INTERFACE ROUGHNESS IN GE/SI SUPERLATTICES

Interface roughness in a (Ge(n)Si(m))p superlattice has been observed with a root mean square height of 3.0 angstrom and a lateral correlation length of 0.4 mum. The roughnesses at different Ge-Si interfaces are not independent, but rather the terrace structure of the substrate is identically replicated, forming a superlattice with vertically correlated (conformal) interface roughness. A staircase structure characteristic of atomic layer steps separated by approximately 1 mum is observed on the same heterostructure. Vertically correlated roughness occurs because at the low growth temperature used (350-degrees-C) step motion on the surface is negligible.