Structural, optical, and electrical properties of TiO2 thin films deposited by ALD: Impact of the substrate, the deposited thickness and the deposition temperature

Abstract

TiO2 films were deposited by ALD on Si and glass substrates. FTIR analysis reveals an incomplete process for deposition temperatures below 160 °C. The transition from the amorphous to the crystallized anatase phase is observed during the variation of the deposition temperature. Films were uniform and homogeneous, with a crystallization threshold temperature depending on the substrate’s nature. This delay in crystallization temperature was highlighted by many characterization techniques and found higher by about 50 °C on glass compared to Si substrate. We have also identified the determining role of the deposition temperature and the thickness in the crystallization process and we propose a growth model, independently of the substrate’s nature, using different structural analyses. TiO2 refractive index (n) and extinction coefficient (k) were studied at various deposition temperature. The evolution of the TiO2 polarizability (αopt) with material density was determined from n values, showing a large variation of polarizability as a function of material density, in agreement and complementary with other studies. The investigation of the dielectric properties at low frequency shows that the losses and relaxation in TiO2 decrease with deposition temperature, reaching at 300 °C a high and frequency-independent dielectric constant, close to the one reported for polycrystalline anatase.