The self-interstitial atom (SIA) is one of two fundamental point defects in bulk Si. Isolated Si SIAs are extremely difficult to observe experimentally. Even at very low temperatures, they anneal before typical experiments can be performed. Given the challenges associated with experimental characterization, accurate theoretical calculations provide valuable information necessary to elucidate the properties of these defects. Previous studies have applied Kohn–Sham density functional theory (DFT) to the Si SIA, using either the local density approximation or the generalized gradient approximation to the exchange-correlation (XC) energy. The consensus of these studies indicates that a Si SIA may exist in five charge states ranging from −2 to +2 with the defect structure being dependent on the charge state. This study aims to re-examine the existence of these charge states in light of recently derived “approximate bounds” on the defect levels obtained from finite-size supercell calculations and new DFT calculations using both semi-local and hybrid XC approximations. We conclude that only the neutral and +2 charge states are directly supported by DFT as localized charge states of the Si SIA. Within the current accuracy of DFT, our results indicate that the +1 charge state likely consists of an electron in a conduction-band-like state that is coulombically bound to a +2 SIA. Furthermore, the −1 and −2 charge states likely consist of a neutral SIA with one and two additional electrons in the conduction band, respectively.

中文翻译：

---

重新检查硅的自间隙电荷态和缺陷能级：密度泛函理论和边界分析研究

自填原子（SIA）是体硅中两个基本点缺陷之一。隔离的Si SIA很难通过实验观察。即使在非常低的温度下，它们也可以在进行典型实验之前进行退火。鉴于与实验表征相关的挑战，准确的理论计算提供了阐明这些缺陷的性质所必需的有价值的信息。先前的研究已将Kohn-Sham密度泛函理论（DFT）应用于Si SIA，使用局部密度近似或广义梯度近似来表示交换相关（XC）能量。这些研究的共识表明，Si SIA可能存在于从-2到+2的五个电荷状态中，缺陷结构取决于电荷状态。这项研究的目的是根据最近得出的缺陷水平上的“近似界”来重新检查这些电荷态的存在，这些缺陷水平是通过有限大小的超级单元计算和使用半局部XC近似和混合XC近似进行的新DFT计算获得的。我们得出的结论是，DFT仅将中性和+2电荷状态直接支持为Si SIA的局部电荷状态。在目前DFT的精度范围内，我们的结果表明+1电荷状态可能由一个导电带状电子构成，该电子与库仑结合到+2 SIA。此外，-1和-2电荷状态可能由中性SIA组成，该中性SIA在导带中分别具有一个和两个其他电子。