NiO is a wide-bandgap p-type metal oxide that has extensive applications in optoelectronics and photocatalysts. Understanding the carrier dynamics in p-type NiO is pivotal for optimizing device performance, yet they remain largely unexplored. In this study, we employed femtosecond transient absorption spectroscopy to delve into the dynamics of photogenerated carriers in NiO films containing distinct prominent native defects: undoped NiO with oxygen vacancies (V_O) and O-rich NiO (denoted as NiO_1+δ) with nickel vacancies (V_Ni). Our findings unveil significant disparities between the two types of NiO thin films. The undoped NiO film exhibits a broad photoinduced absorption signal spanning the spectral range of 360–600 nm, whereas a photobleaching signal within the spectral range of 400–600 nm is observed in the O-rich NiO_1+δ film, which can be attributed to their unique native defects. We ascertain that the fast formation of small electron polarons (SEPs) occurs within a delay time of approximately 200 fs. Subsequently, the photogenerated carriers undergo rapid trapping by localized states (e.g., grain boundary states) in undoped NiO and O-rich NiO_1+δ within time scales of around 1–8 and 5–7 ps, respectively, followed by relatively slow trapping and recombination processes via native defects V_O and V_Ni within time scales of approximately 200 ps and ∼2 ns, respectively. These findings illuminate the fundamental processes governing carrier dynamics in NiO thin films with different native defects, offering crucial insights for the advancement of NiO-based devices.

中文翻译：

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p 型可多分宽带隙 NiO 中的天然缺陷依赖性超快载流子动力学


NiO 是一种宽带隙 p 型金属氧化物，在光电子学和光催化剂中具有广泛的应用。了解 p 型 NiO 中的载流子动力学对于优化器件性能至关重要，但它们在很大程度上仍未得到探索。在这项研究中，我们采用飞秒瞬态吸收光谱深入研究了 NiO 薄膜中光生载流子的动力学，这些薄膜包含明显的突出天然缺陷：具有氧空位 （VO_{） 的}未掺杂 NiO 和具有镍空位 （V_Ni） 的富含 O 的 NiO （表示为 NiO_1+δ）。我们的研究结果揭示了两种类型的 NiO 薄膜之间的显着差异。未掺杂的 NiO 薄膜在 360-600 nm 的光谱范围内表现出宽泛的光诱导吸收信号，而在富含 O 的 NiO_1+δ 薄膜中观察到 400-600 nm 光谱范围内的光漂白信号，这可归因于它们独特的天然缺陷。我们确定小电子极化子 （SEP） 的快速形成发生在大约 200 fs 的延迟时间内。随后，光生载流子在分别在大约 1-8 和 5-7 ps 的时间尺度内，在未掺杂的 NiO 和富含 O 的 NiO_1+δ 中通过局部状态（例如晶界态）进行快速捕获，然后通过天然缺陷 V_O 和 V_Ni 进行相对缓慢的捕获和复合过程分别在大约 200 ps 和 ∼2 ns 的时间尺度内。这些发现阐明了控制具有不同天然缺陷的 NiO 薄膜中载流子动力学的基本过程，为基于 NiO 的器件的发展提供了重要的见解。