Experimental and theoretical investigation of thermal stress relief during epitaxial growth of Ge on Si using air-gapped SiO2 nanotemplates

We demonstrate that SiO2 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 × 10⁷ cm^-2. However, we observe that twin defects form upon Ge coalescence over the template, and the density is approximately 2.8 × 10⁷ cm^-2. The coalescence occurs without direct contact with SiO2, leaving a void between Ge and SiO2 that further reduces the thermal stress. The stress obtained from finite element modeling corroborates the experimental observation.