Flux Dependent Non-Linearity:The Evil Twin of Persistence

Mike Regan, Kevin Lindsay, Eddie Bergeron, Rachel Anderson

Photons captured in the depletion region yield an electron/hole pair.

As charge accumulates, the depletion region gets smaller exposing empty traps to free charge.

After a reset trapped electrons and holes are left in the depletion region.

During the next exposure the electrons/holes decay from the traps and are seen as an increase in the voltage.

But what happens during the original exposure?

During an exposure traps capture charge decreasing the observed voltage.

This model makes several predictions.

• Flat field response will be lower at low fluxes in high trap regions.

• Detector bias changes that decrease the size of the depletion region will induce “negative persistence”.

• Slopes after cosmic rays will be lower.

Trap Density Map in our “Beautiful” Device.

Flat Fields

The Ratio of high and low flux flat fields shows a difference in the high trap region.

Flux ratio was a factor of 60.

Bias change to decrease depletion region

The measured slopes on the device are negative after we change the bias.

The negative observed rates decay away just like persistence.

Cosmic Rays

The slope after a cosmic ray is lower and is proportional to the magnitude of the CR

Conclusions

• The model matches all the observations.

• The observed QE is a function of the flux -> Flux dependent QE

• Determining slopes when there is a cosmic ray is not simple (as I thought before).