Thickness and Morphology Dependent Electrical Properties of ALD‐Synthesized MoS<sub>2</sub> FETs
Reyhaneh Mahlouji, Marcel A. Verheijen, Yue Zhang, Jan P. Hofmann, W. M. M. Kessels, Ageeth A. Bol
Abstract
Abstract MoS 2 is a layered 2D semiconductor with thickness‐dependent electrical properties. Often, 6–12 nm of MoS 2 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 MoS 2 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 MoS 2 FETs are studied. A two‐step approach is used for the synthesis of MoS 2 , wherein large‐area and thickness‐controlled MoO x films are initially grown using plasma‐enhanced (PE‐)ALD and subsequently sulfurized in H 2 S gas. The number of MoO x PE‐ALD cycles is varied systematically to obtain MoS 2 films with a thickness range of 1–10 nm. Current–voltage ( I–V ) characterization of the fabricated MoS 2 FETs with various channel thicknesses reveals that ≈1.2 nm MoS 2 suffices in attaining the best device electrical performance. Scanning transmission electron microscopy imaging elucidates that the synthetic MoS 2 films are polycrystalline and the resultant ≈1.2 nm of MoS 2 are not completely continuous. The empty areas in the polycrystalline MoS 2 network can serve as locations for side contact formation, leading to substantial improvements in the device metrics fabricated from such ultrathin MoS 2 films.