In the energy band diagram of a material shown below, the open circles and filled circles denote holes and electrons respectively. The material is a/an

Options

A. `p`-type semiconductor
B. insulator
C. metal
D. `n` type semiconductor

Answer

A

Explanation

The given figure represents `p`-type semiconductor as described below
When one of the silicon atom (valence =`4`) has been replaced by an atom of aluminium (valence `=3`), the aluminium atom can bond covalently with only three aluminium atom can bond covalently with only three silicon atoms, so there is now a "missing" electron (a hole) in one alumiumium-silicon bond with a small expendicture of energy, an electron can be torn from a neigbouring silicon-silicon bond to fill this hole, thereby creating a hole in that bond. similarly, an electron from some other bond can be moved to fill the second hole. In this way, the hole can migrate through the lattice.

The alumunium atom is called an acceptor atom because it readily accetps an electron from a neighbouring bond that is from the valence band of silicon. As figure suggests, this electron occupies a localized acceptor satate that lies within the energy gap, at an average energy interval `E_(a)` above the top of the valence band. By adding acceptor atoms, it is possible to increase very greately the number of holes in the valence band.