Excimer laser crystallization of a-SiCx on glass

Abstract

Silicon carbide (SiC) is a promising material for the fabrication of optoelectronic devices. In the amorphous state physical-vapor-deposited SiC is already an essential part of the production of electron beam liquid phase crystallized silicon absorbers, because of its good wettability for the silicon melt. The resulting polycrystalline thin film absorbers exhibit excellent electrical properties (B. Eggleston et al. MRS Online Proc. Libr. 1426, 251 (2012)) and demonstrate the potential of this technology (J. Dore et al. IEEE J. Photovolt. 4, 33 (2014)). A drawback of amorphous SiC interlayers is their poor optical properties. In this work we investigate two different approaches. Firstly, we show how those properties can be improved by depositing SiCxOy layers to enhance the transmittance while maintaining the wettability. Secondly, the laser crystallization of amorphous silicon–carbon compounds is studied as a function of their composition and the applied laser fluence. Compared to the amorphous SiC layers a clear reduction of the absorption coefficient was achieved upon laser annealing without losing wettability. Raman backscattering measurements showed that laser annealing of reactively sputtered amorphous SiC leads to a material with a vibrational mode at 770 cm−1 that is indicative of 6H–SiC. Atomic force microscopy measurements of those crystalline layers also show an ordered triangular grain structure, which was not observed in the amorphous material. It is shown that segregation effects are strongly affected by the stoichiometry and the applied laser fluence.