Charge trapping due to defects in semiconductor quantum dots (QDs) is expected to challenge the applicability of QDs in future technologies. The efficient elimination of defects from QDs demands an understanding of their origin and of their impact on (photo)electronic properties. Here, we identify the presence of two charge states of a defect in CdSe QDs using electron paramagnetic resonance (EPR), combined with electronic tuning of QDs via chemically induced Ag doping. From light-induced EPR, we show that these defects have a central role in Fermi level pinning in ensembles of intrinsic QDs. By analyzing the dependence of the EPR signal of the defects on the concentration of Ag dopants, we further demonstrate that the defects act as effective electron traps in the QDs. Our study also provides support to the proposed behavior of Ag dopants in CdSe QDs, according to which Ag atoms are n-type dopants at concentrations below 2 Ag atoms per QD and become p-type dopants for higher Ag concentrations. From temperaturedependent EPR, we estimate a lower limit for the ionization energy of the studied defects. Based on the characteristics of the EPR spectrum, we propose that these defects are associated with Se vacancies with the paramagnetic state being the positively charged state of the defect.

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We demonstrate few-charge occupation of electron and hole quantum dots in silicon via charge sensing. We have fabricated quantum dot (QD) devices in a silicon metal-oxide-semiconductor heterostructure comprising a single-electron transistor next to a single-hole transistor. Both QDs can be tuned to simultaneously sense charge transitions of the other one. We further detect the few-electron and few-hole regimes in the QDs of our device by active charge sensing.

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