Current-induced brightening of vacancy-related emitters in hexagonal boron nitride

We perform photoluminescence measurements on vacancy-related emitters in hexagonal boron nitride (hBN) that are notorious for their low quantum yields. The gating of these emitters via few-layer graphene electrodes reveals a reproducible, gate-dependent brightening of the emitter, which coincides with a change in the direction of the simultaneously measured leakage current across the hBN layers. At the same time, we observe that the relative increase of the brightening effect scales linearly with the intensity of the excitation laser. Both observations can be explained in terms of a photo-assisted electroluminescence effect. Interestingly, emitters can also show the opposite behavior, i.e. a decrease in emitter intensity that depends on the gate leakage current. We explain these two opposing behaviors with different concentrations of donor and acceptor states in the hBN and show that precise control of the doping of hBN is necessary to gain control over the brightness of vacancy-related emitters by electrical means. Our findings contribute to a deeper understanding of vacancy-related defects in hBN that is necessary to make use of their potential for quantum information processing.