High electron mobility of β-HgS colloidal quantum dots with doubly occupied quantum states

Electron occupation of the lowest electronic state of the conduction band (1S_e) of a semiconducting nanocrystal offers numerous opportunities to efficiently utilize the quantization of the colloidal quantum dot. The steady-state electron occupation of the 1S_e gives rise to unprecedented electrical, optical, and magnetic properties. We report an electron mobility of ∼1.29 cm² V^-1 s^-1 measured in a mercury sulfide (β-HgS) quantum dot field effect transistor (FET), demonstrating the best carrier mobility for the HgS colloidal nanocrystal solid. The high electron mobility of the HgS nanocrystals with the doubly occupied quantum state originates from the efficient ligand exchange from oleylamine to thiocyanate, better carrier hopping via shortened inter-dot-distance, and the packing of nanocrystals by optimized thermal annealing conditions.