document: Ever since the identification of the paramagnetic E′ centre in SiO2 as an unpaired electron localised in an sp3 hybrid orbital of an Si atom backbonded to three oxygen atoms, a number of attempts has been made at explaining the optical and electronic properties of SiO2 in the presence of E′ centres. The irradiation or hole injection induces trapping of positive charge in thin layers of a-SiO2 grown on silicon surfaces by thermal oxidation. This effect has been correlated with paramagnetic E′ centre signals and led to the initial assignment of the neutral oxygen vacancy as the major hole trap in a-SiO2 [1–3]. In this model, originally proposed for E′ centres in α-quartz, upon trapping a hole, one Si atom from the two Si atoms constituting the vacancy remains neutral and hosts the localised unpaired electron while its counterpart becomes positively charged. Although this model has initially been accepted widely for its simplicity, it fails to account for a number of observations, such as the positive charge trapping without generation of E′ centres [4], the formation of high density of E′ centres without the corresponding density of positive charge [5], and the absence of correlation between the decrease of the E′ centre density and the density of positive charge upon post-irradiation electron injection in SiO2 [6].
doc_bio_tags: O O O O O O O B I O B O O B I O O O B I I O O B I O O O B I O O O O O O O O O O O O O O O B O O O O B I O B O B I O O O B I O O O O O O O B I O B I O O O O O O O B I O O O O O O O O O B I I O O B I I O O O O O O O O O B I O O O O O O O B I O O O B I O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O B I O O O O O B I O O O O O O O O O O O B I O O O O O B I O O O O O B O
extractive_keyphrases: e′ centre e′ centres hole injection irradiation localised unpaired electron major hole trap neutral oxygen vacancy oxygen atoms positive charge si atom si atoms silicon surfaces sio2 sp3 hybrid orbital thermal oxidation unpaired electron
abstractive_keyphrases: a-sio2 e′ centres in α-quartz explaining the optical and electronic properties of sio2 in the presence of e′ centres high density of e′ centres identification of the paramagnetic e′ centre in sio2 paramagnetic e′ centre paramagnetic e′ centre signals positive charge trapping post-irradiation electron injection trapping of positive charge in thin layers of a-sio2 grown on silicon surfaces