(Ga,In)(N,As)-based solar cells grown by molecular beam epitaxy

(Ga,In)(N,As) could be a promising material for use in monolithic four-junction solar cells since it can be grown lattice-matched to substrates such as GaAs and Ge, and its bandgap of 1 eV is complementary to that of the three other semiconductors Ge, GaAs and (Ga,In)P. The growth by molecular beam epitaxy of (Ga,In)(N,As)-based solar cells is reported. It was checked by high-resolution X-ray diffraction that the 1-μm-thick (Ga,In)(N,As) layers were lattice-matched to GaAs. The spectral responses of the solar cells provide evidence that (Ga,In)(N,As) converts photons with energy down to 0.9 eV. The comparison with reference GaAs solar cells indicates, however, a degradation of the short-circuit current, revealing short minority-carrier diffusion lengths. A (Ga,In)(N,As) 2 mm×2.5 mm solar cell with a p-i (Ga,In)(N,As) n-GaAs structure delivers a 2.1 mA/cm² short-circuit current and has an open-circuit voltage of 0.264 V under natural solar illumination (air mass ∼1.5).