Effect of strain relaxation layer insertion on carrier recombination and escaping processes in superlattice solar cell structures using photoluminescence spectroscopy

We discuss the effect of interlayer insertion into the light absorption region of a carrier escape process for superlattice (SL) solar cells determined by the temperature dependence of photoluminescence (PL) signals. 20-period SL solar cells, with and without interlayers, were prepared. The temperature dependence of the integrated PL intensities due to the transition between quantum levels is well explained by the carrier relaxation models consisting of four processes: radiative and nonradiative recombinations in the SL, thermionic emission to the barrier, and tunnelling after thermal excitation from the lower to the upper levels. We observed that the activation energy for the carrier thermal escaping the quantum well was significantly reduced by the insertion of an interlayer. Moreover, the carrier thermal escaping was also found to be dominant in all processes at 300 K from the calculation of the relevant lifetimes. These results indicate that the insertion of an interlayer results in SL solar cells with a higher efficiency than conventional solar cells.