How Do Recombination and Drift Current Influence Diode Operation?

[vigi04]

1.what is the link between recombination and drift current for the current flow process in a diode(1.for unbiased condition 2. for biased condition) at equilibrium. i have the feeling that both are same as i read that diffusion compensates drift at some places and at other places, diffusion compensates recombination. i want to know the exact difference between the current contributed by drift and that contributed by recombination and how they sum up to the diode current.

2.how can we view drift current and diffusion current in a band diagram of a diode.(both biased and unbiased.)?

 

[Valkarie]

1. In an unbiased diode, the drift current is due to the movement of electrons and holes in the diode material by the electric field generated by the applied voltage. The recombination current is due to the recombination of electrons and holes at the junction of the diode, which results in a net current flow. The sum of the drift and recombination currents is the total current flowing through the diode. In a biased diode, the drift current is still due to the movement of electrons and holes in the diode material by the electric field generated by the applied voltage. However, the recombination current is now due to the injection of carriers from the external circuit into the diode, which results in a net current flow. The sum of the drift and injection currents is the total current flowing through the diode. 2. The drift current in a diode can be viewed as the current flowing in the conduction band due to the electric field generated by the applied voltage. The diffusion current can be viewed as the current flowing in the valence band due to the diffusion of carriers across the junction. In a band diagram, both the drift and diffusion currents can be seen as arrows directed along the conduction and valence bands, respectively.

 

[Mene]

Recombination and drift are two important processes that contribute to the current flow in a diode. In order to understand the link between these two processes, it is important to first understand what they are.

Recombination is the process by which free electrons and holes combine to form a bound state, releasing energy in the form of a photon. This process is important in semiconductor devices, as it determines the efficiency of the device in converting electrical energy into light.

Drift current, on the other hand, is the movement of charge carriers (electrons or holes) under the influence of an electric field. In a diode, the electric field is created by the built-in potential between the p and n regions.

Now, coming to the link between recombination and drift current in a diode at equilibrium. In an unbiased condition, the net current flow is zero as the diffusion current (due to the concentration gradient of charge carriers) is equal and opposite to the drift current (due to the electric field). This is known as the recombination current, as the two currents cancel each other out.

In a biased condition, the electric field is stronger and the drift current dominates over the diffusion current. However, even in this case, there is some recombination occurring, which contributes to the total current flow in the diode.

To understand the exact difference between the current contributed by drift and recombination, we need to look at the band diagram of a diode. In an unbiased condition, the band diagram shows a flat energy profile, indicating that there is no net current flow. In a biased condition, the band diagram shows a slope, indicating the presence of an electric field and hence, a drift current.

The diffusion current, on the other hand, is not shown in the band diagram as it is a result of the concentration gradient of charge carriers. However, it can be understood that the diffusion current opposes the drift current, and in equilibrium, the two cancel each other out.

In summary, recombination and drift are two important processes that contribute to the current flow in a diode. In an unbiased condition, they cancel each other out, while in a biased condition, the drift current dominates but recombination still occurs to some extent. The band diagram can help visualize and understand the relationship between these two processes.