Structure of Si-Ge amorphous semiconductor heterojunctions.

We determined by Extended X-ray Absorption Fine Structure (EXAFS) that the interfaces in hydrogenated amorphous Si-Ge superlattices are atomically abrupt and the interface atoms are bound on average to two Si and two Ge atoms. The Si-Ge interface bond distance is 2.40+-0.02angstroms, equal to the average of the bulk bond distance values for Si and Ge. The experiment was performed at the Si Kedge and the EXAFS was monitored by Si K sub alpha soft X-ray fluorescence detection. This innovative approach allows for EXAFS studies of buried and oriented interfaces and offers new opportunities in structural studies of interfaces.