MOVPE growth of III-V solar cells on silicon in 300 mm closed coupled showerhead reactor
III-V multi-junction solar cells grown on Ge substrates have achieved the highest solar cell conversion efficiency of 41.6 %. However, this device manufacturing is still costly and a major share of the cost can be attributed to the cost of the Ge substrate. Therefore, a replacement of Ge by Si would be beneficial. However, elaborate challenges arise from the 4.1% difference in lattice constant for Si and GaAs and due to the non-polar to polar interface leading to threading dislocations and anti-phase domains, respectively. To meet the required high crystalline quality for III-V multi-junction solar cells this paper presents approaches for the Si-to-GaAs transition evaluated on an industrial 300 mm CRIUS Closed Coupled Showerhead MOVPE reactor. Anti-phase domain free GaP nucleation layers with only 0.36% lattice mismatch at room temperature were grown on Si substrate. On top of these layers step-graded Ga1-xInxP buffer structures mediate the lattice constant to GaAs although present process parameters have not yet enabled confinement of threading dislocations inside the buffer structure. A promising alternative route is the growth of an all Ge buffer layer directly on Si. Here we report on the results of the used twostep growth process.