Postgrowth annealing effects on structural, optical, and electrical properties of β-MoO3 films grown by molecular beam epitaxy

We report the postgrowth annealing effects on the structural, optical, and electrical properties of a low-temperature grown β-phase MoO3 film on a c-plane sapphire substrate by molecular beam epitaxy. By employing the postgrowth annealing at 600°C in an oxygen atmosphere, the film was completely transformed from β-phase to thermo-dynamically stable α-phase. On the other hand, oxygen deficient MoO3-x domains were introduced into the film by the annealing at the same temperature in a nitrogen atmosphere. The latter film exhibited a high absorbance in a visible region accompanied by a decrease in resistivity.