Compare P-type semiconductor with
N-type semiconductor, point of comparison: valence impurity.
We can begin this comparison
starting with a base material many semiconductors are made of. Silicon is a material often used
this way, and we know that silicon has four electrons in its valence shell. This means that when silicon atoms
are combined together in lattice formation, the interior atoms have a full valence
electron shell with eight electrons.
This bulk semiconductor material
has no net positive or negative charge. We create P for positive-type or
N for negative-type semiconductors by adding an impurity in to this lattice
formation. When we dope a semiconductor with
an impurity that has three electrons in its valence shell, such as boron, for
example, now when we surround this boron atom with silicon, there is a hole where an
electron used to be, where the boron atom silicon.
This electron hole repeated many
times over the lattice formation gives the semiconductor its overall positive
charge. We can say that any atom with three
electrons in its valence shell, that is, a trivalent atom, can help us create a
On the other hand, an N-type
semiconductor is created using an impurity that has five electrons in its valence
shell. An example of an atom like this is
antimony. Surrounded by silicon atoms,
antimony has a full valence shell plus one electron which is free to move. It’s this excess electron that
overall gives the semiconductor a negative-type charge. And it was created by doping the
semiconductor with an impurity that has five electrons in its valence shell, that
is, a pentavalent impurity. These then are the differences in
the valence impurities between P- and N-type semiconductors.