Abstract: Intermediate band solar cells (IBSC) have the potential to achieve high power conversion efficiency under solar concentration, 63% compared with 41% for a single junction solar cell under maximum light concentration. However, implementing an intermediate band with two photon absorption and carrier generation requires effective de-coupling from the conduction and valence bands and a partially filled band. In this respect GaSb/GaAs quantum ring solar cells (QRSC) have been reported, where the type-II band alignment provides longer carrier lifetime enhancing the extracted photocurrent. Larger short circuit current density can be obtained compared to the type-I InAs/GaAs system. However, due to reduced electron – hole overlap the absorption of type-II structures is somewhat lower. Also, in many such QRSC an intermediate band is not formed due to QR layers not coupling with each other.

Here we present a study of the coupling effect between GaSb QR layers stacked in a GaAs matrix, to investigate the formation of the intermediate band and its behaviour in such structures. Several simulations have been performed using Nextnano software, and miniband formation is observed when the distance between QD layers is smaller than. GaSb/GaAs QR with small spacing and increasing number of layers have been grown by MBE and characterised by photoluminescence. These samples showed a similar energy shift to that predicted by the simulations. Further study will give us better understanding of the role that strain and QR morphology play in such structures.


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