1.6/1.1Â eV metamorphic GaInP/GaInAs solar cells grown by MOVPE on Ge

This paper focuses on the metal-organic vapor-phase epitaxy (MOVPE) growth of 2-junction (2J) solar cells where epitaxial Ga0.29In0.71P top and Ga0.77In0.23As bottom subcells are grown lattice-mismatched on a Ge substrate. Single-junction metamorphic devices with 23%-In GaInAs are grown on 100-mm dia. (0 0 1) Ge substrates. Layers are observed to be fully relaxed by high-resolution X-ray diffraction. Threading dislocation densities of 3.1×106 cm−2 are measured. Single-junction devices in the 1.1-eV materials demonstrate near 100% internal quantum efficiency above the band gap and an open-circuit voltage comparable to world-record silicon photovoltaic devices. The presence and strength of CuPtB ordering is explored in controlling the band gap of the Ga0.29In0.71P top subcell devices between 1.647 and 1.593 eV. An order parameter of 0.28 is measured by X-ray measurement of the forbidden 12(115) reflection for the low-band gap material. The presence of low-resistance shunt pathways is observed as the present obstacle to reaching the potential efficiency of 30% for these metamorphic dual-junction devices.