A diode is an electrical device and a single-direction conductor that allows electrical flow in one direction without a reverse flow. Photo means light rays. There are different types of diode available; a photodiode is one of them. A photodiode transmits or receives a one-directional light impulse.

It converts light impulse to electrical impulse. This means that a photodiode picks photons (elements that makeup light rays) and converts them to electrical currents. Other photodiodes made from various semiconductor materials include Indium Antimonide, Indium Gallium Arsenide, Mercury Cadmium Telluride, etc.

Silicon Photodiode 

A great option for numerous visible-light applications, silicon photodiode makes a fine photodiode and semiconductor material. Suitable for high-speed applications, silicon photodiode is highly sensitive and emits a low dark charge. Their compact size, electrical response, and reduced noise make them useful in civilian and defense settings.

Silicon photodiodes are mostly used to produce optical data receivers since they have low capacitance and receive digital data. Though silicon photodiodes are commonly used in the 800-900nm wavelength, they can be used for various wavelengths like ultraviolet, infra-red, and others.

So how does a silicon photodiode work?

Recall that a diode needs a conductive material and a resistive material to achieve a one-directional flow of impulse. The conductor’s impulse must reach a certain value that overcomes the insulator material’s resistive value to attain the one-directional flow.

The flow in that direction is brought about by Silicon, a semiconductor material (i.e., a material that possesses both conductor and insulator properties) that can conduct and resist. The resistive property prevents the return direction movement in a diode. The conductive property helps lower the insulator’s required impulse to overcome the conductor’s impulse flow resistance. So that at a low impulse, resistive action of the insulating material is still achieved. The Silicon photodiode will transmit the barest minimum light photons to be converted to electrical currents while still maintaining a unidirectional current. This design makes it possible for Silicon to sense even very low light rays.

Germanium Photodiode

Compared to a silicon photodiode, germanium photodiode is less sensitive with wavelengths larger than 900nm. Unlike Indium Gallium Arsenide (IGA), which is quite expensive, Germanium is cost-efficient and can detect large areas up to 1cm in diameter. Germanium photodiode produces dark current and is noisier than Silicon and Indium Gallium Arsenide. The higher the signal and temperatures, the greater the noise level.

Ultraviolet Detectors

To increase sensitivity to wavelengths, silicon photodiode may be augmented to improve ultraviolet (UV) response. The tools for boosting UV response are known as UV-enhanced silicon photodiodes. Silicon carbide photodiode makes a great UV detector.

Indium Gallium Arsenide (InGaAs)

At room temperature, Indium Gallium Arsenide (InGaAs) is more responsive with shorter wavelengths (mostly in the infrared regions).  It produces less noise and is highly stable than Germanium.

Indium Antimonide (Infrared detectors)

Indium Antimonide has less sensitivity and a short wavelength. It works well with heat applications. For the photodiode to perform at an optimal level, cool the photodiode to cryogenic temperatures.

The use of photodiodes in our everyday life

From electronic systems to medical uses, photodiodes have a vast range of applications. In fiber-optic communications, photodiodes are components of cameras that help measure light and control the shutter. Their applications are evident in x-ray detection, surveying instruments, barcode scanners, among others.

How is Silicon photodiode different from other photodiodes?

Silicon photodiode makes an excellent choice for visible light applications. It’s less expensive and produces less noise than Germanium. Compared to Germanium and Indium Gallium Arsenide, silicon photodiodes are less sensitive to wavelengths greater than 900nm.