High-performance metamorphic tunnel junctions for III?V/Si multijunction solar cells

Various metamorphic tunnel junction designs, targeted for application toward Ga_0.56In_0.44P/GaAs_0.9P_0.1/Si triple-junction and GaAs_0.75P_0.25/Si dual-junction solar cells, grown via both molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), have been demonstrated. Ga_0.56In_0.44P/GaAs_0.9P_0.1 double heterostructure tunnel junctions, grown by MBE on Si substrates at both target lattice constants, yielded at least 50% improved electrical performance (peak tunnel current and resistance-area product), with nominally reduced optical losses, compared to previously demonstrated GaAs_0.9P_0.1 homostructure devices. Initial MOCVD-grown Al_0.4Ga_0.6As_0.9P_0.1/GaAs_0.9P_0.1 heteroface tunnel junctions were also fabricated and exhibited a > 3x electronic performance improvement over comparable GaAs_0.9P_0.1 homostructure devices. Such tunnel junctions reveal great promise for use within Si-based multijunction solar cells for both one-sun and concentrator applications.