Introduction
A PM diode, also photodiode, is a photodetector that converts light into current or voltage. A diode is known for allowing currents to flow in one direction. A PM diode is the same, except that it is more controlled to reach a certain part of a device. The way diodes are situated together determines the direction in which the current will flow.
Materials
The properties of a PM diode are determined by the materials that are used. Electrons are only excited when the corresponding protons has enough energy to move across the bandgap of the materials. Significant photocurrents are only produced in this instance.
Some of the most commonly used materials to produce PM diodes are:
• Silicon
• Germanium
• Indium gallium arsenide
• Lead sulfide
The greater the bandgap, the less noise is generated during operation. Silicon material has less bandgap range and lead sulfide has the greatest wavelength range.
How They Work
A PM diode is also known as a PN junction or PIN structure. To understand how they work, you must first understand some of the mechanisms behind them. Only a sufficiently-charge proton striking the diode can excite a neutron. This creates a positively-charged electron hole and a mobile electron. The created electron travels to the cathode of the diode, and the electron hole moves towards the anode. This causes the current to be produced.
Modes of Operation
The PM diode has four modes of operation; photovoltaic, photoconductive, avalanche photodiodes and phototransistor. Photovoltaic mode is when the diode is in a zero bias state that causes the flow of the current to be restricted so that the voltage builds up. In photoconductive mode, the diode is reversed biased. This means that the width of the depletion layer is increased and results in faster response times. In avalanche photodiodes, the response ability of the device is increased by the diode operating in a higher reverse bias. Phototransistors are a transistor that allows light to carry to the base-collector junction, resulting in a slower response time.
What are they used for
PM diodes are generally found in consumer electronic products. Items such as CD players, remotes and smoke detectors are the most common devices with PM diodes. In these items, the PM diodes are used as photodetectors.
The main reason that PM diodes are used is to determine an accurate measurement of light intensity. The medical community has found advantages in using them in medical applications such as tomography and immunoassay. They have also been used in instruments to analyze samples and blood gas.
Tags: avalanche photodiodes, diode also, diodes used, electron hole