Effects of Graded Buffer Design and Active Region Structure on GaAsP Single-Junction Solar Cells Grown on GaP/Si Templates

We investigated the effect of GaAs
_y
P
_1-y
graded buffer layer design and cell structure on GaAsP solar cells grown on GaP/Si templates. Heavy Si doping in the graded buffer layer increases threading dislocation density (TDD) by 2.7× compared to no doping, while heavy Be doping has little or no effect on TDD. Higher TDD increases the bandgap-voltage offset, but its effect on short-circuit current density is more complex. For example, by implementing an n
⁺
/i/p structure in cells with elevated TDD, we could obtain significantly higher internal quantum efficiencies at 500-750 nm compared to n
⁺
/p structures with low TDD. All cells investigated here achieved efficiencies of 15.5-15.9% despite TDD values ranging from 4.5×10
⁶
-1.2×10
⁷
cm
^-2
.