“…In our QDIP structures, the QDs are undoped and the carriers are supplied through background doping and electron injection from the contact layers. At small electric fields, as the electric field is increased, more electrons populate the QDs, resulting in an increase in the average sheet electron density and hence an increased dark current [51]. When a large fraction of the QD states are filled, further increase of the electric field does not significantly change the sheet electron density.…”