Effects of dopants and defects on light-induced metastable states ina-Si:H

Using photothermal deflection spectroscopy we measure the gap-state optical absorption of light-induced metastable defects in undoped, singly-doped, and compensated a-Si:H. We observe an enhancement in the gap-state absorption after illumination which is shown to be due to the creation of new silicon dangling-bond defects and not to a shift in the Fermi level. For singly-doped material, the number of light-induced defects scales with dopant concentration, while full compensation (counter doping) drastically minimizes the density of these defects. The results provide evidence that the doping level influences the light-induced defect formation mechanism, and imply that simply breaking Si--Si bonds may not be the primary mechanism.