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

Abstract

An extensive electron spin resonance (ESR) analysis has been carried out on structures comprised of Si nanoparticles (∼2 nm across) embedded in a regular pattern in an amorphous SiO2 matrix, fabricated by the SiO/ SiO2 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 (DB) 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 Pb (0) and Pb1 defects, the archetypal intrinsic defects of the Si/ SiO2 interface, with no evidence for a D line (Si DBs in disordered Si). This indicates a full crystalline system of randomly oriented Si nanocrystals (NCs). The Pb (0) / Pb1 defect system, pertaining to the NC-Si/ SiO2 interfaces, is found to be both qualitatively and quantitatively much alike that of standard (high-quality) thermal Si/ SiO2. The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of Pb -type defects in standard microscopic Si/ SiO2, the data would comply with Si nanocrystallites, in average, predominantly bordered by (111) and (100) facets, perhaps with morphology, schematically, of [100] truncated (111) octahedrons. Based on independent NC particles counting, there appears a Pb -type center at ∼71% 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 (PL). Upon additional optical irradiation, two more defects appear, i.e., the SiO2 -associated Eγ′ and EX centers, where the observed density of the former, taken as criterion, indicates the SiO2 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/ SiO2 interfaces and the embedding SiO2, alike that of standard thermal Si/ SiO2. In combination with H passivation/depassivation treatments, the degrading impact of the optical excitation (∼360 nm) itself used during PL measurements has been studied, revealing weak ESR reactivation of Pb (0), Pb1, and Eγ′ defects. © 2008 American Institute of Physics.