Experimental Performance of Longpass DBR in 3J IMM with Quantum Wells

Building on previous simulation results, this work examines experimentally the incorporation of a longpass (LP) distributed Bragg reflector (DBR), as compared to a standard matched pair DBR, between the GaAs and InGaAs subcells of a triple junction inverted metamorphic design. The GaAs cell was not optically thick, to improve radiation tolerance, and contained InGaAs quantum wells, to increase subcell current generation. Both DBR structures improved bulk GaAs subcell collection in the physically thin absorber, however the LPDBR significantly reduced optical loss in the bottom junction caused by parasitic low energy reflections present in the standard DBR. This shifted the current limiting junction from the bottom InGaAs junction in the case of the DBR to the top InGaP junction, as designed. Simulation and experimental results of external quantum efficiency are presented and discussed.