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Impact ionization is said to be generation of electron-hole pairs with help of free electrons and holes. I have the intuition on how a free electron would be able to generate electron hole pair. I can't understand how a hole can do so.Please help.

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A hole is just a low energy location in the valence band, where electrons tend to jump.

A hole could be a vacancy left behind by an electron jumping to the conduction band or to another hole or it could be a low energy orbital of an acceptor atom imbedded, via a p-type doping, into semiconductor to promote conductivity in the valence band.

When, under the influence of an electric field, a valence electron jumps to a hole and leaves another hole behind, another electron could jump into that new hole, setting off a chain of jumps and thus creating a current. This could make an impression that a hole itself is moving, giving a rise to the concept of a hole current, which flows in the direction opposite to the direction of the electron current.

In fact, of course, we still have moving electrons, and, similar to free electrons in the conduction band, they could hit neutral atoms and, given a strong enough field, generate new electron-hole pairs.

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  • $\begingroup$ What you are talking about is annihilation of a hole to produce another hole whereas impact ionization means creation of another electron hole pair by a free electron or a hole without either getting annihilated. $\endgroup$ – Rohan Jun 15 '18 at 6:40
  • $\begingroup$ @Rohan I am talking about annihilation of a hole by an electron jumping into a hole just to explain that the hole current is, in fact, the current of electrons, which, unlike holes, are real physical particles that carry energy and, therefore, while they move from one hole to another, can hit neutral atoms and ionize them, thus producing new electron-hole pairs. The hole current is just a convention, introduced to differentiate current made up by free electrons in conduction band and bound electrons in valence band. Semi. currents could be described without ever mentioning holes. $\endgroup$ – V.F. Jun 15 '18 at 10:43

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