Wavefunction engineering in HgSe/HgTe colloidal heterostructures to enhance mid infrared photoconductive properties
Résumé
The use of intraband transition is an interesting alternative path for the design of optically active complex colloidal materials in the mid-infrared. However, so far the performance obtained for photodetection based on intraband transition remain 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 to grow an heterostructure of HgSe/HgTe as a path to achieve enhanced intraband based photoconduction. We first tackle the synthetic challenge of growing an 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, a reduced doping compared to 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 previous generation of material based on core only HgSe, the heterostructure have a lower dark current, stronger temperature dependence, faster photoresponse with time response below 50µs and a detectivity increased by a factor 30.
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