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 v apor deposition at substrate temperatures below 250 degrees C is assum ed 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 SiH3 precursor at the growing surface incorp orating SiH2 into the network. The defect density is experimentally sh own to be proportional to a product of the energy supply frequency, i. e., SiH2 density, and the weak bond density which is obtained by the U rbach energy. By analysis using the configurational coordinate diagram the energy level of the broken weak bond is determined to be 0.2 eV a bove the valence band mobility edge. There is similarity between the d efect formation mechanism during deposition and that of the Staebler-W ronski effect. (C) 1998 Elsevier Science B.V. All rights reserved.