11.9: Diodes
- Page ID
- 470931
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Diode Structure
Diodes involves the junction of two semiconductor type materials, with one side having extra electrons (N) and the other extra "holes" (P). These material can be made by doping elements like Silicon and Germanium (that typically have 4 valence with electrons with similar sized elements that have 3 or 5 valence electrons, with the former creating the P layer and the later the N layer.
Figure \(\PageIndex{1}\): P and N type dopants. (James Fiore, cc 4.0 LibreTexts)Diode Bias
This results in the diode having two polarized terminals with the Anode being the positive terminal and the cathode being the negative terminal.
Figure \(\PageIndex{2}\): Diode symbol showing positive anode and negative cathode. (Belford; CC 0.0)This means that under normal conditions the diode only allows current to flow in one direction, which is from the anode to the cathode.
- Forward Bias: occurs when a positive voltage source is applied to the anode
- Negative Bias: occurs when a negative voltage source is applied to the anode
- Breakdown Voltage: At some voltage the diode will conduct current in the reverse direction and this results in a breakdown of the diodes normal operating behavior.
Falstad Cicuit JS simulation \(\PageIndex{1}\): Forward (left) and reverse (right) biased diodes. Note the diode stops the reverse flow and so is unidirectional.