Evaluation of GaInNAs(Sb) solar cells for use in next generation III-V tandem solar cells

We have evaluated p-GaAs/i-n-GaInNAs(Sb) and p-GaAs/i-GaInNAs(Sb)/n-GaAs solar cells grown by RF-molecular beam epitaxy. The absorption edges of these samples were found within 1170-1200 nm. The currents generated in GaInNAs(Sb) layers, which were calculated from AM 1.5 spectrum and QE spectra at λ >; 870 nm region, were 6.1-7.3 mA/cm², and the open circuit voltages (V_oc) were 0.37-0.41 V. Next we investigated current generation maps by using 405 nm, 785 nm and 1064 nm lasers. The spatial current generation in the top GaAs layers showed uniform distribution which was scanned by 405 nm and 785 nm laser. However, using 1064 nm laser revealed spatially uneven current distribution. This means that carriers generated in GaInNAs(Sb) layers are not collected sufficiently. We believe that this nonuniform carrier collection has connection to the cell parameters, such as defects, dislocations, and/or device structures, and degrades V_oc in GaInNAs(Sb) solar cells.