Direct atomic layer deposition of ultrathin aluminium oxide on monolayer $MoS_2$ exfoliated on gold: the role of the substrate

TL;DR

This study demonstrates the successful direct atomic layer deposition of ultrathin aluminium oxide on monolayer MoS2 supported by gold, revealing substrate-induced effects on nucleation and film uniformity with implications for device fabrication.

Contribution

It introduces a novel method for high-quality ALD of Al2O3 on monolayer MoS2 using a gold substrate, highlighting the substrate's role in nucleation and film quality.

Findings

High-quality 3.6 nm Al2O3 films were grown on MoS2/Au at 250°C.

Nucleation was significantly improved on MoS2/Au compared to other substrates.

Gold substrate induces tensile strain and p-doping, enhancing ALD nucleation.

Abstract

In this paper we demonstrated the thermal Atomic Layer Deposition (ALD) growth at 250 {\deg}C of highly homogeneous and ultra-thin ($\approx$ 3.6 nm) $Al_2O_3$ films with excellent insulating properties directly onto a monolayer (1L) $MoS_2$ membrane exfoliated on gold. Differently than in the case of 1L $MoS_2$ supported by a common insulating substrate ($Al_2O_3/Si$), a better nucleation process of the high-k film was observed on the 1L $MoS_2/Au$ system since the ALD early stages. Atomic force microscopy analyses showed a $\approx 50\%$ $Al_2O_3$ surface coverage just after 10 ALD cycles, its increasing up to $>90\%$ (after 40 cycles), and an uniform $\approx$ 3.6 nm film, after 80 cycles. The coverage percentage was found to be significantly reduced in the case of 2L $MoS_2/Au$, indicating a crucial role of the interfacial interaction between the aluminum precursor and $MoS_2/Au$ surface. Finally, Raman spectroscopy and PL analyses provided an insight about the role played by the tensile strain and p-type doping of 1L $MoS_2$ induced by the gold substrate on the enhanced high-k nucleation of $Al_2O_3$ thin films. The presently shown high quality ALD growth of high-k $Al_2O_3$ dielectrics on large area 1L $MoS_2$ induced by the Au underlayer can be considered of wide interest for potential device applications based on this material system.