These are dialed to precise tolerances, see the section on Zener Diodes in step 3. Zener diodes are designed to conduct in the reverse direction, only when something called the breakdown voltage is reached will the circuit conduct. These can be useful in making projects with a light activated switch, so that a circuit in only active in the presence of light. Photodiodes conduct only when they are exposed to light. The LED emits visible light when electrons jump across the PN junction.The resulting light is referred to as electroluminescence. There are many different kinds of diodes, and each one serves a different purpose as an electronic component.Ī Light Emitting Diode or LED is probably the most well known and most easily identified. The severity of the voltage drop is a function of the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows. When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode's forward voltage drop. In a reverse bias current is blocked so there is no flow of electricity through the circuit. When the diode is in forward bias, the diode allows traffic, or current, to flow from the anode, towards the cathode leg. Think of a diode as a one-way street for electricity. But when a voltage is applied across the junction however, so that the P-type anode is made positive and the N-type cathode negative, the positive holes are attracted across the depletion layer towards the negative cathode, also the negative electrons are attracted towards the positive anode and current flows. There are no charge carriers in this depletion layer and no current can flow across it. Between these layers, where the P-type and N-type materials meet, holes and electrons combine, with excees electrons combining with excess holes to cancel each other out, so a thin layer is created that has neither positive nor negative charge carriers present. The P-type material has a surplus of positive charge carriers (holes) and the N type, a surplus of electrons. A hole happily accepts an electron from a neighbor, moving the hole over a space.ĭiodes are made from two differently doped layers of semiconductor material that form a PN junction. The absence of an electron creates the effect of a positive charge, hence the name P-type. When mixed into the silicon structure, they form "holes" in the lattice where a silicon electron has nothing to bond to. Those elements each have three outer electrons. P-type - In P-type doping, boron or gallium is added to the pure silicon.
It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. Electrons have a negative charge, hence the name N-type. The fifth electron has nothing to bond to, so it's free to move around. Phosphorus and arsenic both have five outer electrons, so they are displaced when they get into the silicon lattice.
N-type: With N-type doping, phosphorus or arsenic is added, in parts per billion, to the silicon in small quantities. The kinds of impurities added to pure silicon can be classified as N-type or P-type. In doping, you mix a small amount of an impurity into the pure crystalline structure. For example, electrons move easily through a piece of metal wire. You can change the behavior of a pure material, like silicon, and turn it into a semiconductor by doping. Consider conduction: its is a measure of the relative ease of which electrons move through a material. Diodes are valuable in electronics and serve a variety of purposes, which will be highlighted in upcoming steps.Ī diode is a semiconducting device, that allows current to flow in one direction but not the other.Ī semiconductor is a kind of material, in this case silicon or germanium, whose electrical properties lie between those of conductors (metals) and insulators (glass, rubber). If you have embarked upon electronics projects in the past, there is a good chance you have already encountered this common component and soldered into your circuit without second thought.