A GaAs-on-Si solar cell for space use

This paper reports on efforts to growing high-quality GaAs films on Si substrates and improvements in the efficiency of GaAs-on-Si solar cells. The epitaxial growth of GaAs on Si was studied using MOCVD. The dislocation density in the active layer of the GaAs solar cell is significantly reduced by combining cyclic thermal annealing and the insertion of buffers such as InGaAs/GaAs and AlGaAs/GaAs. This minimal dislocation density allowed a large size and high conversion efficiency GaAs-on-Si solar cell to be fabricated with a total area of 2 cm square and an efficiency of 18.3% under AMO and one-sum illumination. After 1-MeV electron beam irradiation at 1 x 1015cm-2, the GaAs-on-Si cells show a normalized efficiency of 0.83, which is larger than the 0.71 of a GaAs-on-GaAs cell. The use of GaAs-on-Si solar cells as the power source for satellites now looks feasible because this material is highly efficient, lightweight, inexpensive, and highly radiation resistant