Composition, Microstructure, and Electrical Performance of Sputtered SnO Thin Films for p-Type Oxide Semiconductor

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 (SE) 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.

Material Design of New p-Type Tin Oxyselenide Semiconductor through Valence Band Engineering and Its Device Application

This paper reports a new p-type tin oxyselenide (SnSeO), which was designed with the concept that the valence band edge from O 2p orbitals in the majority of metal oxides becomes delocalized by hybridizing Se 4p and Sn 5s orbitals. As the Se loading increased, the SnSeO film structures were transformed from tetragonal SnO to orthorhombic SnSe, which was accompanied by an increase in the amorphous phase portion and smooth morphologies. The SnSe_0.56O_0.44 film annealed at 300 °C exhibited the highest Hall mobility (μ_Hall), 15.0 cm² (V s)^-1, and hole carrier density (n_h), 1.2 × 10¹⁷ cm^-3. The remarkable electrical performance was explained by the low hole effective mass, which was calculated by a first principle calculation. Indeed, the fabricated field-effect transistor (FET) with a p-channel SnSe_0.56O_0.44 film showed the high field-effect mobility of 5.9 cm² (V s)^-1 and an I_ON/OFF ratio of 3 × 10². This work demonstrates that anion alloy-based hybridization provides a facile route to the realization of a high-performance p-channel FET and complementary devices.