Nb-doped single crystalline MoS₂ field effect transistor

We report on the demonstration of a p-type, single crystalline, few layer MoS₂ field effect transistor (FET) using Niobium (Nb) as the dopant. The doping concentration was extracted and determined to be ∼3-×-10¹⁹/cm³. We also report on bilayer Nb-doped MoS₂ FETs with ambipolar conduction. We found that the current ON-OFF ratio of the Nb-doped MoS₂ FETs changes significantly as a function of the flake thickness. We attribute this experimental observation to bulk-type electrostatic effect in ultra-thin MoS₂ crystals. We provide detailed analytical modeling in support of our claims. Finally, we show that in the presence of heavy doping, even ultra-thin 2D-semiconductors cannot be fully depleted and may behave as a 3D material when used in transistor geometry. Our findings provide important insights into the doping constraints of 2D materials, in general.