KINETICS OF DEFECT FORMATION BY ILLUMINATION AT TEMPERATURE HIGHER THAN 200-DEGREES-C IN HYDROGENATED AMORPHOUS-SILICON

Defect formation in undoped a-Si:H has been investigated by photocondu ctivity transients measured at temperatures to 250 degrees C and illum ination intensities to 1.7 W cm(-2). It is first shown that photocondu ctivity decay observed after application of a constant illumination is due to defect formation. The rise time, tau, of defects is in the ran ge 0.1-10 s depending on temperature and generation rate, G. tau can b e expressed as tau similar to G(-gamma) exp(E-a/kT) with gamma similar to 0.6 and E-a similar to 0.7 eV. It is then shown that a model with a rate equation in which the driving quantity for defect annealing is the carrier density accounts in a semi-quantitative way for the essent ial experimental observations. Furthermore, according to the model, th e steady state carrier concentration should vary as G(1/2) as experime ntally observed and it is then to be expected that hydrogen diffusion coefficient varies as G, in good agreement with the experiment. (C) 19 98 Elsevier Science B.V. All rights reserved.