Semiconductors

Semiconductors              

Q.  n-type and p-type semiconductors.
A. A semiconductor is a material whose ability to conduct electric current is greater than that of an insulator but less than that of metals. Silicon and germanium are the most commonly used semiconductors. Some other compounds like gallium, arsenide, indium, antimonide are-also used. The ability of semiconductors to conduct electricity depends critically upon their purity, or rather their impurity. A pure crystal of silicon or germanium acts more or less as an insulator. However, if an impurity is added to the crystal it becomes more conductive. Semiconductors are the basis of all the sophisticated electronics gadgets we have today. Digital watches, calculators, aircraft, spacecraft, satellites, telephone exchanges, lasers, and many more devices have components or equipment made up of semiconductors.
     The ability of semiconductors to conduct electricity depends critically upon their purity, or rather their impurity. A pure crystal of silicon or germanium acts more or less as an insulator. However, if an impurity is added to the crystal it becomes more conductive. By the way, "impurity" does not mean a 50-50 mixture or even one part of impurity in ten parts of silicon. In useful semiconductors, a ton of silicon may have I mg of the element arsenic. Even the tiny bit of arsenic contributes surplus electrons to silicon, which then becomes a better conductor. Such a piece of silicon would be called an n-type semiconductor. On the other hand, a like amount of boron would cause a different kind of conduction to take place and the piece of silicon so treated would be called p-type semiconductor. The word 'doping' is used by scientists to describe the introduction of such small impurities.