Band Gap of Nanometer Thick Si/SiO_2 Quantum Wells:Theory versus Experiment

摘要

In opto-electronics and photonics, the severe disadvantage of an indirect band gap has limited the application of elemental silicon. Amongst a number of diverse approaches to engineering efficient light emission in silicon nanostructures, one system that has received considerable attention has been Si/SiO_2 quantum wells. Engineering such structures has not been easy, because to observe the desired quantum confinement effects, the quantum well thickness has to be less than 5 nm. Nevertheless, such nanometer thick structures have now been produced by a variety of techniques. The SiO_2 layers are amorphous, but the silicon layers can range from amorphous through nanocrystalline to single-crystal form. The fundamental band gap of the quantum wells has been measured primarily by optical techniques and strong confinement effects have been observed. A number of theories based primarily on ab initio approaches have been developed to explain these results with varying degrees of success. In this review, a detailed comparison is made between theoretical and experimental determinations of the band gap in Si/SiO_2 quantum wells.