Semiconductor Physics: Conductivity, Diodes, and Transistors

Metals are very good conductors of electricity and high conductivity is due to the fact that there are e-free in the last layer of atoms, which can move freely between the atoms of metal.

In the Ag and Cu, in the last layer is a single e-, as it is somewhat linked to the core, moves haphazardly within the solid metal.

Between metallic conductors and insulators are semiconductor bodies, so named because they are worse drivers than metals, but better in the insulating gral.

The most important semiconductors Ge and Si, and in its latest report 4 e-coat.

For the study of semiconductors, we will focus on the covalent bond, characterized in that the valence e-are shared two to two adjacent atoms.

A crystal of Ge and pure Si no free electrons and is not conductive, but if you add other substances (impurities) that become part of the crystal structure are known to increase the conductivity.

If you add atoms that have 5 e-, the new structure is formed make an e-free, since the other 8 are shared by the link coovalente.

The glass or material is said to be type N or e-donor.

If added to the semiconductor atoms that have 3e-, the new structure is formed make a hole to fill the last layer (missing e-). This material is said to be of type P or e-.Cuando acceptor join If Ge or P type with Type N, the contact surface of both materials have an exchange of charges for P-type semiconductor difusión.Del holes pass the N-type semiconductor and recombine there with e-.Del Similarly, semiconductor N-type pass and the P-type semiconductor and recombine huecos.Si directly polarizes the dielectric zone disappears, and if it is polarized to the upside is much greater, ie, increases the diffusion zone, blocking the passage of the diode corriente.Un can not maintain their property to block the current to a reverse voltage infinitely high, as exceeded a certain value, electrically opens a gap in the potential barrier and establish a strong R in the opposite direction, called current disruption.

Transistor

The transistor is a semiconductor component with three consecutive regions of a semiconductor and a P N.
There are NPN and PNP transistors
The central region is called the base (B) and the two outer emitter (E) and collector (C). The intensity of the base current is a function of the emitter voltage, collector. If this voltage is zero, no current flows any base, and hence no current flows from emitter and collector.
By raising the base voltage, the emitter current increases rapidly, reaching high values. The more intense becomes the emitter current, the more e-arrive at the base.

The transistor amplifier is used as current, voltage and electronic switch.