Mercury chalcogenide nanocrystals are an interesting platform for the design of low cost infrared photodetectors.1 However up to recently it was impossible to push their absorption spectrum above 5µm (≈250meV).2 In HgTe and HgSe, the Bohr radius is pretty large (≈40nm), thus large nano-objects need to be synthetized to reduce confinement and obtain narrower energy transitions.
HgSe nanocrystals are self-doped nanocrystals which give access to intraband transition to address the infrared range of the electromagnetic spectrum.3 We will in particular discuss the origin of doping and how the surface chemistry can be used to tune the doping level.4 We then further investigate the electronic properties of these nanocrystals made from a semimetal as the size is increasing and the quantum confinement is vanishing. We demonstrate, using a combination of X-ray photoemission, IR spectroscopy and transport measurements, that as the confinement is disappearing the nanoparticles behavior switches from a confined semiconductor to a metal behavior.5
To finish, I will briefly discuss our last results where we have been able to push the absorption of colloidal nanocrystals to the THz range (and up to 200µm).
Recent Progresses in Mid Infrared Nanocrystal based Optoelectronics, E. Lhuillier et al IEEE J Selec Top Quantum Elec 23, 1 (2017)
Mid-infrared HgTe colloidal quantum dot photodetectors, S. Keuleyan et al, Nat Photon 5, 489-493. (2011).
Infrared photo-detection based on colloidal quantum-dot films with high mobility and optical absorption up to the THz, E. Lhuillier et al, Nano Lett 16, 1282 (2016)
Surface Control of Doping in self-doped Nanocrystals, A. Robin et al ACS Appl. Mat. Interface 8, 27122−27128 (2016).
HgSe self-doped nanocrystals as a platform to investigate the effects of vanishing confinement, B. Martinez, et alACS Appl. Mat. Inter. (2017).