Preparation and Investigation of optoelectronic properties of polarity-controllable titanium oxide thin films using high-power impulse magnetron sputtering

Abstract

In this study, we employed High Power Impulse Magnetron Sputtering (HiPIMS) to fabricate TiO_x thin films on the Si (100) as well as Corning eagle XG glass substrates and investigated their optical, electrical, and crystalline properties for application in optoelectronic devices. We examined the effects of varying the oxygen flow ratios (f_O2) on the chemical composition, crystalline structure, optoelectronic properties, and microstructure of the TiO_x films. The results showed that as f_O2 increased, the dominant bonding states within the films shifted from Ti⁰, Ti²⁺, and Ti³⁺ (at f_O2 = 0 %) to mainly Ti²⁺, Ti³⁺, and Ti⁴⁺ (at f_O2 ≥ 0.5 %); the conductivity type of the films also changed from n-type to p-type due to the transformation of the dominant oxidation state to Ti³⁺. Additionally, the film's transmittance significantly increased. The best p-type TiO_x film with optimal properties was obtained with f_O2 = 0.5 %.

Furthermore, we investigated the effects of deposition pressure on the film's properties. It was observed that as the deposition pressure increased, the resistivity of the film gradually increased, while the transmittance showed a significant enhancement. These changes were attributed to alterations in the crystal structure and the transformation of Ti positions into Ti³⁺ and Ti⁴⁺. Finally, to evaluate the suitability of these titanium oxide films for light-sensing applications, we measured the variations in I-t and I-V curves for samples with different f_O2 and deposition pressure. We further analyzed the response time of the current rise and decay when the films were exposed to UV light and their sensitivity towards the UV light source. p-type TiO_x films with excellent light-sensing properties can be used in monitoring systems for energy conservation and carbon reduction.