Formation of a p-n Junction and Depletion Region

Start with carrier concentration difference. State electron diffusion from n to p and hole diffusion from p to n. Add recombination near the junction. Identify fixed ions left behind. State that these ions create an electric field and potential barrier. End with equilibrium between diffusion and drift effects.

Draw p-side on the left and n-side on the right. Label holes, electrons, depletion region, fixed negative acceptor ions on the p-side, fixed positive donor ions on the n-side, electric field direction from n-side positive ions to p-side negative ions, and potential barrier.

Saying that the depletion layer forms because charges physically disappear is wrong. Mobile electrons and holes recombine near the junction, while fixed ionised impurities remain and create the barrier field.

A p-n junction is formed when p-type and n-type semiconductor regions are joined. Electrons and holes diffuse across the junction, recombine near it, and leave behind fixed ionised impurities, creating a depletion region and a built-in potential barrier.

A p-n junction is formed when p-type and n-type semiconductor regions are joined. Electrons and holes diffuse across the junction, recombine near it, and leave behind fixed ionised impurities, creating a depletion region and a built-in potential barrier. Key physics rule: diffusion current is caused by concentration gradient, while drift current is caused by the electric field of the depletion region. At equilibrium, diffusion tendency is balanced by the built-in electric field. The potential barrier opposes further majority-carrier diffusion. In a silicon p-n junction, electrons initially diffuse from the n-side to the p-side and holes from the p-side to the n-side. After recombination near the junction, a narrow depletion region forms. The built-in electric field then reduces further diffusion, establishing equilibrium.

When p-type and n-type regions are in contact, electrons from the n-side diffuse into the p-side and holes from the p-side diffuse into the n-side because of carrier concentration differences. Near the junction, electrons and holes recombine. This leaves uncovered positive donor ions on the n-side and negative acceptor ions on the p-side. These fixed ions form an electric field across the junction, opposing further diffusion. The region depleted of mobile carriers is called the depletion region, and the corresponding barrier is called the potential barrier. Key physics rule: diffusion current is caused by concentration gradient, while drift current is caused by the electric field of the depletion region. At equilibrium, diffusion tendency is balanced by the built-in electric field. The potential barrier opposes further majority-carrier diffusion. Explain the effect of increasing doping on the depletion width. Higher doping means more ionised impurity atoms are present near the junction. A smaller physical width is needed to build the required space-charge region, so the depletion layer becomes narrower compared with a lightly doped junction. This concept appears in explanation-based questions, assertion-reason items, and diagram-labelling tasks. Students may be asked why a potential barrier forms or why the depletion layer resists further carrier diffusion. Saying that the depletion layer forms because charges physically disappear is wrong. Mobile electrons and holes recombine near the junction, while fixed ionised impurities remain and create the barrier field.