Atomic Layer Deposition of p-Type Epitaxial Thin Films of Undoped and N-Doped Anatase TiO₂

Abstract

Employing atomic layer deposition, we have grown p-type epitaxial undoped and N-doped anatase TiO2(001) thin films on c-axis Al2O3 substrate. From X-ray diffraction and transmission electron microscopy studies, crystallographic relationships between the film and the substrate are found to be (001)TiO2//(0001)Al2O3 and [1̅10]TiO2//[011̅0]Al2O3. N-doping in TiO2 thin films enhances the hole concentration and mobility. The optical band gap of anatase TiO2 (3.23 eV) decreases to 3.07 eV upon N-doping. The epitaxial films exhibit room-temperature ferromagnetism and photoresponse. A TiO2-based homojunction diode was fabricated with rectification from the p-n junction formed between N-doped p-TiO2 and n-TiO2.

Epitaxially grown BaM hexaferrite films having uniaxial axis in the film plane for self-biased devices

“…Unsurprisingly, the dislocations periodically appear at the interface every dozen of lattice fringes, or about every 8 unit cells, indicating a misfit parameter of ~7% between BaM and sapphire in the (0001) planes. The formation of misfit dislocations at the interface by strain relaxation infers the epitaxial growth of the film on substrate495051. The strains initiated at the interface will influence the magnetic properties of the entire film, as will be shown by the following VSM results.…”

Synthesis of p‐type N‐doped TiO2 thin films by co‐reactive magnetron sputtering

“…On the contrary, films 1 and 3 (prepared using the lowest ϕN 2 values) characterized by a lower concentration of dopant present proper electrical properties for DSSCs applications that are in line with ALD synthesized N-doped TiO 2 . [34] Other remarks concern the measured hole mobility which is clearly enhanced compared with previously reported values for sputtered NiO (<0.5 cm 2 ·V −1 ·s −1 ) and a quite similar conductivity which could be due to a lower concentration of carriers, that is,~10 15 to 10 16 cm −3 versus~10 17 to 10 19 holes/cm 3 for NiO. [21,49] In the end, we succeed to switch the semiconductor conductivity of TiO 2 from n-to p-type by N doping and the mobility was greatly improved.…”

“…To our knowledge, only one work reports on the successful synthesis of p‐type TiO 2 :N by ALD. In the latter, the p‐type character has been associated with the generation of Ti vacancies . Unfortunately, this kind of doping is not suitable for an application as a charge transport layer into a DSSCs because of the generated trap states below the conduction band and the bad affinity between the dyes and a Ti‐deficient semiconductor surface.…”

“…In the latter, the ptype character has been associated with the generation of Ti vacancies. [34] Unfortunately, this kind of doping is not suitable for an application as a charge transport layer into a DSSCs because of the generated trap states below the conduction band and the bad affinity between the dyes and a Ti-deficient semiconductor surface. In the present work, we rely on the possible fine-tuning of the chemistry offered by the co-reactive magnetron sputtering technique to successfully grow p-type TiO 2 :N with transmittance close to the TiO 2 one in the near UV-visible light region and higher hole mobility than NiO.…”

Nanoengineering Energy Conversion and Storage Devices via Atomic Layer Deposition

“…Some single crystalline films have been obtained under layer-bylayer homoepitaxy and heteroepitaxial growth models, such as anatase (101) and rutile (110) TiO 2 films on rutile TiO 2 (110) substrates, [268] anatase (001) TiO 2 film on c-axis Al 2 O 3 substrate, [269] and Sn-doped In 2 O 3 (ITO) film on Y-stabilized ZrO 2 (YSZ) substrates. However, most of the synthesized ALD materials are limited to polycrystalline and amorphous.…”