ALXGA1-XAS SI (X=0-0.22) TANDEM SOLAR-CELLS GROWN BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION/

Studies of AlxGa1-xAs/Si (x=0-0.22) tandem solar cells have been carri ed out by using metal organic chemical vapor deposition (MOCVD). The G aAs/Si tandem solar cell consists of a GaAs top cell with the Al0.3Ga0 .7As buffer layer and a Si bottom cell with the n(+)-p-p(+) structure. The theoretical analyses of the Si bottom cell are carried out for ta ndem solar cell application. The suitable resistivity of the p-Si subs trate for the Si bottom cell has been found to be 10 Omega . cm, which corresponds to the experimental results. The active-area conversion e fficiency of 19.5% (1sun, AM0) for the GaAs/Si tandem solar cell has b een achieved in the three-terminal configuration. In the case of the A lxGa1-xAs/Si tandem solar cell, x varies from 0.1 to 0.22. The crystal line quality of the AlxGa1-xAs heteroepitaxial layer grown on Si is im proved, using a high-temperature growth process (800 degrees C) and th ermal cycle annealings (300-900 degrees C). The active-area conversion efficiencies of 20.0% and 19.0% (1sun, AM0) for the Al0.15Ga0.85As/Si tandem solar cell are obtained with four-terminal and two-terminal co nfigurations, respectively.