Toolbox of Advanced Atomic Layer Deposition Processes for Tailoring Large-Area MoS₂ Thin Films at 150 °C

Abstract

Two-dimensional MoS2 is a promising material for applications, including electronics and electrocatalysis. However, scalable methods capable of depositing MoS2 at low temperatures are scarce. Herein, we present a toolbox of advanced plasma-enhanced atomic layer deposition (ALD) processes, producing wafer-scale polycrystalline MoS2 films of accurately controlled thickness. Our ALD processes are based on two individually controlled plasma exposures, one optimized for deposition and the other for modification. In this way, film properties can be tailored toward different applications at a very low deposition temperature of 150 °C. For the modification step, either H2 or Ar plasma can be used to combat excess sulfur incorporation and crystallize the films. Using H2 plasma, a higher degree of crystallinity compared with other reported low-temperature processes is achieved. Applying H2 plasma steps periodically instead of every ALD cycle allows for control of the morphology and enables deposition of smooth, polycrystalline MoS2 films. Using an Ar plasma instead, more disordered MoS2 films are deposited, which show promise for the electrochemical hydrogen evolution reaction. For electronics, our processes enable control of the carrier density from 6 × 1016 to 2 × 1021 cm–3 with Hall mobilities up to 0.3 cm2 V–1 s–1. The process toolbox forms a basis for rational design of low-temperature transition metal dichalcogenide deposition processes compatible with a range of substrates and applications.

Nb Doping and Alloying of 2D WS2 by Atomic Layer Deposition for 2D Transition Metal Dichalcogenide Transistors and HER Electrocatalysts

“…In both films, a significant amount of hydrogen is observed at 7.1 TFU (12–14%), which likely originates from the use of H 2 S plasma (which contains hydrogen radicals) in the preparation of the films, as has been reported before . Similar behavior was also observed in our recent work on the PEALD of MoS 2 . , In that work, we have shown that it is possible to mitigate H incorporation during PEALD by using advanced ALD supercycle approaches . Future studies will aim to minimize unintentional hydrogen content, thus enabling more stable resistivity values.…”

“…7 Similar behavior was also observed in our recent work on the PEALD of MoS 2 . 46,47 In that work, we have shown that it is possible to mitigate H incorporation during PEALD by using advanced ALD supercycle approaches. 47 Future studies will aim to minimize unintentional hydrogen content, thus enabling more stable resistivity values.…”

“…46,47 In that work, we have shown that it is possible to mitigate H incorporation during PEALD by using advanced ALD supercycle approaches. 47 Future studies will aim to minimize unintentional hydrogen content, thus enabling more stable resistivity values. Back-gated test structures (see Figure S6) were prepared from these two films.…”

Two-Dimensional Semiconductors and Transistors for Future Integrated Circuits

“…However, in terms of the cost effectiveness and mass production, MOCVD and CVD methods are more suitable for industrialization than PLD and MBE. Additionally, benefiting from the layer-by-layer growth mode at low temperatures and high scalability, atomic layer deposition (ALD) is also a promising method for synthesizing large-area 2D materials with a uniform thickness. − However, the 2D materials synthesized by ALD have lower crystallinity than samples synthesized by the other bottom-up deposition approaches mentioned above. Therefore, a subsequent high-temperature annealing process is generally preformed to improve crystallinity …”

Structural Aspects of MoSx Prepared by Atomic Layer Deposition for Hydrogen Evolution Reaction

“…Regardless, most of the available ALD processes offer limited control over stoichiometry and crystallinity of MoS x . Plasma-enhanced ALD (PEALD) offers more freedom in tailoring film properties, − which also enables control of HER performance. ,, Recently, we have shown that controlling the plasma chemistry via feed gas composition enables tailoring stoichiometry, crystallinity, morphology, and electronic properties of MoS x within a broad range …”