We have investigated wide-bandgap, metamorphic GaAs 1-x P x and In yGa 1-yP solar cells on GaAs as potential subcell materials for future 4-6 junction devices. We identified and characterized morphological defects in tensile GaAs 1-xP x graded buffers that lead to a local reduction in carrier collection and a global increase in threading dislocation density (TDD). Through adjustments to the graded buffer structure, we minimized the formation of morphological defects and, hence, obtained TDDs 10 6 cm -2 for films with lattice mismatch ≤1.2%. Metamorphic In yGa 1-y P solar cells were grown on these optimized GaAs 1-xP x graded buffers with bandgaps (E g) as high as 2.07 eV and open-circuit voltages (V oc) as large as 1.49 V. Such high bandgap materials will be necessary to serve as the top subcell in future 4-6 junction devices. We have also shown that the relaxed GaAs 1-xP x itself could act as an efficient lower subcell in a multijunction device. GaAs 0.66 P 0.34 single-junction solar cells with E g = 1.83eV were fabricated with V oc 1.28 V. Taken together, we have demonstrated that GaAs 1-xP x graded buffers are an appropriate platform for low-TDD, metamorphic GaAs 1-xP x and In yGa 1-yP solar cells, covering a wide bandgap range.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering