Visible light emission from Si/SiO₂ multilayers in planar microcavities

Bright quantum-confined photoluminescence (PL) at visible wavelengths can be obtained from ultrathin-layer Si/SiO₂ superlattices. We demonstrate that with the use of an optical resonator the PL peak wavelength and bandwidth can be modified selectively. The strong enhancement and subsequent decrease in the PL intensity in these superlattices with decreasing Si layer thickness has been investigated theoretically. Calculations of the band structure of a Si quantum well separated by crystalline SiO₂ barriers using a tight-binding method reveal that the confined conduction and valence bands along the [0 0 1] symmetry direction are essentially dispersionless, are strongly nested, and have a direct band-gap character. The enhanced band-edge density of states and the stronger electron-hole interaction across the low-dielectric barriers lead to a competition between several length scales and produce the PL intensity variation with well width observed.