High efficiency GaAs solar cells fabricated on Si substrates

High-efficiency, large-area GaAs solar cells were fabricated on Si substrates. Two types of layered structures are examined. One is a conventional GaAs/Ge/Si structure. The other is a GaAs/Si structure in which crystalline GaAs is grown directly on the Si substrate. Active layers of p-GaAlAs/p-GaAs/n-GaAs are grown by MOVPE. Maximum intrinsic conversion efficiency at AM0 for a 1-sq cm cell is 11.5 percent for GaAs/Ge/Si cells and 14.0 percent for GaAs/Si cells. Short-circuit current is about 28 mA and open-circuit voltage is about 0.8 V. This performance is made possible by improved materials preparation. The electrical characteristics of the cells as well as their crystal structural properties are described. The results of electron irradiation and thermal stress tests are reported.