Formation of Metallic States between Insulating SnO and SnO2

Arwa Albar, Zhenwei Wang, Husam Niman Alshareef, Udo Schwingenschlögl, "Formation of Metallic States between Insulating SnO and SnO2"
​Adv. Mater. Interfaces 2016, 1500334​
Arwa Albar, Zhenwei Wang, Husam Niman Alshareef, Udo Schwingenschlögl
interface; metallicity; semiconductors; tin oxide
​​Transparent conducting oxides are frequently applied in solar cells and flat panel displays.[1] While there are many n-type materials in this class, such as In2O3, ZnO, and SnO2, only few p-type materials are known, including CuAlO2, SrCu2O2, and ZnRh2O4. In addition, p-type transparent conducting oxides typically show a much lower mobility than the n-type analogues.[2] Recently, substantial progress has been achieved in this respect, as a record hole mobility has been obtained in SnO,[3] which opens up many new possibilities in transparent electronics. Sn supports the oxidation states +2 and +4, which indeed leads to two stable oxides, SnO and SnO2. SnO2 is a well-known semiconductor with a direct band gap of 3.6 eV and is frequently used in modern technology.[4] Similar to many other oxides, the conduction band minimum is dominated by dispersive states, which can host n-type conductivity, while the valence band maximum is dominated by O 2p states, which are rather localized so that it is difficult to achieve reasonable p-type conductivity.[5] The n-type behavior of SnO2 usually is attributed to O vacancies.[6] However, it is now accepted that, in addition, substitution of H for O results in shallow donor states.