Drift Current And Diffusion Current In Semiconductors Pdf

drift current and diffusion current in semiconductors pdf

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Published: 26.05.2021

Abu Tahir Aug 3,

Any motion of free carriers in a semiconductor leads to a current. This motion can be caused by an electric field due to an externally applied voltage, since the carriers are charged particles. We will refer to this transport mechanism as carrier drift.

What are Drift Current and Diffusion Current : Their Differences

In a semiconductor either it may be p-type or n-type there exists some of the majority and the minority charge carriers. As the p-type and n-type present on a single crystal at the center, there is the formation of the p-n junction. The basic device formed because of the above process is the p-n junction diode. We cover the basic differences between Drift Current and Diffusion Current below with a comparison table. In the p-n junction diode if it is doped non-uniformly then there exists a movement of charge carriers from higher concentration to lower concentration. This results in the recombination of the carriers and leads to the process of diffusion.

P-n junction diodes form the basis not only of solar cells, but of many other electronic devices such as LEDs, lasers, photodiodes and bipolar junction transistors BJTs. A p-n junction aggregates the recombination, generation, diffusion and drift effects described in the previous pages into a single device. A p-n junction with no external inputs represents an equilibrium between carrier generation, recombination, diffusion and drift in the presence of the electric field in the depletion region. Despite the presence of the electric field, which creates an impediment to the diffusion of carriers across the electric field, some carriers still cross the junction by diffusion. In the animation below, most majority carriers which enter the depletion region move back towards the region from which they originated. However, statistically some carriers will have a high velocity and travel in a sufficient net direction such that they cross the junction. Once a majority carrier crosses the junction, it becomes a minority carrier.

This is the current which is due to the transport of charges occurring because of non-uniform concentration of charged particles in a semiconductor. The drift current, by contrast, is due to the motion of charge carriers due to the force exerted on them by an electric field. Diffusion current can be in the same or opposite direction of a drift current. The diffusion current and drift current together are described by the drift—diffusion equation. It is necessary to consider the part of diffusion current when describing many semiconductor devices.

Carrier Transport Study Notes for Electronics and communication Engineering

In a semiconductor , the majority and minority charge carriers will exit in p-type or n-type. Because both the types of semiconductors will present over a single crystal at the center so that PN-junction can be formed. When the doping of this junction diode is done non-uniformly then charge carriers movement will be an exit from high to low concentration which leads to the recombination of carriers as well as to the diffusion process. There is an additional method is also occurs based on the applied electric field namely drift current. This article discusses the main differences between drift current and diffusion current.

Difference Between Drift Current and Diffusion Current

Drift and diffusion are responsible for generating current in semiconductors and the overall current density is the sum of the drift and diffusion currents. Drift current arises from the movement of carriers in response to an applied electric field. Positive carriers holes move in the same direction as the electric field while negative carriers electrons move in the opposite direction. The net motion of charged particles generates a drift current that is in the same direction as the applied electric field.

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