Visible luminescence from Si/SiO2 quantum wells and dots: confinement and localization of excitons

We have studied luminescence properties of crystalline silicon (c-Si) and amorphous silicon (a-Si)-based quantum wells and quantum dots. The PL peak energies of excitons of c-Si and a-Si quantum structures are blueshifted from those of bulk c-Si and a-Si. In c-Si/SiO2 and a-Si/SiO2 quantum dots, excitons are localized at the interface between the Si interior and the surface SiO2 layer. In c-Si/SiO2 quantum wells, TO-phonon-related fine structures are observed in resonantly excited luminescence spectra. In two-dimensional (2D) wells, 2D excitons and localized excitons at the c-Si/SiO2 interface contribute to a visible luminescence at low temperatures. The confinement and localization of excitons in Si quantum structures is discussed.