Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA.
Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics, Università Cattolica del Sacro Cuore di Brescia, Via Musei 41, Brescia 25121, Italy.
Phys Rev Lett. 2014 Jan 24;112(3):036404. doi: 10.1103/PhysRevLett.112.036404. Epub 2014 Jan 23.
Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase TiO2 significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large (∼1 eV) band gap reduction of noncompensated codoped rutile TiO2. It is shown that Cr/N codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr 3d3 levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr 3d and delocalized N 2p states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.
最近的研究表明，对诸如锐钛矿 TiO2 等宽带隙氧化物半导体进行非补偿的阳离子-阴离子共掺杂，可显著降低光学带隙，从而强烈增强可见光吸收[W. Zhu 等人，Phys. Rev. Lett. 103, 226401 (2009)]。我们使用软 X 射线光谱技术，全面确定了杂质能级的位置和性质，这些杂质能级是导致非补偿共掺杂金红石 TiO2 的带隙大幅减小（约 1eV）的原因。结果表明，与单元素掺杂相比，Cr/N 共掺杂可强烈增强替代 N 的含量。带隙的减小是由于在带隙的下半部分形成了 Cr 3d3 能级，而导带最小值则由局域的 Cr 3d 和离域的 N 2p 态组成。带隙的减小和载流子的离域化是氧化物半导体中实现高效光电流转换的关键因素。这些发现提高了在各种光伏和光催化应用中使用具有特定电子特性的共掺杂氧化物半导体的前景。
