1 / 16

Characterization of Detectors

Learn about photomultiplier tubes, microchannel plates, detection sensitivity, and engineering considerations of detectors for various applications. Explore challenges and advantages of photoconductors in sensor technology.

browneva
Télécharger la présentation

Characterization of Detectors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Characterization of Detectors • NEP= noise equivalent power = noise current (A/Hz)/Radiant sensitivity (A/W) • D = detectivity = area/NEP • IR cut-off • maximum current • maximum reverse voltage • Field of view • Junction capacitance

  2. Photomultipliers e e e e hf e e PE effect Secondary electron emission Electron multiplication

  3. Photomultiplier tube hf • Combines PE effect with electron multiplication to provide very high detection sensitivity • Can detect single photons. e- Anode Dynode chain Cathode -V

  4. Microchannel plates • The principle of the photomultiplier tube can be extended to an array of photomultipliers • This way one can obtain spatial resolution • Biggest application is in night vision goggles for military and civilian use

  5. Microchannel plates • MCPs consist of arrays of tiny tubes • Each tube is coated with a photomultiplying film • The tubes are about 10 microns wide http://hea-www.harvard.edu/HRC/mcp/mcp.html

  6. MCP array structure http://hea-www.harvard.edu/HRC/mcp/mcp.html

  7. MCP fabrication http://hea-www.harvard.edu/HRC/mcp/mcp.html

  8. Disadvantages of Photomultiplers as sensors • Need expensive and fiddly high vacuum equipment • Expensive • Fragile • Bulky

  9. Photoconductors • As well as liberating electrons from the surface of materials, we can excite mobile electrons inside materials • The most useful class of materials to do this are semiconductors • The mobile electrons can be measured as a current proportional to the intensity of the incident radiation • Need to understand semiconductors….

  10. Evac Ec Ef Ev Metal Photoelectric effect with Energy Bands Evac Ef Semiconductor Band gap: Eg=Ec-Ev

  11. To amplifier e Ec Evac Ef Ev Semiconductor Photoconductivity

  12. Photoconductors • Eg (~1 eV) can be made smaller than metal work functions f (~5 eV) • Only photons with Energy E=hf>Eg are detected • This puts a lower limit on the frequency detected • Broadly speaking, metals work with UV, semiconductors with optical

  13. Band gap Engineering • Semiconductors can be made with a band gap tailored for a particular frequency, depending on the application. • Wide band gap semiconductors good for UV light • III-V semiconductors promising new materials

  14. 5m Example: A GaN based UV detector This is a photoconductor

  15. Response Function of UV detector

  16. Choose the material for the photon energy required. • Band-Gap adjustable by adding Al from 3.4 to 6.2 eV • Band gap is direct (= efficient) • Material is robust

More Related