Semiconductor Devices and their Uses:

If a junction  is formed between a p-type and an n-type'semiconductor,  the device called a p- n  junction diode acquires a peculiar pppeny. It conducts current only in one direction! Hence, it  is usedto convert alternating current (a.c.),into  direct current (44 The device acts as an open circuit in Fig. It acts as ag  open circiit Fig. And since it is a non-mechanical  switch, it acts very fast. 

More complicated devices using n-p-n  or p-n-p combinations of semiconductor mat6rial are called transistors.  They have even more interesting properties. They can be so  connected to batteries that a small variation of current on one side, can lead to a large variation on the other side. In technical jargon, the transistor can 'amplify' small signals. Transistors can also be connected  to other electrical components (resistors, capacitors etc.) to produce a.c. of high frequency.   

Semiconductor devices are extremely small in size. Their properties can be controlled at will. This may be done by changing the amount of doping or by  introducing more sections of p-type or n-type semiconductors on the same crystal. A large number of new semiconductor devices have been made in this way. Further, by  suitable methods, they can be produced  in a large chain or according to a desired pattern'on  a non-conducting surface called a chip. When a large number of semiconductor devices are produced on a single chipto perform specific functions, the resulting device is called an integrated circuit (IC). Because of their small size and their sturdiness, and because they consume almost no energy, these devices hive become very popular as components in TV sets, computers and many kinds of  instruments used for communication and control.