Xu Qiang, Sobhan Mushtaq, Yang Qian, Anariba Franklin, Ong Khuong Phuong, Wu Ping
Entropic Interface Group, Engineering Product Development, Singapore University of Technology and Design, 20 Dover Drive, Singapore 138682, Singapore.
Dalton Trans. 2014 Jul 28;43(28):10787-93. doi: 10.1039/c4dt00468j.
We employ first-principles methods to study the mechanism controlling the electrical conduction in BiFeO3 (BFO). We find that under oxygen-rich conditions, Bi vacancies (V(Bi)) have lower defect formation energy than O vacancies (V(O)) (-0.43 eV vs. 3.35 eV), suggesting that V(Bi) are the acceptor defects and control the conductivity of BFO, making it a p-type semiconductor. In order to obtain further insight into the conduction mechanism, we calculate the effect of donor (Sn(4+)) and acceptor (Pb(2+)) impurities in BFO. Results indicate that Sn impurities prefer to substitute Fe sites to form shallow donor defects, which compensate the acceptor levels derived from V(Bi). Meanwhile, Pb atoms favour the substitution of Bi sites to form acceptor defects, reducing the overall concentration of holes (h(+)). Theoretical findings were later surveyed by current-voltage characteristics of Sn- or Pb-doped BFO nanofibers. This study is of general interest in carrier transport in charge compensation semiconductors, and of particular relevance within the context of defect-mediated conductivity in BFO.
我们采用第一性原理方法来研究控制BiFeO3（BFO）中导电机制。我们发现，在富氧条件下，Bi空位（V(Bi)）的缺陷形成能低于O空位（V(O)）（-0.43 eV对3.35 eV），这表明V(Bi)是受主缺陷并控制BFO的电导率，使其成为p型半导体。为了进一步深入了解导电机制，我们计算了施主（Sn(4+)）和受主（Pb(2+)）杂质在BFO中的影响。结果表明，Sn杂质倾向于替代Fe位点形成浅施主缺陷，这补偿了由V(Bi)产生的受主能级。同时，Pb原子倾向于替代Bi位点形成受主缺陷，降低空穴（h(+)）的总体浓度。理论研究结果随后通过Sn或Pb掺杂的BFO纳米纤维的电流-电压特性进行了验证。这项研究对于电荷补偿半导体中的载流子输运具有普遍意义，并且在BFO中缺陷介导的电导率背景下具有特别的相关性。
