第一性原理计算绝缘体-金属转变临界掺杂浓度：Co重掺杂Si体系
First-Principles Calculations of the Insulator-Metal Transition Critical Doped Concentration: the Case of Co Hyperdoped Si System

基于密度泛函理论的第一性原理方法，本文旨在探索确定绝缘体-金属转变临界浓度的理论计算方法。以Co重掺杂Si为研究对象，构建并计算了10个Co不同掺杂浓度模型的晶体结构、杂质形成能及其电子性质。发现在Co掺杂Si体系的带隙中形成了杂质能级，杂质能级的位置和宽度随着Co浓度的增加呈线性变化。当Co掺杂浓度较高时杂质形成能逐渐稳定，且杂质能级穿过费米能级使体系表现出金属性。综合杂质形成能的变化趋势，以及杂质能级极小值与费米能级间的距离条件，可预测出发生绝缘体-金属转变的Co掺杂浓度为2.601？1020 cm-3，与实验结果相一致。上述两条依据应用于S重掺杂Si体系和Se重掺杂Si体系同样成立。
Using the first principle method based on density functional theory, the method of theoretical calculation to determine the critical concentration of insulator-metal transition (IMT) is explored. The Co hyperdoped Si is chosen as the research object. The crystal structure, impurity formation energy and electronic properties of 10 models with different doping concentrations of Co are calculated. It is found that the impurity levels are formed in the band gap of Co-doped Si system. The position and width of impurity levels vary linearly with the increase of Co concentration. When the doping concentration is higher, the impurity formation energy tends to be stable. At the same time, the impurity level passes through the Fermi level to make the system exhibit metallicity. Based on the variation trend of the impurity formation energy and the distance between the minimum of impurity level and the Fermi level, it is predicted that the insulator-metal transition occurs when the doping concentration of Co reaches 2.601？1020 cm-3, which is consistent with the experimental results. The above two criteria also hold for the S hyperdoped Si system and Se hyperdoped Si system.