First-principles calculations of the adsorption and dissociation of PH3 on Si(001)-(2 x 1)

Using a first-principles pseudopotential method we have studied the adsorption and dissociation of the common n-type dopant molecule PH3 on the Si(0 0 1)-(2 x 1) surface. We have found that phosphine adsorbs molecularly on one side of the Si-Si dimer and, at temperatures around 110 K. fully dissociates into PH2 + 11, with each component attached to one side of the dimer. After dissociation, the surface is characterized by an elongated dimer, symmetric for the dissociated case and asymmetric for the molecular case. The H-P-H angles and H-P bond lengths for the dissociative case have exactly the same values as obtained for the PH3 molecule. However, for the molecular case, while the H-P bond lengths are the same as observed for the PH3 molecule, the H-P-H angles are similar to8% bigger. Our dissociative adsorption model is further supported by our calculated vibrational modes, which are in good agreement with available experimental works. (C) 2001 Elsevier Science B.V. All rights reserved.