- Avalanche Breakdown Definition: Avalanche Breakdown is a phenomenon in a p-n junction where a rapid increase in reverse current occurs due to carrier multiplication.
- Carrier Multiplication: Fast-moving electrons collide with atoms, releasing more electrons and significantly increasing the current flow.
- Avalanche Breakdown Voltage: This is the specific reverse voltage at which Avalanche Breakdown occurs, denoted as VBR.
- Conditions for Avalanche Breakdown: It typically occurs in lightly doped p-n junctions when the reverse voltage exceeds 5 V.
- Temperature Effect: The Avalanche Breakdown Voltage increases with rising junction temperature, indicating a positive temperature coefficient.
A p-type semiconductor material in contact with an n-type semiconductor material forms a p-n junction in which a depletion region occurs around the plane of contact. The width of this depletion region is seen to vary depending on the bias applied at the terminals of the p-n junction i.e. an increase in the applied voltage reduces the width of the depletion region in case of forward bias, while it increases the depletion region width for the case of reverse bias. Further the span of the depletion region is found to be more for a lightly doped material when compared to that of a heavily doped material.
Figure 1 shows the I-V characteristics of such a p-n junction both for the case of forward- as well as reverse-bias. From the figure, it is clear that the current through the semiconductor rises with an increase in the magnitude of the applied voltage when the p-n junction is forward biased. Further it is seen that there will be a certain amount of minimum current flowing through the p-n junction under the reverse bias condition. This current is referred to as the reverse saturation current (IS) and is due to the minority charge carriers in the semiconductor device.
Initially, IS is nearly independent of the applied voltage. However, at a certain point, the junction breaks down, causing a heavy flow of reverse current. As the reverse voltage increases, the kinetic energy of the minority charge carriers increases, causing them to collide with atoms and release more electrons.
The released electrons cause more electrons to be freed from atoms by breaking covalent bonds, a process called carrier multiplication. This leads to a significant increase in current flow through the p-n junction. This phenomenon is known as Avalanche Breakdown, and the specific voltage at which it occurs is called the Avalanche Breakdown Voltage (VBR). It is central to the working of avalanche diodes.
The efficiency of Avalanche breakdown can be expressed in terms of multiplication factor, M given by
Here, V and VBR represent the applied voltage and the breakdown voltage, respectively.
Avalanche breakdown happens in lightly doped p-n junctions when the reverse voltage exceeds 5 V. This phenomenon is hard to control because the number of generated charge carriers cannot be directly managed. Additionally, the Avalanche Breakdown Voltage increases with rising junction temperature, showing a positive temperature coefficient.
