AlGaAs/InGaAlP tunnel junctions for multi-junction solar cells

A number of different high bandgap tunnel junctions have been examined for use in advanced monolithic multijunction solar cells. All of the tunnel junctions are grown by metal-organic vapor phase epitaxy. An Al/sub 0.9/Ga/sub 0.1/As-In/sub 0.5/Ga/sub 0.3/Al/sub 0.2/P tunnel junction has the necessary optical and electrical properties for use in an advanced four junction device, and the authors demonstrate a working device. The bandgap of the Al/sub 0.9/Ga/sub 0.1/As and the In/sub 0.5/Ga/sub 0.3/Al/sub 0.2/P are both 2.1 eV. The J/sub p/ of the device is 1,500 mA/cm/sup 2/, and the series resistance is 2.5/spl times/10/sup -2/ /spl Omega/cm/sup 2/. The Al/sub 0.9/Ga/sub 0.1/As is doped with carbon, while the In/sub 0.5/Ga/sub 0.3/Al/sub 0.2/P is doped with tellurium. SIMS analysis indicates minimal tellurium memory effect and outdiffusion, and hence minimal tellurium doping in ensuing layers.