function measurements in a hydrogen atmosphere. The Si overgrowth of B-T₄ surface phases has been studied by STM. In comparison with the overgrowth of a B-S₅ surface phase, epitaxial growth occurs at lower temperatures. As a result of the increased surface mobility on the B-T₄ BSP, the density of epitaxial islands formed during overgrowth is much lower compared with the overgrowth of a B-S₅ phase or of Si(111)-7 × 7.