Ge–Si intermixing in Ge quantum dots on Si(001) and Si(111)

Abstract

Exploiting Ge K-edge x-ray absorption spectroscopy we provide direct evidence of Si–Ge intermixing in self-organized strained and unstrained Ge quantum dots on Si, and provide a quantitative measurement of the average composition. For Ge/Si(001) dots with equivalent thickness in the range 5.8–38 nm and morphology ranging from that typical of coherently strained to that associated with relaxed dots we find that the average Si composition is approximately 30%. For Ge/Si(111), we find that the wetting layer has a Si composition near 50%. We discuss these results in terms of the energetics of dot formation and argue that strain-enhanced diffusion of Si into Ge should be considered as an important factor in minimizing the strain energy of the system.