Insulators, Conductors and Semiconductors

Energy Band Gap

determines the energy needed to allow electrons to move from the valence band to the conduction band the larger the band gap, the larger energy is needed for electrons to move

Crystalline Structure

when silicon attain stability by combining with other silicon, it forms a crystalline structure this crystalline structure has unique properties

N- Type Material

when a pentavalent element is doped in a pure semiconductor material, say we used arsenic, some of the existing atoms in the material is this place with arsenic atoms. we know that an arsenic atom has five valence electrons, and atoms in the crystal only needs to share 4 valence electrons, a free electron is added to the material. adding more impurities than results in more free electrons by analyzing what happened, the impurity added, in this case the arsenic, becomes a donor atom, because it gives an extra electron in the material. knowing this, the number of electrons in the material becomes greater as compared to the holes. this means that in this material, electrons become the majority carriers and the holes are the minority carriers.

Insulators in a Circuit

when an insulator of electricity is connected to a circuit, there is a closed circuit thus, electricity will not flow through the bulb, preventing it from lighting up

Valence Electrons

which service charge carriers, are located in the valence band, in the ground state the conduction band is occupied with no electrons. between the two energy bands there is a band gap, it's width affects the conductivity of materials

Conductors

high electrical conductivity low electrical resistivity

Bohr's Atomic Model of Silicon

there are four electrons in the third energy level

Trivalent Elements

these are atoms with three valence electrons examples are indium gallium

Active Material

unstable materials such as silicon

Doping

using pure semiconductors such as silicon crystals seems easy, however, upon observation of scientists, it is found that the electrical conductivity of the semiconductors by introducing impurities.

Insulators

very low to almost zero electrical conductivity high electrical resistivity

Valence / Valency of an Atom or Element

determines its ability to gain or lose electrons which is a factor in changing its electrical and chemical properties

Valence Electrons

electrons on the outermost energy level of an atom

N-Type and P-Type

essential in producing semiconductor components

Keypoints

a material which exhibits a very high electrical resistivity resulting to impended flow of electricity is considered an insulator a material with very low electrical resistivity is considered a good conductor

Keypoints

a material which exhibits high electrical conductivity is considered as a conductor a material with very low to almost zero electrical conductivity is considered an insulator testing the conductivity of a material also leads to classification of conductors

Stability of An Atom

an atom needs to have eight valence electrons in order to be stable

Examples of Semi-conductors

germanium silicon gallium arsenide silicon carbide

Insulator

has a wide band gap this gap prevents electrons from moving between the valence band and the conduction band. in a sense, we can also say that its electrons are not evenly distributed in the material

Keypoints

at room temperature, pure silicon crystals are poor conductors and behave like insulators

Pentavalent Elements

atoms with 5 valence electrons examples are arsenic and antimony

Semiconductors

basic components of electronic equipment its primary function is controlling voltage and current to produce a desired result

Nucleus

center of an atom wherein protons and neutrons are found

Energy Band Structure

is an energy schema to describe the conductivity of conductors, insulators and semiconductors. This schema consists of two energy bands (valence and conduction band) and the band gap

Resistivity

is the measure of how much a material resists carrying an electrical current

Conductivity/ Electrical Conductivity

is the measure of the ease at which an electric charge or heat can pass through a material

When an electron breaks the covalent bond, two things happen:

it becomes a free electron and thus become a carrier of a small amount of electrical current if an electrical voltage is applied it leaves a hole, or a space in the valence orbit of a silicon atom. When this happens, the atomic structure of the crystal is disrupted because nearby electrons will try to fill up the hole and thus break their own covalent bond to form a new one. the cycle goes on unless the applied voltage is removed

Conductors in a Circuit

when a conductor of electricity is connected to a circuit, there is a closed circuit thus, electricity flows through the bulb, allowing it to light up

Electrical Conductors

materials that allow electricity to pass through them typically have positive temperature coefficient

Electrical Insulators

materials that do not allow electricity to pass through them typically have negative temperature coefficients

Positive Temperature Coefficient

means that as the temperature increases, is resistance increases

Negative Temperature Coefficient

means that as the temperature increases, its resistance decreases

Examples of Conductor

metals, salt solution, carbon (graphite)

Silicon

most commonly used semiconductor material

Properties of Semi-conductors

negative temperature coefficient - this means that as the temperature increases its resistance decreases the resistance of a silicon crystal is cut in half for every six degrees celsius of rise in temperature if heat energy is applied to the crystal, some electrons absorb the energy and breaks the covalent bond. This allows the crystals to support current flow

P- Type Material

on the other hand, if we doped a trivalent element in a pure semiconductor material, say for example indium, we are actually adding additional holes in the material. considering the fact that atoms in the material will have to combine with the impurity by forming covalent bonds, five electrons will be needed to be shared to the indium instead the four. by looking at this scenario, the trivalent atom, indium accept electrons therefore they are called acceptor atoms. the material produced by doping trivalent atoms into a pure semiconductor is called p-type material. having more holes means that the material has holes as majority carriers and electrons as the minority carriers

Energy Level

orbit like structure and has shells that holds the electrons

Valence Shell

outer orbit

Classification of Conductors

poor conductors good conductors

Covalent Bonding

process of sharing valence electrons

Intrinsic Semi-conductors

pure semiconductors

Extrinsic Semiconductors

semiconductors produced by adding impurities

Silicon Stability

silicon have 4 valence electrons does it needs to gain additional four electrons to be stable however, silicon atoms are able to gain stability by sharing valence electrons in a process called covalent bonding

Semiconductors

the band gap is small and that a conduction band and valence band is closed but is not touching

Conductors

the conduction band and valence band is touching, or in some other sources its overlapping. this does not necessary indicate that the material does not have an energy band gap, however even if an energy band gap exists it is negligible. the electrons are evenly distributed in the material

Keypoints

the energy band gap of an insulator is too large making it hard for electrons to move from the valence band to the conduction band the energy band gap of a semiconductor is a small, this also means that a small energy is needed for electrons to move between the energy bands the energy band gap of a conductor is virtually non-existent, therefore electrons may freely move between the energy bands with the very small energy the distribution of electrons in each material affects its electrical properties