Wave-Function Engineering in HgSe/HgTe Colloidal Heterostructures To Enhance Mid-infrared Photoconductive Properties

The use of intraband transition is an interesting alternative path for the design of optically active complex colloidal materials in the mid-infrared range. However, so far, the performance obtained for photodetection based on intraband transition remains much smaller than the one relying on interband transition in narrow-band-gap materials operating at the same wavelength. New strategies have to be developed to make intraband materials more effective. Here, we propose growing a heterostructure of HgSe/HgTe as a means of achieving enhanced intraband-based photoconduction. We first tackle the synthetic challenge of growing a heterostructure on soft (Hg-based) material. The electronic spectrum of the grown heterostructure is then investigated using a combination of numerical simulation, infrared spectroscopy, transport measurement, and photoemission. We report a type-II band alignment with reduced doping compared with a core-only object and boosted hole conduction. Finally, we probe the photoconductive properties of the heterostructure while resonantly exciting the intraband transition by using a high-power-density quantum cascade laser. Compared to the previous generation of material based on core-only HgSe, the heterostructures have a lower dark current, stronger temperature dependence, faster photoresponse (with a time response below 50 μs), and detectivity increased by a factor of 30.