Departmental Seminar

Final PhD seminar-Characterizing the structural properties of the NPs formed by ion implantation in different dielectric matrices

Ms Sahar Mirzaei

In this study, we characterize the structural properties of the nanoparticles (NPs) formed in different dielectric matrices namely: Si3N4 and SiOxNy by ion implantation followed by thermal annealing. Two different types of Si3N4 matrix, PECVD and LPCVD, were examined. Also, SiOxNy with different stoichiometries, close to pure SiO2 and Si3N4,were examined. This study focuses on understanding the role of the host matrix on the structural properties and size evolution of embedded NPs. TEM, Raman and RBS measurements were performed to study the size, vibrational and compositional properties of NPs. Furthermore, the structure and local environment of NPs were investigated using x-ray absorption spectroscopy.

Semiconductor nanoparticles (NPs) embedded in a dielectric matrix are of technological interest because of their ability to emit light and store charge.  Ge NPs have been investigated for novel optoelectronic and non-volatile memory devices. Intensive research has focused on the structural and vibrational properties of Ge NPs embedded in SiO2. These properties are typically size dependent and highly reliant on the host matrix. An alternative dielectric matrix commonly used in the fabrication of micro-electronic and optoelectronic devices is Si3N4. Chemical vapor deposition (CVD), in particular low pressure (LPCVD) and plasma enhanced (PECVD) techniques, are the main methods for depositing an amorphous Si3N4 film. Many studies have been performed on the properties of Si NPs embedded in LPCVD and PECVD Si3N4. However, few studies have focused on the structural properties of Ge NPs embedded in Si3N4 by ion implantation. Therefore, a better understanding of the matrix role on the properties of the NPs could lead to the fabrication of more efficient optoelectronic devices. Here, we discuss the various structural properties and phase transformation of both the embedded NPs and the host matrix.

Ge ions were implanted into amorphous PECVD and LPCVD Si3N4 and SiOxNy thin layers. The implantations were performed at 400 °C. Samples were subsequently annealed at different temperatures (700, 900, and 1100 °C) for 1 hour under a N2 atmosphere.

Different types and sizes of NPs were obtained depending on the host matrix. The EXAFS study confirms the size-dependent properties of NPs, which vary significantly depending on the host matrices. The most striking difference between LPCVD and PECVD was the formation of both SiGe and Ge NPs. NP formation in SiOxNy matrices were significantly different from pure SiO2 or Si3N4, an effect that is attributed to the role on N on Ge diffusivity.  Finally, we report an impurity induced phase transition (crystallization) for Si3N4 matrices (LPCVD and PECVD) during annealing at 1100oC. We investigate and isolate different mechanisms involved with this low temperature crystallization process.

Our research has made inroads into understanding the role of the matrix and thermal annealing on properties of Ge NPs.

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