Characterization of oxide nanocomposites formed at annealed TiN/SnS₂ heterostructure thin film

The compositional evolution of TiN/SnS₂ thin films exposed to post-deposition annealing (PDA) at various O₂ pressures (P(O₂) = 0, 0.1, 1, 2 and 5 Torr) was examined using X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy and transmission electron microscopy. All the results of the analyses showed that the PDA oxidized the hetero-structured films to form SnO₂+TiO₂ nanocomposites throughout the film, driving out sulfur ions. The chemical and microstructural evolution according to the oxidation was confirmed by TEM and the energy-dispersive spectroscopy analyses. The XAS analysis particularly showed that with increasing P(O₂), the composition of the nanocomposites changed and the microstructure of the titania in the nanocomposites evolved from an anatase to a rutile structure gradually. The conduction band structure also changed in accordance with this microstructural evolution. Electrical measurements on devices with the oxidized SnS₂/TiN heterostructure and additional thick TiN metal electrode, further showed that the contact resistance decreased dramatically after the PDA. This implies that the formation of SnO₂+TiO₂ at the interface between semiconducting SnS₂ and metallic TiN can be an effective way to improve the metal-semiconductor contacts.