Ngamwongwan Lappawat, Fongkaew Ittipon, Jungthawan Sirichok, Hirunsit Pussana, Limpijumnong Sukit, Suthirakun Suwit
School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand and Center of Excellence in Advanced Functional Materials, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand and Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, Bangkok 10400, Thailand.
National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), 111 Thailand Science Park, Pathum Thani 12120, Thailand and Research Network NANOTEC - SUT on Advanced Nanomaterials and Characterization, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
Phys Chem Chem Phys. 2021 May 19;23(19):11374-11387. doi: 10.1039/d0cp06002j.
The formation of native point defects in semiconductors and their behaviors play a crucial role in material properties. Although the native defects of V2O5 include vacancies, self-interstitials, and antisites, only oxygen vacancies have been extensively explored. In this work, we carried out first-principles calculations to systematically study the properties of possible native defects in V2O5. The electronic structure and the formation energy of each defect were calculated using the DFT+U method. Defect concentrations were estimated using a statistical model with a constraint of charge neutrality. We found that the vanadyl vacancy is a shallow acceptor that could supply holes to the system. However, the intrinsic p-type doping in V2O5 hardly occurred because the vanadyl vacancy could be readily compensated by the more stable donor, i.e., the oxygen vacancy and oxygen interstitial, instead of holes. The oxygen vacancy is the most dominant defect under oxygen-deficient conditions. However, under extreme O-rich conditions, a deep donor of oxygen interstitial becomes the major defect species. The dominant oxygen vacancy under synthesized conditions plays an important role in determining the electronic conductivity of V2O5. It induces the formation of compensating electron polarons. The polarons are trapped at V centers close to the vacancy site with the effective escaping barriers of around 0.6 eV. Such barriers are higher than that of the isolated polaron hopping (0.2 eV). The estimated polaron mobilities obtained from kinetic Monte Carlo simulations confirmed that oxygen vacancies act as polaron-trapping sites, which diminishes the polaron mobility by 4 orders of magnitude. Nevertheless, when the sample is synthesized at elevated temperatures, a number of thermally activated polarons in samples are quite high due to the high concentrations of oxygen vacancies. These polarons can contribute as charge carriers of intrinsic n-type semiconducting V2O5.
半导体中本征点缺陷的形成及其行为在材料性能中起着至关重要的作用。尽管V2O5的本征缺陷包括空位、自间隙原子和反位缺陷，但只有氧空位得到了广泛研究。在这项工作中，我们进行了第一性原理计算，以系统地研究V2O5中可能的本征缺陷的性质。使用DFT+U方法计算了每个缺陷的电子结构和形成能。使用具有电荷中性约束的统计模型估计缺陷浓度。我们发现钒氧基空位是一种浅受主，可以向系统提供空穴。然而，V2O5中几乎不会发生本征p型掺杂，因为钒氧基空位很容易被更稳定的施主（即氧空位和氧间隙原子）而不是空穴补偿。在缺氧条件下，氧空位是最主要的缺陷。然而，在极端富氧条件下，氧间隙原子的深施主成为主要的缺陷种类。合成条件下占主导地位的氧空位在决定V2O5的电子电导率方面起着重要作用。它诱导了补偿电子极化子的形成。极化子被困在靠近空位位置的V中心，有效逃逸势垒约为0.6 eV。这些势垒高于孤立极化子跳跃的势垒（0.2 eV）。从动力学蒙特卡罗模拟获得的估计极化子迁移率证实，氧空位充当极化子捕获位点，这使极化子迁移率降低了4个数量级。然而，当样品在高温下合成时，由于高浓度的氧空位，样品中的许多热激活极化子相当高。这些极化子可以作为本征n型半导体V2O5的电荷载流子。
