question_answer

To a germanium sample, traces of gallium are added as an impurity. The resultant sample would behave like:

A)  a conductor

B)  a p -type semiconductor

C)  an n-type semiconductor

D)  an insulator

Correct Answer: B

Solution :

Key Idea: Gallium has three valence electrons in its outermost orbit. When gallium is added to germanium all of the three valence electrons form covalent bonds with one each valence electron of the three- nearest germanium atom while the valence electron of the fourth nearest germanium atom is not able to form bond. Thus, there is a deficiency of one electron. This is called hole. Such an impure germanium crystal is called p-type semiconductor.