# Current Limitation in a PN junction

• maximaniac
In summary, the limiting physical mechanism for current flow in a p-n junction with negligible recombination in the space charge region is diffusion in forward bias and drift in reverse bias. The equations that describe this process are I = I_s (e^(V_{DD}/V_T)-1) + q(n_A D_A - n_D D_D) for forward bias and I = q n_A μ_A E + q n_D μ_D E for reverse bias. If there is recombination in the space charge region, the total current in both cases will include an additional term for recombination rate.
maximaniac

## Homework Statement

Describe the limiting physical mechanism for current flow in a p-n junction where there is negligible recombination in the space charge region. Write the equations that describe this current flow process. Define all parameters.

a) for the general case where the junction is forward biased.
b) under reverse bias.
c) describe the total current in (a) and (b) if there is recombination in the space charge region.

## The Attempt at a Solution

The expression with the defined reverse saturation current comes from the diffusion current densities at the depletion region endpoints, and the recombination will account for a term that depends on the lifetime of going through the depletion region:

Diffusion current is dominant in front bias and current is 'limited' by diffusion of minority carriers, and drift current is dominant in reverse bias and apparently is also 'limited' by the majority carriers.

I'm not sure what is meant by 'limiting' here?

a) For the general case where the junction is forward biased, the limiting physical mechanism for current flow is diffusion. The equation that describes this current flow process is: I = I_s (e^(V_{DD}/V_T)-1) + q(n_A D_A - n_D D_D) where I_s is the reverse saturation current, V_DD is the applied voltage across the junction, V_T is the thermal voltage, q is the charge of an electron, n is the doping concentration, and D is the diffusion coefficient. b) Under reverse bias, the limiting physical mechanism for current flow is drift. The equation that describes this current flow process is: I = q n_A μ_A E + q n_D μ_D E where q is the charge of an electron, n is the doping concentration, μ is the mobility, and E is the electric field. c) If there is recombination in the space charge region, then the total current in (a) will be: I = I_s (e^(V_{DD}/V_T)-1) + q(n_A D_A - n_D D_D) + q R where q is the charge of an electron, n is the doping concentration, D is the diffusion coefficient, V_DD is the applied voltage, V_T is the thermal voltage, and R is the recombination rate. The total current in (b) will be: I = q n_A μ_A E + q n_D μ_D E + q R where q is the charge of an electron, n is the doping concentration, μ is the mobility, E is the electric field, and R is the recombination rate.

## 1. What is a PN junction?

A PN junction is a type of semiconductor junction that forms when a P-type semiconductor (with an excess of positive charge carriers) is attached to an N-type semiconductor (with an excess of negative charge carriers). This junction acts as a barrier to the flow of electrical current, creating a diode.

## 2. How does a PN junction limit current?

A PN junction limits current by creating a depletion region, a thin layer between the P and N regions where there are no free charge carriers. This depletion region acts as a barrier to the flow of current, allowing only a small amount of current to pass through in one direction.

## 3. What factors affect the current limitation in a PN junction?

The current limitation in a PN junction can be affected by several factors, including the doping levels of the P and N regions, the width of the depletion region, and the applied voltage. Temperature can also have an impact on the current limitation in a PN junction.

## 4. What are the implications of current limitation in a PN junction?

The current limitation in a PN junction has several implications, including its use in diodes and transistors as a means of controlling the flow of current. It also plays a crucial role in the functionality of electronic devices, such as solar cells, LEDs, and integrated circuits.

## 5. How can current limitation in a PN junction be overcome?

Current limitation in a PN junction can be overcome by applying a higher voltage, which can increase the number of charge carriers in the depletion region and allow more current to flow. Another way is by using specialized materials or techniques, such as using a Schottky diode or doping the P or N regions with different elements to alter the depletion region.

Replies
2
Views
2K
• Electrical Engineering
Replies
3
Views
842
• Other Physics Topics
Replies
2
Views
2K
• Electrical Engineering
Replies
12
Views
1K
• Atomic and Condensed Matter
Replies
2
Views
2K
• Electrical Engineering
Replies
3
Views
2K
• Electrical Engineering
Replies
1
Views
1K
• Electrical Engineering
Replies
5
Views
2K
Replies
1
Views
2K
Replies
6
Views
6K