5: N-type and P-type
and P-type semiconductor are created in a fabrication plant by adding
elements to pure semiconductor under carefully controlled conditions.
Both are better conductors than pure semiconductor, but it is the
interaction between adjacent layers which creates electronic devices.
with five valence electrons (such as arsenic, phosphorus and antimony)
are added to pure silicon, the fifth electron is free to move through
the crystal, much like the single valence electron in copper. These
elements are referred to as donor elements. The resulting compound
is known as N-type semiconductor. (This does not mean that it has
a negative charge, merely that it has free electrons.) When a voltage
is applied, the free electrons will move through the crystal.
is formed when elements with three valence electrons (such as boron,
aluminium, gallium, or indium) are added to a pure semiconductor."Holes"
are formed where the fourth electron would be, which can be filled
by an available electron, so these elements are called acceptor
elements. P-type semiconductor is electrically neutral, but when
a voltage is applied, electrons can move through it by moving from
one hole to another.