Silicon is the dominant semiconductor in the microelectronics industry. Over the last 40 years, it has gone through the most amazing technological transformation and growth, which leads to the extraordinary high levels of integrated circuit complexities. The desire to integrate optical and microelectronic functions on the same chip to realize optoelectronic integrated circuits (OEICs) based on silicon ideally requires the active photonic components to be integrated with the silicon-based platform. However, the indirect bandgap characteristic of silicon prohibits efficient radiative recombination of electrons and holes to result in coherent optical emission. Hence, various solutions have been tried to overcome this physical challenge. In 1994, the first quantum cascade laser (QCL), which is based on intersubband transition, was successfully demonstrated by scientists in Bell Labs. The realization of the QCL provides a promising technique to produce Si-based laser, because the transition mechanism for the QCL can avoid the indirect band property of Si and SiGe.

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