Question

Which one of the following elements of doping with germanium , make it a p-type semiconductor ?
A.$Bi$
B.$Sb$
C.$As$
D.$Ga$

Answer 1

Hint: Germanium is a group 14 element which has four valence electrons , therefore to make it a p- type semiconductor we have to dope it with such an element which has three valence electrons in its outer shell .

Complete step by step answer:
Semiconductors are not very good conductors so to increase their conductivity , impurities are added . The process of adding impurities to a crystalline substance so as to change its properties is known as doping .
Two types of impurities can be added to group 14 elements , they are
electron rich impurities - When group 15 elements are doped with group 15 elements four covalent bonds are formed with the four electrons of group 14 element and one electron is extra which increases the conductivity . It is known as n-type semiconductor .
electron deficient impurities - When group -1 4 elements are doped with group 13 elements only three covalent bonds are formed thus , a hole is created in place of the fourth electron . It is known as a p- type semiconductor .
Hence to make germanium a p- type semiconductor we have to add a group 13 element which is $Ga$ .
Hence option D is correct .


Note:
The conductivity in p- type semiconductors is due to presence of holes . When a vacancy is created , to fill the vacancy an electron from a neighbouring site comes and occupies the hole but in doing so it creates a vacancy in its original place and so the flow of electrons continues .