Influence of composition on structure, morphology and dielectric properties of Bi_xAl_yO_z composite films synthesized by atomic layer deposition

In this experiment we used atomic layer deposited Bi₂O₃ and Al₂O₃ films to fabricate the Bi_xAl_yO_z nanocomposite films. Bismuth composition was modulated in a series of samples via altering the number of bismuth subsidiary cycles. We discovered that the bismuth composition in atomic percent did not monotonically increase with the rise of the number of bismuth cycles. To explain this unconventional variation trend we proposed a growth mechanism regarding the steric hindrance of Bi(thd)₃ and the diffusion of TMA. A single Debye-like relaxation can be determined for the Bi_xAl_yO_z films with a parallel RC element to reflect it. The change in the dielectric response, such as dielectric constant and ac conductivity, was found to be in agreement with the variation of bismuth concentration. This could be attributed to the effect of 6s² lone pair electrons in Bi-O dipoles. To further confirm the conductive strength, we estimated the optical band gap (E_g) using plots of (αhν)² versus hν. The value of E_g would decrease from 5.62 eV to 5.00 eV as the bismuth content rises in the Bi_xAl_yO_z films.