Charge Carrier Diffusion and Recombination near Misfit Dislocations in GaAsP/GaInP Heterostructures

GaAsP alloys are good candidates for the upper junction in Si-based dual-junction tandem solar cells. However, monolithic growth of GaAsP on Si is limited by dislocation formation due to lattice mismatch. When metamorphic GaAsP is grown on GaAs substrates, dark crosshatch features can be observed in spatially-resolved electroluminescence and photoluminescence measurements. These features can be attributed to misfit dislocations in the epitaxial layers. We compare photoluminescence imaging with complementary confocal mapping measurements to test models of diffusion and recombination near misfit dislocations in a GaAsP/GaInP heterostructure. The crosshatch features become sharper with increased photoexcitation in accordance with reduced lifetimes and diffusion distances. However, the imaging and mapping experiments require different defect-related recombination rates in our computational models.