Technolgy in microelectronics

Technology in Microelectronics
Basic Definitions
Insulators:
Electrical insulation is the absence of electrical conduction. Electronic band theory (a branch of physics) predicts that a charge will flow whenever there are states available into which the electrons in a material can be excited. This allows them to gain energy and thereby move through the conductor (usually a metal). If no suchstates are available, the material is an insulator.
These materials are used in parts of electrical equipment, intended to support or separate electrical conductors without passing current through themselves.
Conductors:
Is a material which contains movable electric charges. In metallic conductors, such as copper or aluminium, the movable charged particles are electrons. Positive charges mayalso be mobile in the form of atoms in a lattice that are missing electrons (known as holes).
All conductors contain electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the direct current is proportional tothe voltage (as determined by Ohm's law), provided the temperature remains constant and the material remains in the same shape and state.
Most familiar conductors are metallic. Copper is the most common material used for electrical wiring. Silver is the best conductor, but is expensive. Gold is used for high-quality surface-to-surface contacts. However, there are also many non-metallic conductors,including graphite, solutions of salts, and all plasmas.
Semiconductors
A semiconductor is a material that has electrical conductivity between that of a conductor and an insulator. Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices.
Semiconductor devices include the various types of transistor,solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits.

Model of Atoms
(see figure)
Paring and Recombination
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Doping
P-doting by Boron
A P-type semiconductor (P for Positive) is obtained by carrying out a process of doping, that is adding a certain type of atoms to thesemiconductor in order to increase the number of free charge carriers (in this case positive).
When the doping material is added, it takes away (accepts) weakly-bound outer electrons from the semiconductor atoms. This type of doping agent is also known as an acceptor material and the vacancy left behind by the electron is known as a hole.
The purpose of P-type doping is to create an abundance ofholes. In the case of silicon, a trivalent atom (typically from group IIIA of the periodic table, such as boron or aluminium) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bonds normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. This iswhy such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of half of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negatively-charged dopant ion, and the semiconductor remains electrically neutral as a whole.
n-doting by Phosphorus
An N-type semiconductor (N for Negative) is a materialobtained by carrying out a process of doping, that is, by adding some amount of an element with more electrons to a semiconductor element with fewer electrons, in order to increase the number of free charge carriers. In this case the charge carriers are negatively-charged, hence "N-type". The impurity is called a "donor material," because it gives away (donates) weakly-bound outer electrons to the...