Investigation of Hybrid Tunnel Junction Architectures for III-V/Si Tandem Solar Cells

We fabricated n-Si/p-GaAs and p-Si/n-GaAs junctions, by combining low temperature (under 200°C) RF-PECVD for Si and MOVPE for GaAs. In particular, we focused on low-resistance Si/GaAs tunnel junctions (< 1 mΩ.cm 2) suitable for the interconnection of two subcells in tandem III-V/Si solar cells. We first demonstrate the growth of highly doped epitaxial silicon films on GaAs despite the 4% lattice-match between these two materials. Spectroscopic ellipsometry measurements were used to confirm the quality of the epitaxial Si layers. The electrical properties of the grown junctions were measured based on four-point probes method and analyzed using TCAD simulations on Silvaco. We demonstrate a very low resistance for the p-Si/n-GaAs junction, down to 3.10-5 .cm 2 , with current densities above 10.000 A/cm 2 , suitable for ultra-high concentration photovoltaics, largely exceeding the requirement for our low concentration targeted conditions (below 20 suns).