Band Gap Behavior and Order/Disorder in Sn_1-xGe_xO₂ Alloys for Deep UV Transparent Conducting Oxides

Transparent conducting oxides (TCOs) with deep ultraviolet (DUV) transparency have a wide range of applications, including optoelectronics, sensors, and optical coatings. However, achieving high optical transmittance in the DUV range (&lt; 300 nm) remains challenging due to the empirical trade-off in conductivity with increasing band gap, and conventional TCOs having optical band gaps too small for DUV transparency. To address this, recent studies have shown that the addition of germanium (Ge) to rutile-SnO₂ can increase the band gap from 3.79 eV to 4.09 eV (at x = 0.7), making it a promising candidate for DUV-TCO applications.¹<br/><br/>In this work, we employ a comprehensive modelling approach combining hybrid-Density Functional Theory (DFT) calculations, Cluster Expansion and Monte Carlo simulations to investigate the band gap behaviour of Sn_1-x Ge_xO₂ alloys (0 ≥ x ≥ 1). Our methodology allows us to determine the ground state atomic structure and calculate the band structure for each composition. Additionally, we analyse the extent and impact of cation disorder in the alloyed systems.<br/><br/>Understanding the order/disorder behaviour in these alloyed systems is crucial as it directly influences the band gaps, electronic properties, and optical characteristics of the material. Furthermore, we explore the effect of dopants on disorder, building upon previous research that suggests the incorporation of Ta⁵⁺ impurities can enhance conductivity.¹<br/><br/>By elucidating the order/disorder relationships, their impact on the properties of Sn_1-x Ge_xO₂ alloys and the interaction of bulk disorder with impurity doping, this study provides valuable insights for the design and optimization of DUV-TCO materials.<br/><br/>1 Y. Nagashima, M. Fukumoto, M. Tsuchii, Y. Sugisawa, D. Sekiba, T. Hasegawa and Y. Hirose, <i>Chem. Mater.</i>, 2022, <b>34</b>, 10842–10848.