WIDE-BANDGAP EPITAXIAL HETEROJUNCTION WINDOWS FOR SILICON SOLAR-CELLS

The efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction “window.” For silicon (lattice constant a = 5.43 Å), nearly lattice-matched wide-bandgap materials are ZnS (a = 5.41 Å) and GaP (a = 5.45 Å). Isotype n-n heterojunctions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical-vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched (111) faceted) surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length. © 1990 IEEE