Engineering Silicon Surface Stresses to Enhance Band-gap Emission via Sol-gel Ceramic Coatings

  • Ali Dhaif Allah Abdullah

Student thesis: Master's Thesis

Abstract

In this thesis, Er-doped silica are synthesized and deposited on crystalline Si with the objective of enhancing light emission from Si at the bandgap. The silica films are investigated and characterized, and the process parameters are adjusted to improve film uniformity and emission. There are two major procedures in conducting this research work: Firstly, we looked at how different parameters such as doping concentration, heat treatment and acid type could affect the sol viscosity, where thin layers are deposited using different acid catalysts of Erbium-doped silica onto silicon substrates. Secondly, Er-doped silica with various doping concentrations were deposited onto silicon substrates, annealed at multiple temperatures ranging from (500 oC-900 oC), using acid-base catalyst. The first methodology is showing a range of viscosity tests utilizing various acids catalysts, doping concentration, and heat treatment to get deep understanding about the chemistry of the synthesized films seeking high uniformity. Under the same experimental conditions, it is found that the acid catalyst utilized has a significant impact on the thickness of the films formed. The major aspect influencing this behavior is the viscosity of the sols and the gelation period, which vary greatly depending on the acid utilized. Furthermore, the presence of erbium in the silica matrix alters the refractive index, which has a direct influence on film thickness. In comparison to weak acids, strong acids form films with the highest resistance to shrinkage during annealing. The photoluminescence of silicon near band-edge (1162 nm) and (~1535) nm bands from Er3+ ions in the silica film was investigated in the second procedure at various Erbium-doped silica deposited onto silicon substrates, annealed at multiple temperatures ranging from (500 oC-900 oC) with incremental increases of 100 oC, using acid-base catalyst. Thinner films were observed to induce the most emission near the Si band-edge, where inhomogeneous stresses caused by the film on the Si substrate could be the greatest. The high refractive index of Er-doped films has a noticeable influence on Si light emission, particularly at low doping concentrations when the probability of absorption increases, resulting in a decrease in light emission efficiency. High-temperature annealed samples show better emission within the 4f erbium transition band (1532 – 1536 nm). The photoluminescence results (taken at 800 oC and 900 oC for 3% and 6% Er doping) largely demonstrated linear relationships between multiple pumping power and area under the curves at both the Silicon band-edge and the Erbium 4f transition band. It can be observed that emissions from silicon are unaffected by doped erbium while increasing pumping powers.
Date of AwardMay 2022
Original languageAmerican English

Keywords

  • Silicon Band-gap emission
  • sol-gel chemistry
  • ceramic coating
  • Photo luminescence.

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