Reverse Biased Diode

Reverse Biased Diode

Introduction

• In semiconductor devices, such as diodes, the concept of reverse biasing is crucial for controlling the flow of electric current.
• Reverse biasing involves connecting the diode in such a way that the p-type region is connected to the negative supply terminal, and the n-type region is connected to the positive supply terminal.

Electric Field and Depletion Layer

• When a diode is reverse-biased, the electric field across the depletion layer within the p-n junction increases significantly.
• The depletion layer, as explained earlier, is a region at the junction boundary where no free charge carriers are present.

Barrier to Electron Flow

• The increased electric field in reverse biasing acts as a stronger barrier to the flow of electrons.
• Electrons in the n-type region are pushed away from the junction, and holes in the p-type region are pushed away from the junction as well.

Valence Band Energy Levels

• One of the key effects of reverse biasing is the change in the energy levels within the p-n junction.
• In the p-type material, the valence band's energy level is raised above the energy level of the free electrons in the conduction band of the n-type material.
• This energy level difference is a result of both the doping process (introducing impurities) and the electric field created by reverse biasing.

Barrier to Current Flow

• The raised energy level of the valence band in the p-type material and the lowered energy level of the conduction band in the n-type material create a larger energy barrier at the junction.
• This barrier prevents the free electrons in the n-type region from easily transitioning into the p-type region.

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Reverse Biased Diode

Current Flow in Reverse Bias

• In a reverse-biased diode, there is a very small leakage current, often referred to as reverse saturation current.
• This current is due to a tiny number of charge carriers (electrons and holes) that can overcome the energy barrier and cross the junction, albeit at a very low rate.

Applications

• Reverse biased diodes find applications in various electronic circuits, such as rectifiers and voltage regulators, where they are used to control and manipulate the flow of current.

Key Points

• Reverse biasing involves connecting the diode with the p-type connected to the negative supply terminal and the n-type connected to the positive terminal.
• The increased electric field in reverse bias creates a strong barrier to electron flow.
• Energy level differences at the junction result in a significant energy barrier that restricts current flow in reverse bias.
• Reverse-biased diodes exhibit very low leakage current.

Summary

• Reverse biasing is a fundamental concept in diode operation, where the diode is connected in a way that impedes the flow of electric current. The increased electric field and energy barrier at the p-n junction prevent significant current flow, making reverse biased diodes useful for specific electronic applications.