Key Takeaways
- Forward biasing occurs when the positive terminal of a voltage source is connected to the p-type semiconductor. This lowers the barrier potential and allows current flow.
- Reverse biasing connects the positive terminal to the n-type semiconductor, increasing the barrier potential and preventing current flow.
- Forward biasing turns a diode “on” allowing current to flow, while reverse biasing turns it “off”, blocking current.
What is Forward Biasing?
Forward biasing is a term used in electronics to describe the application of a voltage that allows current to flow through a diode or a semiconductor junction. In forward biasing, the positive terminal of a power source is connected to the P-region (positive region) of the diode or junction, while the negative terminal is connected to the N-region (negative region).
When a diode is forward-biased, it allows current to flow easily through it. This is because the positive voltage applied to the P-region repels the majority charge carriers (holes) toward the junction, while the negative voltage applied to the N-region repels the minority charge carriers (electrons) away from the junction. As a result, the depletion region (the region near the junction with no charge carriers) narrows, allowing current to pass through.
What is Reverse Biasing?
Reverse biasing is the application of a voltage that opposes the normal flow of current through a diode or a semiconductor junction. In reverse biasing, the positive terminal of a power source is connected to the N-region (negative region) of the diode or junction, while the negative terminal is connected to the P-region (positive region).
When a diode is reverse biased, it inhibits the flow of current through it. This is because the positive voltage applied to the N-region attracts the majority charge carriers (electrons) away from the junction, while the negative voltage applied to the P-region attracts the minority charge carriers (holes) toward the junction. As a result, the depletion region (the region near the junction with no charge carriers) widens, creating a barrier that prevents the flow of current.
Difference Between Forward Biasing and Reverse Biasing
- In forward biasing, the diode or junction allows current to flow easily in the forward direction, from the anode to the cathode. In reverse biasing, the diode or junction inhibits the flow of current and blocks it from flowing in the reverse direction.
- In forward biasing, the positive terminal of the power source is connected to the P-region of the diode or junction, while the negative terminal is connected to the N-region. In reverse biasing, the polarity is reversed, with the positive terminal connected to the N-region and the negative terminal connected to the P-region.
- Forward biasing narrows the depletion region (the region near the junction with no charge carriers) in a diode or junction, allowing current to pass through. Reverse biasing widens the depletion region, creating a barrier that prevents current flow.
- Forward biasing requires a voltage higher than the forward voltage drop (around 0.6 to 0.7 volts for a silicon diode) to overcome the barrier and allow current flow. Reverse biasing requires a voltage higher than the reverse breakdown voltage to create a significant reverse current flow.
- Forward biasing allows a diode to behave like a closed switch, conducting current in the forward direction. Reverse biasing causes a diode to behave like an open switch, blocking the flow of current in the reverse direction.
Comparison Between Forward Biasing and Reverse Biasing
| Parameter of Comparison | Forward Biasing | Reverse Biasing |
|---|---|---|
| Current Flow | Allows current flow in the forward direction | Blocks current flow in the reverse direction |
| Voltage Polarity | Positive terminal connected to the P-region | Positive terminal connected to the N-region |
| Depletion Region | Narrows the depletion region, enabling current conduction | Widens the depletion region, creating a barrier for current flow |
| Voltage Requirement | Requires a voltage higher than the forward voltage drop | Requires a voltage higher than the reverse breakdown voltage |
| Diode Behaviour | Acts as a closed switch, allowing current flow | Acts as an open switch, blocking current flow |
- https://aip.scitation.org/doi/abs/10.1063/1.363935
- https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.201302818
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