semiconductors.All semiconductors have crystalline structure.The most
commonly used semiconductor materials are germanium,silicon, and
gallium arsenide have practical applications in electronics.But most
frequently used semiconductors are germanium and silicon because the
energy required to break their covalent bonds and release an free
electron from their valence bands is lesser than that required for
gallium arsenide.The energy required for releasing an electron from
the valence band is 0.66eV for germanium,1.08eV for silicon and 1.58eV
for gallium arsenide. Germanium can
be purified relatively well and crystallised easily.Germanium is an
earth element and it is obtained from the ash of the certain coals or
from the flue dust of the zinc smelters.The recovered germanium is in
the form of germanium dioxide powder which is then reduced to pure
germanium.Germanium diodes are used as infrared detectors in
fibre-optic communication system because of narrower energy gap.
Silicon is an element found in most
of the common rocks.Sand is silicon dioxide which is then reduced to
100% pure silicon.Silicon dioxide is a natural insulator which is
useful in the fabrication of semiconductor devices and integrated
circuits.Silicon is largely preferred to germanium because of its
large gap energy,which produces improved device properties at high
temperatures. Silicon is a better thermal conductor and is required to
remove unavoidable heat developed in the device.
Gallium arsenide has higher electron mobility,which
leads to faster switching capabilities.It has high temperature
operating capabilities because of its larger energy gap. 09:10
