Macroscopically smooth Si layer growth by LPE on cast metallurgical-grade Silicon substrates

An ideal solvent system, Cu‐Al, has been found for growth of Si layers with thicknesses of tens of microns on cast MG‐Si substrates by LPE at temperatures near 900 °C. This solvent system utilizes Al to ensure good wetting between the solution and substrate by removing silicon native oxides, and employs Cu to control Al doping into the layers. Isotropic growth is achieved because of a high concentration of solute silicon in the solution and the resulting microscopically rough interface. As a result, macroscopically smooth Si layers have been grown on cast MG‐Si that are suitable for device fabrications. The thin layers (∼30 μm) grown on the MG‐Si substrates have doping levels of 3×1017 cm−3 and up, benign grain boundaries, and minority‐carrier diffusion lengths greater than the layer thicknesses.