Formation of light-emitting Si nanostructures in SiO2 by pulsed anneals

Intense excimer laser pulses, flash lamp annealing and rapid thermal annealing were used to form Si nanocrystals in thin SiO2 layers implanted with high doses of Si ions. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Laser annealing produced light sources luminescing in the wavelength range of 400-600 nm. They were attributed to the Si clusters formed as a result of the fast segregation of Si atoms from the SiO2 network. There were no indications of nanocrystal formation in the as-implanted layers after 20 ns laser pulses; however, nanocrystals formed when, before the laser annealing, the amorphous Si nanoprecipitates were prepared in the oxide layers. Evaluations show that the crystallization may proceed via melting. A photoluminescence band near 800 nm, typical of Si nanocrystals, was found after 20 ms and 1 s anneals. Calculations revealed that the annealing times in both cases were too short to provide the diffusion-limited crystal growth if one uses the values of stationary Si diffusivity in SiO2. This points toward the existence of a transient rapid growth process at the very beginning of the anneals.