# Small bandgap IR detectors need to work in crogenic temperature

• chenhon5
In summary, small bandgap IR detectors, such as InSb photodetectors, need to work in cryogenic temperatures because at room temperature, there is enough thermal energy to knock electrons out of the band and cause them to conduct, reducing the sensitivity of the detector. This is due to the small bandgap, which means less energy is needed to knock electrons out. Increasing the carrier capture time can potentially improve the detector's performance at higher temperatures.
chenhon5
Is anybody 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, anybody 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.

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.

mgb_phys said:
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?

## 1. What is a small bandgap IR detector?

A small bandgap IR detector is a type of infrared detector that is made from materials with a narrow bandgap, meaning they require less energy to excite electrons. This makes them more sensitive to infrared radiation and able to detect a wider range of wavelengths.

## 2. Why do small bandgap IR detectors need to work in cryogenic temperatures?

Small bandgap IR detectors need to work in cryogenic temperatures because at lower temperatures, the electrons in the detector's material are more tightly bound to their nuclei. This allows the detector to better differentiate between the energy levels of the excited electrons, resulting in a more accurate and sensitive detection of infrared radiation.

## 3. What are the benefits of using small bandgap IR detectors at cryogenic temperatures?

The main benefit of using small bandgap IR detectors at cryogenic temperatures is their increased sensitivity and accuracy in detecting infrared radiation. Additionally, operating at lower temperatures can reduce electronic noise in the detector, resulting in clearer and more precise measurements.

## 4. What are some common applications of small bandgap IR detectors at cryogenic temperatures?

Small bandgap IR detectors at cryogenic temperatures are commonly used in scientific research for studying the infrared spectrum of various materials and objects. They are also used in astronomy for detecting infrared radiation from distant objects, as well as in military and security applications for thermal imaging and target detection.

## 5. Are there any challenges in using small bandgap IR detectors at cryogenic temperatures?

Yes, there are some challenges in using small bandgap IR detectors at cryogenic temperatures. One challenge is the need for specialized equipment to maintain and control the low temperatures required for the detector to function properly. Another challenge is the potential for the detector to become damaged if the temperature is not carefully controlled and monitored.

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