How Does Current Flow in a P-N Junction at Equilibrium?

[atlbraves49]

I've been doing some practice semicon. problems and there are a few remaining ones I've been having issues solving. I'll do one at a time

Question: What happens when an n-type and p-type material are merged to form a p-n junction? Provide an explanation as to the amount of net current flow in a p-n junction under equilibrium.



I know that under reverse-bias, there is minimal current flow to cross the p-n junction but what about under equilibrium? Also I know generally what happens in a p-n junction but can't specifically put to words what is occurring on a more exact level... any suggestions ?

 

[Defennder]

What is the definition of "thermal equilibrium" in semiconductor physics? You need to explain what happens during the formation of a pn junction in terms of the hole/electron concentrations and the respective diffusion/drift currents.

 

[piercas]

When an n-type and p-type material are merged to form a p-n junction, a depletion region is formed at the interface between the two materials. This depletion region is created due to the diffusion of majority carriers (electrons in the n-type material and holes in the p-type material) towards the opposite material. This creates a region with a lack of majority carriers and an excess of ionized impurities, resulting in a depletion of free charge carriers.

Under equilibrium, there is still a flow of current in the p-n junction, but it is balanced by an equal and opposite flow in the opposite direction. This results in a net current flow of zero. The flow of current is due to the diffusion of minority carriers (electrons in the p-type material and holes in the n-type material) across the junction. However, this diffusion is counteracted by the built-in electric field in the depletion region, which prevents the majority carriers from crossing the junction.

In simpler terms, under equilibrium, there is a balance between the diffusion of minority carriers and the built-in electric field, resulting in a net current flow of zero. This balance is maintained due to the presence of the depletion region, which acts as a barrier to the flow of majority carriers.

To put it more precisely, the built-in electric field in the depletion region creates a potential barrier that prevents the diffusion of majority carriers. This potential barrier is known as the built-in potential and is dependent on the doping concentrations of the n-type and p-type materials. The magnitude of the built-in potential determines the amount of net current flow in the p-n junction under equilibrium. As the built-in potential increases, the barrier for majority carriers also increases, resulting in a decrease in net current flow.

I hope this explanation helps to clarify the concept of net current flow in a p-n junction under equilibrium. If you are still having trouble understanding, I suggest further studying the concepts of majority and minority carriers, diffusion, and the formation of the depletion region. You can also refer to textbooks or online resources for more detailed explanations and examples.