Synthesis and Structural Characterization of β‐Ketoiminate‐Stabilized Gallium Hydrides for Chemical Vapor Deposition Applications

Abstract

Bis-β-ketoimine ligands of the form [(CH2 )n {N(H)C(Me)CHC(Me)O}2 ] (L(n) H2 , n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(L(n) )X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The β-ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(L(n) )H] (n=2 (7); n=3 (8)), which have been structurally characterised for the first time, confirming the formation of five-coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β-ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L(3) {GaMe2 }2 ] (5) and the hydride [Ga(L(3) )H] (8). The resulting films (F5 and F8, respectively) were amorphous as-deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric (F5) and oxygen-deficient (F8) Ga2 O3 thin films.

Molecular Main Group Metal Hydrides

“…Systems containing anionic (X-type) oxygen-based ligands, such as alkoxides, show an increased tendency to adopt oligomeric structures reflecting, at least in part, the smaller steric profile of OR substituents (cf., NR 2 ). Synthetically, Ga–O bonds in systems of this type tend to be accessed in facile fashion via protonolysis reactions of existing Ga–H linkages with alcohols and related OH-containing reagents. − Insertion of a carbonyl function into an existing Ga–H bond offers an alternative approach, for example, in the formation of O i Pr substituents from acetone . Regarding protonolysis, Veith, has reported the synthesis of a range of cyclic siloxygallanes derived from the reactions of [H 2 Ga­(μ-O t Bu) 2 GaH 2 ] ( 672 ) with silanols .…”

“…863 In similar fashion, β-ketoiminate ligands can be employed for the stabilization of monomeric gallium hydride complexes by exploiting reactions between Me 3 N•GaH 3 and the corresponding protio ligands. 860,861 Systems such as 675 and 676 (Figure 53) accessed this way have been targeted as welldefined precursors for the deposition of gallium oxide films.…”

Advances in Deposition of Main‐Group Metal Oxides and Rare‐Earth Oxides from Metal Enolates

“…Carmalt and coworkers discussed the synthesis, characterization, and deposition properties of aluminum, gallium, as well as indium hydride β-ketoiminate (15) and hydride β-diketonate metallorganic complexes [48][49][50] . The synthesis of metal hydride β-ketoiminate (15) complexes is depicted in Scheme 2.…”

“…The synthesis of metal hydride β-ketoiminate (15) complexes is depicted in Scheme 2. Formation of complex 15 from ligand 12 via the "logical" intermediate steps 13 and 14 is precluded by the failure of the latter chloride β-ketoiminate complex to undergo exchange with a series of hydride reagents (LiH, NaH, NaBH 4 , LiAlH 4 , NaBEt 3 H); reaction of 12 with the metal hydride complex [MH 3 (NMe 3 )] was successful 48,49 . The penta-coordinated gallium complex 15 (M = Ga, n = 2) was successfully applied as a single-source precursor for the aerosol-assisted chemical vapor deposition (AA-CVD) of Ga 2 O 3 48 .…”

“…The film composition and morphology were determined by EDX and XRPD, whereas UV-vis spectroscopy confirmed its high transparency (80-90%) and low reflectivity 48 . Gallium complexes of the type [Ga 2 Me 4 (L 13 )] and [GaH(L 13 )] (15, M = Ga, n = 2, 3) served as precursors for the AA-CVD of stoichiometric and oxygen-deficient Ga 2 O 3 thin films on glass 49 . Thermogravimetric analysis pointed to the onset temperatures of 215 (n = 2) and 235 ∘ C (n = 3).…”