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 L-1- and L-3-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 (SE) were also used to scrutinize the electronic structure. The direct bandgap of the annealed film was estimated to be similar to 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.