Trapping and release of impurities in TiN: A first-principles study

Films of titanium nitride, a prototype refractory material, typically contain a sizeable amount of impurities that are known to affect the properties of the host crystal. Here, we use first-principles calculations to identify the atomic-scale mechanisms that control the presence of the most common impurities (O, H, C, Ar, and He) in TiN. We identify the role of N vacancy sites as very efficient trapping centers, but we also show that the interaction between trapped species and N interstitials can lead either to impurity release or the formation of stable defect complexes. The results explain the fundamentals of key processes in the preparation of TiN films such as postgrowth impurity removal through nitridation or thermal desorption. We also present results on the effect of impurities on the electronic properties of TiN and on local vibrational modes around extrinsic species. We describe the bonding topology in the vicinity of impurities using the electron localization function and we discuss the relevance of our findings for physical traits of TiN films.