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(NMe 2 ) 3 ] 2 reacted with i -BuOH and i -PrOH to yield the tetramers Ga[( μ -OR) 2 Ga(OR) 2 ] 3 where R = i -Bu and i -Pr, respectively. Consistent with previous observations, the solution equilibrium Ga[( μ -O- i -Pr) 2 Ga(O- i -Pr) 2 ] 3 ⇄ 2[Ga( μ -O- i -Pr)(O- i -Pr) 2 ] 2 was observed (Δ H ° = 8.7(0.4) kcal/mol, Δ S ° = 27(1) eu, and Δ = 0.63(0.04) kcal/mol). For the less sterically crowded tetramer Ga[( μ -O- i -Bu) 2 Ga(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 EtMe 2 COH reacted with [Ga(NMe 2 ) 3 ] 2 at room temperature to yield mixtures of the dimer [Ga( μ -OR)(OR) 2 ] 2 and the amine adduct Ga(OR) 3 (HNMe 2 ), while i -PrMe 2 COH and Et 2 MeCOH reacted to produce Ga(OR) 3 (HNMe 2 ) compounds exclusively. Upon heating in an open system, the amine could be removed from the Ga(OR) 3 (HNMe 2 ) 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 O 2 precursors gave Ga 2 O 3 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.