Afa History Essay

1575 WordsMar 21, 20117 Pages
DIODES configuration 1.The atom's electrons orbit the nucleus in a specific shell 2. each shell has a predefined capacity and is always filled from the inner shell to outer shell, or valence shell 3. The number of electrons in valence shell determines how the atom will react with other atoms The atoms with four valence electrons are not stable and will tend to combine chemically with other atoms to acheive a stable state. This menas that the atom will try to obtain 8 electrons in its valence shell. This process of sharing electrons is called covalent bonding. N TYPE SEMI-CONDUCTORS manufacturers introduce specific impurities into the semiconductor material in order to change their electrical characteristics. This process called doping. Doping changes the crystal's electrical characteristics by reducing the internal resistance of the crystal. Materials doped with impurities containing excess electrons (five- arsenic) are called N type semiconductors. In N tpe semiconductors the electrons are called the majority carrier and any free holes introduced is caled the minority carrier. P TYPE SEMICONDUCTORS Materials doped with impurities containing less valence electrons (three - aluminium) are called P type semiconductors.When aluminium is used to dope silicon crystals, an incomplete covalent bond is formed. This missing bond in the crystal acts as positive charge and attractive free electrons. These positive charges can be thought of as "holes" and move through the crystal just as electrons do but in the opposite direction.In P tpe semiconductors the holes are called the majority carrier and any free electrons introduced is caled the minority carrier. Thermal effects The heat increases the number of minority carriers. As heat enters the crystal, electrons gain more energy and break their covalent bond. Each broken bond produces a free

More about Afa History Essay

Open Document