Dr. Dattaraj Vidyasagar

The PN junction diode conducts only in one direction. So it is known as unidirectional current device. Before going to understand the energy level diagrams, please read construction and biasing of diode.

When the external voltage applied to the PN junction is in such a direction that it cancels the potential barrier, thus permitting current flow, is called as forward biasing.

A PN junction diode is the first semiconductor device in semiconductor family. It is also known as unidirectional current device, because it allows current only in one direction through it.

The devices like diodes, transistors, ICs used in electronic circuits are manufactured with the help of extrinsic semiconductor. When a trivalent or pentavalent element is mixed with pure Silicon crystal (i.e. intrinsic semiconductor), the new material is formed known as extrinsic semiconductor.

The pure crystal of semiconductor (Si or Ge) is known as intrinsic semiconductor at room temperature. The Silicon atom has 14 electrons revolving around its nucleus. In first orbit it contains 2 electrons, in second orbit 8 electrons i.e. 4 electrons in last orbit, known as valence electrons.

Some substances like Germanium, Silicon, Carbon, etc. are neither good conductors like copper nor insulators like glass. The resistivity of these materials lies in between conductors and insulators. Such substances are known as semiconductors.