Formation of light-emitting Si nanostructures inSiO2 by pulsed anneals

Abstract

Intense excimer laser pulses, flash lamp annealing and rapidthermal annealing were used to form Si nanocrystals in thinSiO2 layers implanted with high doses of Si ions. The pulse durations were20 ns, 20 ms and 1 s, respectively. Laser annealing produced light sourcesluminescing in the wavelength range of 400–600 nm. They were attributed to theSi clusters formed as a result of the fast segregation of Si atoms from theSiO2 network. There were no indications of nanocrystal formation in the as-implanted layersafter 20 ns laser pulses; however, nanocrystals formed when, before the laser annealing, theamorphous Si nanoprecipitates were prepared in the oxide layers. Evaluations show thatthe crystallization may proceed via melting. A photoluminescence band near 800 nm,typical of Si nanocrystals, was found after 20 ms and 1 s anneals. Calculationsrevealed that the annealing times in both cases were too short to provide thediffusion-limited crystal growth if one uses the values of stationary Si diffusivity inSiO2. This points toward the existence of a transient rapid growth process at the very beginningof the anneals.