Growth of Al-rich AlGaN thin films by purely thermal atomic layer deposition

AlGaN films with high Al content (Al/Ga ∼5.5) were successfully grown via thermal atomic layer deposition at low temperature (342 °C) using trimethylaluminum and triethylgallium as Al and Ga precursors, respectively, and ammonia as reactant gas. Incorporation of GaN into AlN is evidenced by the dependence of the growth rate on the pulse ratio of AlN and GaN subcycles. Chemical analysis reveals the composition of the AlGaN film and the existence of GaN chemical bonding state irrespective of the pulse ratio. Although the chemical composition of AlGaN film was little affected by the pulse ratio between AlN and GaN cycles, the electrical properties of the films could be modulated. Layer-by-layer growth with close to theoretical dielectric constant could be achieved by the introduction of sufficient number of AlN subcycles. Density functional theory calculations were utilized to assess the surface reaction mechanism of the Al and Ga precursors and ammonia reactant during deposition, which show smaller reactivity of the Ga precursor compared to that of Al would affect the doping ratio of the ALD AlGaN films.