Toward metamorphic multijunction GaAsP/Si photovoltaics grown on optimized GaP/Si virtual substrates using anion-graded GaAsyP1-y buffers

Using migration enhanced epitaxy nucleation followed by molecular beam epitaxy bulk growth on pristine, intentionally offcut Si(001) substrates, we have produced high-quality GaP/Si virtual substrates, successfully demonstrating full control and elimination of heterovalent nucleation-related defects (antiphase domains, stacking faults, and microtwins). These virtual substrates provide a pathway to direct integration of III-V photovoltaic materials and devices on Si substrates. Prototype GaAsP solar cell test devices grown on anion-sublattice step-graded GaAs_yP_1-y buffers on early-stage GaP/Si substrates show good preliminary performance characteristics and offer great promise for future devices integrated with the newly-developed defect-free GaP/Si virtual substrates.