Characterisation of silicon epitaxial layers for solar cell applications

The growth and detachment of epitaxial layers of semiconductor material on a suitable substrate, with subsequent re-use of the substrate, is of interest due to its potential for significant reductions in the cost of the epitaxial material, and therefore in the cost of solar cells fabricated on epitaxial layers. Recently the epilift technique was introduced which allows the fabrication of single crystalline layers of silicon of arbitrary size and shape by liquid phase epitaxy (LPE) on single crystal silicon substrates which have been patterned with a suitable masking layer material such as SiO2. Detachment of the layers proceeds by etching through the regions where the epitaxial layer is attached to the substrate. The substrate can be re-used many times. The quality of the epitaxial layers was investigated by SEM following defect etching and the lifetimes of several samples were measured by microwave photoconductive decay after detachment from the substrate. The light trapping for the epilift structure was modelled for a just-closed epilayer as double-sided inverted pyramids with zero layer thickness at the tips of the pyramids. It was found that the light trapping is as good as for double-sided inverted pyramids whose height is small compared with the layer thickness. We show that the quality of epitaxial layers and the texturing inherent in the epilift technique allows fabrication of high quality, single crystal silicon films which are particularly suitable for the production of high efficiency solar cells