Stability, binding and charge localization in p-type amorphous SnO and Sn-Ta-O from ab-initio molecular dynamics

The search for high-performance p-type metal oxides – which would enable realization of complementary circuits, transparent p-n junction and other electronic devices – remains one of the unsolved issues in oxide electronics. Tin monoxide has been shown to produce p-type thin-film transistors, owing to a promising hole mobility of 2.4 cm²/Vs that arises from the s² electronic configuration of Sn²⁺ and dispersed valence band in the layered SnO. However, the practical use of crystalline SnO is limited due to (i) stability and dupability issues of SnO associated with tin preference for valence 4 (as in well-known n-type SnO₂); (ii) small band gap ~0.7 eV; and (iii) anisotropic hole effective mass. Further search for p-type MOs should involve amorphous phases of SnO-based multi-cation materials where metal composition helps stabilize Sn²⁺ and open the band gap, while the disordered structure ensures uniform isotropic electronic properties and favors large polaron appearance.

In this work, density-dependent ab-initio liquid-quench molecular dynamics simulations are performed for amorphous SnO and Sn-Ta-O to determine the role of disorder and Ta doping on the structural stability and the short- and medium-range structural characteristics; to understand the origin of electronic tail states near the top of the valence band; and to provide practical design principles for continued search of metal oxides with useful p-type behavior.