(Invited) Theory of Silicon-Based Light Emitting

Why silicon and germanium are both indirect band gap and most of group III-V and all group II-VI semiconductors are direct band gap is a long standing puzzle. In this talk, I will first present our recently developed unified theory to explain why diamond, Si, Ge, and Al-containing group III-V semiconductors have indirect band gap, and the remaining group III-V and II-VI semiconductors, except GaP, have direct band gap. We excluded Si QDs as a candidate for on-chip lasers. We also discovered that Si/Ge magic sequence superlattices exhibit orders more efficient at emission light than their existing counterpart records and approach more than 10% brightness of real direct gap materials, such as GaAs. We further propose to insert external atoms into interstitial sites of Ge to induce an effective tensile uniaxial strain on Ge toward direct band gap Ge. This scheme is highly compatible with CMOS fabrication process.