Inherent paramagnetic defects in layered Si/SiO2 superstructures with Si nanocrystals

Abstract

An extensive electron spin resonance ͑ESR͒ analysis has been carried out on structures comprised of Si nanoparticles ͑ϳ2 nm across͒ embedded in a regular pattern in an amorphous SiO 2 matrix, fabricated by the SiO/ SiO 2 superlattice approach, with the intent to reveal and quantify occurring paramagnetic defects. The as-grown state is found to exhibit only a Si dangling bond ͑DB͒ signal, which through combination of first and second harmonic X-, K-, and Q-band observations in combination with computer spectra simulation, could be conclusively disentangled as solely comprised of overlapping powder pattern spectra of P b͑0͒ and P b1 defects, the archetypal intrinsic defects of the Si/ SiO 2 interface, with no evidence for a D line ͑Si DBs in disordered Si͒. This indicates a full crystalline system of randomly oriented Si nanocrystals ͑NCs͒. The P b͑0͒ / P b1 defect system, pertaining to the NC-Si/ SiO 2 interfaces, is found to be both qualitatively and quantitatively much alike that of standard ͑high-quality͒ thermal Si/ SiO 2 . The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of P b -type defects in standard microscopic Si/ SiO 2 , the data would comply with Si nanocrystallites, in average, predominantly bordered by ͑111͒ and ͑100͒ facets, perhaps with morphology, schematically, of ͓100͔ truncated ͑111͒ octahedrons. Based on independent NC particles counting, there appears a P b -type center at ϳ71% of the Si NCs indicating the latter to be comprised of two subsystems-with or without an incorporated strain relaxing interface defect-which in that case will exhibit drastically different defect-sensitive properties, such as, e.g., photoluminescence ͑PL͒. Upon additional optical irradiation, two more defects appear, i.e., the SiO 2 -associated E ␥ Ј and EX centers, where the observed density of the former, taken as criterion, indicates the SiO 2 matrix to be of standard thermal oxide quality. Thus, the properties of the revealed crucial intrinsic point defects bear out a high quality of both the NC-Si/ SiO 2 interfaces and the embedding SiO 2 , alike that of standard thermal Si/ SiO 2 . In combination with H passivation/depassivation treatments, the degrading impact of the optical excitation ͑ϳ360 nm͒ itself used during PL measurements has been studied, revealing weak ESR reactivation of P b͑0͒ , P b1 , and E ␥ Ј defects.

Defect engineering of Si nanocrystal interfaces

“…The blue shift for the N 2 annealed samples is often interpreted in literature as a decrease of the size by Si consumption or as influence of the nitrogen hindering the SiO x phase separation and leading to smaller sizes 15. However, as we demonstrated in 13, our findings contradict such an interpretation. We were able to estimate the N incorporation to be in the order of only one monolayer or even less at the interface of the Si NCs.…”

“…The first one is using the evaporation of SiO powder in a vacuum chamber as described in Ref. 13 resulting in suboxide (SiO ∼1.1 ). The prepared SL are completely free of hydrogen in case of the evaporation process (base pressure of 1 × 10 −6 mbar).…”

Annealing induced defects in SiC, SiOx single layers, and SiC/SiOx hetero‐superlattices

“…It is worthwhile to stress that we do not exclude the presence of other types of paramagnetic defect states reported in the literature 14–17, which might exist in the SiC and SiO x volumes as well as at the Si/SiO x and SiC/SiO x interfaces for our samples under investigation. We assume that in the case of hydrogenated SiC and SiO x materials containing a high amount of hydrogen, the dangling bond density due to hydrogen out‐diffusion during annealing is likely to dominate the spin density.…”

Thermal annealing effects on photoluminescence properties of carbon-doped silicon-rich oxide thin films implanted with erbium

“…32,33 It is suggested that the conflicting effects of the radiative centers and the nonradiative defects result in a moderate increase (a factor $4) in the matrix visible PL intensity, as observed following the postdeposition annealing. Further, the rise in the population of nanoclusters is accompanied with an increase in the density of nonradiative defect centers, such as the asymmetrically relaxed oxygen vacancy or the E 0 center (O 3 :Si), and the Si dangling bond or the P b center (Si 3 :Si).…”