Statement I: When a Si sample is doped with Boron, it becomes P type and when doped by Arsenic it becomes N-type semi conductor such that P-type has excess holes and N-type has excess electrons.
Statement II: When such P-type and N-type semi-conductors, are fused to make a junction, a current will automatically flow which can be detected with an externally connected ammeter.
In the light of above statements, choose the most appropriate answer from the options given below:
Statement II: When such P-type and N-type semi-conductors, are fused to make a junction, a current will automatically flow which can be detected with an externally connected ammeter.
In the light of above statements, choose the most appropriate answer from the options given below:
- A.Both Statement I and Statement II are incorrect
- B.Both Statement I and statement II are correct
- C.Statement I is incorrect but statement II is correct
- D.Statement I is correct but statement II is incorrect
Show answer and solution
Correct option: D
Solution
Statement I is correct: Boron (trivalent) doping creates p-type Si with excess holes, and Arsenic (pentavalent) doping creates n-type Si with excess electrons.
Statement II is incorrect: When a p-n junction is formed, diffusion of carriers does create a built-in electric field and a contact potential (barrier potential) at the depletion region, but this does NOT drive a continuous current through an external ammeter. The built-in potential is a thermodynamic equilibrium condition — it exactly opposes further diffusion, resulting in zero net current. No external work is done and no sustained current flows, so an ammeter would read zero. This is consistent with the second law of thermodynamics; a p-n junction alone cannot act as a source of EMF.
Statement II is incorrect: When a p-n junction is formed, diffusion of carriers does create a built-in electric field and a contact potential (barrier potential) at the depletion region, but this does NOT drive a continuous current through an external ammeter. The built-in potential is a thermodynamic equilibrium condition — it exactly opposes further diffusion, resulting in zero net current. No external work is done and no sustained current flows, so an ammeter would read zero. This is consistent with the second law of thermodynamics; a p-n junction alone cannot act as a source of EMF.
[JEE Main 2023 · 25 Jan · Shift 2]