Working Principle of Photodiode

Photo diode

The photo diode to convert the sunshine energy received from the optical maser diode into electricity.

Photons absorbed by the photo  diode excite electrons among the photo diode during a method known as intrinsic absorption.

When stirred with an outdoor bias voltage, these electrons turn out a current flow through the photo diode and therefore the external circuit providing the bias voltage.

In associate electrical device, as shown below, light-weight absorbed by the photodiode produces current flow through the complete external circuit.

As current flows through the resistance, it produces a drop across the resistance.

This drop is input to associate electronic equipment for amplification.

One of the keys to the performance of the fiber optic receiver is that the photodiode itself.

The response times of the diodes govern the speed of the information that may be recovered.

Although avalanche diodes provide high speed they are also more noisy and require a sufficiently high level of signal to overcome this.

Testing photodiodes square measure important to the dependability of the photodiode semiconductor.

Various testing methods such as burn-in, accelerated life testing, are performed by Automatic Semiconductor Test Equipment designed for photodiodes.

Working Principle of Photodiode

When a diode is in reverse biased condition, there would be a reverse saturation current flowing through it from positive to the negative terminal of the diode.

The ineluctable minority charge carriers cause this reverse saturation current within the semiconductor crystal.

The value of this reverse saturation current does not depend on the applied reverse voltage across the diode rather it depends on the concentration of minority charge carriers in the semiconductor crystal. Hence for a certain range of reverse voltage across the diode, this current remains almost constant.

We can management the reverse saturation current in a very diode by dominant the concentration of minority charge carriers within the semiconductor crystal.

We can modification the concentration of minority charge carriers in a very semiconductor by activity external energy to the crystal.

In the photodiode, we do the same to control the conductivity of the device.

As the name suggests within the photodiode, the pn junction gets exposed in the light.

Depending on the intensity of the light, the covalent bonds in the crystal get broken and generate free electron-hole pairs across and nearby the pn junction.

As a result, the reverse current within the diode gets exaggerated or in different words the conduction of the device will increase.

 Here it's to be noted that during a photodiode, solely the pn junction portion of the diode should be exposed in light-weight this can be as a result of if the

light falls away from the junction, the electron-hole pairs created away from the junction get sufficient time to recombine hence they can not contribute reverse current. But electron-hole pairs created in the junction or very nearby to the junction, can propagate easily towards opposite polarity due to the influence of electric field across the junction and hence the current through the photodiode gets increased.

Construction of Photodiode

The photodiodes are available in a metallic package.

The diode could be a p n junction, mounted in an insulated plastic substrate.

Then we have a tendency to seal the plastic substrate within the metal case.

On the highest of the metal case, there is a transparent window, which allows light to entire up to the PN Junction.

Two leads, anode and cathode of the diode take off from all-time low of the metal case.

A tab extending from the side of the bottom portion of the metal case identifies the cathode lead.

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