Semiconductor Diode

What is Semiconductor Diode?

A semiconductor, as the name mentions, is an element that bears partial conducting ability. A semiconductor does neither fit itself under the category of conductors nor under the category of the insulator. Generally, some impurities are always added to the semiconductor for the best results. This process is commonly termed as doping. Based on the type of impurity, semiconductors are further categorized into two types- a) p-type semiconductor (positively charged) and b) n-type semiconductor (negatively charged). P and N-type semiconductors have limited usage when they are used in isolation. But when we make a collaborative usage for both p and n-type semiconductors, it is called a p-n junction.

When a p-n junction is affixed to some external voltage provider, for instance, a battery, the complete set up will be known as Semiconductor diode. Though the entire set up is bi- terminal, the passage of current is unidirectional.

Semiconductors are classified under two heads on the basis of connection used:-

  1. Semiconductor Diode Forward Bias: It is a very well known fact that a battery has two terminals- a positive terminal and the other negative one. So, when the semiconductor's N and P end is fixed with the negative and positive sides of the battery, respectively, the set up is coined as Semiconductor diode forward bias. Since the negative extreme will drive away free electrons in the front of the junction, and the P end of the semiconductor will thrust the holes, they will merge at the junction. But free electrons coming out of the battery will penetrate into the N region, and the valence electrons abandon the P region, thus creating a movement of current.

  2. Semiconductor Diode Reverse Bias: As the name suggests, it is basically just the opposite concept of forwarding bias. Now, the semiconductor's N side is affixed with the positive end of the battery. This entire set up is known as Semiconductor diode reverse bias. The electrons that arise from the N side of the semiconductor will be directed along with the positive terminal of the battery. The negative terminal will drive the holes away from the junction. The holes and electrons do never meet at the junction, and there is a clog of current in this setup. As we can see, the majority current does never flow in the reverse bias. Instead, there is a reverse flow of current in this situation due to minority carriers.

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Symbol of the Circuit

There are certain symbols used to express an electrical circuit. Following the above discussions, we can create a symbol of the semiconductor diode. It is represented as:-

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Semiconductor Diode Characteristics

There is a graphical representation of the voltage and current, as applied in the case of semiconductor diode forward bias and semiconductor diode reverse bias. When a forward bias is raised, we also observe a rise in current up to a stable voltage called knee voltage in a linear fashion. But after this voltage, the current differs in a non-linear way. 

As we know, reverse current does not depend on the reverse bias. Rather this current depends on the temperature of the junction. It is calculated that the current multiplies to the extent of 7% for every 1-degree rise in temperature.

Zener Breakdown

If the reverse bias is raised to a large extent, the electric field also gets expanded, which in turn creates a huge number of electrons and holes. It is defined as a Zener breakdown.

Dynamic Resistance

It is explained as the ratio of minor changes in the voltage to the ratio of minor changes in the current. It is expressed in the form of rd. Therefore the numerical expression of voltage resistance is rd = \[\frac{\triangle V}{\triangle I}\].

Numerical:- A diode is made constant use in a circuit. The voltage falls by 0.5 V, and the highest power marked is 100 mW. What should be the value of the resistor R, which is attached in series to this diode?

Solution:- Current that flows among the diode , I = \[\frac{\text{Power}}{\text{Voltage}}\]

Therefore, \[I = \frac{100\times 10^{-3}}{0.5 V}\] (as we know 1mW= 10-3 W)

= 0.2 A

\[{\text{Resistance}} = \frac{\text{Net Voltage}}{\text{Current}}\] 

= \[\frac{1.5 - 0.5}{0.2}\] = 5 Ohm.

FAQ (Frequently Asked Questions)

1. What are the Benefits of a Semiconductor Diode?


If you go through the semiconductor diode notes, you will come across certain ideas that show how they are beneficial for us. These are:-

  1. There is no scope of any noisy sound in the device.

  2. It is useful as there is a relatively lower usage of power.

  3. The device does not consume any extra time for preparing itself.

  4. It may serve for a longer period of time.

Apart from these, there are certain limitations too. These are:-

  1. The current does not flow in reverse bias.

  2. The adapting and reporting of voltage is of a quite inferior type.

  3. Another significant limitation is that if we provide high voltage and temperature, the diode may face the possibility of breaking down.

2. What are the Applications of a Semiconductor Diode?


There are several applications of semiconductor diodes. Some of which have been listed:-

  1. Semiconductor diodes in logic gates: These are also used to perform logic operations. Both small and large states of logic gates are comparable with forward and reverse the biased state of semiconductor diodes. Thus diodes help in OR, NAND, AND gates.

  2. Semiconductor diode as a rectifier: Diodes are generally used to convert Alternating current to direct current.

  3. Semiconductor diode in clamping circuit: These are used to switch over to a positive from a negative input signal or vice versa.

  4. Semiconductor diode in clipping circuit: These are widely used in the FM transmitters.

  5. A semiconductor diode is used in LED devices. The main agenda is to release infrared light.

  6. Zener diode, as studied earlier, is used in the stabilizer. It primarily stops the overflow of current.