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.