# Small bandgap IR detectors need to work in crogenic temperature

## Main Question or Discussion Point

Is any body can give me a detailed explanation or reference why the small bandgap IR detectors (eg. InSb photodetecotr) need to work in the cryogenic temperature?

In addition, any body knows what is carrier capture time? Since some article said the photodetector detectivity is proportional to the square root of the carrier capture time, so increased capture time have the potential for higher temperature operation. Any thought? Thanks.

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A small band gap means that very little energy is needed to knock an electron out of the band and make it conduct.
At room temperature there is enough thermal energy to do this with a large number of electrons.
It depends on how much sensitivity you need, how strong your signal is compared to the thermal noise, so firefighters infrared displays aren't cooled but astronomical cameras are.

A small band gap means that very little energy is needed to knock an electron out of the band and make it conduct.
At room temperature there is enough thermal energy to do this with a large number of electrons.
It depends on how much sensitivity you need, how strong your signal is compared to the thermal noise, so firefighters infrared displays aren't cooled but astronomical cameras are.
Thank you for your reply. As I know the energy due to the temperature is k*T=0.0259eV, however, the bandgap of InSb is about 0.17eV, which is much larger than the thermal noise. Do you mean even the bandgap of InSb is larger than the thermal noise, but their values are more closed than other materials (say 1eV), so they will knock out much more electrons than wide bandgap materials?

Do you have an idea for the second question for my post about the carrier capture time?