Optical absorption and photoluminescence of self-assembled silicon quantum dots

Hemispherical silicon quantum dots with an average height of 6.3, 3.3 or 1-2 nm covered with an ultrathin SiO2 layer have been spontaneously formed on SiO2/Si(100) and quartz substrates by the thermal decomposition of pure silane at low pressure. It is found that the optical absorption edge determined from photothermal deflection spectroscopy exhibits blue shifts from 1.9 to 2.5 eV when the average dot size was decreased from 6.3 to 1-2 nm and correspondingly, the luminescence peak energy increases from 1.2 to 1.4 eV at room temperature. The large Stokes shift suggests that the localized, radiative recombination centers existing presumably in the SiO2/Si dot interface are responsible for the efficient; room-temperature luminescence from the silicon quantum dots.