Identification of dislocations in n-type Si/Si0.88Ge0.12/Si heterostructures by deep-level transient spectroscopy

Plastic relaxation of Si1-xGex layers on (100) Si leads to formation of misfit dislocations at the heterointerface and threading dislocations through the heterostructure. We report here a deep-level transient spectroscopy (DLTS) investigation of dislocations in n-type Si/Si0.88Ge0.12/Si heterostructures grown by selective epitaxy using low-pressure chemical vapour deposition (LPCVD). DLTS was used to detect deep states correlated with dislocations. Measurements were performed on large-area samples (relaxation degree of 63%) as well as on small areas (relaxation degree of 4%) grown selectively on the same wafer. The bias-dependent DLTS peak heights are consistent with a spatially varying dislocation density. This variation, and the combined interpretation of the corresponding DLTS peaks from large and small areas, allowed us to associate one of the deep levels with misfit dislocations at the heterointerface, a second one with threading dislocations and the third one with defects present in the SiGe layer near the interface.