High-efficiency (>20% AM0) GaAs solar cells grown on inactive-Ge substrates

Results showing successful formation of high-efficiency GaAs cells (over 20% efficiency air mass zero (AM0)) grown on inactive Ge substrates under production conditions are discussed. The growth conditions varied considerably from those previously considered essential for good-quality heteroepitaxial growth. This work opens the way for the near-future implementation of large-area, lightweight, high-efficiency solar cells on spacecraft arrays. High-quality heteroepitaxial layers can be grown over a wider range of deposition conditions than previously used. Growth conditions that minimize the interaction of the grown layers and the substrate can be used. This is an advantage in growing monolithic cascade cells, particularly with cell structures that use optimized bottom cells as the substrate for epitaxial growth of the top cell. One combination being tested is the growth of an AlGaAs cell (with low concentration of Al) on a previously completed Ge cell.>