Gate tunable vertical geometry phototransistor based on infrared HgTe nanocrystals

Infrared nanocrystals are promising building blocks for the design of low-cost infrared sensors. Vertical geometry diode is, among possible geometries, the one that has led to the best performance so far. However, this geometry suffers from a lack of tunability after its fabrication, slowing down possible improvements. Here, we demonstrate gate control on a vertical diode in which the active layer is made of HgTe NCs absorbing in the extended short-wave infrared (2.5 μm). To reach this goal, we take advantage of the electrostatic transparency of graphene, combined with the high capacitance LaF₃ ionic glass to design a gate tunable photodiode. The latter behaves as a work function-tunable electrode which lets the gate-induced electric field tune the carrier density within the nanocrystal film. In particular, we show that the gate allows to tune the band profile leading to more efficient charge extraction and thus an enhanced photoresponse (×4 compared to the device with a floating gate). This work also demonstrates that photoelectron extraction can still be improved in the existing diode, by better controlling the doping profile of the stack.