Growth of metamorphic GaAsP solar cells on GaP

In this work, we demonstrate metamorphic GaAs_xP_1-x/GaP solar cells grown by molecular beam epitaxy for potential dual-junction integration with Si. We investigate the appropriate substrate orientation and growth conditions necessary to obtain smooth surface morphology with high open-circuit voltage (V_oc). Growing nearly identical GaAs_xP_1-x/GaP (x=0.65±0.01) cells at three different substrate temperatures allowed us to investigate the dislocation dynamics in the graded buffer, revealing that we are not in the ideal glide-limited regime. We expect this is due to thread interactions with morphological defects. To satisfy the design requirements of the ideal dual-junction device, we grew 1.71 eV GaAs_0.73P_0.27/GaP cells, attaining a high V_oc of 1.15 V. With increased short-circuit current through the addition of a window layer and antireflection coating, the GaAs_xP_1-x cells presented here cascaded with Si could reach efficiencies as high as 30%.