Fabrication and Characterization of Europium Doped Silicon-based Thin Films

Abstract

This Ph.D. research presents a comprehensive investigation of europium-doped silicon-based thin films for the development of CMOS-compatible light-emitting materials. Europium (Eu) is an attractive rare-earth element because it can emit in the blue (in some cases, green) and red spectral regions. This blue emission from the Eu2+ ion and red emission from Eu³⁺ make Eu very interesting to study for different light-emitting applications, including photonics and solid-state lighting. To understand how the host matrix governs Eu incorporation, charge state, and optical activation, three material systems, silicon oxynitride (SiOₓNy), silicon nitride (SiN), and silicon (oxy)carbonitride (Si(O)CN), were systematically studied. All films were fabricated using a custom-made electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) system integrated with in-situ magnetron sputtering, enabling precise control over matrix composition and rare-earth doping. With a wide variety of host matrices, detailed structural, compositional, and optical characterization was performed using advanced characterization techniques including Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), variable angle spectroscopic ellipsometry (VASE), X-ray diffraction (XRD), and room-temperature photoluminescence (PL). Eu-doped SiOₓNy films revealed tunable luminescent emission, governed by varying the O/N ratio in the host matrix and a transition from Eu²⁺ blue to Eu³⁺ red emission was observed. In Eu-doped SiN, we studied the optical and mechanical properties of the luminescent thin film and investigated the effects of sputtering power and argon flow on the luminescent properties. This study demonstrates that thin films properties are mostly governed by the sputtering power and that Ar flow to the deposition chamber has minimal impact. Also, the luminescence intensity strongly depends on sputtering power, governed by dopant concentration. We found that high-temperature annealing activated Eu³⁺ emission without forming silicon nanocrystals, instead producing Eu-containing phases within the amorphous nitride matrix. Eu-doped Si(O)CN films were investigated as SiCN provides wide optical tunability and high thermal, chemical and mechanical stability. These Eu-doped Si(O)CN films exhibited a unique response compared to the other host matrices studied in this thesis. The as-deposited Si(O)CN films produced a broad band emission however, after high-temperature annealing, the broad emission band was completely suppressed, and sharp Eu³⁺ emission lines in the red were observed. According to XRD analysis, the film annealed at 800 °C remained fully amorphous, while Eu-containing crystalline phases began to appear in samples annealed at higher temperatures (from 1000 °C to 1200 °C) Collectively, these results provide an in-depth understanding of Eu-doped thin films, and these findings are very promising for their applications in silicon-based lighting applications.