Photodiode and Photovoltaic Detectors


When a photon strikes a semiconductor, it can promote an electron from the valence band (filled orbitals) to the conduction band (unfilled orbitals) creating an electron(-) - hole(+) pair. The concentration of these electron-hole pairs is dependent on the amount of light striking the semiconductor, making the semiconductor suitable as an optical detector. There are two ways to monitor the concentration of electron-hole pairs. In photodiodes, a voltage bias is present and the concentration of light-induced electron-hole pairs determines the current through semiconductor. Photovoltaic detectors contain a p-n junction, that causes the electron-hole pairs to separate to produce a voltage that can be measured.

Schematic of semiconductor detector

Photodiode detectors are not as sensitive as PMTs but they are small and robust.

Wavelength range

Table 1: Wavelength range
Detector typeLambda
Si0.2 - 1.1
Ge0.4 - 1.8
InAs1.0 - 3.8
InSb1.0 - 7.0
InSb (77K)1.0 - 5.6
HgCdTe (77K)1.0 -25.0

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Further Information

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Copyright © 1996 by Brian M. Tissue

updated 2/21/96