Hey friends, welcome to Kohiki.com. In this article, we will briefly learn about semiconductor materials. The semiconductor materials are mainly used for manufacturing electronic devices like transistors, diodes, and integrated circuits.
So, if anyone wants to learn about the basic semiconductor devices, first of all, one needs to understand a little bit about semiconductor physics and semiconductor materials. So, first of all, let’s understand why semiconductors are used in electronics. And to understand that first of all, let’s see the classification of the materials in terms of conductivity. So, in terms of conductivity, the materials are classified into three categories. Conductor, insulator, and the semiconductor. Now, for any material, the conductivity defines how easily this material allows the flow of charge. And this conductivity is measured in siemens per meter.
So, the conductor has very good conductivity or we can say that whenever the voltage is applied to this conductor then it allows the generous flow of charge.
So, silver, copper, gold, and aluminum are a few examples of conductors. And if we take the example of the copper, then its conductivity is roughly around 10 to the power of 7 Siemens per meter.
On the other end, if we see any insulator then it hardly allows any flow of charge. Or we can say that this insulator has very poor conductivity. So, wood, glass, Teflon are a few examples of the insulator.
And if we take the example of dry wood, then its conductivity is roughly around 10 to the power minus 14 Siemens per meter. So, wood is a very good insulator.
On the other end, if we take the case of semi-conductor then its conductivity is between the insulator and the conductor. So, whenever the voltage is applied to this semiconductor, then it allows a moderate amount id current.
And moreover that by adding the impurities, the conductivity of the semiconductor material can be changed. And this property is very useful for designing various electronic devices. So, silicon, germanium, and the Gallium Arsenide are a few examples of semiconductor materials.
And here, we will understand the behavior of the semiconductor by taking the example of silicon, which is extensively used in the electronics industry. Now, the atomic number of this silicon is14. So, if we see the atomic structure of this silicon, it has 14 protons and the 14 electrons. So, these 14 protons reside in the nucleus and 14 electrons rotate around this nucleus. And if you see the outermost orbit of the silicon, then it has 4 electrons. Or we can say that the silicon has 4 valence electrons.
Now, whenever the silicon atoms combine to form a solid, then they arrange themselves in a particular pattern which is known as the crystal. And in this crystal structure, each silicon atom shares its four electrons with the neighboring atoms. And the sharing of the electrons happens in such a way that, each silicon atom has 8 valence electrons.
And in this way, by sharing the electrons these silicon atoms forms the covalent bond. now, at the temperature just above the 0-degree kelvin, due to the thermal energy, the atoms in the silicon crystal starts vibrating. And due to this vibration, some of the electrons may get enough energy, so that they can break these covalent bonds. And by breaking these bonds, this electron will act as a free electron. So, at room temperature, you will find many such free electrons in this silicon structure.
Now, whenever this electron, departs from its position then it creates a vacancy at that particular position. And this vacancy is known as the hole. Now, we know that the charge of the electronic 1.6 x 10 ^ -19 C. And it has a negative charge. So, by not having an electron at a particular position creates a positive charge. And this positive charge is known as the hole. So, this hole can attract the other free electrons which are roaming in this vicinity. So, as shown in the figure, let’s say in this silicon structure, these two electrons are the free electrons. And due to these two free electrons, these two holes have been created.
Now, let’s say, this electron gets recombine with this hole. So, if it gets recombined with this hole, then the equivalent silicon structure will look like this. And here let’s say, due to the thermal energy, this electron becomes free and it gets recombined with this hole. So, in this way, for any silicon structure, at room temperature, the generation and the recombination of holes and electrons happens continuously.
And one more thing if you observe, for every generated electron, the hole is also getting generated. So, we can say that at the given temperature an equal number of holes and electrons are created in this silicon structure. And one more thing if you observe, as the electrons are moving from one place to the other place, the holes are also moving from one place to the other place. So, in semiconductor, we get a flow of current due to the two types of charges.
Types Of Flow In Semiconductor
One is due to the electrons and the second is due to the holes. Ans this the biggest difference between the conductor and the semiconductor. Because in the case of a conductor, we used to get a flow of current only due to electrons.
Now, this semiconductor can be classified into two categories. One is an intrinsic semiconductor and the second is an extrinsic semiconductor.
One is due to the electrons and the second is due to the holes. Ans this the biggest difference between the conductor and the semiconductor. Because in the case of a conductor, we used to get a flow of current only due to electrons. Now, this semiconductor can be classified into two categories. One is an intrinsic semiconductor and the second is an extrinsic semiconductor.
So, the intrinsic semiconductor is the pure semiconductor without any kind of impurity atoms. So, if we take the case of silicon crystal, then in the intrinsic semiconductor, all the atoms would be silicon atoms. On the other end, in the extrinsic semiconductor, the external impurities are added to change the conductivity of this semiconductor. And the process of adding these impurities known as doping.
So, by doping the semiconductor, we can change the conductivity of the semiconductor material. And by changing the conductivity, we can control this semiconductor to behave in a specific manner. So, this is the reason, these semiconductor materials are preferred in the electronics industry. So, depending on the type of impurity or the dopant, the extrinsic semiconductors can be further classified as p-type or n-type semiconductors.
So, in the case of a p-type semiconductor, the trivalent atoms are added with the silicon atoms. Now, the trivalent atom means, these atoms have three electrons in the outermost orbit. And the aluminum, boron, and gallium are the few examples of this trivalent atoms. So, since this trivalent atoms have three electrons in the outermost orbit, the three electrons are shared with the neighboring atoms. But still, if you see, the one vacancy remains in the outermost orbit. And due to this vacancy, we can say that the hole is created in the silicon structure.
So, we can say that every trivalent atom creates one hole. So, in this way, by adding the trivalent atoms we can create an excessive amount of holes in the crystal structure. And these trivalent atoms are known as the acceptor atoms. Because each hole which is created by the atoms can accept the external free electron. Similarly, by adding the pentavalent impurities, the n-type semiconductor can be formed. So, in the pentavalent atoms, there are five electrons in the outermost orbit.
And the few examples of pentavalent atoms are arsenic, antimony, and phosphorus. So, whenever the pentavalent atom is added with the silicon atoms then out of the five electrons, the four electrons of these pentavalent atoms will be get shared with the neighboring atoms.
But still, if you see, the one-electron in the valence orbit. So, this electron will act as a free electron, and it can roam around in the crystal structure. So, we can say that each pentavalent atom creates one free electron. So, by adding these pentavalent impurities, we can create an excessive amount of electrons in the crystal structure.
So, in the case of a p-type semiconductor, there is an excessive amount of holes, while in the case of an n-type semi-conductor, there is an excessive amount of electrons. So, in n-type semiconductors, the electrons will be the majority carriers, while the hole will be the minority carriers. Similarly, in the case of a p-type semiconductor, the holes will be the majority carrier and the electrons will be the minority carrier.
Meaning that whenever we apply the voltage to the p-type semiconductor, then the majority of the current which we will get is because of the holes. So, whenever we apply a voltage source to this-type semiconductor, then the holes will get attracted towards the negative terminal, while the electrons will get attracted towards the positive terminal.
But as the number of electrons is less in this p-type semiconductor, the majority of the current we will get is due to the holes. Similarly in the n-type semiconductor, whenever we apply a voltage source then electrons will get attracted to the positive terminal and the holes will get attracted to the negative terminal. And the majority of the flow of current is due to the electrons.
So, in this way, in the semiconductor, we used to get a flow of current due to the two types of charges. So, in the next article, we will see what will happen when we combine this n-type and the p-type semiconductors. So, I hope in this article, you understood the basics of this semiconductor. So, if you have any questions or suggestions,do let me know here in the comment sections below.