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Abstract
The tandem photovoltaic structure using all Si quantum dots (QD) was proposed and investigated at UNSW. The material with Si quantum dots (QD) embedded in silicate matrices has potential for tunable optical absorption through band-gap engineering.
Si QD materials are generally fabricated by RF-Sputtering followed by high temperature solid-phase crystallization. According to the results of former researchers [9,44], the poor film quality of sputtered films might be responsible for the low conductivity and lifetime of the films hindering the possibility to improve the short circuit current in a Si QD p-i-n structure.
This thesis focuses on ultra thin film silicon rich oxide (SRO) deposition using Microwave-Plasma Enhanced Chemical Vapor Deposition (MW-PECVD), which has the potential of giving higher film quality for intrinsic Hydrogen involvement and less defects after chemical reactions. The electrical properties were not included in this thesis to directly show the advantages of PECVD materials due to the lack of doping gas in MW-PECVD, but the deposition details and the material characterization make the essential way to the electrical property test in future. More advanced doping methods, ion implanting, diffusion source layer or laser assist doping, will be investigated in future.
Another advantage of this technique is its compatibility with large area and high-rate deposition. The parameters related to the deposition rate and the chemical composition were calibrated and will be presented in this thesis.
Thin film superlattice structures were fabricated using a bilayer structure of SRO/SiO2 with 6nm per bilayer. High temperature annealing was carried out for Si QD crystallization. The characterization of chemical properties of SRO was carried out by FT-IR with the support of XPS to identify Si-O, Si-N and Si-H bonds composition before and after annealing. According to the results, the composition of SRO films from PECVD is different from that of the films deposited by RF-Sputtering, especially due to the Nitrogen involvement and the resulting Si crystallization. X-Ray Reflectivity (XRR) was the main approach to determine thin film thickness. X-Ray Diffraction (XRD) and Ramam spectroscopy were applied for the determination of the Si nano-crystal structure. Further improvements for the PECVD thin film deposition and the SRO materials will be discussed. Future work on the utilization of other characterization techniques and the doping of SRO and Si QD will also be discussed.