Which of the following elements when added as an impurity into the germanium produces a p – type semiconductor?

Al

A p – type semiconductor is obtained when Si or Ge is doped with a trivalent impurity like indium (In), boron (B), aluminium (Al) etc. whereas an n – type semiconductor is obtained when Si or Ge is doped with a pentavalent impurity line arsenic (As0, antimony (Sb), phosphorous (P) etc.