Electrical Properties and Structural Defects in Lattice Mismatched InGaAs Solar Cells

Higher conversion efficiency has been predicted theoretically for InGaP/In_0.16Ga_0.84As/Ge lattice-mismatched triple junction solar cells owing to widening of the effective range of the solar spectrum than the conventional lattice-matched solar cells. The most serious problem in lattice-mismatched system is the large lattice mismatch (~1%) between In_0.16Ga_0.84As and Ge cells. The effect of a thermal cycle annealing (TCA) process which is expected to reduce the defect density in this system has been discussed from electrical and structural viewpoints. The minority carrier lifetime in In_0.16Ga_0.84As emitter layers were improved after TCA treatment from TR-PL measurement. EBIC measurements showed a reduction of the structural defect such as misfit dislocations due to the TCA process in In_0.16Ga_0.84As base layers. The misfit components observed in the base layers may have some influence through the emitter layers