Experimental and theoretical investigation of thermal stress relief during epitaxial growth of Ge on Si using air-gapped SiO_2 nanotemplates

摘要

We demonstrate that SiO_2 nanotemplates embedded in epitaxial Ge grown on Si relieve the stress caused by the thermal expansion mismatch between Ge and Si. The templates also filter threading dislocations propagating from the underlying Ge-Si interface, reducing the density from 9.8 × 108 to 1.6 × 10~7cm~(-2). However, we observe that twin defects form upon Ge coalescence over the template, and the density is approximately 2.8 × 10~7cm~(-2). The coalescence occurs without direct contact with SiO_2, leaving a void between Ge and SiC>2 that further reduces the thermal stress. The stress obtained from finite element modeling corroborates the experimental observation.