Simplified Passive Device Guide : PhotoResistor

What is a Photoresistor?

A photoresistor is widely known as a light dependent resistor. Its evolution has come a long way since it was first introduced in 1873 by a scientist Smith. Actually, its discovery happened when Smith was working hard to trace photo conductivity in various materials. Thus the researcher got the desired result while experimenting with selenium.

However, many scientists, since the photoresistor was brought first, have come up with their own improved versions with recommendable efficiency. Thus the making of photoresisrors is not confined to selenium only, but materials like germanium, cadmium sulphide, gallium arsenide and silicon have emerged as the leading production support for them.

The versatility in the use of materials for its production has led us to produce many low price photoresistors. Interestingly, their versatilities and the way they are used as passive devices in various technological components gave them a series of alternative names. Presently, these photoresistors are also called as photocells, photoconductors, photoconductive cells, photo resistors etc.

How a Photoresistor is Made?

While making a photoresistor, a layer of an active semiconductor is spread on insulated substrates. As this resistor needs a better conductivity, the semiconductors used while their making are doped. A mild doping is enough to make a semiconductor with a better conductivity.

After then, some contacts are fixed on these substrates. To get the maximum of these photoresistors, the exposed area, between the contacts, on the substrates are never kept straight and even.

Rather, the area is given some comparative complex patterns. It can be a zig zag looking interdigital pattern most of the time. Thus a complex pattern between the contacts increases the distance between them many times.

Naturally, at maximum instances, any widely used semiconductor is used to make a photoresistor. Such phtoresistors turn out to be a bit costly. However, manufacturers, in order to make some cost-effective photoresitors, use polycrystalline semiconductor on ceramic substrates.

Some Basic Uses of Photoresistors :

The most famous uses of photoresistors are seen in various types of security devices such as burglar detectors, fire and smoke alarms etc. Basically, it is used in photographic light meters extensively. They are used in street lights and card readers too.

Also, a photoresistor is used in many consumer appliances such as clocks, cameras, light meters etc. Further, they are used in some designs of dynamic compressors too.

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