Recently, to sandwich InAs QDs with GaAs1-xSbx layers have attracted enormous attention. It is expected to achieve a transition from type-I to type-II band alignment at ~ x=12%. The type-II InAs/GaAs1-xSbx QDs are predicted to be one of the optimizing active region materials for achieving high efficient intermediate-band solar cells.
We first investigate PL properties of InAs/GaAs1-xSbx QD structures of different Sb compositions (x=0, 0.15, and 0.25) in the GaAs1-xSbx capping layer. By capping the InAs QDs with GaAs0.85Sb0.15 and GaAs0.75Sb0.25 layer, we are able to gain type II QDs. These type II QDs exhibit a clear multi-peaks characteristic under increasing laser excitation intensity, which stems from different carriers recombination routes due to the combination of InAs QDs with GaAs1-xSbx capping layer. Time-resolved PL measurements further confirm our assignment for the mnulti-peaks in the PL spectra. We then study carrier coupling inside vertically aligned InAs/GaAs and InAs/GaAs1-xSbx QD pairs. The features of InAs/GaAs1-xSbx QD pairs are very different from the traditional InAs/GaAs QD-pairs. Again, clear multi-peaks characteristic are observed under stronng laser excitation intensity, which stems from different carriers recombination routes from the top InAs/GaAs1-xSbx QDs.
Our investigations indicate that the optical behavior and carrier dynamics in type-II InAs/GaAs1-xSbx QDs and QD-pairs are much more complicated than the InAs/GaAs QDs counterparts. This study provide useful information for understanding the band structure and carrier dynamics of the InAs/GaAs1-xSbx QDs for high efficiency solar cell applications.
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