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-tert-butylacetamidinato, 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.