Unformatted text preview: Diodes
Semiconductors Can act like a conductor or an insulator
Most semiconductor chips and transistors are created with silicon. Silicon
Silicon Silicon is a very common element
Example: it is the main element in sand and quartz. Carbon, silicon and germanium have a unique property in their electron structure each has four electrons in its outer orbital. Forms nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In silicon, the crystalline form is a silvery, metalliclooking substance. In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons to conduct electric current. This makes a silicon crystal an insulator rather than a conductor. Doping
Doping You can change the behavior of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal. There are two types of impurities: Ntype Ptype Ntype Doping
Ntype Doping Phosphorous is added to the silicon in small quantities. It has five outer electrons, so it’s out of place when it gets into the silicon lattice. Fifth electron has nothing to bond to, so it's free to move around. Ntype Doping
Ntype Doping Takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. Ntype silicon is a good conductor.
Electrons have a negative charge, hence the name Ntype. Ptype Doping
Ptype Doping Boron is the dopant.
It has only three outer electrons. When mixed into the silicon lattice, it form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name Ptype. Ptype Doping
Ptype Doping Holes can conduct current.
A hole accepts an electron from a neighbor, moving the hole over a space.
Ptype silicon is a good conductor. What is a diode
What is a diode A diode is the simplest possible semiconductor device A diode allows current to flow in one direction but not the other. Used for illumination These are diodes.
These are diodes. Reverse Bias When you put Ntype and Ptype silicon together as shown in this diagram, you get a very interesting phenomenon that gives a diode its unique properties. •Combination shown in the diagram does not conduct any electricity. Forward Bias If you flip the battery around, the diode conducts electricity.
The free electrons in the Ntype silicon are repelled by the negative terminal of the battery. At the junction between the Ntype and P
type silicon, holes and free electrons meet.
Electrons fill the holes. Current flow takes place. Diode Uses
Diode Uses A device that uses batteries often contains a diode that protects the device if you insert the batteries backward. The diode simply blocks any current from leaving the battery if it is reversed this protects the sensitive electronics in the device. Anode and Cathode
Anode and Cathode FANCY words for + side and – side
Anode = positive
Cathode = negative Identification
Cathode Cathode Anode Anode Diodes in a circuit
Diodes in a circuit
Cathode Cathode Anode Anode Wiring up a diode
Wiring up a diode + ...
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- Spring '11
- Cathode, silicon lattice, Ptype Doping