Surface cross-hatch roughness typically developed during the growth of lattice-mismatched compositionally graded buffers and could limit misfit dislocation glide. The cross-hatch roughness during growth of a compressive GaInP/GaAs graded buffer was reduced by increasing the phosphine partial pressure during the metamorphic growth. Changes in the average misfit dislocation length were qualitatively determined by characterizing the threading defect density and residual strain. The decrease of cross-hatch roughness led to an increase in the average misfit dislocation glide length, indicating that the surface roughness was limiting dislocation glide. Growth rate was also analyzed as a method to reduce surface crosshatch roughness and increase glide length, but had a more complicated relationship with glide kinetics. Using knowledge gained from these experiments, high-quality inverted GaInAs 1eV solar cells were grown on a GaInP compositionally graded buffer with reduced roughness and threading dislocation density. The open circuit voltage was only 0.38V lower than the band-gap potential at a short circuit current density of 15mA/cm2, suggesting that there was very little loss due to the lattice mismatch.

Reduction of Crosshatch Roughness and Threading Dislocation Density in Metamorphic GaInP Buffers and GaInAs Solar Cells. R.M.France, J.F.Geisz, M.A.Steiner, B.To, M.J.Romero, W.J.Olavarria, R.R.King: Journal of Applied Physics, 2012, 111[10], 103528