Semiconductors

A semiconductor is a material that has a resistivity between that of a conductor (very low) and an Insulator (very high).

Semiconductors are usually based on the Group IV elements Silicon and Germainium. These elements naturally form crystalline solids. The conductivity of these substances changes dramatically with changes in temperature.

n type conduction

where the impurity adds more electrons to the lattice, therefore electrons (negative charges) are the charge carriers

p type conduction

where the impurity adds less electrons to the lattice, therefore the lack of electrons (holes(Positive charges)) are the charge carriers

PN Junction

Forward Biased, ie

where the P type Semi-conductor is connected to the +ive side of the battery

leads to a small depletion layer

Allows a current to flow.

Reverse Biased,

i.e. where the N type Semi-conductor is connected to the +ive side of the battery

leads to a Large depletion layer

Leads to a very small current to flow

Semiconductor Devices

Diodes

A semiconductor device which conducts electric current run in one direction only. This is the simplest kind of semiconductor device, it has two terminals and a single PN junction. One diode can be used as a half-wave rectifier or four as a full-wave rectifier.

Transistors

Because they "transfer resistance", like "resistors" they are"transistors".

References in each case to charge carriers.

Conduction in semiconductors: the distinction between intrinsic and extrinsic conduction;

p-type and n-type semiconductors.

The p-n junction: basic principles underlying current flow across a p-n junction.

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