Role of dimer stacking-fault structures in Si(111) growth and etching

Molecular halogens are used to strip away the Si adatom layer and to expose the Si rest-layer, the structural heart of the Si(111)-(7 x 7) surface. The released Si adatoms are in the form of silicon halide species and behave as silicon growth precursors. Using these methods we have studied Si homoepitaxial growth and chemical etching of the Si(111)-(7 x 7) rest-layer. Growth is shown to nucleate in those regions where the rest-layer is transformed from a 7 x 7 to a 1 x 1 bulk structure. This transformation occurs most readily at defects and antiphase domain boundaries, and explains why these regions are nucleation sites in Si CVD and MBE. The preference for triangular growth and etch features of a particular orientation is shown to be due to the relative stability of [<(11)over bar>2] and [11 (2) over bar] steps. [11 (2) over bar] steps are a higher energy configuration due to the presence of dimer-stacking fault (DS) structures along the upper terraces of these steps. As a result, Si(111) islands formed during CVD growth adopt triangular structures bounded by [<(11)over bar>2] step edges. Similarly, etch pits formed on the Si(111) substrate by molecular halogens are oriented in the [<(11)over bar>2] direction, allowing each step that bounds the etch pit to be of the [<(11)over bar>2]-type. In all instances, deviations from [<(11)over bar>2]-type steps results in the formation of [11 (2) over bar] step segments and the incorporation of additional DS structures on the surface. (C) 1997 Elsevier Science B.V.