MOCVD AlGaAs/GaAs solar cells on GaAs, Ge and Ge/Si substrate

AlGaAs/GaAs heteroface solar cells were fabricated on the GaAs, Ge, and Ge/Si substrates by MOCVD. A thin Ge epitaxial layer was grown on the Si substrate by MBE. The Ge and Si substrates were oriented (100) 2 deg off and 4 deg off toward (111), respectively. If the Ge and Si substrates were oriented exact (100) or (100) with a few degrees off toward (110), antiphase domain structures have been observed in the GaAs layers and solar cell performances were reduced. GaAs solar cells have been obtained with a 19.7, 18.6 and 5.5 percent conversion efficiencies at AM0 on the GaAs, Ge and Ge/Si substrates, respectively. Intrinsic efficiencies were 21.5, 20.3 and 6.0 percent, respectively.