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 photo detection 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 mu s), and detectivity increased by a factor of 30.