Gate tunable vertical geometry phototransistor based on infrared HgTe nanocrystals

International audience; 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.This project is supported by a ERC starting grant blackQD (Grant No. 756225). We acknowledge the use of clean-room facilities from the “Centrale de Proximité Paris-Centre” and from the STnano platform. This work has been supported by the Region Ile-de-France in the framework of DIM Nano-K (Grant dopQD). This work was supported by French state funds managed by the ANR within the Investissements d'Avenir programme by Labex Matisse (No. ANR-11-IDEX-0004-02) and Labex NIE (Nos. ANR-11-LABX-0058 and ANR-10-IDEX-0002-02). A.N.R. also funded grants FRONTAL (No. ANR-19-CE09-0017), IPER-Nano2 (No. ANR-18CE30-0023-01), Copin (No. ANR-19-CE24-0022), and Graskop (No. ANR-19-CE09-0026), NITQuantum. A.C. thanks Agence Innovation Defense for the Ph.D. funding.