The first electronic device to be introduced is called the diode. It is the simplest ofsemiconductor devices but plays a very vital role in electronic systems, having characteristicsthat closely match those of a simple switch. It will appear in a range of applications,extending from the simple to the very complex.


“The characteristics of an ideal diode are those of a switch that can conduct current in only one direction.”

which means that Ideally, a diode will conduct current in the direction defined by the arrow in the symbol and act like an open circuit to any attempt to establish current in the opposite direction.

you can refer to the graph shown below, for better understanding:

Types of bias in semiconductor diodes

Basically semiconductor diodes have two types of bias ,forward and reverse bias. But there is the third one that is not very important, “the no-bias condition” is when we just check the potential difference between the two terminals of diode, that is not connected to any source of current. 

Forward bias

A forward-bias or “on” condition is established by applying the positive potential to the p-type material and the negative potential to the n-type material

A semiconductor diode is forward-biased when the association p-type and positive and n-type and negative has been established.

what happens at the insides:

The application of a forward-bias potential “V” will “pressure” electrons in the n-type material and holes in the p-type material to recombine with the ions near the boundary and reduce the width of the depletion region

The resulting minority-carrier flow of electrons from the p-type material to the n-type material (and of holes from the n-type material to the p-type material) has not changed in magnitude (since the conduction level is controlled primarily by the limited number of impurities in the material), but the reduction in the width of the depletion region has resulted in a heavy majority flow across the junction. An electron of the n-type material now “sees” a reduced barrier at the junction due to the reduced depletion region and a strong attraction for the positive potential applied to the p-type material. As the applied bias increases in magnitude the depletion region will continue to decrease in width until a flood of electrons can pass through the junction, resulting in an exponential rise in current.


If an external potential of V volts is applied across the p-n junction such that the positive terminal is connected to the n-type material and the negative terminal is connected to the p-type materialthe number of uncovered positive ions in the depletion region of the n-type material will increase due to the large number of “free” electrons drawn to the positive potential of the applied voltage. For similar reasons, the number of uncovered negative ions will increase in the p-type material. The net effect, therefore, is a widening of the depletion region. This widening of the depletion region will establish too great a barrier for the majority carriers to overcome, effectively reducing the majority carrier flow to zero.

 The number of minority carriers, however, that find themselves entering the depletion region will not change, resulting in minority-carrier flow vectors of the same magnitude.

That’s it for diodes and types of bias, if you wanna know from whare these minority and majority charge carriers came from,don’t forget to check the “doping and charge carrier theory ” post.

To visit “Doping and charge carrier”post:

To visit “graphical analysis ” post:

Wait!! Diodes topic is not finished yet, in next post check out the graphical methods and difference between silicon and germanium diode to understand the working and behaviour of diodes under biasing & much more ……..

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