Photodetection Theory: Photo-Oltaic, Photo-Emissive, Photo-Conductive

[DaTario]

Hi All,

I would like to know if there is someone here who is able to explain the difference between these three approaches in photo detection:

photo-oltaic
photo-emissive
photo-conductive.

thank you

DaTario

 

[country boy]

Photo-voltaic: change of voltage due to photon absorption.
Photo-emissive: emission of an electron following photon absorption.
Photo-conductive: change of resistance due to photon absorption.

Or you can Google them.

 

[DaTario]

Ok, it's more or less intuitive this kind of definition. But I would like to know the causes.

Thank you anyway,

best wishes

DaTario

 

[country boy]

You're right, I'll try to be a little less intuitive.

In a photoconductor, a photon causes a bound electron to transition to a free state, thereby moving more easily and lowering the resistance. Photoemission is similar, but the electron escapes the material. In a photovoltaic device, a photon causes an electron-hole separation in an electric field at a boundary, thereby creating a change in voltage.

 

[DaTario]

thank you very much.

 

[cesiumfrog]

What are the motivations for each different approach?

Is emission (lending itself to cascade) the only one that can count individual photons? Is voltaic used just for power generation? What advantage does photo-conductive have?

 

[country boy]

What are the motivations for each different approach?

Is emission (lending itself to cascade) the only one that can count individual photons? Is voltaic used just for power generation? What advantage does photo-conductive have?

I like this question. The motivation is usually a combination of what you want to measure and what is possible. The goal usually is sensitivity. Photoconductor detectors can be made to work at longer wavelengths (in the infrared) than photovoltaic detectors. But photovoltaic detectors can be more sensitive. You are correct that photovoltaic devices are related to solar cells, but in detectors a voltage is usually applied externally to improve performance. Single photons are usually detected by creating cascades of carriers (electrons) that amplify the signal. This can be done within a material and does not require an electron to be emitted.