n‐Type Doping Effect of CVD‐Grown Multilayer MoSe2 Thin Film Transistors by Two‐Step Functionalization

Abstract Molybdenum diselenide (MoSe 2 ) has attracted attention as a potential semiconductor platform. However, the as‐synthesized MoSe 2 field‐effect transistors (FETs) tend to exhibit the arbitrary properties of n‐type, p‐type, or ambipolar behavior due to the uncontrolled growth condition. Here, two‐step functionalization is proposed to achieve n‐doping effect and long‐term stability in chemical vapor deposition (CVD)–grown MoSe 2 FETs using oxygen plasma treatment followed by the deposition of an Al 2 O 3 layer. After the two‐step surface functionalization procedure, three types of multilayer MoSe 2 FETs are all converted to n‐type with the improvement of their electrical characteristics and stability; the n‐doped multilayer MoSe 2 FETs exhibit an enhancement in field‐effect mobility from 12.23 to 31.57 cm 2 V −1 s −1 and a 3 times higher I on / I off , compared to pristine multilayer MoSe 2 FETs. This enhancement of electric performance is attributed to the oxidation of topmost MoSe 2 to interfacial MoO x with SeO x induced by the oxygen plasma treatment, as well as to the existence of fixed positive charges in deposited Al 2 O 3 . The functionalized devices exhibit excellent stability against stress, as confirmed with negative bias illumination stress tests for 7200 s. Moreover, an environmental stability test for 21 days reveals no degradation in electric performance of MoSe 2 FETs.