GeCl4-based High Quality Ge epitaxy on Engineered Ge Substrates for Thin Multi-junction Solar Cells

Germanium, a critical raw material, is used as a template for III-V epitaxial growth and as a bottom cell in multi-junction solar cells. To reduce the amount of germanium used, a detachable substrate is very interesting, especially if the Ge foil thickness can be adjusted as needed. In this study, the potential of GeCl 4 -based epitaxy was demonstrated. A growth rate up to 190 nm/min and a thickness up to $15\mu\mathrm{m}$ were achieved. Detachable foils were then formed by porosification, annealing and epitaxial growth. The effective minority-carrier lifetime in the surface-passivated foil could be measured and proved quite high: over 25µs. Results presented in this contribution confirm that the so-prepared foils constitute a suitable platform for the fabrication of high-performance multi-junction solar cells.