Hello friends! Welcome back to ElectroDuino. This blog is based on Semiconductor Material. Here we will discuss what is a Semiconductor Material, Property, Types, Examples, Advantages, Disadvantages and Application.
What Is a Semiconductor Material?
A semiconductor is one type of substance or material, whose resistivity lies between conductors and insulators (non-conductors). It means that the electrical conductivity of semiconductors is not as good as the conductor materials, but not as bad as insulators materials (that’s why their name “semi-conductor”). These materials have very few “free electrons” because their atoms are closely grouped together by the valence electrons in a crystalline pattern, it’s called a “crystal lattice”. But under special conditions, these valence electrons are able to flow. The Semiconductor materials can be pure elements, such as silicon (Si) and germanium (Ge), or compounds such as Gallium Arsenide (GaAs), Cadmium Sulfide (CdS), Gallium Nitride (GaN), and Gallium Arsenide Phosphide (GaAsP). Silicon is most widely used in the electronics industry.
Properties of semiconductor material
- Semiconductor’s resistivity is less than insulators and more than conductors.
- The resistance in semiconductors increases with the decrease in temperature and resistance decreases with the increase in temperature, because it has negative temperature co-efficient.
- The current Conductivity properties of a Semiconductor change, when a suitable metallic impurity (Arsenic, Phosphorus, Boron, Gallium) is added to it.
- Current flow in a semiconductor due to electrons and holes
Holes and Electrons in Semiconductors
Semiconductor materials have two charge carriers, these are free electrons and holes, which responsible for the flow of current in semiconductors. Electrons are the negatively charged particles and the hole represents a missing electron, it can be considered as a unit positive charge. But both electrons and holes are equal in magnitude.
We know that in the atomic structure the outermost shell has the valence electrons which are loosely attached to the nucleus. The atom has valence electrons, when another atom comes close to it, then the valence electrons of both these atoms combine to create “Electron pairs”. This bonding is not so much strong and hence it is a Covalent bond.
For example, a Silicon Atom has 14 electrons. In its atomic structure, the first orbit has 2 electrons, 8 in the second orbit, and 4 in the last orbit. These 4 electrons are valence electrons of the silicon atom. These valence electrons tend to combine with the valence electrons of closest atoms and form the electron pairs.
Creation of Hole
When sufficient thermal energy supplied to the crystal, then some valence electrons tend to move from the valence band to the conduction band and break the covalent bonds. As a result, free electrons are produced which wander randomly. But when valence electrons moved away to the conduction band, then they create an empty space or valence in the valence band. The moved away electrons create empty spaces or valences behind, these are called holes. The number of holes is equal to the number of free electrons.
Types of Semiconductors Material
There are two types of semiconductors, the first one is Intrinsic Semiconductor or Pure Semiconductor and another one is extrinsic semiconductor or Impure Semiconductor. The following block diagram shows the classification of semiconductors.
The extremely pure form of the semiconductor material is known as the intrinsic type semiconductor material. These types of semiconductor material is also known as an undoped semiconductor or i-type semiconductors, because Intrinsic Semiconductor is made of only a single type of element.
The most common intrinsic semiconductor metarial are Germanium (Ge) and Silicon (Si). They both have 4 valence electrons in valence band of atomic structure. Valence electrons are bound to the atom by covalent bond at absolute zero temperature. When the temperature increase, due to collisions, few valence electrons are unbounded and they jump from the valence band to the conduction band. As a result, few free electrons are produced. These electrons are creating an absence/ vacancy in the valence band, these are holes. So in the intrinsic semiconductor material, the number of free electrons is equal to the number of holes; n = p. These free electrons and holes are the cause of the conduction of electricity in the semiconductor.
The properties of pure semiconductor
- After gaining thermal energy they created electrons and holes.
- The number of free electrons is equal to the number of holes.
- At absolute zero Kelvin temperature, it has no free electrons so it acts as a perfect insulator.
- When the temperature is increasing in few valence electrons jump into the conduction band and it behaves like a poor conductor.
An extrinsic semiconductor is made by adding a small amount of impurity atom to the intrinsic semiconductor material. In this way, the conductivity of semiconductors can be greatly improved. The process of adding impurity atoms to the intrinsic or pure semiconductor is called DOPING and the impurity atom is called Dopant. An impurity atom from a different periodic table group is used for ‘doping’ which has more or less electrons in the valence band than the semiconductor atom itself. For this reason, creates either an excess or shortage of electrons in the atomic structure. In this way, the extrinsic semiconductor can be classified into two types: N-type extrinsic Semiconductor, P-type extrinsic Semiconductor
N-type Extrinsic Semiconductor
When an intrinsic or pure semiconductor (like, Silicon or Germanium) is doped by a small amount of pentavalent (Arsenic, Phosphorus, Antimony) impurity, it is known as an N-Type extrinsic semiconductor. This pentavalent impurity (P, As or Sb) has five valence electrons, four valence electrons among them are create bonds with the four electrons of the intrinsic Semiconductor (Ge or Si). So, the fifth electron of the dopant remains as a free electron. Thus, this free electron for conduction in the lattice. Pentavalent impurities are known as donor impurities because it shares a free electron with the semiconductor. The number of free electrons increases in this extrinsic semiconductor, so the negative charge carriers are also increased. That’s why its name is n-type semiconductor. Under the influence of a potential difference, the free electrons overall movement in one direction, for this reason an electric current flows. In an n-type Extrinsic Semiconductor, electrons are the MAJORITY CARRIERS and holes are the MINORITY CARRIERS.
For example, an Arsenic (As) atom has five valence electrons and a germanium (Ge) atom has four valence electrons. When the “As” atom is added to the “Ge” atom, four out of the five valence electrons get attached with the “Ge” atoms and one electron remains as a free electron.
- P-type Extrinsic Semiconductor
When an intrinsic or pure semiconductor (like, Silicon or Germanium) is doped by a small amount of trivalent (Boron (B), Gallium (G), Indium(In), Aluminium(Al)) impurity, it is known as an P-Type extrinsic semiconductor. This trivalent impurity (P, As or Sb) has three valence electrons, these three valence electrons among them are create bonds with the four electrons of the intrinsic Semiconductor (Ge or Si). But there is a shortage of electrons in the impurity. So a vacancy/absence creates in the crystal lattice, it is a “Hole“. These impurity atoms which are ready to accept bonded electrons are called “Acceptors“. Holes are the positive charge carriers, when the number of impurities increases then the number of holes are also increased. That’s why it’s named P-type semiconductor. Electrons of intrinsic Semiconductor may move from one empty position (vacancy/absence) to another and in this case, it can be considered that the holes are moving. Under the influence of a potential difference, the holes can be seen to flow in one direction, for this reason an electric current flows. In a p-type Extrinsic Semiconductor, holes are the MAJORITY CARRIERS and electrons are the MINORITY CARRIERS.
Difference Between N-type and p-type Semiconductors
|N-type Semiconductors||P-type Semiconductors|
|In the N-type semiconductor group-V element of the periodic table is added as a doping element.||In the P-type semiconductor group-III element of the periodic table is added as a doping element.|
|Pentavalent impurities are added in N-type.||Trivalent impurities are added in P-type.|
|In this case electrons are majority carriers||In this case holes are majority carriers|
|Its minority carriers are Holes||Its minority carriers are Electrons|
|The electron density is greater than the hole density.||The hole density is greater than the electron density.|
|The donor energy level is close to the valence band and absent from the conduction band.||The acceptor energy level is close to the valence band and absent from the conduction band.|
Difference Between Intrinsic and Extrinsic Semiconductor Material
|Intrinsic Semiconductor||Extrinsic Semiconductor|
|Pure or undoped semiconductor||Impure or doped semiconductor|
|Number of electrons is equal to the number of holes||Number of electrons is not equal to the number of holes|
|Its Electrical conductivity is poor||Its Electrical conductivity is good|
|Its Electrical conductivity is dependent on temperature only||Its conductivity does not depend only on temperature as well as on the amount of impurity.|
|No impurities are added||Trivalent impurity or pentavalent impurity are added|
Advantages of a semiconductor
- Cheaper as compared to vacuum tubes
- Small size and lighter weight
- These have Long life
- Less power consumption
- It can be operated at low voltage
- These are Shock-proof
- semiconductor devices are not required warm-up time
- Good power efficiency
- they does not produce any current in the absence of applied voltage.
Disadvantages of a semiconductor
- They cannot tolerate high power input
- It cannot tolerate high reverse voltage
- poor response
Application of Semiconductor Material
Semiconductors are take important role in electronics industry to manufacture electronics components. These are used in almost all electronic devices. Diode, Light Emitting Diode (LED), DIAC, Transistor, TRIAC, Thyristor, microchips, etc. are the important electronic components which is made by semiconductor.