Photodiode vs. Photomultiplier: Key Differences Explained

This page compares Photodiode Vs Photomultiplier and mentions the difference between Photodiode and Photomultiplier tubes.

Photodiode

Photodiode

It consists of a normal p-n junction housed in a small enclosure with a transparent window through which light can fall inside. Figure-1 depicts a photodiode from OSRAM and the symbol of a photodiode.

A photodiode is basically a type of photodetector capable of converting light into either current or voltage. A photodiode is operated in reverse bias, in which leakage current increases in proportion to the amount of light falling on the junction. This is a result of light energy which breaks the bonds in the crystal lattice of the semiconductor, producing electrons and holes. This effect is similar to a photovoltaic cell.

• Photodiodes have high quantum efficiency and are compact in size.
• They are insensitive to magnetic fields.
• Available as conventional photodiodes and avalanche photodiodes.
• Conventional photodiodes do not have internal amplification.

Photomultiplier Tube

Photomultiplier Tube construction

• PMTs (Photomultiplier Tubes) are used for the light detection of very weak signals.
• It is a photo-emissive device in which the absorption of a photon results in the emission of an electron.
• It is one of the class of vacuum tubes also known as vacuum phototubes.
• It is a visible range photon sensor.
• Earlier PMTs were of larger size having glass vacuum envelopes, now they are available in smaller sizes.
• Nowadays, PMTs are replaced by avalanche photodiodes, but still they are in use in a variety of applications such as Raman spectrophotometry, Fluorescent molecular tagging applications, and single bubble sonoluminescence.

Major Difference between Photodiode and Photomultiplier Tube

The following are the major differences between a photodiode and a photomultiplier tube.

• Photodiodes convert one photon into one electron, while photomultipliers amplify electrons.
• Photomultiplier tubes use a detector which changes photons into electrons so that they can be detected. Later, the photomultiplier tube uses dynodes to amplify the electrons.