Double layer antireflection coating and window optimization for GaAsP/SiGe tandem on Si

A double layer ARC for a GaAsP/SiGe tandem cell on Si is designed with a transfer matrix model. The importance of considering window thickness and material to be variable parameters in both design optimization and robustness investigation is demonstrated. In this process, optical constants of GaA_s.84P_.16, Ga_.59In_.41P, and Al_.65In_.35P are measured and used to estimate non-zero collection probability in the window layer. Experimental deposition of the ARC verifies the model and achieves a Spectral Weighted Reflectance of 1.9 %. Further modeling will better define the collection probability and suggest additional strategies for device efficiency improvement.