Optical and electrical analysis of graded buffer layers in III?V/SiGe on silicon tandem solar cells

A graded buffer layer is needed in order to grow III-V/SiGe on silicon substrate because of the lattice mismatch. In this work, optical absorption in the graded buffer layer is quantified by measuring the transmittances. We demonstrate a 7 μm graded buffer layer with Ge composition from 0% to 82% is equivalent to a 2 μm SiGe film with 82% Ge composition in terms of optical absorption. A SiGe solar cell was fabricated and characterized. Quantum efficiency measurements show that around 1 mA/cm² short circuit current is generated from the graded buffer layer in the fabricated solar cell.