The photoluminescence (PL) from silicon nanocrystals (Si-ncs) embedded in an amorphous silicon nitride matrix was examined both experimentally and through theoretical simulations. The film was prepared using low-pressure chemical vapor deposition with subsequent high-temperature annealing. The experimental parameters required for the PL modeling were determined using Raman spectroscopy. A novel method to estimate the nitrogen content, which allowed the determination of both the Urbach energy and the Tauc gap, was reported. The luminescence could be attributed to different origins, namely, Si-ncs, amorphous silicon nanodots, nitrogen and silicon defects, and amorphous matrix. A comparison between the experimental results and the modeling indicated that the existing models are unable to satisfactorily explain the observed PL.
Silicon nanocrystals have been produced by thermal annealing of SiNx thin film obtained by low pressure chemical vapor deposition using a mixture between disilane and ammonia. Morphological, structural, and photoluminescence properties of the thin film were investigated using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and photoluminescence spectroscopy. The results revealed a high crystallinity of film with a crystalline volume fraction exceeded 70 %, and a dominance of silicon nanocrystallites having the sizes within the range 2.5-5 nm and density ~1.98.10 12 /cm 2. The PL peaks consist of nanocrystalline silicon and amorphous silicon. The luminescence from the silicon nanocrystals was dominant.
In this work, we investigate the formation of silicon nanocrystals in annealed low pressure chemical vapor deposition in situ nitrogen doped silicon thin films (SiN x ) obtained at low temperature (465 • C) by using a mixture of disilane (Si 2 H 6 ) and ammonia (NH 3 ). Results show that nitrogen content in films plays an important role in defining the obtained films morphology in terms of crystallites sizes and their distribution. Indeed, according to the nitrogen content introduced in films, the crystalline state of films varies from a submicron crystalline structure to a nanocrystalline structure. An average silicon nanocrystalline size of 10 nm was obtained for film with x = 0.07 nitrogen content, annealed under a temperature of 850• C during 2 h.
We propose through this work a correlation method leading to a determination of a semi-empirical relationship between optical and electrical properties in terms of refractive index and dark conductivity of doped silicon nanocrystals based on experimental data published in literature. First, an analytical model relating the conductivity and bandgap of doped silicon nanocrystals was derived. Using an empirical expression relating the refractive index to the bandgap energy, we correlated the electrical and optical parameters of N-type nanocrystalline silicon with a semi-empirical expression. The semi-empirical relationship was found to account correctly for the experimental results and yield a reasonably good agreement in an interval of the bandgap energy variation of N-type silicon nanocrystal films. The values of the fitting parameters were calculated for the N-type silicon nanocrystal films having their bandgap energy between 1. 7 eV and 2.2 eV.
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