Question

Silicon doped with group 13 and group 15 elements are called as _______ semi conductors

• A. p-type, n-type
  
• B. n-type, p-type
• C. p-type
  
• D. n-type

Answer 1

The correct option is A p-type, n-type


When silicon is doped with group 13 elements such as B and Al, there will be a electron hole left in the lattice of the doped crystal due to the presence of only three valence electrons in B and Al, whereas Si has four valence electrons. Si forms four covalent bonds with the nearby atoms, whereas B and Al can form only three bonds. This site of defeciency of electron is called the electron hole. The electrons from the nearby atoms shift to this hole and thus delocalisation of electrons take place. This type of semi-conductors are called as p-type semi-conductors.

On the contrary, when Si is doped with group 15 elements like P and As, there will be an extra electron from the doped group 15 element which will be delocalised, since Si can form only four covalent bonds with the neighbouring atom. The group 15 elements have five electrons in their valence shell out of which four is used for bonding with the nearby atom and one electron will be delocalised. This type of semi-conductors are called the n-type semi-conductors.