Abstract
Silicon nanocrystals in silicon nitride matrix are fabricated by thermal annealing of SiNx/Si3N4 multilayered thin films, and characterized by transmission electron microscopy, X-ray reflectivity and diffraction analysis, photoluminescence and X-ray photoelectron spectroscopy techniques. Si nanocrystals with a mean size of about 4 nm are obtained, and their properties are studied as a function of SiNx layer thickness (1.6–2 nm) and annealing temperature (900–1250 °C). The effect of coalescence of adjacent nanocrystals throughout the Si3N4 barrier layers is observed, which results in formation of distinct ellipsoidal-shaped nanocrystals. Complete intermixing of multilayered film accompanied by an increase of nanocrystal mean size for annealing temperature as high as 1250 °C is shown. Near-IR photoluminescence with the peak at around 1.3–1.4 eV is detected and associated with quantum confined excitons in Si nanocrystals: Photoluminescence maximum is red shifted upon an increase of nanocrystal mean size, while the measured decay time is of order of microsecond. The position of photoluminescence peak as compared to the one for Si nanocrystals in SiO2 matrix is discussed.
Highlights
Following the early studies on porous silicon photoluminescence (PL) [1], optical properties of silicon nanocrystals (Si NCs) in solid matrices have been a focus of thorough research
In the present study we demonstrate the formation of silicon nitride-embedded Si NCs, which emit in near-IR region with a characteristic PL lifetime in a microsecond timescale
Silicon nanocrystals can be seen as sets of lattice fringes in HRTEM images for both samples
Summary
Following the early studies on porous silicon photoluminescence (PL) [1], optical properties of silicon nanocrystals (Si NCs) in solid matrices have been a focus of thorough research. Bright luminescence at room temperature from Si NCs, not observable for bulk silicon, appears very intriguing from the point of view of optoelectronic applications [2]. Different host matrices for Si NCs such as silicon oxide, nitride, and carbide are examined [3,4,5], while the most intense luminescence is typically observed for Si NCs in SiO2 matrix due to the smallest concentration of PL quenching centers [6]. At the same time, enhanced electron transport properties of Si NCs array in matrices with lower band gap (silicon nitride or carbide) are preferable for the photovoltaic applications [4].
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