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Cathode diode9/5/2023 This voltage is needed to start the hole-electron combination process at the junction.Ĭome Visit our Facebook Page! - Electrical-info.Electrode where reduction takes place Diagram of a copper cathode in a galvanic cell (e.g., a battery). In silicon, this voltage is about 0.7 volts. When f orward-biased, there is a small amount of voltage necessary to get the diode going. Usually, the breakdown voltage is a lot more voltage than the circuit will ever see, so it is irrelevant. And if you apply enough reverse voltage (V), the junction breaks down and lets current through. A real diode lets perhaps 10 micro amps through - not a lot, but still not perfect. When reverse-biased, an ideal diode would block all current. The effect is that current flows through the junction. Those holes and free electrons cease to exist, and new holes and electrons spring up to take their place. At the junction between the N-type and P-type silicon, holes and free electrons meet. The holes in the P-type silicon are repelled by the positive terminal. The free electrons in the N-type silicon are repelled by the negative terminal of the battery. If you flip the battery around, the diode conducts electricity just fine. No current flows across the junction because the holes and the electrons are each moving in the wrong direction. The positive holes in the P-type silicon get attracted to the negative terminal of the battery. The negative electrons in the N-type silicon get attracted to the positive terminal of the battery. When you put N-type and P-type silicon together, you get a very interesting phenomenon that gives a diode its unique properties.Įven though N-type silicon by itself is a conductor, and P-type silicon by itself is also a conductor, the combination shown in the diagram does not conduct any electricity. A diode allows current to flow in one direction but not the other. That’s what happens in diodes.ĭiodes are the simplest possible semiconductor device. N-type and P-type silicon are not that amazing by themselves but when you put them together, you get some very interesting behavior at the junction. P-type silicon is a good conductor.Ī minute amount of either N-type or P-type doping turns a silicon crystal from a good insulator into a viable conductor, hence the name “semiconductor.” A hole happily accepts an electron from a neighbor, moving the hole over a space. The absence of an electron creates the effect of a positive charge, hence the name P-type. When mixed into the silicon lattice, they form “holes” in the lattice where a silicon electron has nothing to bond to. Boron and gallium each have only three outer electrons.
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