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

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. (C) 2000 American Institute of Physics. [S0003-6951(00)00706-3].