TY - JOUR
T1 - Short-range order in amorphous oxygen-deficient TaOx thin films and its relation to electrical conductivity
AU - Amrani, Tamir
AU - Basha, Adham
AU - Azulay, Amram
AU - Levi, George
AU - Kohn, Amit
AU - Goldfarb, Ilan
N1 - Publisher Copyright:
© 2023 Author(s).
PY - 2023/8/7
Y1 - 2023/8/7
N2 - Thin films of tantalum oxide hold promising functional properties for electronic applications such as resistive random-access memory. For this aim, correlating the structure and charge transport properties of oxygen-deficient derivatives is crucial. Here, using electron scattering measurements from nanoscale volumes in a transmission electron microscope (TEM), we report how oxygen content affects short-range order in amorphous TaOx thin films, where 1.34 ≤ x ≤ 2.50. By extracting the bond lengths, we observe that the dominant type of Ta-Ta distances change with decreasing oxygen content from next-nearest-neighbor, ∼3.8 Å, to nearest-neighbor, ∼3 Å. We relate this decrease to the Ta-O polyhedral network within the film, namely decreasing oxygen content increases the presence of TaO5 at the expense of TaO6 polyhedra. The reduction in oxygen content is accompanied by a significant reduction of electrical resistivity of the films from over 4.3 × 103 to (4 ± 0.05)×10−3 Ω × cm. In particular, we observe a sharp percolative decrease in resistivity of three orders of magnitude, at x ∼ 1.9. Ta oxidation states, measured by x-ray photoelectron spectroscopy, suggest that the main polyhedral building block within the TaO2.5 film is TaO6, while in oxygen-deficient films, the relative fractions of TaO5 polyhedra and metallic Ta increase. At even lower oxygen content, x ∼ 1.34, TEM and x-ray diffraction detect crystallites of Ta with cubic and metastable tetragonal structures. We propose that TaO5 polyhedra and Ta crystallites increase conductivity due to direct bonding of Ta atoms, as manifested by nearest-neighbor Ta-Ta bond length, thus enabling conductive paths for charge transport.
AB - Thin films of tantalum oxide hold promising functional properties for electronic applications such as resistive random-access memory. For this aim, correlating the structure and charge transport properties of oxygen-deficient derivatives is crucial. Here, using electron scattering measurements from nanoscale volumes in a transmission electron microscope (TEM), we report how oxygen content affects short-range order in amorphous TaOx thin films, where 1.34 ≤ x ≤ 2.50. By extracting the bond lengths, we observe that the dominant type of Ta-Ta distances change with decreasing oxygen content from next-nearest-neighbor, ∼3.8 Å, to nearest-neighbor, ∼3 Å. We relate this decrease to the Ta-O polyhedral network within the film, namely decreasing oxygen content increases the presence of TaO5 at the expense of TaO6 polyhedra. The reduction in oxygen content is accompanied by a significant reduction of electrical resistivity of the films from over 4.3 × 103 to (4 ± 0.05)×10−3 Ω × cm. In particular, we observe a sharp percolative decrease in resistivity of three orders of magnitude, at x ∼ 1.9. Ta oxidation states, measured by x-ray photoelectron spectroscopy, suggest that the main polyhedral building block within the TaO2.5 film is TaO6, while in oxygen-deficient films, the relative fractions of TaO5 polyhedra and metallic Ta increase. At even lower oxygen content, x ∼ 1.34, TEM and x-ray diffraction detect crystallites of Ta with cubic and metastable tetragonal structures. We propose that TaO5 polyhedra and Ta crystallites increase conductivity due to direct bonding of Ta atoms, as manifested by nearest-neighbor Ta-Ta bond length, thus enabling conductive paths for charge transport.
UR - http://www.scopus.com/inward/record.url?scp=85168123136&partnerID=8YFLogxK
U2 - 10.1063/5.0156335
DO - 10.1063/5.0156335
M3 - Article
AN - SCOPUS:85168123136
SN - 0003-6951
VL - 123
JO - Applied Physics Letters
JF - Applied Physics Letters
IS - 6
M1 - 063502
ER -