The key difference between diffusion current and drift current is that diffusion current forms due to the diffusion of charge carriers, whereas drift current forms due to the motion of charge carriers caused by force exerted on the charges by an electric field.
Diffusion current and drift current are two types of current passing mechanisms that use different mechanisms to produce a current.
CONTENTS
1. Overview and Key Difference
2. What is a Diffusion Current
3. What is a Drift Current
4. Diffusion Current vs Drift Current in Tabular Form
5. Summary – Diffusion Current vs Drift Current
What is Diffusion Current?
Diffusion current or diffusion current density is a type of current in a semiconductor that is caused by the diffusion of charge carriers. The charge carriers in this context are holes and electrons. This type of current forms due to the transport of charges occurring in non-uniform concentrations of charge particles in a semiconductor. Moreover, diffusion current can be in either the same or the opposite directions of a drift current according to the drift-diffusion equation.
Figure 1: Formation of Diffusion Current Occurs due to the Diffusion of Charge Carriers
When considering a semiconductor device, the current close to the depletion region of a p-n junction is mostly diffusion current. However, inside the depletion region, we can observe both types of currents (diffusion and drift currents). Furthermore, at the equilibrium in a p-n junction, we can observe that the forward diffusion current in the depletion region is balanced with the drift reverse drift current. Therefore, there is no net current.
What is Drift Current?
Drift current can be described as a type of current in a semiconductor that is caused by force exerted on the charge carriers by an electric field. This external force is often known as electromotive force. Moreover, drift velocity can be described as the average velocity of the charge carriers in the drift current. The term drift current is mostly useful in the context of electrons and holes in semiconductors. However, this same concept can be applied to metals, electrolytes, etc.
During the creation of a drift current, the charged particles are pushed by the electric field. Electrons are negatively charged, and they get pushed in the opposite direction to the electric field. This results in conventional current points in the same direction.
What is the Difference Between Diffusion Current and Drift Current?
Diffusion and drift current are two types of electric currents that are formed due to different methods of the current movement. The key difference between diffusion current and drift current is that diffusion current forms due to the diffusion of charge carriers, whereas the drift current forms due to the motion of charge carriers caused by force exerted on the charges by an electric field. Moreover, Diffusion current obeys the Fick’s law while drift current obeys the Ohm’s law. In addition, when considering the direction of the current, diffusion current depends on the slope of the carrier concentration, while drift current is always in the direction of the electric field.
The below infographic presents the differences between diffusion current and drift current in tabular form for side by side comparison
Summary – Diffusion Current vs Drift Current
Diffusion current and drift current are two types of current passing mechanisms that use different mechanisms to produce current. The key difference between diffusion current and drift current is that diffusion current forms due to the diffusion of charge carriers, whereas the drift current forms due to the motion of charge carriers caused by force exerted on the charges by an electric field.
Reference:
1. Shaik, Asif. “Diffusion Current.” Physics and Radio Electronics.
Image Courtesy:
1. “Simple Diffusion” By Elizabeth2424 – Own work (CC BY-SA 3.0) via Commons Wikimedia