Lattice-mismatched GaAsP Solar Cells Grown on Silicon by OMVPE

We report on lattice-mismatched GaAs_0.7P_0.3 solar cells grown on silicon substrates. This composition of GaAs_0.7P_0.3 has a band gap of about 1.7 eV and is well suited as the top junction of a III-V/Si two-junction tandem solar cell. Using a thin, high-quality GaP nucleation layer, a lattice-matched GaN_0.02P_0.98 buffer layer, and a compositionally graded GaAs_xP_1-x buffer layer, the threading dislocation densities was reduced to less than 10⁸ cm^-2 in the active region. The efficiencies of these single-junction cells without any antireflection coatings were as high has 9.8% under the AM1.5G spectrum. The quality of these solar cells based on V_oc is comparable to the best III-V solar cells ever grown on Si substrates with a III-V buffer