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

Using a first-principles pseudopotential method we have studied the adsorpt ion 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 on e side of the Si-Si dimer and, at temperatures around 110 K. fully dissocia tes into PH2 + 11, with each component attached to one side of the dimer. A fter dissociation, the surface is characterized by an elongated dimer, symm etric 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 c ase, while the H-P bond lengths are the same as observed for the PH3 molecu le, the H-P-H angles are similar to8% bigger. Our dissociative adsorption m odel is further supported by our calculated vibrational modes, which are in good agreement with available experimental works. (C) 2001 Elsevier Scienc e B.V. All rights reserved.