Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
ACS Appl Mater Interfaces. 2023 Feb 15;15(6):7969-7977. doi: 10.1021/acsami.2c19275. Epub 2023 Feb 3.
Tantalum nitride (TaN) has gained significant attention as a potential photoanode material, yet it has been challenged by material quality issues. Defect-induced trap states are detrimental to the performance of any semiconductor material. Beyond influencing the performance of TaN films, defects can also accelerate the degradation in water during desired electrochemical applications. Defect passivation has provided an enormous boost to the development of many semiconductor materials but is currently in its infancy for TaN. This is in part due to a lack of experimental understanding regarding the spatial and energetic distribution of trap states throughout TaN thin films. Here, we employ drive-level capacitance profiling (DLCP) to experimentally resolve the spatial and energetic distribution of trap states throughout TaN thin films. The density of deeper energetic traps is found to reach ∼2.5 to 6 × 10 cm at the interfaces of neat TaN thin films, over an order of magnitude greater than the bulk. In addition to the spatial profile of deep trap states, we report neat TaN thin films to be highly n-type in nature, owning a free carrier density of ∼9.74 × 10 cm. This information, coupled with the present understanding of native oxide layers on TaN, has facilitated the rational design of a targeted passivation strategy that simultaneously provides a means for catalyst immobilization. Loading catalyst via silatrane moieties suppresses the density of defects at the surface of TaN thin films by two orders of magnitude, while also reducing the free carrier density of films by over one order of magnitude, effectively dedoping the films to ∼2.40 × 10 cm. The surface passivation of TaN films translates to suppressed defect-induced trapping and recombination of photoexcited carriers, as determined through absorption, photoluminescence, and transient photovoltage. This illustrates how developing a deeper understanding of the distribution and influence of defects in TaN thin films has the potential to guide future works and ultimately accelerate the integration and development of high-performance TaN thin film devices.
氮化钽 (TaN) 作为一种有前途的光电阳极材料引起了广泛关注，但它受到材料质量问题的挑战。缺陷诱导的陷阱态对任何半导体材料的性能都有不利影响。除了影响 TaN 薄膜的性能外，缺陷还可以加速在所需电化学应用过程中水中的降解。缺陷钝化极大地推动了许多半导体材料的发展，但目前对 TaN 来说还处于起步阶段。这在一定程度上是由于缺乏对 TaN 薄膜中陷阱态的空间和能量分布的实验理解。在这里，我们采用驱动级电容剖面法 (DLCP) 来实验确定 TaN 薄膜中的陷阱态的空间和能量分布。结果发现，在纯净 TaN 薄膜的界面处，更深的能量陷阱密度达到了 ∼2.5 到 6×10 cm ，比体相高出一个数量级。除了深陷阱态的空间分布外，我们还报告说纯净 TaN 薄膜本质上是高度 n 型的，具有约 9.74×10 cm 的自由载流子密度。这一信息，加上对 TaN 上本征氧化层的现有理解，促成了有针对性的钝化策略的合理设计，该策略同时提供了催化剂固定化的手段。通过硅烷醇酯部分加载催化剂，将 TaN 薄膜表面的缺陷密度降低了两个数量级，同时将薄膜的自由载流子密度降低了一个数量级以上，有效地将薄膜掺杂到约 2.40×10 cm。TaN 薄膜的表面钝化抑制了光激发载流子的缺陷诱导捕获和复合，这可以通过吸收、光致发光和瞬态光电压来确定。这说明了深入了解 TaN 薄膜中缺陷的分布和影响如何有可能指导未来的工作，并最终加速高性能 TaN 薄膜器件的集成和发展。
