Expalin why does conductivity of germainum crystals increase on doping with galium ?

Explanation

Germanium (Ge) belongs to Group 14 while Gallium (Ga) belongs to Group 13. Ge has 4 electrons in the valence shell whereas Ga has only 3. When Ge is replaced by Ga, an electron vacancy is created Electrons from neighbouring atoms move to fill this vacancy . As a result, a hole is created in its original position. When an electric field is applied , electrons move towards the position plate and conduct electricity. The holes move towards the negative plate.