LIQUID-PHASE EPITAXY OF SILICON ON MULTICRYSTALLINE SILICON SUBSTRATES

Epitaxial layers of silicon of about 30 mu m thickness were grown on multicrystalline substrates from an In or In/Ga melt, at temperatures below 1000 degrees C and a cooling rate of either 0.5 or 2 degrees C/min. Grooves of variable depth were observed on the epitaxial layer, corresponding to reduced growth in the vicinity of grain boundaries. These grooves can extend nearly all the way to the substrate-epi interface. We found evidence of preferential meltback at some grain boundaries, even for growth from a supersaturated solution. Grain boundaries were observed to change direction at the substrate-epi interface. Twins, on the other hand, only lead to some waviness of the epitaxial layer surface and do not change their direction at the interface. The deep grooves have implications for solar cell design. The surface morphology was found to be dependent on the cooling rate, with low cooling rates giving a smooth surface, while higher cooling rates lead to rougher surfaces with an increasing tendency towards the formation of facets.