Defect formation mechanism during plasma enhanced chemical vapor deposition of undoped a-Si:H

Defect formation mechanism in a-Si:H during plasma enhanced chemical vapor deposition at substrate temperatures below 250 degrees C is assumed to be associated with breaking of weak bonds in the Urbach tail. To break weak bonds, extra energy is necessary. This energy is supplied by the reaction energy of SiH(3) precursor at the growing surface incorporating SiH(2) into the network. The defect density is experimentally shown to be proportional to a product of the energy supply frequency, i.e., SiH(2) density, and the weak bond density which is obtained by the Urbach energy. By analysis using the configurational coordinate diagram the energy level of the broken weak bond is determined to be 0.2 eV above the valence band mobility edge. There is similarity between the defect formation mechanism during deposition and that of the Staebler-Wronski effect. (C) 1998 Elsevier Science B.V. All rights reserved.