The light induced effect in boron doped and phosphorous doped amorphous silicon films has been investigated by conductivity measurements. After illumination for one hour at AM-1, the conductivities were decreased to $10^{-2}~10^{-3}$ of their original values and the activation energies were increased by 0.1~0.25eV.
From the relation between illumination time and Fermi level shift, the density of states at Fermi level was obtained. For 500 ppm phosphorous doped sample, it was found that a valley in the distribution of density of states existed at 0.5eV below conduction band.
It was also found that the activation energies of slightly boron and phosphorous doped samples changed by large amount after illumination, and it can be explained by negative correlation energy.
