Photoconductive Detector
Definition and meaning of Photoconductive Detector in chemistry.
A photoconductive detector is a device that detects electromagnetic radiation by measuring changes in the electrical conductivity of a photoconductive material when it absorbs photons. The conductivity increase is proportional to the intensity of incident light.
In more detail
In a photoconductive detector, incident photons excite electrons from the valence band to the conduction band in a semiconductor, creating free charge carriers (electrons and holes). An external voltage is applied across the material, and as conductivity increases upon light absorption, the resulting current change is measured and converted to a signal. This photoconductive effect occurs in materials like cadmium sulfide and lead sulfide, making them useful for light measurement and spectroscopic applications.
Key facts
| Field | Physical Chemistry |
|---|---|
| Common semiconductors | Cadmium sulfide (CdS), lead sulfide (PbS), lead telluride (PbTe) |
| Detection principle | Photon-induced increase in electrical conductivity due to charge carrier generation |
| Response time | Typically 10 milliseconds to 1 second depending on material |
Cadmium sulfide (CdS) photoconductive detectors are commonly used in photographic light meters because they respond strongly to visible light wavelengths (400-700 nm) and provide reliable current output proportional to illumination levels.
Frequently asked questions
How does a photoconductive detector differ from a photodiode?
A photoconductive detector relies on changes in bulk resistance when photons excite charge carriers, requiring an external bias voltage. A photodiode uses a PN junction to generate photocurrent directly without external bias. Photoconductive detectors generally have slower response times but lower cost.
What determines the wavelength range a photoconductive detector can sense?
The bandgap energy of the semiconductor material determines the minimum photon energy (and maximum wavelength) that can excite electrons. Visible-light detectors use wider-bandgap materials like CdS, while infrared detectors use narrower-bandgap materials like PbS.