INTRODUCTION
Electronics is an applied physical science concerned with the development of electrical circuits using thermionic valves, semiconductors, and other devices in which the motion of electrons is controlled.
Certain substances like germanium, silicon, etc. are neither good conductors nor insulators. The resistivity of these materials lies in between conductors and insulators. Such substances are called semiconductors. If a junction is formed between a sample of a p-type semiconductor and a sample of an n-type semiconductor, then this device is called a PN junction or junction diode. When a third doped element is added to a junction diode, the resulting device is known as a transistor. In diodes and transistors, holes and electrons play a part in the conduction process.
In this article, we will study the introduction of semiconductors and the construction and working of diodes and transistors.
CLASSIFICATION OF SOLIDS
1. Conductor:
When the outermost orbit of an atom has less than one-half the maximum of eight electrons i.e., four electrons, the material is usually metal or conductor. These materials offer the least resistance to the flow of electric current and have a resistivity in order of 10-8 to 10-6 ohm-m.
Ex: Silver, Copper, etc.,
These materials permit detachment of the electrons from the outermost orbit and offer little hindrance to their flow through atoms.
2. Insulator:
When the outermost orbit of an atom has more than one half of the maximum of eight electrons i.e., four electrons. The material usually is a non-metal or insulator. These materials offer high resistance to the flow of electric current and their resistivity lies in order to 1012 to 1018 ohm-m.
Ex: Rubber, Paper, Mica, etc.,
3. Semiconductor:
When the outermost orbit of an atom has exactly one half of the maximum of eight electrons i.e., four electrons, the material has both metal and non-metal properties and is usually a semiconductor. The resistivity of these materials lies in between ranges of conductor and insulator and is of the order of 1 to 100 ohm-.m
Ex: Germanium, Silicon, etc.....,
These materials will act as insulators at 0° K temperature.
