In an unbiased p-n junction, holes diffuse from the p-region to n-region becausea)Free electrons in the n-region attract themb)They move across the junction by the potential differencec)Hole concentrate in p-region is more as compared to n-regiond)All the aboveCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

There are two types of extrinsic semiconductor
p type - when intrinsic(pure form)semiconductor is doped with a trivalent (grp 13)element like B, Al,Ga,In, then its 3 valence electrons form covalent bonds with 3 Ge or Si atoms while the 4th valence electron of Ge or Si is not able to form the bond,thus there remain a hole.
n type - when Ge or Si crystal is doped with pentavalent (grp 15) like P,As,Sb,then it form covalent bond with all 4 electrons of Ge or Si atom and one valence electron is left,thus there is a free electron.
Since p type(+ve) has larger no. of holes (represent +ve)than no. of electrons and anything moves from its higher concentration to its lower concentration if no ext. force is applied, holes move from p to n region.

Answer

The diffusion of charge carriers across a junction takes place from the region of higher concentration to the region of lower concentration. In this case, the p-region has greater concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes diffuse from the p-region to the n-region.

Answer

Explanation:

In an unbiased p-n junction, holes diffuse from the p-region to the n-region because of the difference in the concentration of charge carriers in the two regions. This phenomenon is driven by the principle of charge neutrality.

Charge Neutrality:
In an unbiased p-n junction, the p-region is doped with a higher concentration of acceptor atoms, which create a surplus of holes (positively charged carriers). On the other hand, the n-region is doped with a higher concentration of donor atoms, which create a surplus of free electrons (negatively charged carriers). At equilibrium, the total positive and negative charges in the p-n junction must balance each other out, resulting in a neutral charge distribution.

Diffusion Process:
The diffusion process occurs due to the random thermal motion of charge carriers. When there is a difference in concentration of charge carriers between the p-region and the n-region, the charge carriers tend to move from the region of higher concentration to the region of lower concentration.

Explanation of Option C:
Option C states that holes concentrate in the p-region more as compared to the n-region, which is correct. In the p-region, there is an excess concentration of positively charged holes due to the acceptor atoms. On the other hand, in the n-region, there is a lower concentration of holes. This difference in concentration creates a concentration gradient, causing the holes to diffuse from the p-region to the n-region.

Explanation of Other Options:
- Option A: Free electrons in the n-region attract holes - This statement is not accurate. While it is true that free electrons and holes have opposite charges, it is the concentration gradient that drives the diffusion process, not the attraction between free electrons and holes.
- Option B: Holes move across the junction by the potential difference - This statement is not accurate. While there is a potential difference across the p-n junction, it does not directly cause the movement of holes. The movement is primarily driven by the concentration gradient.
- Option D: All of the above - This option is incorrect since options A and B are not accurate explanations for the diffusion of holes in an unbiased p-n junction.

In conclusion, the correct answer is option C, as it accurately explains the diffusion of holes from the p-region to the n-region in an unbiased p-n junction based on the concentration gradient.

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