Optical effects of Si-delta doping of GaAs spacer layer on the vertical coupled multi-stacked InAs/InGaAs/GaAs intermediate-band solar cells

We report, in this work, the effects of Si-delta doped GaAs spacer layer on the optical properties of 20-stacked InAs/InGaAs/GaAs vertical coupled quantum dots heterostructures intermediate band solar cells (QD-IBSCs). The samples were grown by solid-source molecular beam epitaxy (SS-MBE) and investigated via photoluminescence (PL) and photocurrent (PC) spectroscopy. Two different families of quantum dots (QDs) were observed in the photoluminescence spectra and clearly identified in the atomic force microscopy image (AFM). With doping the GaAs spacer layer an opposite optical effect compared with previous works is investigated, the PL spectrum shows a dramatic decrease in PL intensity and a remarkable peak shift to higher energy. This is may be due to the incorporation of non-radiative impurities by doping. Moreover, it results in the more frequent filling by the additional electron of the sub-band level in the InAs QDs and promoted by the strain driven In/Ga intermixing between InAs/InGaAs QDs and GaAs spacer layer. The PC measurement exhibits a drop of the photocurrent accompanied by weak absorption in the extended range with doping, which is in good agreement with the (PL) results.