semiconductor

electronics A material, typically crystaline, which allows

current to flow under certain circumstances. Common

semiconductors are silicon, germanium, gallium arsenide.

Semiconductors are used to make diodes, transistors and

other basic "solid state" electronic components.

As crystals of these materials are grown, they are "doped"

with traces of other elements called donors or acceptors

to make regions which are n- or p-type respectively for the

electron model or p- or n-type under the hole model.

Where n and p type regions adjoin, a junction is formed which

will pass current in one direction (from p to n) but not the

other, giving a diode.

One model of semiconductor behaviour describes the doping

elements as having either free electrons or holes dangling

at the points in the crystal lattice where the doping elements

replace one of the atoms of the foundation material. When

external electrons are applied to n-type material (which

already has free electrons present) the repulsive force of

like charges causes the free electrons to migrate toward the

junction, where they are attracted to the holes in the p-type

material. Thus the junction conducts current.

In contrast, when external electrons are applied to p-type

material, the attraction of unlike charges causes the holes to

migrate away from the junction and toward the source of

external electrons. The junction thus becomes "depleted" of

its charge carriers and is non-conducting.

(1995-10-04)