The term IGBT is a short form of insulated gate bipolar transistor, it is a three-terminal semiconductor device with huge bipolar current-carrying capability. Many designers think that IGBT has a CMOS i/p and bipolar o/p characteristic voltage controlled bipolar device. So, this device is designed to make use of the benefits of both BJT and MOSFET devices in the form of monolithic. It combines the best qualities of both to attain the characteristics of an optimal device. [Read more…]
Majority of street lights, outdoor lights, and a number of indoor home appliances are typically operated and maintained manually in many occasions. This is not only risky, however additionally it leads to wastage of power with the negligence of personnel or uncommon circumstances in controlling these electrical appliances ON and OFF. Hence, we can utilize the light sensor circuit for automatic switch OFF the loads based on daylight’s intensity by employing a light sensor. This article discusses in brief about what is a light dependent resistor, how to make a light dependent resistor circuit and its applications. [Read more…]
The switch is an electrical device that is used to break or make an electrical circuit manually or automatically. The working principle of switch depends on ON/ OFF mechanism. Various electrical or electronic circuits use switches to control or trigger the owl circuit. The types of switches depend on the connections of the circuit they make. Two essential components such as pole and through can confirm what types of connections a switch can make. These two components are also used to define variations of switch contact. [Read more…]
Both p-n-p and the n-p-n transistors are the basic transistors which come under the category of bipolar junction transistors. These are used in the various amplifications circuits and the modulating circuits. The most frequent one among its applications is it’s fully ON and the OFF operating mode which is referred to as switch.
NPN and PNP transistors are bipolar junction transistors, and it is a basic electrical and electronic component which is used to build many electrical and electronic projects. The operation of these transistors involves both electrons and holes. The PNP and NPN transistors allow current amplification. These transistors are used as switches, amplifiers or oscillators. Bipolar junction transistors can be found either as large numbers as parts of integrated circuits or in discrete components. In PNP transistors, majority charge carriers are holes, whereas in NPN transistors, electrons are the majority charge carriers. But, field effect transistors have only one type of charge carrier.
The formation of these transistors is based on the diodes with the junction p-n. As in the n-p-n transistors n-types are in majority therefore there includes excess amount of electrons as the charge carriers. In p-n-p transistors there are two p-types in it resulting in the majority charge carriers as holes.
The main difference between the NPN and PNP transistor is, an NPN transistor turns on when the current flows through the base of the transistor. In this type of transistor, the current flows from the collector (C) to the emitter (E). A PNP transistor turns ON, when there is no current at the base of the transistor. In this transistor, the current flows from the emitter (E) to the collector (C).Thus, knowing this, a PNP transistor turns ON by a low signal (ground), where NPN transistor turns ON by a high signal (current).
Difference between NPN and PNP Transistors and their Making
The PNP transistor is a bipolar junction transistor; In a PNP transistor, the first letter P indicates the polarity of the voltage required for the emitter; the second letter N indicates the polarity of the base. The working of PNP transistor is the exact opposite to the NPN transistor. In this type of transistor, the majority charge carriers are holes. Basically, this transistor works the same as the NPN transistor. The materials which are used to construct the emitter, base and collector terminals in the PNP transistor are different from those used in the NPN transistor. The PNP transistor bias setup is shown in the below figure. The base-collector terminals of the PNP transistor are always reversed biased, then the negative voltage must be used for the collector. Therefore, the base terminal of the PNP transistor must be negative with respect to the emitter terminal, and the collector must be negative than the base.
Making of PNP Transistor
The PNP transistor configuration is shown below. The characteristics of both PNP and NPN transistors are similar except that the biasing of the voltage and current directions are reversed for any one of the possible three configurations such as a common base(CB), common emitter(CE) and common collector(CC).The voltage between the base and emitter terminal VBE is negative at the base terminal and positive at the emitter terminal because for a PNP transistor, the base terminal always biased negative with respect to the emitter. Also, the emitter voltage is positive with respect to the collector (VCE).
The voltage sources are connected to a PNP transistor, which is shown in the figure. The emitter is connected to the Vcc with the RL; this resistor limits the max current flowing through the device, which is connected to the collector terminal. The base voltage VB is connected to the base resistor RB, which is biased negative with respect to the emitter. To cause the base current to flow during a PNP transistor, the base terminal must be more negative than the base terminal by approx. 0.7volts or a Si device.
The fundamental difference between a PNP and a PN transistor is the proper biasing of the transistor junctions; the current directions and the voltage polarities are always opposite to each other.
Basics of P-N-P
The p-n-p transistors are formed with n-type present in between the p-types. The majority of the carriers those are responsible for the generation of the current are in this transistor are holes. The working operation is similar to that of n-p-n. But the applications of the voltages or currents in terms of polarity are different.
The NPN transistor is a bipolar junction transistor, In an NPN transistor, the first letter N indicates a negatively charged layer of material and a P indicates a positively charged layer. These transistors have a positive layer, which is located in-between two negative layers. NPN transistors are generally used in circuits for switching, amplifying the electrical signals that pass through them. These transistors comprise three terminals namely, base, collector and emitter and these terminals connect the transistor to the circuit board. When the current flows through the NPN transistor, the transistor base terminal receives the electrical signal, the collector makes a stronger electric current than the one passing through the base, and the emitter passes this stronger current on to the rest of the circuit. In this transistor, the current flows through the collector terminal to the emitter.
Generally, this transistor is used because it is so easy to produce. For an NPN transistor to work properly, it needs to be formed from a semiconductor material, which carries some electric current, but not the maximum amount as very conductive materials like metal. “Si” is one of the most commonly used semiconductor, and NPN transistors are the easiest transistors to make out of silicon. The application of an NPN transistor is on a computer circuit board. Computers need all their information to be translated into binary code, and this process is accomplished through a plethora of small switches flipping on and off on the computers circuit boards. NPN transistors can be used for these switches. A powerful electric signal turns the switch on, whereas a lack of a signal turns the switch off.
Making of NPN Transistor
The construction of an NPN transistor is shown below. The voltage at the base terminal is positive and negative at the emitter terminal because of an NPN transistor. The base terminal is always positive with respect to the emitter terminal, and also collector supply voltage is positive with respect to the emitter terminal. In NPN transistor, the collector is connected to the VCC through the load resistor RL. This load resistor limits the current flowing through the maximum base current. In this transistor, the movement of electrons through the base terminal that constitutes transistor action. The main feature of the transistor action is the link between the input and output circuits. Because, the transistor amplifying properties come from the consequent control that the base employs upon the collector to emitter current.
The transistor is a current operated device. When the transistor is switched on, the large current IC flows between the collector and emitter within the transistor. However, this only happens when a small biasing current Ib flows through the base terminal of the transistor. It is a bipolar NPN transistor; the current is the ratio of these two currents (Ic/Ib), called the DC current gain of the device and it is denoted with the symbol “hfe” or nowadays beta. The value of beta can be large up to 200 for standard transistors, and it is this ratio between Ic and Ib, which makes the transistor a useful amplifier. When this transistor is used in an active region, then Ib provides the input and Ic provides the output. Beta has no units as it is a ratio.
The current gain of the transistor from the collector to the emitter is called alpha that is, Ic/Ie, and it is a function of the transistor itself. As the emitter current Ie is the sum of a small base current and large collector current, the value of the alpha is very close to unity, and for a typical low power signal transistor this value ranges from about 0.950 to 0.999.
Difference Between NPN and PNP Transistor:
Bipolar Junction transistors are three terminal device and these are made of doped materials, often used in amplifying and switching applications. In essence, there are a couple of PN junction diodes in every BJT. When the pair of diodes joined then it forms a sandwich that places a type of semiconductor in between the same two types. Therefore, there are only two types of bipolar sandwich, which are namely PNP and NPN. In semiconductors, the NPN’s has characteristically higher electron mobility compared to the hole mobility. Therefore, it permits a large amount of current and operates very fast. And also, the making of this transistor is easy from silicon.
- Both PNP and NPN transistors are composed of different materials and current flow of these transistors is also dissimilar.
- In an NPN transistor, the current flows from the collector (C) to the Emitter (E), whereas in a PNP transistor, the current flows from the emitter to the collector.
- PNP transistors are made up of two layers of P material with a sandwiched layer of N The NPN transistors are made up of two layers of N material and sandwiched with one layer of P material.
- In an NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to For PNP transistor, a positive voltage is given to the emitter terminal to produce current flow from the emitter to collector.
- The working principle of an NPN transistor is such that when you increase current to the base terminal, then the transistor turns ON and it conducts fully from the collector to emitter. When you decrease the current to the base terminal, the transistor turns ON less and until the current is so low, the transistor no longer conducts across the collector to emitter, and shuts OFF.
- The working principle of a PNP transistor is such that when the current exists at the base terminal of the transistor, then the transistor shuts OFF. When there is not current at the base terminal of the PNP transistor, then the transistor turns ON.
This is all about difference between NPN and PNP transistors which are used to build many electrical and electronic projects. Furthermore, any queries regarding this topic or electrical and electronics projects you can give your feedback by commenting in the comment section below.
Comparison in between N-P-N and P-N-P Transistor
1). In this the majority of n-types are present.
1). In this the majority of p-type materials are present.
2). The majority of the concentrations of the carriers are electrons.
2). The majority of the concentrations of the carriers in this type of transistors are holes.
3). In this if the terminal base is supplied with the increased amounts of current then the transistor gets switch to ON mode.
3). In this case for the low values of the currents the transistor is ON. Otherwise for high values of currents transistors it is OFF.
4). The symbolic representation of n-p-n transistor is
4). The symbolic representation of p-n-p transistor is
5). In the n-p-n transistor the flow of current is evident from the collector to the emitter terminals.
5). In the p-n-p transistor the flow of current can be seen from the terminals of the emitter to the collector.
6). In this transistor the arrow is pointing out.
6). In this transistor the indication of arrow is always pointing in.
The arrows in the transistors both n-p-n and p-n-p shows the main differences between the transistors. The arrow in n-p-n is pointed towards the emitter whereas for p-n-p the arrow is in the reverse direction. In both the cases the arrow indicates the direction of the flow of current.
Hence the construction of n-p-n and the p-n-p is simple. The operating will be same but its polarities of biasing differ. Now after discussing regarding the basics of n-p-n and the p-n-p can you tell which one is preferred during amplification and why?
There are various basic electrical and electronic components which are commonly found in different circuits of peripherals. In many circuits, these components are used to build the circuit, which are classified into two categories such as active components and passive components. . Active components are nothing but the components that supply and control energy. Passive components can be defined as the components that respond to the flow of electrical energy and can dissipates or store energy. These components can be found in numerous peripherals like hard disks, mother boards, etc. Many circuits are designed with various components like resistors, capacitors, inductors, transistors, transformers, switches, fuses, etc. Therefore, this article gives a brief information about different types of electronic and electrical components that are used in various electronic and electrical projects.The following paragraphs describe each & every component in detail with diagrams. [Read more…]
A crystal that has its conduction value in between conductor and insulator is termed as the semiconductor.It can be formed by the addition of impurities. It can be referred to as either p-type or n-type. Hence its conduction is based on the types and the amount of impurity added. These solids conduction value is proportional to the temperature value. As the temperature increases its conduction value increases as temperature degrades then the conduction of the semiconductor tends to decrease.
Semiconductor and its Types
These semiconductors are further classified into two basic types based on their purity and the doping value, For more detailed comparison between the two semiconductor types, refer to the article – Difference Between Intrinsic and Extrinsic Semiconductor
(1) Intrinsic Semiconductor
The semiconductor in its pure form is termed an intrinsic semiconductor. It is also related to its energy gaps for the silicon in its pure form the energy gap will be 1.1 electron volts and for germanium, it is 0.72 electron volts. In this type semiconductor at room temperature, the number of carriers and number of holes is equal to each other indicating the neutral condition.
(2) Extrinsic Semiconductor
Once the impurity is added to the semiconductor then its purity gets affected and also there is the increment in the charge carriers. These types of semiconductors are known as extrinsic semiconductors. Further, this is classified into two types’ p-type and n-type. In these types, the numbers of electrons are more in n-type whereas the number of holes in p-type.
What is a P-Type Semiconductor?
If the intrinsic semiconductor is doped with an electron acceptor in order to make it as a p-type semiconductor. The electron acceptor is responsible for the formation of a hole by accepting an electron from the lattice.
As a result, majority carriers in the p-type semiconductor formed are holes. In this way, a p-type semiconductor is defined based on its electron acceptor capability.
Formation of P-type Semiconductor
In order to form a p-type semiconductor the basic step is to dope intrinsic semiconductor with trivalent impurity. In this type, the valence shell consists of three electrons requires further one more electron.
This is possible by sharing the electron. As it is accepting electrons it is generally referred to as acceptor. The acceptor impurities are Boron, indium, gallium. Once these are added to either silicon or germanium p-type semiconductors are formed.
Let us take boron as the trivalent impurity so that we can add it to the silicon in order to make it extrinsic. Everything here is completely based on the concept of sharing.
The covalent bond concept is preferred during accepting the electrons. Boron atomic number is five. Based on its valence shell electronic configuration concept the numbers of valence electrons present in boron are three.
Hence each valence electron forms a covalent bond with the neighboring silicon atoms. The number of bonds formed with a number of silicon atoms is based on the number of valence electrons present.
It is evident that to boron there are four neighbouring silicon atoms as per that there must be four electrons but there are only three valence electrons present. Then the absence of fourth electron or the vacancy of the electron is termed as a hole.
It indicates that one electron is accepted by the boron atom. The vacancy or the need of electron can be fulfilled. The number of vacancies and the acceptance of electrons are proportional to each other.
Now it is clear that boron comes under trivalent impurity because it is responsible for the formation of holes in the semiconductor. Therefore doping pure form of silicon with boron leads to the formation of p-type semiconductor.
Example of P-Type Semiconductor
Trivalent impurities such as boron or gallium are commonly used in silicon as doping impurity. Then silicon doped with boron or gallium is a perfect example for a p-type semiconductor.
Whether silicon is doped with gallium or indium the process is also can be represented by utilizing the same concept of boron and silicon.
In this way, the semiconductors that are rich in holes as there carriers formed by the trivalent impurities comes under the list of p-type semiconductors.
Whether silicon or germanium if they are added with a trivalent impurity that belongs to p-type of the semiconductor.
Conduction in P-Type Semiconductor
When the external supply of voltage is given to the p-type semiconductor there majority carriers present in valence band tends to move towards the negative terminal of the supply and the minority carriers that are electrons present in the conduction band move towards the positive terminal.
However, the concentration of electrons is less in the conduction band and the majority of holes are present in the valence band.
Hence the current in the p-type is because of majority carriers in valence band a little amount of current is in conduction band because of few electrons that are their minority carriers.
Energy Diagram of P-Type Semiconductor
As it is doped with trivalent impurity there are a huge number of holes formed in the p-type. Hence it has a majority concentration of holes and minority concentration of electrons in it.
P-type because of majority a-holes it referred to as a positive type. As it is a p-type semiconductor the Fermi level is present near to the valence band rather than conduction band.
Once the impurity is inserted in the pure semiconductor numerous amounts of holes are formed in the valence band. There are thermal excitation’s also in the semiconductors because of this same amount of electrons are also present in the conduction band.
As always majority wins, more amount of hole compared to electrons makes p- types majority carriers as holes.
As the energy band diagram suggests there is less number of electrons in conduction band in p-type compare to that of n-type making the state of conductivity of n-type double than that of p-type.
The reason behind this is the excitation’s will release a tremendous amount of energy and also enhances the flow of current making to mold it purposefully based on requirements.
As the doping concept introduced in extrinsic and made it p-type and n-type. The formation of these types made changes in the development of modern electronics.
For example, it can be LASER, LED or a BJT everything is interlinked to each other. In what ways do you think p-type is preferred over n-type?
When a p-type and n-type interfaced together that leads to the formation of a PN Junction. The commonly suggested semiconductor for this p-n junction is either silicon or germanium based on its preferred electrical properties and its abundance. Basically the p-type and n-type of a semiconductor is formed due to doping impurities.
There is an interesting concept evolved from it clearly states that both the p and n regions are conducting until the formation of a barrier. Once it has been formed the p and n regions become neutral in terms of conduction. This evolving concept has been utilized for the development of modern electronics.
The Theory Behind The Formation of PN Junction
Based on the required conditions one can easily say that there are two types of materials involved in a single crystal to interface in such a way that PN Junction has formed. P-type is formed because of trivalent doping impurity.
These impurities accept free electrons and they become negatively charged ions. Similarly n-type is formed by doping it with pentavalent impurity and donates the free electrons in order to become positively charged ions.
Rather than using the same material if we use different semiconductors for the formation of the PN Junction there will be a phenomenon of scattering that inhibits the flow of charge carriers. Because of this reason single crystal with doping concept is preferred.
Charge Representation of P-Type and N-Type
As the p and n-type semiconductor have been interfaced or fused together in such a way that at the center there must be action between majorities of the charge carriers that tend to the formation of the junction in between them.
Now, there are charges in both p and n-types. P-type consists of holes as majority charge carriers and n-type have electrons as the majority. When these types are in contact with each other there majority carriers tend to move and the process of diffusion occurs. This is only possible when n-type and p-type both are formed on a single crystal.
As the charges flow from higher concentration to lower concentration and the process impacts in such a way that some charge has been imposed at the center on the impure ions. These carriers form a layer that is static and adjacent towards the junction. Then this static layer becomes so strong in terms of electric charge that towards n-type electrons lied statically while p-type has holes for that purpose.
However, the concentration will be on the major part but there will be some minority carriers in each region showing the impact of their presence. As p-type has minority carriers as electrons it tends to move and crosses the PN Junction and gets combined in n-type region. A similar concept is also applied for n-type minority carriers. As a result, the regions tend to attain the condition of neutrality.
This makes the junction to attain a state of equilibrium. In this state, the donor tends to oppose holes and the acceptors repel the electrons. This phenomenon leads to the formation of a zone called “potential barrier”. The barrier doesn’t have any free carriers left it means that all the free electrons are combined by respective holes in it.
Interaction of N-Type and P-Type
As a result, there must not be any free carriers across both p and n-types junction. Then both p and n regions are now termed as neutral regions. In other words, these free carriers are depleted. Hence the region of the p-n junction is termed as Depletion region and the charge will be neutral on both sides.
In the formation of depletion layer n-type loosen its free electrons while p-type has lost free holes. Both the sides have some ions and its nature is impure. This results in the existence of an electric field in it. The problem is, in order to overcome the barrier it requires some extra charge. Hence the electric field generated due to the process of diffusion without any application of power supply is can be given as
Here ND represents the donor impurity concentration; NA represents the acceptor’s impurity concentration. Where ni refers to the intrinsic concentration.
Once the barrier is formed at the center there is the existence of the other two processes. Firstly, the concentration of the carriers is different and when the holes tend to diffuse from p-type to n-type there some current has been generated at the junction termed as diffusion current. Secondly, because of this depletion, there is some movement in minority carriers in such a way that electric field is imposed because of this electron from p-side tends to flow towards n-side resulting in drift current.
Diffusion current is possible only by the movement of majority carriers whereas drift is possible by the influence of minority carriers. After the formation of a barrier if charges require movement then it is possible by applying it with suitable voltages. This concept is termed as biasing. Without any power supply, there is the presence of some potential in the semiconductor based on its relevance.
If it is silicon then it has 0.6-0.7 volts as the basic potential across the depletion region. In case germanium is used then it has 0.3-0.35 volts. As it is referred to potential barrier it opposes the flow of charge carriers on both sides of the junction. The PN Junction barrier is formed during the process of manufacturing itself compared to germanium silicon has the highest barrier potential. This potential is highly sensitive to the variations in the temperature, the element or material utilized in its fabrication as well as the concentration of doping required based on the type and the factors.
The most major factor of inbuilt potential inside the interfaced PN Junction is responsible for repelling the flow of electrons and holes once the barrier has formed. The flow of charged particle in such interfacing will always be in a unified direction. This is a huge application
These PN Junction devices are considered as the fundamental units for any type of transistors, a few modifications in it can be used for various purposes based on requirements. Now, these are the basics that made p-n junction more popular in all the aspects termed for modern electronics. Have you ever thought of how and when these types of p or n-types are replaced and utilized in any other respective equipment?
John Dalton in 1800 was the one who explained regarding the law on multiple proportions. Atom represents the fundamental units that can be divided into subatomic particles. This leads to the development of atomic models. In 1898 Thomson proposed a model by stating that mass of the atom is equally distributed or spread over it but Rutherford’s scattering experiment demolishes the statement in 1909.
Hence the existence of the nucleus with some electric charge at the center has been estimated along with the revolving of electrons around it. Further Bohr’s model unable to explain the structure of atom that consists of multiple electrons and it disobeys Heisenberg uncertainty principle. Later in 1926 Schrodinger’s equation has been proposed. As per the model based on quantum, it’s clear that numbers of electrons are arranged in the respective shells. Atom size measured in terms of angstrom that is 10-10 meter.
What Structure Does Atom Consists?
Each atom has its nucleus and the electrons bound to it. Protons and neutrons present inside the nucleus are known as nucleons. Mostly the nucleus is responsible as the major constituent for the mass of the atom. The structure of the atom mainly surrounds around electron, proton, and neutron. Atom’s behavior is relevant to the orbital in which electrons are revolving and the chemical properties are determined by the shells.
The General Structure of Atom
An electron is negatively charged, a proton is positive in charge whereas a neutron is neutral. If the atom has equally balanced electrons and protons in that case atom become neutral otherwise it leads to the formation of an ion. Based on the highest content of electrons and protons one can describe either the charge of the atom is positive or negative.
Electromagnetic force binds electrons and nucleus. Protons and neutrons consist of nuclear force to attract each other inside the nucleus. The presence of a number of protons indicates the atomic number. Similarly, a number of neutrons describe the isotopes. Magnetic properties of the element can relate to the presence of the number of electrons in it. Atoms interaction and distraction towards each other leads to the physical changes in the environment. This can be done by chemical bonding between them.
There exists a quantum state in which proton must be present in the nucleus but it should differ for every proton that is it follows Pauli’s exclusion principle. Therefore protons, neutrons , and electrons are categorized under fermions. As the charge has been classified neutrons compared to protons are heavier in terms of mass. Electrons have a mass of 9.109382911*10-28 gram. Proton or neutron comparison with the electron is 1,836 times heavier.
As the electron tends to rotate in order to obtain stability it jumps from one orbital to another one this makes the behavior of the atomic spectra so unpredictable. This technique is known as a quantum leap. When it occurs from a higher level to the next lower level there is an emission of radiation in terms of photons.
Properties of Atom:
Based on the number of protons, electrons and neutrons atom properties can be described:
(1) Atomic number:
Presence of the number of protons in the nucleus derives the atomic number it relates to the chemical properties of an atom. The symbol used for the representation of an atomic number is Z. it is clearly stated that atomic number is influenced by the positively charged particles. If the elements consist of the equal number of protons and electrons results in a neutral atom. Carbon is one of the neutral atoms.
Example: Z = 6, represents carbon.
(2) Atomic mass:
Mostly the weight or mass of the atom is dependent on its nucleus. Nucleus weight is dependent on the sum of the masses of proton and neutrons. This type of mass is known as atomic mass. The symbol A denotes atomic mass. If the neutrons and protons are different in number then it is termed as Isotopes.
Hydrogen is the best suitable example that can relate to this condition. Based on neutrons it is classified as
(a) Protium: It consists of 99.985% of the hydrogen atom with only one proton in it.
(b) Deuterium: It has one proton and one neutron.
(c) Tritium: It possesses two neutrons and a proton it. Naturally, this condition is not possible one has to make it based on requirement.
The variations in the number of protons and neutrons lead to the changing in a nucleus. Then the respective atom is known as radioactive. This condition is nothing but an unstable nucleus. At this stage, the atoms will be in the same state until it becomes stable. The elements that have an atomic number more than the limit of 82 are said to be radioactive.
(4) The spin of electrons:
There is a property regarding spinning of electrons as it comes under fermions it takes only half of the integer spin. Example helium is a chemical element based on its number of protons its atomic number is two. In order to occupy in the same orbit, it should be spin in different directions. This results in the movement of electric charge so that they are considered as a magnet in tiny shape. Electrons do have a magnetic moment and it is almost 9.28*10-24 joule per tesla.
(5) Electric charge:
Atoms that involved in the movement of electron and in the formation of bonds in order to achieve stability results in the formation of an ion. In this process the atom that is a giver becomes positive and the one who takes it becomes negative.
(6) Relative atomic mass:
As the numbers of protons are equivalent to the numbers of neutrons in the carbon making it a neutral atom the relativity in atomic mass is comparatively average per mass of the one carbon atom.
This article explains the basics of atoms and the way its structure has been classified based on the concept of orbital, basing on subatomic particles chemical properties of atoms can be explained. Mainly its objective is to give the basic structure details and deal with the basic properties. The way electron, proton, neutron lies in the atom and in the way its masses are related and the charges of the fermions have been discussed. There is a strong influence of charge particles in the atom. Based on the charges the classification of ions and the effect of increase and decrease of subatomic particles results have been overviewed. The energies associated in between nucleus and electrons have been discussed.
Hence the atoms are the fundamental units of any basic structure its classification on subatomic particles has been helped in figuring out the presence of various chemical elements in the periodic table. Based on the classification we can deal with the properties of basic atoms. Generally we use lead pencils in our day to day activities have you ever get a thought of it how the leads are joined and made as a solid pencil?
Semiconductors are materials which exhibit properties of both conductors and insulators. The semiconductors are of two types, Intrinsic and Extrinsic Semiconductors. The intrinsic semiconductors are the one with no doping and therefore called as pure semiconductors. The extrinsic conductors are doped with impurity atoms. Based on the type of impurity added they are classified as: N-type and P-type Semiconductors.
What is an N-type Semiconductor?
A N-type semiconductor is defined as a type of extrinsic semiconductor doped with a pentavalent impurity element which has five electrons in its valence shell. The pentavalent impurity or dopant elements are added in the N-type semiconductor to increase the number of electrons for conduction.
Doping in N-type Semiconductor
The N-type semiconductor is doped with pentavalent impurity elements. The pentavalent elements have five electrons in the valence shell. The examples of pentavalent impurities are Phosphorus (P), Arsenic (As), Antimony (Sb). The pentavalent impurity is added in a very minute fraction in the N-type semiconductor such that the crystal structure of the original intrinsic semiconductor is not disturbed. The pentavalent impurity atom makes covalent bonds with four silicon atoms and one electron is not bonded with any silicon atom. Each pentavalent impurity atom donates one electron to the N-type semiconductor hence it is called as a Donor impurities. Thus, there are more number of electrons in the N-type semiconductor.
N-type Semiconductor Example
An intrinsic semiconductor material like Silicon (Si) has 14 electrons with a configuration of 2,8,4 and Germanium (Ge) has 32 electrons with a configuration of 2,8,18,4. Each atom requires 8 electrons in its valence shell to be stable. Hence intrinsic semiconductor atoms have covalent bonds based on sharing the electrons of a nearby atom to achieve 8 electrons to balance their atomic structure.
A N-type semiconductor is created by doping this pure silicon crystal lattice with a pentavalent impurity element like Antimony (Sb). In an N-type semiconductor the atom of pentavalent impurity element Antimony (Sb) is in between silicon atoms. The Silicon atoms have four electrons in the valence shell. Each of the silicon atom creates a covalent bond with an electron of the prevalent impurity atom.
The Antimony (Sb) impurity element electron form covalent bonds with only four silicon atoms. The fifth electron of the impurity atom is not bonded with any semiconductor atom in the crystal lattice. This electron is loosely bonded to its parent impurity atom. Thus, as external voltage or heat is applied this fifth electrons easily breaks its bond with the parent atom and takes part in conduction.This fifth electron majorly contributes to the current in an N-type semiconductor.In the N-type Semiconductor the electrons become the majority carrier.
Energy Diagram of n-Type Semiconductor
The Energy diagram represents two energy bands, the valence band and the conduction band. The electrons in the valence band in the energy diagram represent the electrons which are in the valence band of the atom and they are still bonded to the parent atom. The electrons in the conduction band in the energy diagram represent atoms which take part in conduction. The energy gap between the valence and conduction band is called as the forbidden band or band gap.
In an N-type semiconductor because of the pentavalent impurity a number of loosely bonded electrons are available in the lattice structure. As the voltage is applied, these electrons break free from the covalent bonds andare ready to conduct. These electrons are depicted in the conduction band.When a certain amount of voltage is applied, these electrons gain energy to cross the forbidden gap and leave the valence bandto enter into the conduction band. A very less number of holes are formed in the valence band as the electron leaves valence band to enter conduction band. The Fermi level is near the conduction band as more number of electrons enter the conduction band.
Conduction through N-type Semiconductor:
The conduction through an N-type semiconductor is majorly caused by the electrons. The pentavalent donor impurity has imparted extra electrons to the lattice structure. As a voltage is applied or the semiconductor is subject to external heat the electrons gain energy. The electrons break covalent bonds and more electrons are released into the conduction band. The electron which breaks away from its covalent bond, leaves a void space or hole in its place.
As the negatively charged electron leaves a hole, this empty space attracts other electrons. Hence the hole is considered to be positively charged. Thus the N-type conductor has two types of carriers,negatively charged electrons and positively charged holes. In an N-type semiconductor the electrons are greater in number and hence they are termed as the majority carriers and the holes are termed as minority carriers as they are less in number. The current constituted in an N-type semiconductor by electrons is called a majority carrier current and the current constituted by holes is called the minority charge current.
When a covalent bonds break and the electrons leaves a hole in its place, some other electron breaks away from its covalent bond and gets attracted towards this hole. Thus the electron and holes move in opposite directions. The electrons get attracted towards positive terminal of the battery and holes are attracted towards negative terminal of the battery. As the electrons and holes travel through the lattice current starts following in the N-type semiconductor.
The N-type extrinsic semiconductor has majority carrier as electrons and hence has greater conductivity. Because of this reason the N-type Semiconductor in combination with a P-type semiconductor is used to manufacture all the major semiconductor components and devices. The basic components like PN Diode, Bipolar Junction Transistor and Field effect Transistors have their working based on the properties and characteristics of N-type semiconductor.
A conductor has a number of charge carriers, which are ready to take part in conduction after a certain voltage or heat is applied. Non-conductors do not have any free charges to take part in conduction even after applying an external voltage or heat. The materials which exhibit properties of both conductors and non-conductors are called the semiconductors. The Semiconductor materials behave as an insulator for a certain voltage level and conduct only after the specific voltage level is applied at the input. The commonly available semiconductor materials are Silicon (Si) and Germanium (Ge). The compound semiconductors are prepared by alloying different elements, one of the examples is Gallium Arsenide (GaAs).
There are two types of semiconductors namely intrinsic and extrinsic semiconductors. The classification is based on the type and concentration of carriers that majorly contribute to the flow of current these types of semiconductors.
Silicon and Germanium are tetravalent elements. It means that they have four electrons in its outermost shell. Each atom of Silicon forms a covalent bond with four neighboring Silicon atoms. Thus, with the help of sharing of atoms the lattice crystal structure of the semiconductor is formed.
Intrinsic Semiconductor :
An intrinsic semiconductor is the purest form of the semiconductor. Doping element or impurity is not added to the intrinsic semiconductor. The electrons are bonded to the parent semiconductor atom, but at a certain voltage or heat is applied, these valence electrons, they leave the parent atom are moved freely in the lattice. Such free electrons constitute current in the intrinsic semiconductor material. The electron from the valence band crosses the forbidden gap to enter into the conduction band. This electron leaves a positive hole or void in its place in the valence band. This void or positive space is termed a ‘hole’.
An extrinsic semiconductor is formed by doping an intrinsic semiconductor. Doping is a process where a very small fraction of impurity atom is added to the intrinsic semiconductor. The extrinsic semiconductors are of two types based on the doping elements used.
Types of Extrinsic Semiconductor are N-type and P-type.
- N-type Semiconductor : The intrinsic semiconductor is doped with Pentavalent impurity element. Such an impurity element has five electrons in the valence shell. The elements like are Phosphorus (P), Arsenic (As), Antimony (Sb) is the pentavalent impurities used for N-type semiconductor.
- P-type Semiconductor: The intrinsic semiconductor is doped with the Trivalent impurity element. Such an impurity element has five electrons in the valence shell. The elements like Boron (B), Gallium (G), Indium (In), Aluminium (Al) is used for P-type semiconductors.
Key Differences between Intrinsic and Extrinsic Semiconductor
The intrinsic and extrinsic semiconductors can be differentiated on the following parameters:
1) Crystal Lattice Structure:
The schematic of an intrinsic Silicon (Si) semiconductor is shown in Figure 1 which depicts the covalent bonds in neighboring Silicon atoms.
Each Silicon atom shares its four electrons with four neighboring silicon atoms to form covalent bonds.
Figure 3. P-type semiconductor with acceptor impurity
The N-type Extrinsic semiconductor in Figure 2 shows a pentavalent impurity atom of Antimony (Sb) along with the free electron which is freely roaming in the crystal structure and it is ready to conduct. The P-type Extrinsic semiconductor in Figure 3 shows a trivalent impurity atom of Boron (B) along with a void space formed in the covalent bond with a neighboring silicon atom. This hole attracts electrons and participates in conduction.
2) Doping Level:
Intrinsic semiconductor is a pure semiconductor with no doping on the crystal structure. There is an equal number of holes and electrons in an intrinsic material. This is termed as electrical neutrality.
An external semiconductor is a doped intrinsic semiconductor. An N-type semiconductor is doped with a pentavalent impurity and a P-type semiconductor is doped with a Trivalent impurity. The pentavalent impurities are called as Donor impurities as they give an extra electron to the lattice of the semiconductor. The Trivalent impurities are termed as Acceptor impurities as they create a void or positive hole in the crystal structure which can accept an electron.
3) Carrier Concentration:
In intrinsic semiconductors, there is an equal number of holes and electron concentration as no doping is added. Intrinsic conductors have lower conductivity compared to the extrinsic semiconductor.
In an N-type semiconductor, electrons are called the majority carriers as they are more in number and holes are termed as minority carriers. The conduction in an N-type of semiconductor majorly results from the electrons which are majority carriers.
In a P-type semiconductor, holes are called the majority carriers as they are more in number and electrons are termed as minority carriers. In a P-type of semiconductor conduction results primarily because of the holes which are majority carriers.
4) Fermi Level:
For an intrinsic semiconductor the Fermi level is exactly at the mid of the forbidden band.energy band gap for Silicon (Ga) is 1.6V, Germanium (Ge) is 0.66V, Gallium Arsenide (GaAs) 1.424V. In an extrinsic semiconductor
For n-type and p-type extrinsic semiconductors the Fermi levels are a function of doping level density.
In an N-type semiconductor, the Fermi level is near the conduction band as it has more electrons. In a P-type semiconductor, the Fermi level is near valance band as it has more of the holes.
5) Effect of temperature:
In an intrinsic semiconductor at there are no electrons in the conduction band. As the temperature reaches room temperature of the electrons gain energy to cross the valence band and reach the conduction band.
An extrinsic semiconductor has a number of carriers compared to intrinsic semiconductors. Increase in temperature will increase the conductivity of extrinsic semiconductors as more number of carriers are released for conduction.
Although the intrinsic semiconductor is a pure semiconductor it is not used for practical manufacturing as has low conductivity. The number of free charge carriers is less hence it has higher resistance to conduction of charges.
Whereas an extrinsic semiconductor has greater conductivity as it has a number of free charge carriers. Hence external semiconductors are preferred for practical manufacturing of semiconductor components and devices.