What is the reason that an LED will still emit light when put into reverse bias, but at a lower intensity?

April 21, 2023

Light Emitting Diodes (LEDs) are widely used in electronics and lighting applications due to their energy efficiency and long lifespan. However, have you ever wondered what happens to an LED when it is put into reverse bias? In this article, we will explore the reasons behind this phenomenon.

Firstly, it is important to understand what reverse bias means. An LED is a type of diode that only allows current to flow in one direction, from the anode to the cathode. When an LED is put into reverse bias, the voltage is applied in the opposite direction, from the cathode to the anode. This creates a high resistance to the flow of current, and the LED emits only a small amount of light.

However, even though the LED is in reverse bias, it will still emit some light. This is because of a phenomenon known as "minority carrier injection". When an LED is in reverse bias, a small number of electrons from the n-type semiconductor and a small number of holes from the p-type semiconductor can still cross the junction and combine in the depletion region. This creates a small current flow, which results in the emission of light.

The intensity of the light emitted by an LED in reverse bias is much lower than when it is in forward bias. This is because the current flow is much smaller, and only a small number of electron-hole pairs are formed in the depletion region. In addition, the recombination of these pairs is less efficient due to the high resistance of the diode in reverse bias, resulting in a lower intensity of light emission.

In summary, when an LED is put into reverse bias, it still emits light due to the phenomenon of minority carrier injection. However, the intensity of the light emitted is much lower than when the LED is in forward bias due to the small current flow and less efficient recombination of electron-hole pairs. Understanding this phenomenon can help in the design and optimization of LED-based devices for a variety of applications.

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