Insights into the electronic structure of tin() pyrochlore oxides with 5s lone pair states as transparent p-type oxide semiconductors

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 12; no. 29; pp. 11139 - 11148
• Main Authors: Shi, Jueli, Sheng, Ziqian, Zhuang, Yong-Bin, Qi, Dong-Chen, Zhang, Kelvin H. L
• Format: Journal Article
• Language: English
• Published: 25.07.2024
• DOI: 10.1039/d4tc01455c
• ISSN: 2050-7526

Developing transparent p-type oxide semiconductors has been a long-standing subject of interest for optoelectronic devices, but it has been hindered by the strongly localized valence band (VB) structure intrinsic to metal oxides. Sn 2+ oxides represented by SnO are proposed as promising p-type semiconductors since the Sn 5s 2 state could help to alleviate the carrier localization at the VB. In this work, using a combination of X-ray spectroscopy and density functional theory calculations, we explore the electronic structures of Sn 2+ -based Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 pyrochlores as wide bandgap p-type oxide semiconductors. Our results show that Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 have large optical bandgaps of 2.8 eV and 3.4 eV, respectively, and better chemical stability over SnO. Both the experimental and theoretical calculations verified the presence of Sn 5s 2 states at the top of the VB of Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 , and the Sn 5s 2 states increase the VB dispersion and result in lower hole effective masses of 2.09 m e and 2.23 m e for Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 , respectively, but work less effectively than that for SnO. The different VB features originate from the varied Sn-O interactions influenced by crystal structures. The lattice distortions in SnO allow hybridization between Sn 5p orbitals with occupied (Sn 5s-O 2p)* states, forming asymmetrically distributed electronic states with enhanced dispersion. However, in Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 , these interactions are forbidden by their cubic symmetry and lead to less-dispersive electronic states. Increasing lattice distortions in Sn 2 Nb 2 O 7 and Sn 2 Ta 2 O 7 would be necessary to achieve higher hole mobilities. Our findings elucidate the microscopic origins of the optoelectronic properties of tin ( ii ) pyrochlore oxides, highlighting the significant role of synergistic valence band modulation and crystal structural design in advancing high-performance p-type oxide semiconductors. P-type oxide semiconductor is crucial for advanced electronics. This work reveals the development of tin( ii ) pyrochlore oxides as transparent p-type oxide semiconductor through synergistic valence band modulation and crystal structural design.