Correlated SiGe wires shaped by regular step bunches on miscut Si(113) substrates

Highly regular step bunches have been observed in appropriately strained SiGe/Si multilayers on miscut Si(113) substrates. Owing to the strong step-bunching properties on the Si(113) surface, both the Si layers and the SiGe layers of the multilayers exhibit a regular pattern of large steps. Considerable SiGe material in the SiGe layers accumulates at the edges of the underlying large Si steps (step bunches), forming well-shaped SiGe wires. The SiGe wires in the multilayers manifest an oblique correlation. A bending to vertical correlation is observed when the built-in strain in the multilayers is large enough. The oblique correlation is well described in a thermodynamic model of multilayer growth, based on the calculations of the in-plane strain fields of underlying step-modulated SiGe layers on the free surfaces of Si layers during growth. Si step bunches energetically form in the regions of maximum strain above the SiGe wires and cause lateral agglomeration of SiGe material at Si step edges, resulting in the oblique correlation. The bending to vertical correlation occurs, in contrast, if the in-plane strain field becomes large enough to cause the SiGe material to accumulate directly in the regions of maximum strain.