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| 9.2.2 |
Photovoltaic Effect : |
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Photovoltaic effect can occur in a material which has a space charge layer, e.g. in a p-n junction. |
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A photon of sufficient energy can be absorbed by the detector material to excite an electron from the valence band to the conduction band. The excited electron may be observed through its contribution to the current. A photovoltaic detector can be operated without application of a bias voltage. |
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9.2.3 |
Photoemissive Process : |
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In a photoemissive process (also known as external photoeffect ) incident radiation causes electron emission from photocathode which are to be collected by an anode. Photoemissive detectors have an advantage over other detectors as they have faster speed, higher gain and low noise. However, their spectral range is somewhat limited as the incident photon must have sufficient energy to eject electrons from the photocathode. Photoemissive detectors are, therefore, natural choices in the ultraviolet range. |
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