Epitaxial growth of fully relaxed Si0.75Ge0.25 on SOI substrate

A fully relaxed Si0.75Ge0.25 film with low dislocation densities is fabricated by epitaxial growth on SOI substrate without depositing graded buffers. The relaxation mechanism of the SiGe layer directly grown on SOI substrate is also analyzed. For SiGe grown on SOI with low Ge content, the strain is redistributed between SiGe and the top Si of SOI substrate, and the strain residing in SiGe layer can be fully relaxed by the formation and expansion of dislocation half-loops near the SiGe/Si interface. The surface morphology and crystal quality of all samples are analyzed by optical microscopy and transmission electron microscopy (TEM), respectively. Compared to the Si0.75Ge0.25 layer epitaxially grown on graded buffer, the Si0.75Ge0.25 directly grown on SOI substrate appears good surface morphology and perfect crystal quality.

Research highlights▶ High crystal quality Si0.75Ge0.25 film has been grown directly on SOI substrate with no graded buffer, whose density of surface defects is lower than 104 cm−2. ▶ For SiGe grown on SOI with low Ge content, the strain is redistributed between SiGe and the top Si of SOI substrate, and the strain residing in SiGe layer can be fully relaxed by the formation and expansion of dislocation half-loops near the SiGe/Si interface. ▶ For SiGe layer grown on SOI substrate with high Ge fraction, the lattice constant differences between Si and SiGe cannot be accommodated efficiently due to the restriction of buried oxide.