Bolometer free-electron

Hot Electron Bolometer, Putley Detector. Whether it is more appropriate to include the hot electron bolometer and Putley detector in a list of detectors employing photon effects, or to instead list them with thermal effects, is somewhat arbitrary. Both employ photon effects in that incident photons interact with free electrons in a semiconductor. However, they are thermal (as the name bolometer implies) in that the effects are explainable in terms of a change in the effective temperature of the free electrons. Because the interpretation is mainly from the viewpoint of a photon-electron interaction, they are included here in the list of photon effects. 

Another material used for sensitive bolometers is a thin small disc of doped silicon, where the dopants are donor atoms with energy levels slightly below the conduction band (Fig. 4.82). A small temperature rise AT inaeases the fraction of ionized donors exponentially, thus producing free electrons in the conduction band. Such bolometers have to be operated at low temperatures in order to increase their sensitivity. The detectivity D (4.114) increases with falling temperature because the noise decreases (Fig. 4.83). 

Bolometer with hot electrons Photons interact with free electrons in semiconduchn and transfer their momentum to them, thus changing their effective temptaature... 

---