"Identified the suitable chalcogenide materials for integrating with silicon and silicon compounds. Three target glasses namely Gallium Lanthanum Sulfide (GLS), Erbium-doped Gallium Lanthanum Sulfide (GLS-Er) and Erbium-doped Tellurium Zinc Sodium oxide glass (TZNEr)are fabricated and the laser ablation of these materials in a vacuum chamber under controlled process gas environment and implantation into silicon/silicon compound are tried. An effort has been made to optimise the process by varying the temperature in the range 400 C-660 C. Newly formed alloys are characterised using Raman spectroscopy, High-resolution Transmission electron microscopy (HR-TEM), TEM- EDX, X-ray diffraction (XRD) and Photoluminescence emission spectroscopy techniques. In-situ high-temperature XRD and TEM studies on a silicon compound (silica) platform are also evaluated to assess the high-temperature (300 C- 1000 C) performance of erbium-doped silicate materials. It has been observed that erbium doped silicates could withstand up to 600 C and beyond that temperature, the phase separation of the compound materials occurs. This ensures that such materials can be easily integrated with a CMOS back end of line process where the highest temperature of operation is around 400 C. The engineered material subsequently displays superior spectroscopic properties of Er3+ ions in the silicon/silicate matrix at high concentrations.
An innovative method to realise selective doping for an optical waveguide formation using shadow masking technique have tried and the direct transfer of straight channel patterns are accomplished. Also, direct etching of the silica on silicon substrates to formulate the waveguides are also achieved. Compared to the shadow masking technique, the direct etching gives precise waveguide dimensions while it is an expensive manufacturing technique. Shadow masking is low cost and also provide the versatility of selective doping.
Once an optimised patterning method and precise dimensions are obtained, this method can be further extended to realise more complicated optical nanostructures and sensor heads on silicon and silicon compounds.
Overall the preliminary results obtained under MIRIPSHE are encouraging to continue this research to develop CMOS-mid-IR photonic circuits for sensing and other applications. More time and resources are really needed to drive this research and realise the full potential of the new material engineering process and device developmental activities.
The in-situ high-temperature structural studies were published in Elsevier journal Scripta Materialia (Chandrappan, J.; Khetan,V;Murray, M.;Ward,M; Jose, G. Devitrification of ultrafast laser plasma produced glass layer. Scripta Materialia 2017,131,37-41) and a second journal paper manuscript ""Direct integration of GaLaS on silicon "" is under preparation.
The fellow has submitted an EPSRC early career fellowship application based on the initial results to advance this research and extend the integration technique to other material families including group -IV and compound semiconductors such as Ge and Sn. In this research, the fellow has proposed an international research collaboration with the University of Southampton, UK; Hungarian Academy of Sciences, Hungary; University of Stuttgart, Germany. In addition, Xterra communications, a leader in optical component and underwater communication sector, is also partnered in this research.
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