Optical and transport properties of LaTi1-xMx(O,N)3±δ (x=0; 0.1, M=Nb5+, W6+) thin films prepared by plasma ammonolysis

Abstract

Oxynitride thin films of composition LaTi1−xMx(O,N)3±δ with x=0; 0.1 and M=Nb5+, W6+ were prepared by nitridation via microwave-induced plasma (MIP) ammonolysis, which allowed keeping the nitridation time short (16 min). The higher possible oxidation states of the B-site substituents (Nb5+, W6+) with respect to Ti4+ caused higher N content for LaTi0.9Nb0.1(O,N)3±δ and LaTi0.9W0.1(O,N)3±δ compared to LaTiO2N due to charge-compensation. XPS O 1s and N 1s core level and valence band spectra evidenced for increasing N content in the order LaTiO2N<LaTi0.9Nb0.1(O,N)3±δ<LaTi0.9W0.1(O,N)3±δ. All films were N deficient comparing with their stoichiometric formulas and assuming cations in highest oxidation states. Along with increasing N content, the bandgaps decreased from 2.4 to 2.2 and 2.1 eV for LaTiO2N, LaTi0.9Nb0.1(O,N)3±δ, and LaTi0.9W0.1(O,N)3±δ and the electronic conductivities increased along with the decreased bandgaps. The Seebeck coefficients at 860 K indicated the highest charge-carrier density for LaTi0.9W0.1(O,N)3±δ.