A semiconductor diode is a type of electronic component that allows current to flow in only one direction. It is made from a semiconductor material, such as silicon or germanium, and consists of two layers, one with an excess of positive charge carriers (p-type) and one with an excess of negative charge carriers (n-type).
When the diode is connected in a circuit with the positive voltage applied to the p-type layer and the negative voltage applied to the n-type layer, it allows current to flow easily through the diode. This is because the electrons in the n-type layer are attracted to the positive voltage, and the holes in the p-type layer are attracted to the negative voltage, creating a flow of current across the diode.
However, if the voltage is reversed, with the positive voltage applied to the n-type layer and the negative voltage applied to the p-type layer, the diode will not allow current to flow. This is because the majority carriers (electrons in the n-type layer and holes in the p-type layer) are pushed away from the junction, creating a depletion region that acts as a barrier to current flow.
Semiconductor diodes are used in a wide range of electronic applications, such as rectifiers, voltage regulators, and signal detectors.
Application of Diodes
Diodes have many applications in electronic circuits due to their ability to allow current to flow in only one direction. Some common applications of diodes include:
- Rectification: Diodes are often used in rectifier circuits to convert AC voltage into DC voltage by allowing current to flow in only one direction.
- Voltage Regulation: Zener diodes can be used as voltage regulators to maintain a constant voltage output, even with fluctuations in the input voltage.
- Signal Demodulation: Diodes can be used to demodulate amplitude modulated (AM) radio signals by allowing the high-frequency carrier signal to pass through and rectifying the low-frequency modulated signal.
- Clipping and Clamping: Diodes can be used to clip or limit the voltage of a signal by allowing only a portion of the signal to pass through, or to clamp the signal to a certain voltage level.
- Protection: Diodes can be used as protective devices to prevent damage to electronic components from voltage spikes or reverse polarity.
- Light Emitting Diodes (LEDs): LEDs are a type of diode that emits light when a current is passed through it. They are used in various applications, such as lighting, displays, and indicators.
p-n Junction
When a semiconductor is doped with impurities, it creates excess electrons (n-type doping) or holes (p-type doping) in the material, which can carry electrical charge. These excess electrons or holes can move around the material, allowing for the flow of electric current.
When two differently doped regions of a semiconductor material are brought together, a p-n junction is formed. At the p-n junction, the excess electrons from the n-type region and the holes from the p-type region diffuse across the junction and combine, creating a region that is depleted of charge carriers called the depletion region.
The p–n junction possesses a useful property for modern semiconductor electronics. A p-doped semiconductor is relatively conductive. The same is true of an n-doped semiconductor, but the junction between them can become depleted of charge carriers, and hence non-conductive, depending on the relative voltages of the two semiconductor regions. By manipulating this non-conductive layer, p–n junctions are commonly used as diodes: circuit elements that allow a flow of electricity in one direction but not in the other (opposite) direction.
Bias is the application of a voltage relative to a p–n junction region:
- Forward bias. When a voltage is applied across the p-n junction in the forward bias direction (i.e., the positive terminal is connected to the p-type region and the negative terminal to the n-type region), the depletion region becomes narrower and allows the flow of current through the material.
- Reverse bias. In the reverse bias direction (i.e., the positive terminal is connected to the n-type region and the negative terminal to the p-type region), the depletion region becomes wider, preventing the flow of current through the material. However, if the reverse voltage is increased to a certain threshold value, the material can undergo a process called avalanche breakdown, in which the depletion region suddenly collapses and allows a large amount of current to flow through the material.
The forward-bias and the reverse-bias properties of the p–n junction imply that it can be used as a diode. A p–n junction diode allows electric charges to flow in one direction, but not in the opposite direction; negative charges (electrons) can easily flow through the junction from n to p but not from p to n, and the reverse is true for holes. When the p–n junction is forward-biased, electric charge flows freely due to reduced resistance of the p–n junction. When the p–n junction is reverse-biased, however, the junction barrier (and therefore resistance) becomes greater and charge flow is minimal.
