The Effect of Cd Incorporation on the Electronic Transport in HgTe Nanocrystal Films

Here, we study how the incorporation of Cd into mercury telluride (HgTe) nanocrystal quantum dots affects their electrical transport properties. The radial concentration distribution of Cd in HgTe nanocrystals was controlled synthetically by adding Cd(oleate)₂ into a heated solution of HgTe nanocrystals and excess oleylamine (OAm). OAm serves as a capping ligand and in the ligand-rich environment, the shape of the nanocrystals changes from tripods to spheres and the related surface reconstruction facilitates dopant incorporation. Addition of the Cd reactant at temperatures greater than 200 ^oC produces uniformly doped mercury cadmium telluride (MCT) with a controlled doping concentration. Shells enriched in Cd were deposited with a controlled thickness by adding both Cd and Te reactants at a lower temperature of 175 ^oC. The nanocrystal films in field effect transistor devices exhibit p-type behavior. STEM-EDS maps of the nanocrystals showed that there is a radial distribution of Cd in the nanocrystals with the presence of non-stoichiometric cation vacancies. The carrier mobility in the films of HgTe nanocrystals with Cd-enriched surfaces is 0.03 cm² V^-1s^-1, which is three times higher than the MCT nanocrystals with uniform Cd composition. The higher mobility is attributed to a hole carrier pathway by valence band alignment between HgTe and CdTe and leads to significantly improved, faster photoresponse under solar and IR illumination.