Explain the two processes involved in the formation of a p-n junction diode. Hence define the term 'barrier potential'.
Answer: Diffusion and drift form the depletion region; the opposing potential across it is the barrier potential.
Solution
When a p-n junction is formed, two processes occur:
(i) Diffusion: majority carriers cross the junction because of the concentration gradient — electrons diffuse from the n-side to the p-side and holes from the p-side to the n-side, leaving behind immobile ionised donors (n-side) and acceptors (p-side). This creates a depletion region.
(ii) Drift: the ions set up an electric field (from n to p) across the depletion region, which drives the minority carriers in the opposite direction (electrons from p n, holes from n p).
In equilibrium the diffusion and drift currents balance. The potential difference developed across the depletion region, which opposes further diffusion of majority carriers, is called the barrier potential.
(i) Diffusion: majority carriers cross the junction because of the concentration gradient — electrons diffuse from the n-side to the p-side and holes from the p-side to the n-side, leaving behind immobile ionised donors (n-side) and acceptors (p-side). This creates a depletion region.
(ii) Drift: the ions set up an electric field (from n to p) across the depletion region, which drives the minority carriers in the opposite direction (electrons from p n, holes from n p).
In equilibrium the diffusion and drift currents balance. The potential difference developed across the depletion region, which opposes further diffusion of majority carriers, is called the barrier potential.
CBSE Class 12 Board · 2017 · Subjective