Positron annihilation studies of defects in Si1-xGex/SOI heterostructures

The strain of a SiGe alloy epitaxially grown on Si can be released by heating at 750°C. However the strain relaxation is accompanied by the generation of threading dislocations and associated point defects. The attempted remedy is to let SiGe grow on a very thin Si substrate on top of a SOI heterostructure, with the purpose of concentrating the defects at the Si- SiO2 interface of the SOI substrate. A slow positron beam was used to investigate the effectiveness of the remedy. The positron diffusion length in SiGe decreases after the thermal treatment. This result shows the generation of lattice defects still occurs in the SiGe layer, in spite of the deposition on SOI.