Synthesis of Homoleptic Gallium Alkoxide Complexes and the Chemical Vapor Deposition of Gallium Oxide Films

A general synthetic route to gallium alkoxide complexes involving reactions of gallium tris(dimethylamide) with alcohols was developed and gallium oxide films were prepared by using a gallium alkoxide complex as the precursor in a chemical vapor deposition process. The complex [Ga(NMe2)3]2 reacted with i-BuOH and i-PrOH to yield the tetramers Ga[(μ-OR)2Ga(OR)2]3 where R = i-Bu and i-Pr, respectively. Consistent with previous observations, the solution equilibrium Ga[(μ-O-i-Pr)2Ga(O-i-Pr)2]3 ⇄ 2[Ga(μ-O-i-Pr)(O-i-Pr)2]2 was observed (ΔH° = 8.7(0.4) kcal/mol, ΔS° = 27(1) eu, and Δ = 0.63(0.04) kcal/mol). For the less sterically crowded tetramer Ga[(μ-O-i-Bu)2Ga(O-i-Bu)2]3, there was no evidence for a tetramer−dimer equilibrium. In contrast to the results obtained using i-BuOH and i-PrOH, the bulkier alcohols t-BuOH and EtMe2COH reacted with [Ga(NMe2)3]2 at room temperature to yield mixtures of the dimer [Ga(μ-OR)(OR)2]2 and the amine adduct Ga(OR)3(HNMe2), while i-PrMe2COH and Et2MeCOH reacted to produce Ga(OR)3(HNMe2) compounds exclusively. Upon heating in an open system, the amine could be removed from the Ga(OR)3(HNMe2) compounds to yield the corresponding homoleptic alkoxide dimers. Low-pressure chemical vapor deposition using [Ga(μ-O-t-Bu)(O-t-Bu)2]2 and O2 precursors gave Ga2O3 films at substrate temperatures of 300−700 °C. The as-deposited films were carbon-free, amorphous, and highly transparent in the 350−800-nm region.