First-principles understanding of hole mobility and intrinsic transport mechanisms in Sn(ii) oxides

Abstract

Transparent conducting oxides (TCOs) have attracted considerable attention due to their applications in electronic devices, ranging from solar cells to flat panel displays and touch screens. While n-type TCOs, such as indium tin oxide (ITO) and tin dioxide (SnO₂), have been extensively studied and widely adopted, the development of p-type TCOs remains an important challenge due to several factors, including their low carrier mobilities which arise from the flat valence bands of metal oxides. In this work, we employ first-principles calculations to investigate the transport properties of the binary Sn(II) oxide SnO and four promising ternary Sn(II) oxides: TiSnO₃, K₂Sn₂O₃ (in both cubic and rhombohedral phases), and Rb₂Sn₂O₃. Our results show that the studied ternary Sn(II) oxides exhibit carrier mobilities comparable to state-of-the-art n-type TCOs, with band gaps ranging between 2 and 3 eV. The computational methodology, which provides an exact treatment of the Boltzmann transport equation, yields excellent agreement with experimental mobility values for SnO, suggesting that experimental measurements for the ternary compounds may also follow closely our predictions. In addition, we highlight the importance of effective masses for carrier lifetimes and the number of scattering channels involved, using a new decoupling approach for the scattering rates. Finally, we reveal that in SnO, high-frequency phonon modes involving oxygen motion dominate electron–phonon interactions, while in ternary compounds, vibrational modes involving the third atomic species are also of crucial importance. These findings could offer new perspectives on mitigating these specific vibrations to reduce electron–phonon scattering and enhance transport properties in oxide semiconductors.