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SEMICONDUCTORS: The Beginning of Electronic Devices

The field of Electronics is a branch of Physics that deals with flow of electrons in electronics devices around the electrical circuit.

Anything around us is consist of many of the reference about matter are defined as anything that occupies space and has a mass. Inside the matter, there is a molecule and there are different types of matter, there are Solid, Liquid and Gas.  When we say solid, it is compressed, in molecules in liquid is occupying the space of the container and gas is further apart from each other. Now today, there is a new discovered type of matters. The existence of plasma was first discovered by Sir William Crookes in 1879 using an assembly that is today known as a “Crookes tube”, an experimental electrical discharge tube in which air is ionized by the application of a high voltage through a voltage coil. (Universetoday.com)

Matter cannot be destroyed and created /so it can be change by Physical and Chemical.  By ­ word Physical, it occur the physical characteristics of an elements, it changes the form of physical substance, deforming its original state. Chemical change is made by chemicals changing its composition, it creates a new substance. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions.

Atom is the smallest particle of a matter.  Atom is derived from the Greek word “Atomos” which means “uncuttable”.  Inside the atom, it consists of three (3) particles, the Neutron, Electron and Proton.

3 Particles of Atom:

1. Electron– It is discovered by a British Physicist Sir Joseph Thompson on April 30, 1897. It is a negative charge particle and has a charge of -1.6x10-19 and has a mass of 9.1x1031kg. (http://en.wikipedia.org/wiki/J._J._Thomson)

2. Proton– it is discovered by British Physicist Ernest Rutherford at the Cavendish Laboratory in Cambridge, England. It is a positive electric charge of 1.6x10-19 and has a mass of 1.6727x1027kg

3. Neutron– It was discovered by an English Physicist Sir James Chadwick on 1932. It has no charge. (http://en.wikipedia.org/wiki/James_Chadwick)

Murray Gell-Mann and George Zweig (Physicist) was discovered “Quarks” that is a new particles of neutron and protons. Quarks are fundamental particles that make up everything in the universe. ( http://curiosity.discovery.com/question/who-discovered-quarks)

What is the heaviest particle?

Mass of proton 1, 836 times which of electron and the mass of neutron is slightly heavier that of proton (1,839times the mass of electron).

Atomic number

Is equal to the number of protons in the nucleus, which is the same as the number of electron in an electrical valance (neutral) atom.

Atomic Mass

Is the sum of the number of protons and neutrons of an atom. The maximum number of electrons can occupy in every shell or orbit of an atom is determined by:

N(e)=2n2

Where : N(e) = maximum number of electrons in each shell

N = shell number or position


Atomic Numbers and Common Elements

Copper = +29                        

Silicon = +14

Germanium = +32

Valence Electrons

Is the outermost shell electrons that is located at the outermost shell is called the Valence electrons.

Free Electrons

The free electron is one that has acquired enough energy band break away from the valence band of an atom.

Ionization

Is the process of removal or addition of electrons from or two neutral atom that is resulting atom called Ion, has net positive charge called “cat Ion”(losing of valence electrons), negative charge called “un-Ion”(gaining of valence electron).

A matter can be classified to its conductivity (conductor, inductor, semiconductor, and insulator).

1. Conductor– a material that can conduct electrical currents and it has one valence electron. Most metals are good on conductor, silver, copper, gold (highest conductivity and it is used in connecting a connections in constructing a semiconductor materials), aluminum.

2. Insulators– is material that not conduct electrical current under a normal condition, the valence electrons of insulators are with more than 4 but ideally it has an 8 valence electrons. Rubber, Mica, Plastics, glass and quarts are some examples of insulators.

3. Semiconductors– is has an ability of both conductors, allow easily conduct electrical current, and insulators, does not conduct electrical current and it has four (4) valence electron. The most common used single element semiconductors are silicon, germanium, and carbon. Compound semiconductors commonly used such as Gallium arsenate and Indium Phosphide.

Energy gap

The difference between the valence band and conduction band is called energy gap. It is the amount of energy that a valence electrons in order to move from the valence band into conduction band.

Energy required dislodging an atom from its nucleus:

>  Insulator : Eg > 5eV

Semiconductors: For Si: Eg = 1.1 eV

For Ge : Eg = 0.67 eV

> Conductor : Eg = 0

Note: ELECTRON-VOLT (eV) is unit of energy.

1 eV = 1.6x10^-19 joules

Net Charge

Whenever neutral atom losses one or more of its electron/s, it becomes a positive charge atom and it referred to as a positive ion. If the neutral gains electron/s, it becomes negatively charge and is called a negative ion.

Therefore Net Charge

= +4 if it losses all four (4) valence electrons

= +1 if it losses one (1) valence electrons


Bonding of Atoms:

1. Ionic/ Electrovalent / Electrostatic Bonding:

 -Refers to the bonding resulting from the attractive forces of oppositely charged ions (positive and negative).

2. Metallic Bonding:

 -Refers to the type of bonding that is a product of the attractive forces of group of positive ions and electrons that are generally free to move about among its ions. 

3. Covalent Bonding:

 -is when atoms of materials share electrons with another atom. The shared electrons are attracted simultaneously to                   the two atoms resulting to a force that binds them together.

Important Terms:

1. Bound Electrons– the term for eight (8) valence electrons because they are tightly held by the atoms. When an atom has bound electrons, it is described as filled or saturated since valence orbit can hold not more than eight (8) electrons.

2. Free Electrons – the released electron dislodged from its original shell due to increase in temperature which joins into a larger orbit.

3. Hole– the term used to refer to the vacancy left by free electrons when departs from its original shell and usually behaves like a positive charge since it can attract and capture electron in the immediate vicinity.

4. Recombination– the merging of a free electron and a hole inside the silicon lattice.

5. Lifetime– the amount of time between the creations and disappearance of a free electron.

Two Types of Semiconductors:

1. Intrinsic – is a pure semiconductor, every atom in the lattice is a silicon atom.

2. Extrinsic– a doped semiconductor. It is the result of adding an impurity atom to an intrinsic lattice to alter/ increase its electrical conductivity.

Doping is the process of adding pentavalent or trivalent impurities to an intrinsic material in order to increase the conductivity of the semiconductor material.

Two types of Impurities:

1. Pentavalent atom – with five valence electron (donor atom) such as antimony (SB), arsenic (As) and phosphorus (P).

2. Trivalent atom – with three valence electrons (acceptor atom) such as boron (b), Gallium (Ga) and Indium (In).

Extrinsic Semiconductor can be:

1. N type – produced when a pentavalent atom are added to the molten silicon, producing an excess electrons. The majority carrier in this type is electrons and the minority carriers is holes

2. P type – produced when a trivalent atom are added to the molten silicon, producing an excess holes. The majority carriers in this type is holes and the minority carriers is electrons.

 

(SEMICONDUCTORS: The Beginning of Electronic Devices by RS LAGRIMAS)

Reference: Electronic Device by Thomas Floyd, Excel Review Center Review Material.


 

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