Experimental studies have revealed that defect related properties in hydrogenated amorphous silicon (a-Si:H) can be modified by visible-light illumination during plasma enhanced chemical vapor deposition growth; light-induced degradation after growth and initial defect density has been reduced in the samples prepared under illumination with and without a shield mesh separating the plasma region and a substrate in the deposition chamber, respectively. These properties are metastable below the deposition temperature and are a result of the counterbalance between illumination and the thermal effects during growth. The reduction of the light-induced changes in the present samples does not relate to changes in hydrogen bonding. The defect annihilation reaction during growth has been enhanced and the reaction barrier has been lowered from 0.57 to 0.34 eV under illumination. It has also been found that the defect density depends exponentially on the intensity of incident visible light. © 2002 American Institute of Physics.