Amorphous TiO₂/p-Si Heterojunction Photodiode Prepared by Low-Temperature Atomic Layer Deposition

Amorphous TiO₂ (a-TiO₂) films were deposited on p-type silicon (p-Si) substrates by ALD using TDMAT and H₂O as a Ti and O source, respectively, to fabricate the a-TiO₂/p-Si heterojunction photodiode. The electrical and optical properties of the as-deposited a-TiO₂ films on p-Si substrates by the ALD method have been investigated with annealing treatment effects. In order to understand the charge density and mobility that vary depending on the deposition temperature, the chemical composition of ALD TiO₂ was examined by XPS and I–V characteristics. a-TiO₂ prepared by ALD at low process temperature has exhibited nonstoichiometric TiO₂−x and n-type semiconducting properties, while majority carrier of positive hole increases as increasing growth temperature. The photocurrent was 10⁻⁶ A for UV and 10⁻⁷ A for visible light, while the dark current was 10⁻⁸ A for the ALD TiO₂ diode. After heat treatment, the photocurrent for visible light and UV remarkably decreased, indicating that heat treatment has a negative effect and degrades the optical absorption of TiO₂ film.