A new route toward light emission from Ge: tensile-strained quantum dots.

The tensile-strained Ge quantum dot (QD) is proposed as a new route for the realization of direct band gap conversion in Ge. Ge QDs were successfully grown on an InP substrate by molecular beam epitaxy. The strain field in the QDs were analyzed by high resolution transmission electron microscopy and simulated by the finite element method based on the measured geometries. The strain field in the QDs is found to be non-uniform and the shear component plays a significant role in the energy band structure, leading to larger required hydrostatic strain than that in the Ge thin films under biaxial strain to become a direct band gap.