A novel approach to thin film deposition and rare-earth incorporation for silicon integrated photonics

Abstract

In this thesis, group IV material oxides for silicon photonics applications were deposited using novel deposition techniques. Erbium and terbium doped silicon oxide thin films were deposited through a novel hybrid radio frequency (RF) magnetron sputtering source in an electron cyclotron resonance (ECR)-plasma enhanced chemical vapour deposition (PECVD) reactor chamber. This approach contrasts with traditional doping methods which use metal-organic precursors to introduce rare-earth dopant species into the host matrix. The effects of sputtering power applied to the rare-earth target and system plasma pressure on the thin film properties were investigated. It was found that the sputtering power strongly influences the rare-earth incorporation, and a wide range of control over the doping level can be achieved. The effect of sputtering power on the refractive index, stoichiometry, and film density were also investigated. Doped thin films deposited with this technique showed low as-deposited hydrogen concentrations. In the case of terbium doped silicon oxide (SiOx), photoluminescence (PL) studies were conducted finding bright emission due to 5D4 → 7F5 transitions visible with the naked eye in films annealed above 1150 °C. Further investigation found that silicon nanostructures formed at the high annealing temperatures and were likely sensitizing the Tb3+ ions. These results demonstrate that hybrid sputtering in ECR-PECVD can be an effective tool for integrating optically active rare-earth dopants into silicon-based thin films. Using alternating current (AC) plasma assisted reactive magnetron sputtering (PARMS), low optical loss germanium oxide (GeO2) thin films were also produced. The films were fabricated at low temperature and high deposition rates of 6–38 nm/min on silicon and thermally oxidized silicon substrates. Prism coupling measurements demonstrated losses of 0.1 dB/cm at wavelengths ranging from 638 to 980 nm attributed to good uniformity and low surface roughness demonstrated through atomic force microscopy (AFM) measurements. The thin films materials developed here are highly promising for their applications in silicon photonics devices, including light sources and amplifiers.