Carbon-Hydrogen Pairs in Silicon: A DFT Study

Abstract

Silicon (Si) is one of the basic materials in the semiconductor industry. Its properties and behaviour are characterized by the impurities and defects present in the lattice. Among the most important impurities incorporated in Si are hydrogen (H) and carbon (C). Their presence affects the quality of the material and the operation of the related devices. Therefore, it is necessary to know the reactions that both impurities participate and the properties of the C-H defects that form during the various processing stages of the devices. Here we have employed density functional theory (DFT) calculations to study the structure, electronic structure, and energetics of the carbon substitutional hydrogen pair (C_s-H), the carbon interstitial hydrogen pair (C_i-H), the(C_s-H₂) and (C_i-H₂) defects. The results indicate that carbon substitution is more energetically favourable than interstitial incorporation. Incorporation of a single hydrogen atom is further favoured by 0.80 eV when carbon substitution has occurred. When a single interstitial carbon is already present, hydrogen incorporation becomes exothermic. Molecular hydrogen tends to dissociate and integrate as individual hydrogen atoms rather than as a molecule in C-doped Si, enhancing hydrogen incorporation. For C-interstitials, molecular hydrogen fully dissociates, with both hydrogen atoms forming strong bonds with carbon. However, the overall extent of incorporation is similar to that of single hydrogen incorporation.