GaAs-AlGaAs tunnel junctions for multigap cascade solar cells

Abstract

The growth and characterization of tunneling GaAs homojunctions and GaAs-AlGaAs heterojunctions by molecular beam epitaxy for use as optically transparent interconnects in GaAs and AlGaAs solar cells is described. GaAs tunneling interconnects have been achieved with conductances of 300 A/cm2-V at 0.050 V, and p-AlxGa1−x As/n-GaAs heterojunction structures with x up to 0.4 have been grown which have characteristics comparable to GaAs interconnects. Thin interconnects, 1000 Å total thickness, have also been fabricated with conductances comparable to thicker junctions. The effect of dopant diffusion was found to be minimal at the 580 °C junction growth temperature, but annealing these tunnel junctions at 650 °C for several minutes caused diffusion of about 100 Å distance.