Semiconductor Diode – Definition, Characteristics, Applications


Semiconductor diode – type of diode, which contains “p-n junction” made of semiconductor materials. It’s double-ended, nonlinear element where the end attached to the “p” layer (+) is called anode and “n” layer () – cathode. The main advantage of this electronic component is current flowing only in one direction (from anode to the cathode) after forward-biasing the p-n junction.

semiconductor diode symbol

Semiconductor diode symbol

However, in the opposite direction (reverse bias) current doesn’t flow and we could call this as the electric valve. The diode is constructed from two semiconductors, which were doped in different proportions – “p” and “n” types. They together form the p-n junction. The “n” layer with donor dopants has an excess of electrons where the “p” layer (acceptor dopants) – have a deficiency of them. After combining these on semiconductor diode together, a proportional distribution of electrons begins. Electrons, which previously lacked in “p” layer are transferred there from “n” layer. In this way region called depletion region that prevents the electric flow is formed. With passing time, technological requirements were increasing what resulted in the formation of new types of diodes.

semiconductor diode

When a semiconductor is combined with the corresponding metal, we acquire MS junction (metal-semiconductor), which also possesses rectifying properties (current conduction in one direction) – it is used for example in Schottky diode. MS junctions can have one of two current-voltage characteristics:

  • Unsymmetrical non-linear
  • Symmetrical, linear

MS junction properties depend mainly on the surface state of semiconductor and on the output work difference of electrons from metal and semiconductor itself. Schottky diode is mainly used in systems that require short switching time (small junction capacitance Cj of the diode has a decisive impact) with frequencies up to several tens of GHz.

Semiconductor diode characteristics

The graph below shows the current-voltage characteristics of a semiconductor diode. The graph is standard characteristic for electronic semiconductors. The semiconductor diode is switched to the active state after exceeding the forward voltage value specified by the manufacturer in the data sheet. Semi-thermal diodes are mainly used to protect other electronic components.

semiconductor diode characteristics

Current-Voltage characteristic of semiconductor diode

Illustration of differently biased P-N junctions:

PN junction after reverse bias

PN junction reverse-biased

PN junction in state of thermodynamic equilibrium

PN junction in state of thermodynamic equilibrium

PN junction after forward bias

PN junction forward-biased

How to determine where is the anode and where is the cathode?

Simple multimeter can be used to determine the polarity of a diode. There are at least three ways to do this but I will show two most popular that can be used with cheap multimeters (GET Handheld multimeter Digital VOLTCRAFT VC-11 Calibrated to: Manufacturer’s standards CAT III 250 V Disp):

a) Using ohmmeter (2kΩ range):

semiconductor diode ohmmeter forward

Forward-bias: Ohmmeter will indicate the approximate forward voltage of the diode (near 0,7V)

semiconductor diode ohmmeter reverse

Reverse-bias: Ohmmeter indicates “1” what means very high resistance

You can also use “diode check” function (diode symbol on the multimeter) but the result will be the same as the above with using ohmmeter.

b) Using VDC measurement function:

semiconductor diode voltmeter forward

Forward-bias: Multimeter should indicate voltage drop of approximately 0,7V for silicon diodes

semiconductor diode voltmeter reverse

Reverse-bias: Multimeter will indicate the approximate full voltage of the supply

Experiment for self-execution

This experiment will allow you to visualize the principle of operation of a semiconductor diode, whether current conducts or not. Because you will do it by yourself, you will better remember this lesson.

Items needed:

We will be using two schemes you’ve seen earlier:

semiconductor diode LED1

In this case, LED should conduct current and you should see it lighting

semiconductor diode LED2

Here, LED shouldn’t be lighting – diode not conducting current

Below you can see pictures showing the circuit mounted on the breadboard and visualization in two opposite positions of the LED diode (reverse polarity).

semiconductor diode LED3

Circuit „transferred” to the breadboard (diode is conducting current)

semiconductor diode LED4

In this case, as you can see diode isn’t conducting current (inserted in opposite way)

On the first picture, the LED was put into conducting state. Voltage on her anode was higher (+) than at the cathode (-), so the flow of current was possible. In our experiment we used a 9V battery, so the current flowing through the diode will be about 9mA (from Ohm’s law).

On the second picture, the diode was inserted in the opposite way (the voltage at the cathode was higher (+) than at the anode (-)), so the diode entered a blocking state, which prevented the flow of the current – LED isn’t lit.

Common types of semiconductor diodes (and their main functions):

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