FETs up to a wavelength of 2.1 µm, but the phototransistor required an intermediate TiO2 buffer layer in between the HgTe QDs and the MoS2 to protect the MoS2 transistor and to generate a pn-junction at the HgTe QD/TiO2 interface. In fact, the interface between graphene (or MoS2) and HgTe QDs is critical for achieving functional phototransistors, and the development and fabrication of HgTe QD/graphene phototransistors operating beyond 2.1 µm remain unprecedented.