Characterization of the interface region during the agglomeration of silicon nanocrystals in silicon dioxide

Abstract

Si nanocrystals embedded in thermally grown SiO 2 have been annealed at temperatures between 400 and 900°C in a variety of atmospheres. Positron annihilation spectroscopy has been employed to study changes in the interface regions between nanocrystalline Si ͑nc-Si͒ and SiO 2 with the support of photoluminescence measurements. We find that nitrogen and oxygen are trapped in the voids around nc-Si at low annealing temperatures. High-temperature annealing during the formation of nc-Si causes hydrogen originally residing in the SiO 2 /substrate region to enter the SiO 2 structure. Hydrogen diffuse back to the SiO 2 /substrate region on annealing in vacuum at 400°C because no other impurities block its diffusion channels. At annealing temperatures above 700°C, both nitrogen and oxygen react with nc-Si, resulting in a volume increase. This introduces stress in the SiO 2 matrix, which is relaxed by the shrinkage of its intrinsic open volume. The present data suggest that nitrogen suppresses Si diffusion in SiO 2 , so that the agglomeration of nc-Si is slower during annealing in nitrogen than in oxygen or vacuum.

Probing the formation of silicon nano-crystals (Si-ncs) using variable energy positron annihilation spectroscopy

“…This reduction in Sparameter continues to an annealing time of 100 secs, afterwhich negligible evolution in the shape of the S-E data is observed (data not shown for clarity). Consistent with a previous report [5] we ascribe the 'dip' in the VEPAS data at ~2.5keV with annihilations which take place at the interface of the Sincs and the host SiO 2 .…”

“…Following a second anneal at 500 o C for 600secs in forming gas (containing 5%H 2 ), the trapping of positrons at the interface is significantly suppressed, and hence the 'dip'is removed. This is consistent with the passivation of defects at the Si-nc surface, an effect which has been documented as inducing a large increase in the luminescence yield [5].…”

Optical properties of protocrystalline silicon/amorphous SiC multilayer films

“…Multilayered films composed of alternating thin layers of pc-Si:H and a-SiC were fabricated by HW-PECVD technique in different mixtures of SiH 4 , CH 4 and H 2 which has been detailed elsewhere [13] . It consists of a stainless steel cylinder as the film deposition chamber and an upper quartz tube as the plasma generation source.…”

“…By adjusting the Si spacing, size and barrier height between adjacent silicon in the matrix, the optical and electronic properties can be well tailored [3] . As the potential barrier material, the silicon technological compatible compounds such as SiC, SiO 2 or Si 3 N 4 had been widely adopted [4,5] . For the system of silicon nanolayers or nanoparticles embedded in SiO 2 or Si 3 N 4 compounds, though the band gap widening of the silicon nanoparticles is implemented and efficient optical emission under optical injection is evidenced, it is conceived that they are not suitable for fabricating electrically excited devices due to the wide band gaps of SiO 2 or Si 3 N 4 compared with that of silicon.…”

Depth Profiling of Defects in He Implanted SiO2

“…From '99, works have been carried out to deepen the knowledge on SiO 2 /Si interface [3][4][5][6][7][8] and to study positronium (Ps) formation in SiO 2 thin film on crystalline Si substrate [8,9]. The interface between Si nanocrystals embedded into thermally grown SiO 2 matrix has been also investigated [10,11]. Recently, a new approach based on the interaction of many positrons with the target has been used to study the dynamics of laser-induced paramagnetic centers in a-SiO 2 [12].…”