X-ray spectroscopy study on the electronic structure of Sn-added p-type SnO films

The electronic structure of the Sn-added p-type SnO thin film was examined using X-ray absorption spectroscopy (XAS). Sn was intentionally added to a pristine SnO film, and the film was annealed to form p-type SnO. Sn L1- and L3-edge XAS was used to examine the oxidation states of the Sn-added p-type SnO. Compared to the case of the reference SnO, the spectrum of the Sn-added SnO (after annealing) partly contained the lineshape for SnO2, suggesting that the oxidation of Sn+SnO was progressed such that the film became preferably SnO2+SnO rather than Sn+SnO2. O K-edge XAS, X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry were also used to scrutinize the electronic structure. The direct bandgap of the annealed film was estimated to be ~3.6 eV, consistent with the reported SnO2 bandgap, while that of the as-deposited Sn-added SnO was <2.5 eV. The large bandgap after annealing suggests that the metallic Sn was no longer in existence and manifested the functionality of the annealed Sn+SnO as a p-type semiconductor.