Thickness and Morphology Dependent Electrical Properties of ALD‐Synthesized MoS2 FETs

Abstract

AbstractMoS2 is a layered 2D semiconductor with thickness‐dependent electrical properties. Often, 6–12 nm of MoS2 are advised to be used as the channel material in field‐effect transistors (FETs) for achieving an optimal device electrical performance. However, this notion is based on exfoliated MoS2 flakes that cannot be employed for large‐area and wafer‐scale applications. In this work, the thickness‐dependent electrical properties of atomic layer deposition (ALD)‐based MoS2 FETs are studied. A two‐step approach is used for the synthesis of MoS2, wherein large‐area and thickness‐controlled MoOx films are initially grown using plasma‐enhanced (PE‐)ALD and subsequently sulfurized in H2S gas. The number of MoOx PE‐ALD cycles is varied systematically to obtain MoS2 films with a thickness range of 1–10 nm. Current–voltage (I–V) characterization of the fabricated MoS2 FETs with various channel thicknesses reveals that ≈1.2 nm MoS2 suffices in attaining the best device electrical performance. Scanning transmission electron microscopy imaging elucidates that the synthetic MoS2 films are polycrystalline and the resultant ≈1.2 nm of MoS2 are not completely continuous. The empty areas in the polycrystalline MoS2 network can serve as locations for side contact formation, leading to substantial improvements in the device metrics fabricated from such ultrathin MoS2 films.