Question

Which type of semiconductor is formed when a trivalent impurity is dropped in a pure semiconductor?

Answer 1

Hint: Doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor. Addition of impurity will change the conductor ability and it acts as a semiconductor. The impurity added to the intrinsic semiconductor is called a dopant. Practically only after doping a semiconductor shows enough conductivity and becomes usable.

Complete step-by-step answer:
When a trivalent impurity is doped in a pure silicon semiconductor it forms a P-type semiconductor. The effect of doping on a P-type material is as follows −
When Indium (In) or Gallium (Ga) which are trivalent in nature are added to pure silicon, a P-type material is formed. This type of dopant material has only three valence electrons and thus they being electron deficient are eagerly looking for a fourth electron. This deficiency of one electron is represented by a hole. When this hole is filled up with an electron from silicon, there is a new role created near the silicon atom. This means that P material will have much more holes than the electron-hole pairs of pure silicon. This presence of holes increases the conductivity as the electrons can jump into the successive. Also P-type of semiconductors are not positively charged because the atoms in it are primarily all electrically neutral.
There are, however, holes in the covalent structure of many atom groups. When an electron moves in and fills a hole, the hole becomes void. A new hole is created in the bonded group where the electron left. Hole movement in effect is the result of the increased electron movement.

Note: In addition to Arsenic to pure Silicon, the crystal becomes an N-type semiconductor. Arsenic atoms has additional electrons so it donates one electron to the crystal and they are referred to as donor impurities. An N-type material has extra or free electrons than an intrinsic material. The number of electrons in an N-type silicon is many times greater than the electron-hole pairs of pure silicon. There are abundant current carriers to take part in the current flow and this increases the current flow.