Phase-controlled synthesis of SnOx thin films by atomic layer deposition and post-treatment

Abstract Tin oxide (SnO x ) is a promising oxide semiconductor due to the distinct properties of n-type SnO 2 and p-type SnO based on its stoichiometry. However, the stoichiometry control of SnO x remains challenging due to the thermodynamic instability of SnO. In the study, we focus on establishing the controllable stoichiometry of SnO x via atomic layer deposition (ALD) and subsequent treatment. The controllable synthesis of SnO 2 and SnO is investigated by multiple analyses involving the chemical composition, crystal structure, and band structure. The ALD SnO x is composed mostly of Sn 4+ O bonds with intrinsic oxygen vacancies and is transformed into crystalline SnO 2 phase via post-annealing. The refractive index (~1.8) and optical bandgap energy (~3.6 eV) of ALD SnO x correspond to those of SnO 2 . Post-deposition treatment with H 2 plasma enables the effective transformation of SnO 2 into SnO due to the easy penetration of H + ion into the film and de-bonding of Sn O via ion bombardment. The transformed SnO exhibits a significant amount of Sn 2+ O bonds with a refractive index of 2.8 and optical bandgap energy of ~2.9 eV. Specifically, the transformed SnO exhibits promise as an oxide semiconductor because it exhibits excellent stability with respect to re-oxidation into SnO 2 or further reduction into Sn metal. The present study advances practical applications that require a stable p-n junction through n-type SnO 2 and p-type SnO in various forms of device architectures.