1. (10 points) In a zero biased PN junction, what force counteracts the diffusion of electrons across the junction?

In a zero biased PN junction, the force that counteracts the diffusion of electrons across the junction is Electric Field

Explanation:

A zero biased PN junction is created when free electron present in n-type diffuse into positive hole of the p-type, which combine and cancel out. They also create a space charge region near the PN junction.

The electric field created by the space charge region, opposes the diffusion process for both electrons and holes present in the biased PN junction.

There are two concurrent phenomena that take place in this junction:

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