Thank you Martin for your response. But I am wondering can spatial separation or trap sites can extend the lifetimes to few hours?!! Is there a matematical derivation that shows the lifetime can be extended that long?

Thank you Dr. Martin.

Sudip,

I would like to thank Martin for his contribution. When an electron in the conduction band is captured in a trap defect it has the probability to be reemitted again to the conduction band or to fall to the valence band recombining with a hole in it. The recombination on traps in the bandgap leads to nonradiative recombination.

One of the important parameters is the capture time of the electrons or the holes in the trap. As the capture time increases the persistence increases which means that after cutting the illumination the photo current lasts for a remarkable time.

The capture time of the traps depends on its position in the bandgap and its rate of reemission or recombining. Traps lying in the middle of the band acts as a recombination centers with nearly equal transition rate to either bands while traps lying near one of the bands may have a very different rates.

At the surface there exist defects with strong bond to either electrons or holes.

The release process takes long time making current tails.

Best wishes

Thank you Abdelhalim abdelnaby Zekry