Annealing effects in light-emitting Si nanostructures formed in SiO 2 by ion implantation and transient preheating

Abstract

A dose of 1.6 × 10 17 cm −2 Si + ions was implanted in 500-nm-thick SiO 2 layers with subsequent transient annealing at different temperatures. After the highest temperatures light-emitting Si nanoclusters were found that were formed in SiO 2. Then all the layers were subjected to isochronal (30 min) furnace anneals and their properties were controlled by room temperature photoluminescence (PL) and Raman spectroscopy. The PL intensity from Si nanocrystal-containing layers progressively decreased with an increase in the anneal temperature ( T a) up to 800–900°C, but rapidly arose again in the T a range of 1000–1150°C. Raman scattering has shown that Si nanocrystals vanish at T a ∼ 800°C and that the amorphous silicon signal reappears. When the initial transient annealing failed to form Si nanocrystals, the furnace heat treatment at T a < 700°C gave rise in PL intensity followed by its drop at T a ∼ 800–900°C and a strong increase at T a ∼ 1000–1150°C. The disappearance of Si nanocrystals and PL is considered to result from low stability of the smallest crystallites quenched in SiO 2 by transient processing. When Si nanocrystals were not induced by transient preheating, the increase in T a supposedly led to percolation-like formation of Si inclusions, their transformation to amorphous Si phase nanoprecipitates and, finally, to Si nanocrystals. For all the samples the formation of nanocrystals at T a = 1000–1150°C was provided by the increase in their stability due to diffusion-limited grain growth. The results obtained are considered to support the idea of quantum-confined origin of PL.