Revealing the factors influencing grain boundary segregation of P, As in Si: Insights from first-principles

Abstract

Phosphorous (P) and arsenic (As) segregation at grain boundaries (GBs) usually deteriorate the electrical performance of n-type doped Si-wafers. In order to probe the factors influencing P and As segregation behaviors along Si GBs, a systematic investigation upon the interactions between P, As atoms and a series of coincidence site lattice Si GBs, including Σ3 {111}, Σ9 {221}, Σ27 {552}, Σ3 {112}, was carried out via first-principles calculations. It is revealed that the segregation behaviors of P, As along different GBs are different, which is dependent on both GB characteristics, i.e. the intrinsic lattice distortion, number of dangling/extra bonds, deep levels in the bandgap of density of states, and also the impurity properties. It reveals that smaller P atoms tend to segregate to the compressed atomic sites in GBs, by which the intrinsic GB lattice distortion is reduced. However, GB lattice distortion hardly induce As segregation owing to the similar atomic size between As and Si atoms. Calculations also indicate that under-coordinated core sites with dangling bond along GBs are remarkably attractive for P and As segregation, as a result of the nature of group-V elements to be three-coordinated rather than four-coordinated. Furthermore, GBs having deep levels in the bandgap of density of states, produced either by dangling or extra bonds, show a strikingly high attractive strength for both P and As segregation. The present work is supposed to provide important insights on substitutional impurity segregation along GBs in multi-crystalline Si in the atomic and electronic level.