N Type And P Type Semiconductors Pdf

n type and p type semiconductors pdf

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A semiconductor which is pure and contains no impurity is known as an intrinsic semiconductor. In an intrinsic semiconductor, the number of free electrons and holes are equal. Common examples of intrinsic semiconductors are pure germanium and silicon.

There are two general categories of semiconductors: intrinsic semiconductors, which are composed of only one material, and extrinsic semiconductors, which have had other substances added to them to alter their properties. In semiconductor production, the process of creating extrinsic semiconductors by adding substances to a pure semiconductor for the purposes of modulating its electrical properties is known as doping. Semiconductors are doped to generate either a surplus or a deficiency in valence electrons. Electrons in free atoms have discrete energy values. The highest energy band contains valence electrons available for chemical reactions.

Electrons and “holes’’

A semiconductor which is pure and contains no impurity is known as an intrinsic semiconductor. In an intrinsic semiconductor, the number of free electrons and holes are equal. Common examples of intrinsic semiconductors are pure germanium and silicon.

Schematic band diagram of an intrinsic semiconductor at room temperature is represented. Fig, Energy band diagram of an intrinsic semiconductor. An extrinsic semiconductor is one in which an impurity with a valency higher or lower than the valency of the pure semi conductoris added, so as to increase the electrical conductivity of the semiconductor.

Depending upon the type of impurity atoms added, an extrinsic semiconductor can be classified as N-type or P-type. When a small amount of pentavalent impurity such as arsenic is added to a pure germanium semiconductor crystal, the resulting crystal is called N-type semiconductor. Fig a shows the crystal structure obtained when pentavalent arsenic impurity is added with pure germanium crystal.

The four valence electrons of arsenic atom form covalent bonds with electrons of neighbouring four germanium atoms.

The fifth electron of arsenic atom is loosely bound. This electron can move about almost as freely as an electron in a conductor and hence it will be the carrier of current. In the energy band picture, the energy state corresponding to the fifth valence electron is in the forbidden gap and lies slightly below the conduction band Fig b. This level is known as the donor level.

When the fifth valence electron is transferred to the conduction band, the arsenic atom becomes positively charged immobile ion. Each impurity atom donates one free electron to the semiconductor.

These impurity atoms are called donors. In N-type semiconductor material, the number of electrons increases, compared to the available number of charge carriers in the intrinsic semiconductor. This is because, the available larger number of electrons increases the rate of recombination of electrons with holes. Hence, in N-type semiconductor, free electrons are the majority charge carriers and holes are the minority charge carriers.

When a small amount of trivalent impurity such as indium, boron or gallium is added to a pure semiconductor crystal, the resulting semiconductor crystal is called P-type semiconductor. Fig a shows the crystal structure obtained, when trivalent boron impurity is added with pure germanium crystal. The three valence electrons of the boron atom form covalent bonds with valence electrons of three neighbourhood germanium atoms.

In the fourth covalent bond, only one valence electron is available from germanium atom and there is deficiency of one electron which is called as a hole. Hence for each boron atom added, one hole is created. Since the holes can accept electrons from neighbourhood, the impurity is called acceptor. The hole, may be filled by the electron from a neighbouring atom, creating a hole in that position from where the electron moves.

This process continues and the hole moves about in a random manner due to thermal effects. Since the hole is associated with a positive charge moving from one position to another, this is called as P-type semiconductor.

In the P-type semiconductor, the acceptor impurity produces an energy level just above the valence band. Fig b. Since, the energy difference between acceptor energy level and the valence band is much smaller, electrons from the valence band can easily jump into the acceptor level by thermal agitation.

In P-type semiconductors, holes are the majority charge carriers and free electrons are the minority charge carriers. PDF Download. Please enter your name here You have entered an incorrect email address! Please enter your email address here Save my name, email, and website in this browser for the next time I comment.

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The Doping of Semiconductors

Doping means the introduction of impurities into a semiconductor crystal to the defined modification of conductivity. Other materials are aluminum, indium 3-valent and arsenic, antimony 5-valent. The dopant is integrated into the lattice structure of the semiconductor crystal, the number of outer electrons define the type of doping. Elements with 3 valence electrons are used for p-type doping, 5-valued elements for n-doping. The conductivity of a deliberately contaminated silicon crystal can be increased by a factor of 10 6. The 5-valent dopant has an outer electron more than the silicon atoms.


N and P-type Semiconductors. Neither pure silicon(Si) nor germanium(Ge) are great conductors. They form a crystal lattice by having each atom share all of its 4​.


I. P-Type, N-Type Semiconductors

An extrinsic semiconductor is one that has been doped ; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it different electrical properties than the pure semiconductor crystal, which is called an intrinsic semiconductor. In an extrinsic semiconductor it is these foreign dopant atoms in the crystal lattice that mainly provide the charge carriers which carry electric current through the crystal. The doping agents used are of two types, resulting in two types of extrinsic semiconductor. An electron donor dopant is an atom which, when incorporated in the crystal, releases a mobile conduction electron into the crystal lattice.

A semiconductor which is pure and contains no impurity is known as an intrinsic semiconductor. In an intrinsic semiconductor, the number of free electrons and holes are equal. Common examples of intrinsic semiconductors are pure germanium and silicon. Schematic band diagram of an intrinsic semiconductor at room temperature is represented. Fig, Energy band diagram of an intrinsic semiconductor.

Difference Between p Type and n Type Semiconductor

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The various factors like doping element, nature of doping element, the majority and minority carriers in the p-type and n-type semiconductor. The density of electrons and holes, energy level and Fermi level, the direction of movement of majority carriers, etc. The difference between a p-type semiconductor and an n-type semiconductor is given below in the tabulated form. The p-type semiconductor is formed when the Trivalent impurity is added to the pure semiconductor. Similarly, when a Pentavalent impurity is added to the pure semiconductor n-type semiconductor is obtained. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.

In this tutorial, we will learn about an introduction to semiconductors as they are an essential part of Electronics. Before understanding several devices like Semiconductor Diodes, Transistors, etc. This part of the tutorial will lay out a key foundation in easily learning the PN Junction, which is next in line. There are two types of semiconductor components in electronic and electrical circuits. They are active and passive components. Diodes are the foremost active components and resistors are the foremost passive components in electronic design circuits.

Pure semiconductors are relatively good insulators as compared with metals, though not nearly as good as a true insulator like glass. To be useful in semiconductor applications, the intrinsic semiconductor pure undoped semiconductor must have no more than one impurity atom in 10 billion semiconductor atoms. This is analogous to a grain of salt impurity in a railroad boxcar of sugar. Impure, or dirty semiconductors are considerably more conductive, though not as good as metals. Why might this be?

Intrinsic and extrinsic N-type & p-type Semi Conductors

The process of purposefully adding impurities to materials is called doping; semiconductors with impurities are referred to as "doped semiconductors". In a pure intrinsic Si or Ge semiconductor, each nucleus uses its four valence electrons to form four covalent bonds with its neighbors see figure below. Since there are no excess electrons or holes In this case, the number of electrons and holes present at any given time will always be equal. An intrinsic semiconductor. 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.

The addition of a small percentage of foreign atoms in the regular crystal lattice of silicon or germanium produces dramatic changes in their electrical properties, producing n-type and p-type semiconductors.

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