In p-type semiconductors, the conductivity is due to:

The correct answer is Option (2) → positive holes

A p-type semiconductor is made by doping silicon or germanium with a group 13 element such as B, Al or Ga, which has only three valence electrons. At the place of the fourth electron an electron hole (electron vacancy) is created. An electron from a neighbouring atom can fill the hole, leaving a hole where it was, so the hole appears to move. In an electric field the electrons move towards the positive plate through these holes, and the holes behave as if they were positively charged and moving towards the negative plate. Conduction in p-type semiconductors is therefore due to positive holes.

Why the other options are incorrect

• Option (1) negative holes — Incorrect. A hole is the absence of an electron, so it behaves as a positive charge, not a negative one.

• Option (3) valence electrons — Incorrect. The valence electrons of silicon are held in covalent bonds; they move only by hopping into holes, which is described as the movement of holes.

• Option (4) mobile electrons — Incorrect. Conduction by extra mobile electrons is the case of n-type semiconductors (Si doped with P or As).

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Electron-deficit Impurities – “Silicon or germanium can also be doped with a group 13 element like B, Al or Ga which contains only three valence electrons. The place where the fourth valence electron is missing is called electron hole or electron vacancy. An electron from a neighbouring atom can come and fill the electron hole, but in doing so it would leave an electron hole at its original position. If it happens, it would appear as if the electron hole has moved in the direction opposite to that of the electron that filled it. Under the influence of electric field, electrons would move towards the positively charged plate through electronic holes, but it would appear as if electron holes are positively charged and are moving towards negatively charged plate. This type of semi conductors are called p-type semiconductors.”