EPR and emission study of silicon suboxide nanopillars
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EPR and emission study of silicon suboxide nanopillars V. Bratus’1, I. Indutnyi1, P. Shepeliavyi1, T. Torchynska2 1 V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Kyiv 03680, Ukraine 2 ESFM-Instituto Politécnico Nacional, México D.F. 07738, Mexico ABSTRACT The results of correlated electron paramagnetic resonance (EPR) and photoluminescence (PL) study of obliquely deposited porous SiOx films after step-by-step 15 min annealing within 105 min in vacuum at 950OC are presented. The low intensity symmetrical and featureless EPR line with a g-value g=2.0044 and a linewidth of 0.77 mT has been detected in as-sputtered films and attributed to dangling bonds (DB) of silicon atoms in amorphous SiOx domains with x=0.8. Successive annealing results in decreasing this line and the appearance of an intense EPR line with g=2.0025, linewidth of 0.11 mT and a hyperfine doublet with 1.6 mT splitting. According to the parameters this spectrum has been attributed to the EX center, a hole delocalized over four non-bridging oxygen atoms grouped around a Si vacancy in SiO2. The impact of chemical treatment before annealing and duration of anneals on the defect system, and a correlation of the PL intensity with decreasing of the DB EPR signal are discussed. INTRODUCTION Owing to intense emission at room temperature, the structures consisting of Si nanocrystallites (nc-Si) embedded in silicon oxide SiO2 or suboxide SiOx (1 x 2) show considerable promise for optoelectronic and photonic applications [1-4]. To the fabrication of these structures several techniques like the plasma-enhanced deposition, ion implantation, laser ablation, magnetron sputtering, evaporation in vacuum etc. are used. All these methods allow to fabricate SiOx films with required x. Subsequent thermally induced decomposition of a suboxide and the formation of Si nanoparticles in SiOx matrix are governed by a relation ySiOx o xSiOy + (y – x)Si, where y > x, and SiOy will be evidently consisted of SiO2 and SiOx. The temperature of annealing determines the structure of inclusions: annealing below 10000C favors a coalescence of Si atoms into amorphous clusters, at higher temperature silicon nanocrystals are formed [1-5]. Thermally induced formation of nc-Si results in considerable dispersion of nanocrystallite sizes, that in turn decreases the intensity of photoluminescence (PL) and increases the half-width of PL band. Recently it has been shown that thermal evaporation of silicon monoxide on a substrate obliquely oriented to direction of evaporated substance stream and subsequent annealing in vacuum lead to the formation of porous SiOx films with columnar structure and ncSi inclusions (see [6, 7] and references there). Depending on the angle of evaporation and other technological parameters the diameter of deposited columns varies from 10 to 100 nm. Limited volume of SiOx columns results in smaller dimensions of nc-Si than ones in normally deposited dense films with the same x. Relatively high porosity of obliquely deposited films makes it possible to
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