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

Explanation

On doping germanium with galium some of the positions of lattice of germanium are occupied be galium Galium atom has only three valence electrons , therefore , fouth valency of nearby germanium atom Is not satified and the place remains vacant.
this place is deficient of electrons and fills the hole or electron vacancy Electron from neighbouring atom comes and fills teh hole in its original position .
Under the influence of electric field electrons move towards positively charged plates though these and conduct electricity , the holes appear to move towards negatively chared plates.