Visible iuminescence from SiN-based thin films and its applications

Abstract

We investigate visible photoluminescence and applications of amorphous $Tb^{3+}$ doped silicon oxynitride deposited by plasma enhanced chemical vapor deposition (PECVD) in inductively coupled plasma (ICP) system. The films show broad luminescence due to band-tail states. After Tb doping into the films, we observed strong green luminescence from $Tb^{3+}$ intra-4f transitions superimposed on the background luminescence peak from oxynitride. However, there’s no correlation between them as the composition and the annealing conditions were varied. Photoluminescence excitation spectroscopy shows a strong increase in the $Tb^{3+}$ luminescence intensity as the pump energy is increased above 3.5 eV while the host matrix luminescence decreases. Taken together, the results suggest that there is little energy transfer between band-tail states of silicon oxynitride host matrix and $Tb^{3+}$, and that efficient excitation of $Tb^{3+}$ by carriers requires excitation of carriers into the extended, rare-earth related states in silicon oxynitride. As an application, we investigate using self-luminescent whispering gallery mode (WGM) microdisk of $Tb^{3+}$ doped silicon oxynitride for biosensor application. ‘Self-luminescent microdisk’means that WGM of microdisk can be excited by luminescence from the active material itself by vertical and broadband pumping without any coupling setup such as waveguide or tapered fiber coupling, that can induce some difficulties and complexities. Using FDTD (Finite-Difference Time-Domain) simulation method we evaluated theoretical value of Q factor and sensor functionality, such as Sensitivity and detection limit, of the proposed microdisk. Based on the simulation results, we fabricated 7, 10, and 12 μm diameter microdisks with thickness of ~120 nm using E-beam lithography and dry/wet etching processes. We measured WGMs of the fabricated microdisks and obtained Q factors of 400~900. Finally, the bio-sensing capabilities of the microdisks wer...