GaAs/Si Double-Junction Cells Fabricated by Sacrificial Layer Etching of Directly-Bonded III-V/Si Junctions

A GaAs/Si double-junction cell is fabricated by directly bonding a GaAs single-junction cell structure grown on a GaAs (001) substrate to a n-on-p Si sub-cell and separating the GaAs substrate using a sacrificial layer etching. Before the sacrificial layer etching, the III-V/Si junction is annealed at 300 ℃ for 1 hour so as to recrystallize the interface and achieve an enough bonding strength based on the results of hard X-ray photoemission spectroscopy. We obtain a bonding yield of ~80% after the sacrificial layer etching. We confirm that the fabricated double-junction cell normally operates by measuring its current-voltage and spectral-response characteristics.