What is a diode and how does it work?

Answer 1

When varactor diode is reverse biased then the neutral region between P and N layer increases. When reverse biasing decreases then the neutral region also decreases.

Answer 2

Diode is a two terminal device (di- means "two"). Simply put, it acts as a one-way valve for electrons. Conventional current can flow from the anode to the cathode, but not in the other direction.

If an intrinsic semiconductor is doped with a pentavalent or trivalent impurities you get a diode. A diode is formed when a region of N-type semiconductor touches a section of P-type.

In the N-type region electrons are the majority carriers and in the P-type electron "holes" are the majority carriers.

If forward-biased (applying a positive voltage to the P region and a negative voltage to the N region), the depletion region of the diode decreases. The electrons on the N side are repelled and they move towards the P side thus reducing the size of the depletion layer.

If reverse-biased, the depletion region increases because the electrons are attracted towards the positive voltage and the holes are attracted towards the negative voltage, and hence the current gets reduced and the current flowing will be very small, on the order of microamps. This is called as reverse saturation current.

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Although an ideal diode acts like a switch and it is a useful approximation, real diodes are not ideal: a real diode has other properties that are sometimes useful and sometimes a drawback. For example, a real diode requires some forward voltage to turn on, usually around 0.3-0.6 volts, depending on the type. Also a reverse-biased diode can act like a variable capacitor, which can be used to make voltage controlled oscillators and tuning filters. Reverse-biased diodes (voltage applied so they turn off) will eventually break down if enough reverse voltage is applied, and allow current to flow. This is used to make Zener diodes that breakdown at a specific voltage, useful in voltage regulation.

Answer 3

In a forward bias (when the diode is pointed in the same direction as the current flow) the diode acts as a resistor up to a potential difference of 0.7 volts, from then it lets current flow almost freely. In a reverse bias (when the diode is pointed against the current flow) it acts as a strong resistor, letting negligible current flow, until a potential difference of 50 volts, in which the diode breaks down. Hope that helps!