**Abstract**

In this chapter, an approach to enhance the radiative recombination of the Ge film grown on the Si substrate is presented. The Ge band gap structure could be modified by applying a tensile strain and high n-doping in the Ge epilayers. It thus becomes a direct band gap material with high photoluminescence efficiency which is compatible with mainstream silicon technology. The interdiffusion effect between Ge film and Si substrate is also mentioned in this section. We proposed a new method to suppress the Si/Ge interdiffusion to reduce the effect of Si atoms on the optical property of Ge film due to Si presence.

**Keywords:** Ge, Si technology, tensile strain, n-doping, photoluminescence, interdiffusion
