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Laser-assisted Deposition and Crystallisation of Silicon-Germanium Alloy Thin Films on Plastics for Photovoltaics

Excimer-laser induced deposition and crystallisation of thin films of Si, Ge and SiGealloys on low-cost plastic substrates has been investigated. The depositions have been made both by laser-induced chemical vapour deposition (LCVD) and hot-wire chemical vapour deposition (HWCVD). The parameters of the laser-induced depositions have been altered to investigate the influence on the thin film quality of temperature, laser fluence and laser beam – substrate geometry. The films have been crystallised by the excimer-laser, varying the laser fluence and the number of laser pulses in order to find the range in with the material crystallises. In-situ time-resolved reflectivity measurements were taken for immediate interpretation of the impact of the laser. The films have been deposited on CORNING glass, Silicon, PEN and PI, thus allowing the characterisation of the film through several different techniques. Extensive material characterisation has been performed to evaluate the properties of the deposited and crystallised films: dark conductivity measurements, UV-VIS spectroscopy, XPS, TOFSIMS, profilometry and RAMAN spectroscopy. It was found that films with good characteristics can be deposited at room temperature and crystallised by excimer-laser induced crystallisation if the conditions are right.