Unveiling surface reactivity: the crucial role of auxiliary ligands in Gallium amidinate-based precursors for Atomic Layer Deposition

Abstract

Two novel gallium precursors for Atomic Layer Deposition (ALD), LGaMe₂ and LGa(NMe₂)₂ with L = N,N’-di-tertbutylacetamidinato, were successfully synthesised from a carbodiimide and gallium trichloride. The compounds were characterised by NMR spectroscopy and HR-mass spectrometry, confirming their monomeric nature. Their surface reactivity under ALD conditions with H₂O and H₂S co-reactants was explored using in-situ quartz crystal microbalance (QCM) measurements. LGaMe₂, bearing methyl ligands, was found to inhibit film growth, with deposition halting after three cycles. In contrast, LGa(NMe₂)₂ facilitated the successful growth of films using both H₂O and H₂S leading to Ga2O3 and Ga2S3 respectively, as confirmed by additional thin film ex-situ characterisation.This study underscores the critical role of auxiliary X ligands (here Me or NMe₂) in determining ALD process efficiency, and emphasises the complexity and unique nature of surface chemistry compared to solution-phase behaviour.