Theoretical Investigation of Doped Silicon Nanomaterials Synthesis and Properties
Type of DegreeMaster's Thesis
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With the advent of the fourth industrial revolution and 5G technology era, demand for semiconducting chips is expected to increase explosively. Most semiconductor devices are produced through hundreds of stages of chemical vapor deposition (CVD) method, but the fundamental explanation of the synthesis is still vague. In order to propose a desirable semiconducting material, the first step is considered to understand the properties of molecules, which can be used as a precursor. However, there are limited studies available that predict the properties of silicon alloy hydrides. For this purpose, we conducted a computational study of 46 hydrogenated SiGe clusters and 59 hydrogenated SiN clusters (SixMyHz, M=Ge or N, 1<X+Y≤6) to predict the structural, thermochemical, and electronic properties. The optimized geometries of the SixMyHz clusters were investigated using quantum chemical calculations and statistical thermodynamics. The SiGe clusters contained 6 to 9 fused Si-Si, Ge-Ge, or Si-Ge bonds, i.e., bonds participating in more than one 3- to 4-membered rings, and diﬀerent degrees of hydrogenation, i.e., the ratio of hydrogen to Si/Ge atoms varied depending on cluster size and degree of multifunctionality. The 59 hydrogenated SiN nanostructures contained 1 to 9 fused Si-Si or Si-N bonds i.e., bonds participating in acyclic structures or in more than one 3- to 6-membered rings, and different degrees of hydrogenation, the numbers of nitrogen atoms contributed to stability of molecules. Our studies have established trends in standard enthalpy of formation, standard entropy, and constant pressure heat capacity as a function of cluster composition and structure. A novel bond additivity correction model for SiGe chemistry was regressed from experimental data on 7 acyclic Si/Ge/SiGe species to improve the accuracy of the standard enthalpy of formation predictions. Internal rotation correction was employed for acyclic SiN molecules. Electronic properties were investigated by analysis of the HOMO–LUMO energy gap to study the effect of elemental composition on the electronic stability of SixMyHz clusters. These properties will be discussed in the context of tailored nanomaterials design and generalized using a machine learning approach for SixGeyHz clusters. The stability of SixNyHz was explained with natural bond orbital (NBO) analysis.