Investigations on Thermal Stress Relief Mechanism Using Air-Gapped SiO2 Nanotemplates during Epitaxial Growth of Ge on Si and Corresponding Hole Mobility Improvement

Abstract

We demonstrate the implementation of air-gapped SiO2 nanotemplates embedded in epitaxially grown Ge on Si for relieving stress caused by the thermal expansion coefficient mismatch between Ge and Si. The air-gap is formed around the SiO2 template during growth and eventual coalescence of adjacent Ge islands merging over the template. The stress map obtained from finite element modeling corroborates the experimental observation, suggesting that the thermal stress can be reduced nearly by half. The templates also filter threading dislocations propagating from the underlying Ge-Si interface, reducing the defect density from 9.8×108 to 4.4×107 cm-2 in the demonstration case. We further investigate the influence of threading dislocation density on the effective hole mobility in undoped Ge between substrates grown with the template and without the template. Using the Hall mobility measurements, we have obtained a peak effective hole mobility of 925 cm2/V-s at room temperature for Ge grown with the template, compared to 297 cm2/V-s for Ge grown without the template.