The electrons, protons and neutrons are  composed into an atomic structure which modeled as a solar system. It is called the Rutherford-Bohr model. However, each element is different based on the number of protons and electrons contain in that atom.

Valence electrons are the electrons that are situated at the outermost shell in an atom. It can participate in forming chemical bonds with other atom based on the number of valence electrons. It is either donating, receiving or sharing the electron with another atom. Elements are most stable when they have all eight valence electrons. This is called the octet rule. The only elements that have this electron configuration are  the noble gases. They are inert gas. The elements that are other than noble gases, they need to gain, lose or share electrons in order to achieve a full set of valence electrons. Therefore, they can achieve their stable state of element. The number in the ones place of the group number is equal to the number of valence electrons in that atom. Group 1 elements have 1 valence electron. Group 16 elements have 6 valence electrons.

Electrical conduction is caused by electrons breaking free of their atoms and moving around.  Atoms of some elements which release their outer electrons easily, makes these elements as a good conductors. When we provide with a little electric force to the conductor, it will cause the electron flow in conductors. This is due to electrons called free electrons, which exist in the atoms of conductors. Free electrons are electrons that are very weakly bonded to the atom and by applying a very little force, they can be traded to other atoms, or flow to create electricity. Metals such as copper, silver, and gold are good conductors.

Semiconductors are materials whose conductivity lies between the conductivity of conductors and insulators. Most conductors have just one electron in the valence shell however, semiconductors typically have four electrons in their valence shell. It is neither a good conductor nor a good insulator. The atoms of a semiconductor have no free electrons. They do have an electron that is bonded rather loosely and can be shared with a supply of a moderate electric force. Semiconductors can conduct electricity at a certain level without being damaged. However, it can be damaged with too much electric force. Semiconductors are between groups 1 and 2 in Periodic table. They do not normally pass current easily at room temperature. Unlike metals, the conductivity increases with increasing temperature. Increasing the temperatures to the semiconductor may leads to broken bonds and free electrons are generated. At the location at which the electron was placed, a defect called electron "hole" remains and it is similar to an electron, but with a positive charge. Silicon and germanium are the most common semiconductor. 

such as Boron (B), Gallium (G), Indium(In) and Aluminium(Al) 

is added to the trivalent impurity. It doped with measured quantity of trivalent impurity to an intrinsic or pure conductor such as silicon (Si) or germanium (Ge). The trivalent atom has three electrons in valence shell. Every trivalent dopant atom shares its 3 electrons with 3 neighboring Si atoms to form covalent bond. But, the bond between dopant atom and fourth neighbor is not completed as trivalent atom has no more electron to share. Thus, the fourth covalent bond is incomplete with shortage of one electron. Hence, it create a vacancy that acts as a hole. Trivalent impurities are called acceptor impurities because each atom of them create one hole which can accept one electron. The hole behaves like a positive charge. The holes attract electrons and when an electron moves into a hole, the electron leaves a new hole at its previous location. Thus, in a P-type semiconductor, holes are constantly moving around within the crystal as electrons constantly try to fill them up.

N-type semiconductor is created when the dopant is an element that has five electrons in its valence layer. When a small amount of pentavalent impurity such as Phosphorous (P), Arsenic (As) and Antimony (Sb) is added to a pure semiconductor , it will provide a large number of free electrons in it, the extrinsic semiconductor.

Pentavalent impurity are called a donor impurity because each atom of them donates one free electron crystal. Pentavalent atom has 5 electrons in its valence shell. However, only four of them are bonded to adjacent atoms.Every pentavalent dopant atom finds 4 neighboring Si atoms. It shares its 4 valence electrons with 4 Si atoms to form octet and become stable. Since valence orbit can hold a maximum of 8 electrons, the 1 extra electron of dopant atom is not the part of covalent bonding. Hence it becomes free electron. Due to these extra free electrons in the structure, the number of electrons become greater than the number of holes in the structure.

In a p-type semiconductor, each nucleus uses its valence  electrons to covalent bonds with its neighbours. For example, Si or Ge has 4 valence electrons, therefore they will form covalent bonds with their neighbour nucleus. Each ion which consists of nucleus and non-valent electron has a net charge of + 4 and is surrounded by 4 valence electrons. Since there are no excess electrons or holes In this case, the number of electrons and holes present will always be equal. Other example of p-type semiconductor is from Group 3 element such as Boron (B) or Gallium (Ga) which has 3 valence electrons. The electron-hole balance will be changed due to the imbalance number of electrons in an ion. This impurity will only be able to contribute three valence electrons making the excess one hole to be present. Since holes will "accept" free electrons, Group 3 impurity is also called an acceptor which is considered to be positively-charged. While "p" stands for positive, also notice that the material as a whole remains electrically neutral. In a p-type semiconductor, current is largely carried by the holes, which outnumber the free electrons. In this case, the holes are the majority carriers, while the electrons are the minority carriers.

Meanwhile, in an n-type semiconductor, in replacing one of the lattice atoms with a Group 3 atom, we can also replace it by an atom with five valence electrons. For example, the Group 5 atoms arsenic (As) or phosphorus (P) which in this case, the impurity adds five valence electrons to the lattice where it can only hold four. This means that there is now one excess electron in the lattice. Since it donates an electron, a Group 5 impurity is called a donor. Note that the material also remains electrically neutral making this to have a free electron. Donor impurities donate negatively charged electrons to the lattice, so a semiconductor that has been doped with a donor is called an n-type semiconductor; "n" stands for negative. Free electrons outnumber holes in an n-type material, so the electrons are the majority carriers and holes are the minority carriers.

Conductors are generally substances which have the property to pass different types of energy.An electrical conductor is a substance in which electrical charge carriers, usually electrons, move easily from atom to atom with the application of voltage. Conductivity, in general, is the capacity to transmit something, such as electricity or heat. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. The distribution of charge is the result of electron movement. Since conductors allow for electrons to be transported from particle to particle, a charged object will always distribute its charge until the overall repulsive forces between excess electrons is minimized. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. The transfer of charge between objects occurs more readily if the second object is made of a conducting material. Conductors allow for charge transfer through the free movement of electrons.

Substances called semiconductors act as good conductors under some conditions and poor conductors under other conditions. Silicon, germanium, and various metal oxides are examples of semiconductor materials. In a semiconductor, both electrons and so-called holes electron absences act as charge carriers.The specific properties of a semiconductor depend on the impurities, or dopants, added to it. An N-type semiconductor carries current mainly in the form of negatively-charged electrons, in a manner similar to the conduction of current in a wire. A P-type semiconductor carries current predominantly as electron deficiencies called holes. A hole has a positive electric charge, equal and opposite to the charge on an electron. In a semiconductor material, the flow of holes occurs in a direction opposite to the flow of electrons.

Semiconductors are most often made from silicon. Silicon is an element with four electrons in its outer shell. To make a p-type semiconductor extra materials like boron or aluminium are added to the silicon. These materials have only three electrons in their outer shell. When the extra material replaces some of the silicon it leaves a 'hole' where the fourth electron would have been if the semiconductor was pure silicon.

An N-Type semiconductor is created by adding pentavalent impurities like phosphorus (P), arsenic (As), antimony (Sb), or bismuth (Bi). A pentavalent impurity is called a donor because it is ready to give a free electron to a semiconductor. The impurities are called dopants. The purpose of doing this is to make more charge carriers, or electron wires available in the material for conduction. In n-type semiconductors the number of electrons is more than the holes, so electrons are measured as majority charge carriers and holes are referred to as minority charge carriers.A semiconductor doped with a donor. A free electron is now present.Donor impurities donate negatively charged electrons to the lattice, so a semiconductor that has been doped with a donor is called an n-type semiconductor; "n" stands for negative. Free electrons outnumber holes in an n-type material, so the electrons are the majority carriers and holes are the minority carriers.

You can easily determine the number of valence electrons an atom can have by looking at its Group in the periodic table.

For example, atoms in Groups 1 and 2 have 1 and 2 valence electrons, respectively.

Atoms in Groups 13 and 18 have 3 and 8 valence electrons, respectively. 

Valence electrons are responsible for the reactivity of an element. They determine how "willing" the elements are to bond with each other to form new compounds. If the valence shell of an element is full, such as with a noble gas, then the element does not want to gain or lose an electron.

For example, alkali metals, which all have a valency of 1, want to lose that one electron and are likely to form ionic bonds (such as in the case of NaCl, or table salt) with a Group 17 element, which has a valency of 7 and wants to gain that one electron from the alkali metal (Group 1 element) to form a stable valency of 8.

Semiconductors, such as Silicon (Si) are made up of individual atoms bonded together in a regular, periodic structure to form an arrangement whereby each atom is surrounded by 8 electrons. An individual atom consists of a nucleus made up of a core of protons (positively charged particles) and neutrons (particles having no charge) surrounded by electrons. The number of electrons and protons is equal, such that the atom is overall electrically neutral. The electrons surrounding each atom in a semiconductor are part of a covalent bond. A covalent bond consists of two atoms "sharing" a single electron. Each atom forms 4 covalent bonds with the 4 surrounding atoms. Therefore, between each atom and its 4 surrounding atoms, 8 electrons are being shared.

As an extremely small amount of Gallium impurity has a large number of atoms, therefore, it provides millions of holes in the semiconductor.

n-Type Semiconductor
When a small amount of Pentavalent impurity is added to a pure semiconductor providing a large number of free electrons in it, the extrinsic semiconductor thus formed is known as n-Type Semiconductor. The conduction in the n-type semiconductor is because of the free electrons denoted by the pentavalent impurity atoms. These electrons are the excess free electrons with regards to the number of free electrons required to fill the covalent bonds in the semiconductors.

The addition of Pentavalent impurities such as arsenic and antimony provides a large number of free electrons in the semiconductor crystal. Such impurities which produce n-type semiconductors are known as Donor Impurities. They are called a donor impurity because each atom of them donates one free electron crystal.

When a few Pentavalent impurities such as Arsenic whose atomic number is 33, which is categorised as 2, 8, 15 and 5. It has five valence electrons, which is added to germanium crystal. Each atom of the impurity fits in four germanium atoms.

Hence, each Arsenic atom provides one free electron in the Germanium crystal. Since an extremely small amount of arsenic, impurity has a large number of atoms; it provides millions of free electrons for conduction.

It is useful to study the atomic theory before discussing the p-n junction electronic devices because the p-n junction it consists of atomic theory which is a based knowledge to study. In atomic theory, the structure of atoms and how it works and function would be used in the p-n junction as it related to how the atom in p-n junction work and how the electron moves from the positive to negative. This study also include on how the electron valence will react as if there are force applied which will make it either donate, receive or the electron will determines what kind of element share. Thus, the atomic studies on how the atom works should be study to understand before the p-n junction and how the p-n junction will operate as the atom moves.

Muhammad Aiman Bin Kamarulzaman (1722979)

A valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair. The presence of valence electrons can determine the element’s chemical properties, such as its valence whether it may bond with other elements and, if so, how readily and with how many. For a main group element, a valence electron can exist only in the outermost electron shell in a transition metal, a valence electron can also be in an inner shell. To know the number of valance electron of an element it can be determined by the periodic table group which it have been categorized.

Muhammad Aiman Bin Kamarulzaman (1722979)

            Semi-conductors are insulators that lack commitment. The atoms of a semi-conductor have no free electrons; however, they do have an electron that is bonded rather loosely and can be shared with the application of a moderate electric force. Semi-conductors can conduct electricity at a certain level without being damaged. However, semi-conductors can be damaged with too much electric force.

Muhammad Aiman Bin Kamarulzaman (1722979)

An intrinsic semiconductor. Note each +4 ion is surrounded by four electrons.

Now, if one of the atoms in the semiconductor lattice is replaced by an element with three valence electrons, such as a Group 3 element like Boron (B) or Gallium (Ga), the electron-hole balance will be changed. This impurity will only be able to contribute three valence electrons to the lattice, therefore leaving one excess hole (see figure below). Since holes will "accept" free electrons, a Group 3 impurity is also called an acceptor.

A semiconductor doped with an acceptor. An excess hole is now present.

Because an acceptor donates excess holes, which are considered to be positively charged, a semiconductor that has been doped with an acceptor is called a p-type semiconductor; "p" stands for positive. Notice that the material as a whole remains electrically neutral. In a p-type semiconductor, current is largely carried by the holes, which outnumber the free electrons. In this case, the holes are the majority carriers, while the electrons are the minority carriers.

N-type

In addition to replacing one of the lattice atoms with a Group 3 atom, we can also replace it by an atom with five valence electrons, such as the Group 5 atoms arsenic (As) or phosphorus (P). In this case, the impurity adds five valence electrons to the lattice where it can only hold four. This means that there is now one excess electron in the lattice (see figure below). Because it donates an electron, a Group 5 impurity is called a donor. Note that the material remains electrically neutral.
A semiconductor doped with a donor. A free electron is now present.

Donor impurities donate negatively charged electrons to the lattice, so a semiconductor that has been doped with a donor is called an n-type semiconductor; "n" stands for negative. Free electrons outnumber holes in an n-type material, so the electrons are the majority carriers and holes are the minority carriers.

 
Muhamad Aiman Bin Kamarulzaman (1722979

An understanding about electronic or electricity must begin with the concept that all mater is composed of atoms, and all atoms are composed of charged particles known as electrons and protons. Protons carry a positive charge (+), and electrons carry a negative charge (-). 

It is also because of the static electricity is a phenomenon that involves positive and negative charges. 

It is important that we need to grasp the concept that oppositely charged objects attract each other and like charged objects repel each other. It is important to know which materials tend to acquire negative or positive charges. 

When two different materials come into close contact, one material ends up with an excess of electrons and becomes negatively charged, while the other ends up with a deficiency of electrons and becomes positively charged. This accumulation of imbalanced charges on objects results in the phenomena we commonly refer to as static electricity. 

 

 -There are three different types of sub-atomic particles within an atom namely, electrons(negatively charged particles), protons(positively charged particles), neutrons(neutral particles without any charge on them). 

-The nucleus is located at the centre of the atom, which contains the positively charged protons and the neutrons within it. 

-The negatively charged electrons revolve around the nucleus in separate paths called as orbitals. The atomic structure, resembles the structure of our solar system with the Sun at the centre and the planets revolving around it in different paths.

-The atom has a nucleus which contains the protons and the neutrons collectively called as nucleuons. 

 -The nuclear force is responsible for holding the protons and the neutrons together within the nucleus to form the atomic nuclei(plural of nucleus). 

-Electrons and protons are oppositely charged particles which are attracted towards each other under the influence of electrostatic force of attraction. 

-In an uncharged atom, the number of electrons , is called its atomic number. It is denoted by the symbol “Z”. The total number of nucleons is called its atomic mass which is denoted by the symbol “A”.

A valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair. Atoms can combine to achieve an octet of valence electrons by sharing electrons. The term covalent bond is used to describe the bonds in compounds that result from the sharing of one or more pairs of electrons.

 

 

Semiconductors are those materials whose electrical conductivity is between conductors and insulators. A semiconductor has partially full valence band and partially full conduction band at the room temperature. The conduction band remains fully empty and the valence band remains full of electrons at absolute zero temperature. So, silicon and germanium are insulators at absolute zero temperature. On the other hand with the increasing of temperature the electrical conductivity of semiconductors increase.  A semiconductor will carry electric current, but not as simple as a usual conductor. Some components are intrinsic semiconductors. The semiconductor properties happen in these materials certainly. Most of the semiconductor materials used in electronic devices are extrinsic. This means that left to themselves, they are outstanding insulators. These materials are switched into semiconductors by doping them with slight amounts of foreign atoms. The No.of doping atoms you want to add is very minor. Semiconductors also need less power and it can function at very low voltage.

 

 

 
eg : Gallium atom has 3 valence electrons. It makes covalent bonds with adjacent three electrons of silicon atom.  There is a deficiency of one covalent bond and creates a hole. Therefore trivalent impurity accepts one electron and becomes negative acceptor ion. Trivalent impurity known as acceptor.

 

This is all well and good, but these newly doped N-type and P-type semiconductor materials do very little on their own as they are electrically neutral. However, if we join (or fuse) these two semiconductor materials together they behave in a very different way merging together and producing what is generally known as a “PN Junction“.

When the N-type semiconductor and P-type semiconductor materials are first joined together a very large density gradient exists between both sides of the PN junction. The result is that some of the free electrons from the donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in the P-type material producing negative ions.

However, because the electrons have moved across the PN junction from the N-type silicon to the P-type silicon, they leave behind positively charged donor ions ( N_D ) on the negative side and now the holes from the acceptor impurity migrate across the junction in the opposite direction into the region where there are large numbers of free electrons.

As a result, the charge density of the P-type along the junction is filled with negatively charged acceptor ions ( N_A ), and the charge density of the N-type along the junction becomes positive. This charge transfer of electrons and holes across the PN junction is known as diffusion. The width of these P and N layers depends on how heavily each side is doped with acceptor density N_A, and donor density N_D, respectively.

This process continues back and forth until the number of electrons which have crossed the junction have a large enough electrical charge to repel or prevent any more charge carriers from crossing over the junction. Eventually a state of equilibrium (electrically neutral situation) will occur producing a “potential barrier” zone around the area of the junction as the donor atoms repel the holes and the acceptor atoms repel the electrons.

Since no free charge carriers can rest in a position where there is a potential barrier, the regions on either sides of the junction now become completely depleted of any more free carriers in comparison to the N and P type materials further away from the junction. This area around the PN Junction is now called the Depletion Layer

Fadhli Dzil Ikram (1727999)

Outside of the nucleus are energy levels (also called shells), which contain one or more electrons. The energy levels are often called rings (see more discussion of the Bohr model below).

The neutrons have the greatest mass and have no charge. The protons have slightly less mass than the neutrons and are positively charged. The electrons have almost no mass and are negatively charged. The electrons move around the nucleus in energy levels.

The Bohr model of the atom is the easiest way to indicate the location of the different parts of an atom.

VALENCE ELECTRON

A valence electron is an electron that is the most likely to be involved in a chemical reaction. They are typically the electrons with the highest value of the principle quantum number, n. Another way to think of valence electrons is that they are the outermost electrons in an atom, so they are the most susceptible to participation in chemical bond formation or ionization.

The simplest way to identify the valence electrons is to look for the highest number in the electron configuration of an atom (the principle quantum number).

It's worth noting the IUPAC definition of valence is for the single highest valence value that is displayed by an atom of an element. However, in practical use, main group elements of the periodic table may display any valence from 1 to 7 (since 8 is a complete octet). Most elements have preferred values of valence electrons. The alkali metals, for example, almost always display a valence of 1. The alkaline earths tend to display a valence of 2. The halogens usually have a valence of 1, yet may sometimes display a valence of 7. The transition metals may display a range of valence values because the highest energy electron subshell is only partially filled. Those atoms become more stable by emptying the shell, half-filling it, or completely filling it.

FADHLI DZIL IKRAM(1727999)

When a positive voltage potential is applied to the material these “free electrons” leave their parent atom and travel together through the material forming an electron drift, more commonly known as a current. How “freely” these electrons can move through a conductor depends on how easily they can break free from their constituent atoms when a voltage is applied. Then the amount of electrons that flow depends on the amount of resistivity the conductor has.

Examples of good conductors are generally metals such as Copper, Aluminium, Silver or non metals such as Carbon because these materials have very few electrons in their outer “Valence Shell” or ring, resulting in them being easily knocked out of the atom’s orbit.

This allows them to flow freely through the material until they join up with other atoms, producing a “Domino Effect” through the material thereby creating an electrical current. Copper and Aluminium is the main conductor used in electrical cables as shown.

Generally speaking, most metals are good conductors of electricity, as they have very small resistance values, usually in the region of micro-ohms per metre, (μΩ.m).

While metals such as copper and aluminium are very good conducts of electricity, they still have some resistance to the flow of electrons and consequently do not conduct perfectly.

The energy which is lost in the process of passing an electrical current, appears in the form of heat which is why conductors and especially resistors become hot. Also the resistivity of conductors increases with ambient temperature because metals are also generally good conductors of heat.

SEMICONDUCTOR
Semiconductors materials such as silicon (Si), germanium (Ge) and gallium arsenide (GaAs), have electrical properties somewhere in the middle, between those of a “conductor” and an “insulator”. They are not good conductors nor good insulators (hence their name “semi”-conductors). They have very few “free electrons” because their atoms are closely grouped together in a crystalline pattern called a “crystal lattice” but electrons are still able to flow, but only under special conditions.

The ability of semiconductors to conduct electricity can be greatly improved by replacing or adding certain donor or acceptor atoms to this crystalline structure thereby, producing more free electrons than holes or vice versa. That is by adding a small percentage of another element to the base material, either silicon or germanium.

On their own Silicon and Germanium are classed as intrinsic semiconductors, that is they are chemically pure, containing nothing but semi-conductive material. But by controlling the amount of impurities added to this intrinsic semiconductor material it is possible to control its conductivity. Various impurities called donors or acceptors can be added to this intrinsic material to produce free electrons or holes respectively.

This process of adding donor or acceptor atoms to semiconductor atoms (the order of 1 impurity atom per 10 million (or more) atoms of the semiconductor) is called Doping. The as the doped silicon is no longer pure, these donor and acceptor atoms are collectively referred to as “impurities”, and by doping these silicon material with a sufficient number of impurities, we can turn it into semiconductor

Let us consider, trivalent impurity boron is added to silicon as shown in below figure. Boron atom has three valence electron and silicon has four valence electrons. The three valence electrons of each boron atom form 3 covalent bonds with the 3 neighboring silicon atoms. 

In the fourth covalent bond, only silicon atom contributes one valence electron, while the boron atom has no valence electron to contribute. Thus, the fourth covalent bond is incomplete with shortage of one electron. This missing electron is called hole.

This shows each boron atom accept one electron to fill the hole. Therefore, all the trivalent impurities are called acceptors. A small addition of impurity (boron) provides millions of holes.

Charge on p-type semiconductor

So many people think that p-type semiconductor has large number of holes and current conduction is mainly due to these holes. So, the total electric charge of p-type semiconductor is positive. But this assumption is wrong. Even though p-type semiconductor has large number of holes, but these holes is provided by the trivalent atoms that are electrically neutral. Therefore, the total electric charge of p-type semiconductor is also neutral.

Conduction in p-type semiconductor

Let us consider a p-type semiconductor as shown in below figure. When voltage is applied to p-type semiconductor; the holes in valence band moves towards negative terminal of applied voltage.  Similarly free electrons move towards positive terminal of applied voltage. 

                 

In p-type semiconductor, the population of holes in valence band is more, whereas the population of free electrons in conduction band is less. So, current conduction is mainly because of holes in valence band. Free electrons in conduction band  constitute little current. Hence in p-type semiconductor, holes are called majority carriers and free electrons are called minority carriers.

N-TYPE

When pentavalent impurity is added to an intrinsic or pure semiconductor (silicon or germanium), then it is said to be an n-type semiconductor. Pentavalent impurities such as phosphorus, arsenic, antimony etc are called donor impurity.  

Let us consider, pentavalent impurity phosphorus is added to silicon as shown in below figure. Phosphorus atom has 5 valence electron and silicon has 4 valence electrons. Phosphorus atom has one excess valence electron than silicon. The four valence electrons of each phosphorus atom form 4 covalent bond with the 4 neighboring silicon atoms. The fifth valence electron of the phosphorus atom cannot able to form the covalent bond with the silicon atom because silicon atom does not have the fifth valence electron to form the covalent bond.

Thus, fifth valence electron of phosphorus atom does not involve in the formation of covalent bonds. Hence, it is free to move and not attached to the parent atom.

This shows that each phosphorus atom donates one free electron. Therefore, all the pentavalent impurities are called donors. The number of free electrons are depends on the amount of impurity (phosphorus) added to the silicon. A small addition of impurity (phosphorus) generates millions of free electrons. 

Charge on n-type semicondctor

So many people think that n-type semiconductor has large number of free electrons. So, the total electric charge of n-type semiconductor is negative. But this assumption is wrong. Even though n-type semiconductor has large number of free electrons, but these free electrons is given by the pentavalent atoms that are electrically neutral. Therefore, the total eletric charge of n-type semiconductor is also neutral.

Conduction in n-type semiconductor

Let us consider an n-type semiconductor as shown in below figure. When voltage is applied to n-type semiconductor; the free electrons moves towards positive terminal of applied voltage.  Similarly holes moves towards negative terminal of applied voltage.

In n-type semiconductor, the population of free electrons is more whereas the population of holes is less. Hence in n-type semiconductor free electrons are called majority carriers and holes are called minority carriers. Therefore, in a n-type semiconductor conduction is mainly because of motion of free electrons

FADHLI DZIL IKRAM (1727999)

The reason why it is useful to briefly review atomic theory before discussing the p-n junction and electronic devices because it will facilitate our understanding and it is the fastest way to know  inside out of this topic.  What we need to know is we must understand the properties and characteristics of semiconductor materials.  We also need to recap what we have learn in chemistry about how electron move to form a covalent bond.  The minimum energy for electron needed to overcome the bond and so on.

Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three particles: protons, neutrons and electrons. Protons and neutrons are heavier than electrons and reside in the nucleus at the center of the atom. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. Protons and neutrons have approximately the same mass. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom. The electrons present ib the outermost shell of the atom are known as valence electrons. Valence electrons are important because, the valence electrons decide the reactivity of an element and it decide the manner in which an atom form a bond with another form.

Semiconductor are insulators that lack commitment. The particles of a semiconductor have no free electrons; be that as it may, they do have an electron that is reinforced rather freely and can be imparted to the utilization of a direct electric force. Semiconductor can conduct electricity at a specific level without being harmed; be that as it may, semi-conductor can be harmed with a lot of electric force. Silicon is the most common semiconductor.

The extrinsic p-Type Semiconductor is formed when a trivalent impurity is added to a pure semiconductor in a small amount, and as a result, a large number of holes are created in it. A large number of holes are provided in the semiconductor material by the addition of trivalent impurities like Gallium and Indium. Such type of impurities which produces p-type semiconductor are known as an Acceptor Impurities because each atom of them create one hole which can accept one electron.

In the fourth covalent bonds, only the germanium atom contributes one valence electron, while gallium atom has no valence bonds. Hence, the fourth covalent bond is incomplete, having one electron short. This missing electron is known as a Hole. Thus, each gallium atom provides one hole in the germanium crystal.

In the fourth covalent bonds, only the germanium atom contributes one valence electron, while gallium atom has no valence bonds. Hence, the fourth covalent bond is incomplete, having one electron short. This missing electron is known as a Hole. Thus, each gallium atom provides one hole in the germanium crystal.As an extremely small amount of Gallium impurity has a large number of atoms, therefore, it provides millions of holes in the semiconductor. 

When a small amount of Pentavalent impurity is added to a pure semiconductor providing a large number of free electrons in it, the extrinsic semiconductor thus formed is known as n-Type Semiconductor. The conduction in the n-type semiconductor is because of the free electrons denoted by the pentavalent impurity atoms. These electrons are the excess free electrons with regards to the number of free electrons required to fill the covalent bonds in the semiconductors.

The addition of Pentavalent impurities such as arsenic and antimony provides a large number of free electrons in the semiconductor crystal. Such impurities which produce n-type semiconductors are known as Donor Impurities. They are called a donor impurity because each atom of them donates one free electron crystal.

When a few Pentavalent impurities such as Arsenic whose atomic number is 33, which is categorised as 2, 8, 15 and 5. It has five valence electrons, which is added to germanium crystal. Each atom of the impurity fits in four germanium atoms as shown in the figure.

Hence, each Arsenic atom provides one free electron in the Germanium crystal. Since an extremely small amount of arsenic, impurity has a large number of atoms; it provides millions of free electrons for conduction.

Mohamad Haziq 1727001

 Valence electrons are located at the outermost shell of an atom. The number of valence electrons in an element can be determined by the arrangement of periodic table. The chemical and electrical activities of a material mostly depend on the number of valence electrons.

 

Semiconductor are solids whose conductivity lies between the conductivity of conductors and insulators. The atoms contain no free electrons, however they do have an electron that is bonded rather loosely and can be shared with the application of a moderate electric force. Semiconductors can conduct electricity at a certain level without being damaged. However, it can be damaged with too much electric force. Most common semiconductor is silicon.

 

 

P-type is the addition of trivalent impurities such as boron, aluminium or gallium to an intrinsic semiconductor. It creates deficiencies of valence electrons called holes. Typically, B₂H₆ dibrone gas to diffuse boron into silicon material.

 

N-type semiconductor is the addition of pentavalent impurities such as antimony, arsenic or phosphorus contributes free electrons. It will greatly increase the conductivity of the intrinsic semiconductor. Example, phosphorus maybe added by diffusion of phosphine gas (PH3)

 

Valence electron is the electrons that located at the outermost shell. Valence band electrons are the furthest from the nucleus and have the higher energy levels than electrons in the lower orbits. Here we see this is the surface of the nucleus right here, and then we see the varying energy levels. The closer to the nucleus the lower the energy level and it goes up until get out again to the valence electron. The region beyond the valence band is called the conduction band. This would be the highest level of energy while we're still in the atom, but if this election here gains enough energy it can actually go into what we would call the conduction band and then it can become a free electron. Electrons and conduction band are easily made to be free electrons.

-Maisarah binti Mohamad Sattar
-1728650

Semiconductors materials such as silicon, germanium and gallium arsenide,  have electrical properties somewhere in the middle, between those of a “conductor” and an “insulator”. They are not good conductors nor good insulators (hence their name “semi”-conductors). They have very few “free electrons” because their atoms are closely grouped together in a crystalline pattern called a “crystal lattice” but electrons are still able to flow, but only under special conditions. The ability of semiconductors to conduct electricity can be greatly improved by replacing or adding certain donor or acceptor atoms to this crystalline structure thereby, producing more free electrons than holes or vice versa. That is by adding a small percentage of another element to the base material, either silicon or germanium.

-Maisarah binti Mohamad Sattar
-1728650

n-type semiconductor is semiconductor that doped with impurity atom such as Arsenic, Antimony or Phosphorus into the crystalline structure making it extrinsic (impurities are added). These atoms have five outer electrons in their outermost orbital to share with neighbouring atoms and are commonly called “Pentavalent” impurities. This allows four out of the five orbital electrons to bond with its neighbouring silicon atoms leaving one “free electron” to become mobile when an electrical voltage is applied (electron flow). As each impurity atom “donates” one electron, pentavalent atoms are generally known as “donors”. Antimony (symbol Sb) as well as Phosphorus (symbol P), are frequently used as a pentavalent additive to silicon. The resulting semiconductor basics material has an excess of current-carrying electrons, each with a negative charge, and is therefore referred to as an N-type material with the electrons called “Majority Carriers” while the resulting holes are called “Minority Carriers”. When it is connected to external power source, the electrons freed from the silicon atoms by this stimulation are quickly replaced by the free electrons available from the doped Antimony atoms. Then a semiconductor material is classed as N-type when its donor density is greater than its acceptor density, in other words, it has more electrons than holes thereby creating a negative pole.
-Maisarah binti Mohamad Sattar
-1728650

· Nucleus contains the protons and neutrons collectively called as nucleuons.

· The nuclear force is responsible for holding the protons and neutrons together within the nucleus to form the atomic nuclei.

· Electrons and protons are oppositely charged particles which are attracted toward each other under the influence of electrostatic force of attraction.

· The nuclei of all other elements nearly always contain neutrons in addition to protons.

PROTONS :

· The particle has a positive electrical charge, equal and opposite to that of the electron.

· If isolated, a single proton would have a mass of only 1.673x10²⁷ kilogram, just slightly less than the mass of a neutron.

· The number of protons in an element's nucleus is called the atomic number.

· In the atoms of any particular element, the number of protons in the nuclei is always the same.

NEUTRONS :

· it has no electrical charge; it is neutral.

· A neutron has a mass of 1.67492729 x 10^-27 kg.

· The number of neutrons in an atom determines its isotope.
.  Although it's possible to eject neutrons from the nucleus, the free particles don't last long before reacting with other atoms. On average, a neutron survives on its own about 15 minutes.

ELECTRONS :

·          Negatively charged component of an atom. 

·         exist outside of and surrounding the atom nucleus.

·         Each electron carries one unit of negative charge (1.602 x 10^-19 coulomb) and has a very small mass as compared with that of a neutron or proton. 

·         The mass of an electron is 9.10938 x 10^-31 kg. 

·         A common symbol for an electron is e^-.

 

A valence electron is an electron that is the most likely to be involved in a chemical reaction. They are typically the electrons with the highest value of the principle quantum number, n. Another way to think of valence electrons is that they are the outermost electrons in an atom, so they are the most susceptible to participation in chemical bond formation or ionization.

The simplest way to identify the valence electrons is to look for the highest number in the electron configuration of an atom (the principle quantum number). 
 It's worth noting the IUPAC definition of valence is for the single highest valence value that is displayed by an atom of an element. However, in practical use, main group elements of the periodic table may display any valence from 1 to 7 (since 8 is a complete octet). Most elements have preferred values of valence electrons. The alkali metals, for example, almost always display a valence of 1. The alkaline earths tend to display a valence of 2. The halogens usually have a valence of 1, yet may sometimes display a valence of 7. The transition metals may display a range of valence values because the highest energy electron subshell is only partially filled. Those atoms become more stable by emptying the shell, half-filling it, or completely filling it. 

MAZARINA ABU OTHMAN (1725268)

The structure of atoms are :

1)Atoms are made up of a nucleus which is located at the centre, and a number of orbitals, surrounding the nucleus.

 2) There are three different types of sub-atomic particles within an atom namely, electrons(negatively charged particles), protons(positively charged particles), neutrons(neutral particles without any charge on them). 

3) The nucleus is located at the centre of the atom, which contains the positively charged protons and the neutrons within it.

 4) The negatively charged electrons revolve around the nucleus in separate paths called as orbitals. The atomic structure, resembles the structure of our solar system with the Sun at the centre and the planets revolving around it in different paths.

Valence electrons are the electrons in the valence shell. Valence electrons are the highest energy electrons in an atom and are therefore the most reactive. While inner electrons (those not in the valence shell) typically don't participate in chemical bonding and reactions, valence electrons can be gained, lost, or shared to form chemical bonds.

In a conductor, electric current can flow freely. Metals such as copper typify conductors. "Conductor" implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their electrons tightly. In copper, the valence electrons are essentially free and strongly repel each other. Simply stated, most metals are good electrical conductors. Metals are also generally good heat conductors . Metals are classified as conductors because their outer electrons are not tightly bound, but in most materials even the outermost electrons are so tightly bound that there is essentially zero electron flow through them with ordinary voltages.

Semiconductor

A semiconductor is a substance, usually a solid chemical element or compound, that can conduct electricity under some conditions but not others, making it a good medium for the control of electrical current. Its conductance varies depending on the current or voltage applied to a control electrode, or on the intensity of irradiation by infrared (IR), visible light, ultraviolet (UV), or X rays. The specific properties of a semiconductor depend on the impurities, or dopants, added to it. An N-type semiconductor carries current mainly in the form of negatively-charge electrons, in a manner similar to the conduction of current in a wire. A P-type semiconductor carries current predominantly as electron deficiencies called holes. A hole has a positive electric charge, equal and opposite to the charge on an electron. In a semiconductor material, the flow of holes occurs in a direction opposite to the flow of electrons.
Elemental semiconductors include antimony, arsenic, boron, carbon, germanium, selenium, silicon, sulfur, and tellurium.Silicon is the best-known of these, forming the basis of most integrated circuits . Common semiconductor compounds include gallium arsenide, indium antimonide, and the oxides of most metals. Of these, gallium arsenideis widely used in low-noise, high-gain, weak-signal amplifying devices.

Conductors in materials held together by the metallic bond, electrons float loosely between the metal ions. These electrons will be free to move if an electrical force is applied. For example, if a copper wire is attached across the poles of a battery, the electrons will flow inside the wire. 

The flow of electrons inside a conductor is not quite so simple, though. A free electron will be accelerated for a while but will then collide with an ion. In the collision process, some of the energy acquired by the electron will be transferred to the ion. As a result, the ion will move faster, and an observer will notice the wire’s temperature rise. This conversion of electrical energy from the motion of the electrons to heat energy is called electrical resistance. In a material of high resistance, the wire heats up quickly as electric current flows. In a material of low resistance, such as copper wire, most of the energy remains with the moving electrons, so the material is good at moving electrical energy from one point to another. 

Semiconductor

Semiconductors, such as Silicon (Si) are made up of individual atoms bonded together in a regular, periodic structure to form an arrangement whereby each atom is surrounded by 8 electrons. An individual atom consists of a nucleus made up of a core of protons (positively charged particles) and neutrons (particles having no charge) surrounded by electrons. The number of electrons and protons is equal, such that the atom is overall electrically neutral. The electrons surrounding each atom in a semiconductor are part of a covalent bond. A covalent bond consists of two atoms "sharing" a single electron. Each atom forms 4 covalent bonds with the 4 surrounding atoms. Therefore, between each atom and its 4 surrounding atoms, 8 electrons are being shared.

(Muhd Zulhelmie Samsuri)
1720589

 

P-type is the addition of trivalent impurities such as boron, aluminium or gallium to an intrinsic semiconductor. It creates deficiencies of valence electrons called holes. Typically, B₂H₆ dibrone gas to diffuse boron into silicon material.

 

N-type semiconductor is the addition of pentavalent impurities such as antimony, arsenic or phosphorus contributes free electrons. It will greatly increase the conductivity of the intrinsic semiconductor. Example, phosphorus maybe added by diffusion of phosphine gas (PH3)

Muhammad Farizul Bin Mohd Rade(1722779)

such as Boron (B), Gallium (G), Indium(In) and Aluminium(Al) 

is added to the trivalent impurity. It doped with measured quantity of trivalent impurity to an intrinsic or pure conductor such as silicon (Si) or germanium (Ge). The trivalent atom has three electrons in valence shell. Every trivalent dopant atom shares its 3 electrons with 3 neighboring Si atoms to form covalent bond. But, the bond between dopant atom and fourth neighbor is not completed as trivalent atom has no more electron to share. Thus, the fourth covalent bond is incomplete with shortage of one electron. Hence, it create a vacancy that acts as a hole. Trivalent impurities are called acceptor impurities because each atom of them create one hole which can accept one electron. The hole behaves like a positive charge. The holes attract electrons and when an electron moves into a hole, the electron leaves a new hole at its previous location. Thus, in a P-type semiconductor, holes are constantly moving around within the crystal as electrons constantly try to fill them up.

 

An N-Type semiconductor is created by adding pentavalent impurities like phosphorus (P), arsenic (As), antimony (Sb), or bismuth (Bi). A pentavalent impurity is called a donor because it is ready to give a free electron to a semiconductor. The impurities are called dopants. The purpose of doing this is to make more charge carriers, or electron wires available in the material for conduction. In n-type semiconductors the number of electrons is more than the holes, so electrons are measured as majority charge carriers and holes are referred to as minority charge carriers.A semiconductor doped with a donor. A free electron is now present.Donor impurities donate negatively charged electrons to the lattice, so a semiconductor that has been doped with a donor is called an n-type semiconductor; "n" stands for negative. Free electrons outnumber holes in an n-type material, so the electrons are the majority carriers and holes are the minority carriers.

The 5-valent dopant has an outer electron more than the silicon atoms. Four outer electrons combine with ever one silicon atom, while the fifth electron is free to move and serves as charge carrier. This free electron requires much less energy to be lifted from the valence band into the conduction band, than the electrons which cause the intrinsic conductivity of silicon. The dopant, which emits an electron, is known as an electron donor 

The dopants are positively charged by the loss of negative charge carriers and are built into the lattice, only the negative electrons can move. Doped semimetals whose conductivity is based on free (negative) electrons are n-type or n-doped. Due to the higher number of free electrons those are also named as majority charge carriers, while free mobile holes are named as the minority charge carriers.

P-type conductor

In contrast to the free electron due to doping with phosphorus, the 3-valent dopant effect is exactly the opposite. The 3-valent dopants can catch an additional outer electron, thus leaving a hole in the valence band of silicon atoms. Therefore the electrons in the valence band become mobile. The holes move in the opposite direction to the movement of the electrons. The necessary energy to lift an electron into the energy level of indium as a dopant, is only 1 % of the energy which is needed to raise a valence electron of silicon into the conduction band.

With the inclusion of an electron, the dopant is negatively charged, such dopants are called acceptors (acceptare, lat. = to add). Again, the dopant is fixed in the crystal lattice, only the positive charges can move. Due to positive holes these semiconductors are called p-conductive or p-doped. Analog to n-doped semiconductors, the holes are the majority charge carriers, free electrons are the minority charge carriers.

(Muhd Zulhelmie Samsuri)
1720589

Valence electrons

 

It is important for us to study about atomic theory before discussing about p-n junction and electronic devices because we need to understand carefully on the working operation of atomic structure. We also have to differentiate between insulator, conductor and semiconductor. To do so, we need to study about atomic theory first before we go through the p-n junction and electronic devices. Basic understanding of atomic activity is necessary to understand the operation and application of semiconductor devices in electronic circuits.

1.The atom is the smallest object that retains the properties of an element.

2.Atoms are composed of electrons and a nucleus.

3.The nucleus contains protons and neutrons.

4.All atoms are electrically neutral, because every atom has an equal number of electrons and protons.

5.Nearly all of the atom's mass is located in the nucleus.

6.The nucleus is tiny compared with the total size of the atom.

7.Most of the atom's volume holds the electron cloud, whose mass is tiny.

8.Atoms are generally spherical, although there are indications that atoms of the very heaviest elements may exist as squashed spherical shapes.

9.An atom's chemical behavior is determined by the arrangement of its electrons.

Electron valence:
-an electron of an atom, located in the outermost shell (valence shell) of the atom, that can be transferred to or shared with another atom.

Structure of an atom:

 

Conductor is materials with very low resistance which means the current can flow easily through it. There is no energy gap in conductor, as the valence and conduction bands overlap. With no energy gap, it only takes a small amount of energy for valance electron jumps from the valance band to the

conduction band. Consequently, conductor pass electrons very easily and resulting much current will flow in the conductor.

Semiconductor can be varying either insulators or conductors by reaction of temperature. Its voltage can be controlled. A material that is between conductors and insulators in its ability to conduct electrical current. It has exactly 4 valence electrons. The most common single-element semiconductors are silicon, germanium, and carbon.

p-type semiconductor 

1.Formed when a trivalent impurity is added to a pure semiconductor in a small amount, and as a result, a large number of holes are created in it.

2.It has 3 valence electrons such as boron, indium and gallium (group III).

3.It can increase the number of holes in intrinsic semiconductor. 

4.Since trivalent atom has only 3 valence electrons, it creates a hole when each trivalent atom is added. 

5.Atom from group III: acceptor impurity

6.Majority carriers: HOLES

7.Minority carriers: ELECTRONS

8.Group III + Si = p-type semiconductor

 

n-type semiconductor

1.N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material (e.g. phosphorus in silicon). 

2.This creates an excess of negative (n-type) electron charge carriers.

3.An extra electron from an impurity atom produces an n-type semiconductor.

4.Pentavalent impurity atom has 5 valence electrons – GROUP V (Phosporus /Arsenide)

5.The extra electron is free to move – does not involve in bonding

6.       Atom from group IV: donor impurity

7.       Majority carriers: ELECTRONS

8.       Minority carriers: HOLES

Conductor

Semiconductor

N type semiconductor

1) The atomic theory can help us in a way to understand how electronic devices work, especially p-n junction components

2) In atomic theory, it explains how to differentiate elements that are metal, non-metal, and semi

3) Conductor element has overlapping band which makes electron to be freely move between two points without any sort of high energy

4) Insulator have a big gap that makes electron to move by a specific point of energy

5) Semiconductor which used in electronics component have a small gap between bands that makes electron to move freely just by low heat or energy

1) An atom is made up of three kinds of particles which are protons, neutrons, and electrons

2) Electrons carry a negative charge and the protons carry a positive charge

3) The number of protons=number of electrons

4) The protons and the neutrons will be located at the nucleus and electron will be around the nucleus

5) Valence electrons are the electrons that located in the outermost shell of an atom

Conductor is a substance that allows the flow of electric through it. In electrical conductor, electrons move freely from atom to atom with the existence of voltage. Conductivity is the capacity to transfer electricity and heat. An object made of a conducting material will allow charge to be transferred across the entire surface of the object. The distribution of charge is the result of electron movement. Since conductors allow for electrons to be transported from particle to particle, a charged object will always distribute its charge until the overall repulsive forces between excess electrons is minimized. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. 

Meanwhile, semiconductor allows the flow of electron but in some cases, it cannot be done because it depends on the condition. Silicon and germanium are some of the examples of semiconductor materials. In a semiconductor, both electrons and holes electron absences act as charge carriers. The properties of a semiconductor depend on the impurities or dopants that are added to it. An N-type semiconductor carries current in the form of negatively-charged electrons. A P-type semiconductor carries current predominantly as electron deficiencies called holes. A hole has a positive electric charge, equal and opposite to the charge on an electron.

N-type Semiconductor are formed when a small amount of Pentavalent impurity is added to a pure semiconductor providing many of free electrons in it. The conduction in a n-type semiconductor are caused by the free electrons denoted by the pentavalent impurity atoms. These electrons are the excess of free electrons with regards to the number of free electrons required to fill the covalent bonds in the semiconductors. The addition of Pentavalent impurities such as phosphorus provides some of the free electrons in the semiconductor crystal. Such impurities which produce n-type semiconductors are known as Donor Impurities. They are called a donor impurity because each atom of them donates one free electron.

The extrinsic p-Type Semiconductor is formed when a trivalent impurity is added to a pure semiconductor in a small amount and resulting a large number of holes in it. A large number of holes are provided in the semiconductor material by the addition of trivalent impurities like Gallium and Indium. Such type of impurities which produces p-type semiconductor are known as an Acceptor Impurities because each atom of them create one hole which can accept one electron. A trivalent impurity like gallium, having three valence electrons is added to germanium crystal in a small amount. Each atom of the impurity fits in the germanium crystal in such a way that its three valence electrons form covalent bonds with the three surrounding germanium atoms.

 

2.      Atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and typically a similar number of neutrons. Protons and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, that atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion.

 

A valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair. The presence of valence electrons can determine the element's chemical properties, such as its valence—whether it may bond with other elements and, if so, how readily and with how many. For a main group element, a valence electron can exist only in the outermost electron shell; in a transition metal, a valence electron can also be in an inner shell.

 

 

3.      Conductors are materials that conduct electricity easily. Very little electric force is required to cause electron flow in conductors. This is due to electrons called "free electrons", which exist in the atoms of conductors. "Free electrons" are electrons that are very weakly bonded to the atom. With very little force, they can be traded to other atoms, or flow to create electricity. 

 

Semi-conductors are insulators that lack commitment. The atoms of a semi-conductor have no free electrons; however, they do have an electron that is bonded rather loosely and can be shared with the application of a moderate electric force. Semi-conductors can conduct electricity at a certain level without being damaged; however, semi-conductors can be damaged with too much electric force.

 

4.      P-type semiconductor is when the trivalent impurity is added to an intrinsic or pure semiconductor (silicon or germanium). Trivalent impurities such as Boron (B), Gallium (G), Indium(In), Aluminium(Al) are called acceptor impurity. Consider trivalent impurity boron added to silicon. Boron atom has three valence electrons and silicon has four valence electrons. In the fourth covalent bond, only silicon atom contributes one valence electron, while the boron atom has no valence electron to contribute. Thus, the fourth covalent bond is incomplete with shortage of one electron. This missing electron is called hole. This shows each boron atom accept one electron to fill the hole. Therefore, all the trivalent impurities are called acceptors. A small addition of impurity (boron) provides millions of holes.

 

N-type semiconductor is when pentavalent impurity is added to an intrinsic or pure semiconductor (silicon or germanium). Pentavalent impurities such as phosphorus, arsenic, antimony are called donor impurity.  Consider pentavalent impurity phosphorus is added to silicon. Phosphorus atom has 5 valence electrons and silicon has 4 valence electrons. Phosphorus atom has one excess valence electron than silicon. The four valence electrons of each phosphorus atom form 4 covalent bonds with the 4 neighboring silicon atoms. The fifth valence electron of the phosphorus atom cannot able to form the covalent bond with the silicon atom because silicon atom does not have the fifth valence electron to form the covalent bond. Thus, fifth valence electron of phosphorus atom does not involve in the formation of covalent bonds. Hence, it is free to move and not attached to the parent atom. This shows that each phosphorus atom donates one free electron. Therefore, all the pentavalent impurities are called donors. The number of free electrons are depends on the amount of impurity (phosphorus) added to the silicon. A small addition of impurity (phosphorus) generates millions of free electrons.

The dopants are positively charged by the loss of negative charge carriers and are built into the lattice, only the negative electrons can move. Doped semimetals whose conductivity is based on free (negative) electrons are n-type or n-doped. Due to the higher number of free electrons those are also named as majority charge carriers, while free mobile holes are named as the minority charge carriers.

4. P-type

N-type

We need to study about atomic bahavior in semiconductor before discussing the p-n junction and electronic devices. It is because to illustrate us briefly on how the movement of electron and proton can affect the conductivity of a material. It is to ensure that we understand on the structure of atomic model. We can find that the electrons are orbiting the nucleus ,the farther the electron from the centre the highest their energy. From that, we can made the calculation and estimation of energy required to create semiconductor.

Muhammad Aizul Azim bin Azham

1725809

The reason why we need to discuss the atomic theory before learning about the p-n junction and electronic devices because in atomic theory we learn the structure of atoms and how they works as the p-n junction is one of its application. P-n semiconductor make use of the variation in atomic world such as the valence electron. Therefore we need to know which elements that can donate receive or share electrons to make the semiconductor works.

Discussion 2

Atom is the matter in every existing element which consist of three particle which is nucleus, electron and proton. Electron is the smallest particle that are negatively charged while proton the larger particle than electron are positively charged.

Valence electrons are the electrons that located in the outermost shell of an atom. It plays an important role in bond forming with another atoms. They either receive, donor or hare the electrons. Based on octet rule, an atom needs 8 valence electrons to achieve stable state.

Discussion 3

Conductors are materials that easily conduct electricity and only small amount of forces are needed to cause the electron moving. This happen due to the abundant of free electrons in conductor. The presence of free electrons allows the current to flow. Copper, silver and gold are example of good conductor.

Semiconductor is a conductor which conductivity depends on the environment. Semiconductor can be either insulator or conductor. Semiconductors have enabled electronic to become smaller, faster and reliable. It conductivity can be change due to the atom in it has 4 valence electrons. An atom such as silicon has 4 valence electrons and 4 holes. Thus, combination of these atom can produce a semiconductor. The 4 valence electrons remain in their shell unless there is external forces to break the nucleus bond and push them into the holes that are provide by another atom.

Discussion 4

p-type semiconductors that have more holes than electrons. To make this type of semiconductor, element such as boron that has 3 valence electrons need to be pure semiconductor. The 3 valence electrons from Boron created bond with the silicon valence electrons and left one as a hole.

n-type semiconductors that have more electrons than holes, to make this type of semiconductors, element such as phosphorus that has 5 valence electrons. The 4 electrons have been pair up with pure semiconductor. Thus left one electron that are freely moving around. 

 

Semiconductor are solids whose conductivity lies between the conductivity of conductors and insulators. The atoms contain no free electrons, however they do have an electron that is bonded rather loosely and can be shared with the application of a moderate electric force. Semiconductors can conduct electricity at a certain level without being damaged. Semiconductor operates depend on the temperature. However, it can be damaged with too much electric force. Most common semiconductor is silicon.

Discussion 4
P-type semiconductor

N type semiconductor