Crystal phase-selective epitaxy of rutile and anatase Nb-doped TiO ₂ films on a GaN template by the helicon-wave-excited-plasma sputtering epitaxy method

Crystal phase-selective epitaxy of Nb-doped TiO₂ (TiO ₂:Nb) films on GaN is demonstrated using the helicon-wave-excited- plasma sputtering epitaxy method. On the clean (0001) GaN, rutile (100) TiO ₂:Nb was grown regardless of growth temperature (T_g). On the (0001) GaN covered with a monolayer-thick (100) or (001) β-Ga ₂O₃, anatase (001) TiO₂:Nb was grown with the in-plane relation 〈110〉TiO₂ || 〈112̄0〉GaN under high T_g and low O₂ partial pressure conditions. The transmittance between 450 and 900nm for the 200-nm-thick films was approximately 80%. Typical resistivity of the anatase TiO₂:Nb/GaN heterostructure was as low as 3.6 × 10^-4 ω.cm, due to the interfacial conduction.