New gallium complexes with malonic diester anions as molecular precursors for the MOCVD of Ga2O3 thin films

Five different homoleptic gallium complexes with malonic diester anions [Ga(ROCOCHOCOR)3] [R =Me (1), Et (2), iPr (3), tBu (4) and SiMe3 (5)] have been synthesised and characterised by 1H and 13C NMR, IR spectroscopy, electron ionisation mass spectrometry (EI-MS), and single-crystal X-ray diffraction. The thermal properties of the obtained compounds were evaluated by thermogravimetric studies to assess their suitability as precursors for the metal-organic chemical vapour deposition (MOCVD) of Ga2O3 thin films. MOCVD of Ga2O3 thin films was carried out starting from compound 2 in light of the promising features of this precursor. The as-deposited layers are amorphous and can be transformed into the monoclinic β-Ga2O3 phase upon annealing at 1000 °C ex situ. The film morphology was studied by scanning electron microscopy (SEM), and its composition was investigated by energy-dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). Almost stoichiometric Ga2O3 thin films with low levels of carbon incorporation were obtained.