Effect of built-in electric field in photovoltaic InAs quantum dot embedded GaAs solar cell

In this paper, three p–i–n GaAs solar cells were grown and characterized, one with InAs quantum dot (QD) layers embedded in the depletion region (sample A), one with QD layers embedded in the n− base region (B), and the third without QDs (control sample C). QD-embedded solar cells (samples A and B) show broad photoluminescence spectra due to QD multi-level emissions but have lower open-circuit voltages Voc and lower photovoltaic (PV) efficiencies than sample C. On the other hand, the short-circuit current density Jsc in sample A is increased while it is decreased in sample B. Theoretical analysis shows that in sample B where the built-in electric field in QDs is zero, electrons tend to occupy QDs and strong potential variations exist around QDs which deteriorate the electron mobility in the n− base region so that Jsc in sample B is decreased. Hole trapping and electron–hole recombination in QDs are also enhanced in sample B, resulting in a reduced Voc and thus a worse PV effect. In sample A, a strong built-in field exists in QD layers, which facilitates photo-carrier extraction from QDs and thus Jsc is increased. However, QDs in the depletion region in sample A act also as recombination-generation centers so that the dark saturated current density is drastically increased, which reduces Voc and the total PV effect. In conclusion, a nonzero built-in electric field around QDs is vital for using QDs to increase the PV effect in conventional p–i–n GaAs solar cells.