MATERIAL ENGINEERING-SEMICONDUCTORS

SEMICONDUCTORS

   A semiconductor is a material which can either behave as a conductor or as an insulator. The conductivity of a semiconductor increases with increasing temperature, behaviour opposite to that of a metal.Semiconductors can display a range of useful properties such as passing current more easily in one direction than the other. Because the conductive properties of a semiconductor can be modified by controlled addition of impurities or by the application of electrical fields or light.Semiconductor are based in electronic components such as,transistors, solar cells, many kinds of diodes including the light-emitting diode (LED), the silicon controlled rectifier, photo-diodes, and digital and analog integrated circuits. Understanding the properties of semiconductors relies on quantum physics to explain the motions of electrons through a lattice of atoms. Furthermore,current conduction in a semiconductor occurs via free electrons and "holes", known as charge carriers. Adding impurity atoms to a semiconducting material, or else "doping", greatly increases the number of charge carriers within it. When a doped semiconductor contains excess holes it is called "p-type", and when it contains excess free electrons it is known as "n-type". The semiconductor material used in devices is doped under highly controlled conditions in order to precisely control the location and concentration of p- and n- type dopants. A single semiconductor crystal can have multiple p- and n-type regions; the p-n junctions between these regions have many useful electronic properties.For instance, they are commonly used as diodes: circuit elements that allow a flow of electricity in one direction but not in the opposite one. Most common semiconducting materials are crystalline solids, amorphous and liquid semiconductors,more specifically,diamond,silicon,germanium,aluminium nitride,etc. To sum up,semiconductors are the foundation of modern electronics. Increasing knowledge of semiconductor materials and fabrication processes has made possible continuing increases in the complexity and speed of semiconductor devices.