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

Explanation

Germanium (Ge) is group 14 element and as a semi-conductor with little electrical conductivity. Upon doping with gallium (Ga) which belongs to group 13 some eletron valencies or electron holes get created in the crystal lattice of germanium. Actually an atom of Ga has only three valence electrons available for sharing with the electron of Ge which has four valence electrons This means that the fourth valency of nearby Ge atom remains unstisfied. The place remains vacant. Since it deficient in electron, it is called electron hole or electron vacancy. Electron from neighbouring Ge atom comes to fill this gap. Consequently, a hole gets created in this atom. Under the influence of applied elctric field, electric field, electrons move towards the positively charged plates through these holes and conduct electricity. The holes appear to be moving towards negatively charged plates.