The Ge/Si heterojunction MOS LED can emit ∼2 μm light due to the radiative recombination at type II heterojunction. The fully depleted 800 nm germanium on insulator (GOI) can increase the responsivity and the speed of the MOS detector due to the large absorption of Ge and the electrical field in the active layer, respectively. Moreover, the external strain can tune the emission energy (∼11 meV) by modifying the band structure. The responsivity of GOI MOS detector is also improved by ∼10% using the external strain. Both heterojunction and strain (internal or external) can enhance the performance of Si-based optoelectronics.