Phase-controlled SnO₂ and SnO growth by atomic layer deposition using Bis(N-ethoxy-2,2-dimethyl propanamido)tin precursor

Atomic layer deposition (ALD) of SnO and SnO₂ thin films was successfully demonstrated over a wide temperature range of 70–300 °C using a divalent Sn-precursor, bis(N-ethoxy-2,2-dimethyl propanamido)tin (Sn(edpa)₂). The regulated growth of the SnO₂ and SnO films was realized by employing O₂-plasma and H₂O, respectively. Pure SnO₂ and SnO films were deposited with negligible C and N contents at all the growth temperatures, and the films exhibited polycrystalline and amorphous structures, respectively. The SnO₂ films presented a high transmittance of > 85% in the wavelength range of 400–700 nm and an indirect band gap of 3.6–4.0 eV; meanwhile, the SnO films exhibited a lower transmittance of > 60% and an indirect band gap of 2.9–3.0 eV. The SnO₂ films exhibited n-type semiconducting characteristics with carrier concentrations of 8.5 × 10¹⁶–1.2 × 10²⁰ cm⁻³ and Hall mobilities of 2–26 cm²/V s. By employing an alternate ALD growth of SnO and SnO₂ films, SnO₂/SnO multilayer structures were successfully fabricated at 120 °C. The in-situ quadrupole mass spectrometry analysis performed during ALD revealed that the oxidation of chemisorbed Sn-precursor occurs dominantly during the Sn(edpa)₂/O₂-plasma ALD process, resulting in the production of combustion by-products, whereas the Sn(edpa)₂/H₂O ALD process was governed by a ligand exchange reaction with the maintenance of the original oxidation state of Sn²⁺.