Light sources for photonic circuitry based on Si

Summary form only given. We report the possibility of breaking the indirect-bandgap limitation to efficiently generate light from Si. We theoretically and experimentally discovered that carrier localization could enhance radiative recombination corresponding to bandgap energy of Si for orders of magnitudes. Nearly lasing actions corresponding to Si bandgap energy were even observed with the enhanced radiative recombination. Because of the indirect-bandgap nature of Si, the probability of electron-hole recombination is very low without the involvement of phonons. However, phonon involvement causes the process to be like simultaneous collision of three particles (electron, hole, and phonon), so the probability is also very low. If an electron and a hole already form an exciton, the process will be like a two-particle collision, exciton vs. phonon. The probability then greatly increases. Based on such a concept, we derive a formula for the emission from Si with phonon and exciton involvement. To have the localization of electrons and holes in the same region, we use nanoparticles in the oxide layer of the conventional metal-oxide-semiconductor (MOS) structures. The nanoparticles cause the thickness of the oxide layer to be nonuniform and lead to the following two effects. First, as the MOS structure is forward biased, the band bending of Si toward the thin oxide is more severe than the thick oxide, resulting in three-dimensional potential wells for carrier confinement. Second, in the region with the thin oxide, more carriers tunnel to Si through the thin oxide layer than through the thick oxide layer. As a result, electrons and holes have the similar spatial confinement near the Si/SiO/sub 2/ interface. The above mechanisms significantly enhance the electroluminescence.