Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
J Phys Condens Matter. 2010 Sep 29;22(38):384211. doi: 10.1088/0953-8984/22/38/384211. Epub 2010 Sep 7.
We report a semilocal and hybrid Hartree-Fock density functional study of native defects in three oxide semiconductors: ZnO, SrTiO(3), and SnO. The defect that is responsible for the n-type conductivity of ZnO has been debated, in which the O vacancy, Zn interstitial, their complexes, and residual H impurity are considered candidates. Our results indicate that the O vacancy induces a deep and localized in-gap state, whereas the Zn interstitial is a shallow donor and hence can be a source of the carriers. In view of the formation energies, the O vacancy is likely to form with a substantial concentration under O-poor conditions, but the Zn interstitial is unlikely. We thus propose that the O vacancy is relevant to the nonstoichiometry of ZnO and that a source other than the native defects, such as the H impurity, needs to be considered for the n-type conductivity. For SrTiO(3), the O vacancy and its complexes have been regarded as the origins of some of the remarkable electrical and optical properties. We suggest significant roles of the Ti antisite for a new insight into the defect-induced properties. Two types of Ti antisite, both of which are off-centered from the Sr site but toward different directions, exhibit low formation energies under Ti-rich conditions as does the O vacancy. They can explain optical properties such as visible-light emission, deep-level absorption, and the ferroelectricity observed in reduced SrTiO(3). As an example of p-type conductors, SnO has been investigated with a focus on the acceptor-like native defects. Under O-rich conditions, the Sn vacancy and O interstitial are found to be energetically favorable. The Sn vacancy induces shallow acceptor levels and can therefore be a source of carriers. The O interstitial shows no in-gap levels and hence it is inactive in terms of the carrier generation and compensation. However, this defect is a key to the understanding of the structures of intermediate compounds between SnO and SnO(2).
我们报告了 ZnO、SrTiO(3) 和 SnO 这三种氧化物半导体中本征缺陷的半局域和混合 Hartree-Fock 密度泛函研究。对于 ZnO 的 n 型导电性的原因，一直存在争议，其中 O 空位、Zn 间隙、它们的复合物和残余 H 杂质被认为是候选者。我们的结果表明，O 空位诱导了深而局域的带隙态，而 Zn 间隙是浅施主，因此可以成为载流子的来源。鉴于形成能，O 空位很可能在 O 贫条件下形成高浓度，但 Zn 间隙不太可能。因此，我们提出 O 空位与 ZnO 的非化学计量比有关，并且需要考虑非本征缺陷以外的来源，例如 H 杂质，以解释其 n 型导电性。对于 SrTiO(3)，O 空位及其复合物被认为是一些显著的电学和光学性质的起源。我们建议 Ti 反位在缺陷诱导性质方面具有重要作用。两种类型的 Ti 反位，都偏离 Sr 位但朝向不同方向，在 Ti 富条件下具有低的形成能，这与 O 空位相同。它们可以解释可见发光、深能级吸收和还原 SrTiO(3)中观察到的铁电性等光学性质。作为 p 型导体的一个例子，SnO 已被研究，重点是受主型本征缺陷。在 O 富条件下，Sn 空位和 O 间隙是有利的。Sn 空位诱导浅受主能级，因此可以成为载流子的来源。O 间隙没有带隙能级，因此在载流子产生和补偿方面没有活性。然而，这个缺陷是理解 SnO 和 SnO(2)之间的中间化合物结构的关键。
