14-11-2012, 02:20 PM
Properties of Crystals, Semiconductors, PN Junction (Pg 407)
[attachment=39429]
Objective
At he end of the lesson student will:
Be familiar with the atomic structure of electrical material
Describe semi conductor material and thir behavior
Describe n-type and p-type material
Familiar with construction of diode
Semi Conductor Material
All materials can be classified (electrically) into three categories:
Conductors.
Insulators.
Semiconductors
Conductorseasily allow current to pass through them.
Insulatorsdo notallow current to pass through them.
Semiconductorsare a group of material that posses the property of neither insulator nor good conductor, but somewhere in between Example of semiconductors are silicon(Si) and germanium (Ge).
Pure semiconductors are poor conductors, because the low number of free electrons. However, the resistivity can be reduced (so that it conducts more current) by putting in impurities into the pure semiconductors. The process of introducing a small amount of impurities (during manufacturing) into the semiconductors is called doping.
Types of semiconductors
Silicon And Germanium are the most important semiconductors used in the electronics industry
As the temperature of these materials is raised above room temperature, the resistivity is reduced and ultimately a point is reached where they effectively become conductors
As the temperature of a semiconductor is reduced below normal room temperature, the resistivity increases until, at very low temperatures the semiconductor becomes an insulator
A semiconductor normally are in the form of a crystal.
Properties Of Crystals
The structure of a solid substance have symmetric & non-symmetric arrangement of its atoms or molecules. Non-symmetric is termed amorphous.
In some crystalline substances, the imperfections in the molecular structure will confer additional properties on the material -luminescence, chemical or electrical effects.
Semiconductors are crystals of substances which exhibit electrical properties due to imperfections in their molecular structure.
Intrinsic Conduction
Although intrinsic conduction is taking place within the structure of the semiconductor crystal, there is overall electrical equilibrium, i.e. at all times there will be as many free electrons as there are holes.
Intrinsic conduction, because of its randomness, is not a useful property in a semiconductor crystal.
Two materials commonly used as semiconductor crystal are silicon and germanium.
A crystal of silicon is usually preferred as it has a lower level of intrinsic conduction.
Passive Components
Components in an electrical circuit which do not of themselves act to change or modify circuit conditions are termed ‘passive’.
Examples of ‘passive’ components, resistors, thermostats, inductors, capacitors, quartz crystal, silicon temperature sensors.
Quartz crystals are used in the form of a thin plate in resonant circuits and such circuits are used to produce oscillation.
Doping
The introduction of controlled quantities of impuritiesinto a semiconductors crystal when it is being formed can produce a crystal latticewith a predominance of electrons or holes.
The introduction of impurities into a semiconductors crystal (usually about one part in 1010parts) is termed ‘doping’.
The materials used for doping are selected so that their atoms will be combined into the crystal lattice without distortingit and that the required predominance of either electrons or holes is obtained.
N-type & P-type Materials
Adding extremely small amounts of impurities to pure semiconductors in a controlled manner is called doping.
Antimony, arsenic and phosphorus are called n-type impurities and form an n-type material when any of these impurities are added to silicon or germanium
Indium, aluminium and boron are called p-type impurities and form a p-type material when any of these impurities are added to a semiconductor
[attachment=39429]
Objective
At he end of the lesson student will:
Be familiar with the atomic structure of electrical material
Describe semi conductor material and thir behavior
Describe n-type and p-type material
Familiar with construction of diode
Semi Conductor Material
All materials can be classified (electrically) into three categories:
Conductors.
Insulators.
Semiconductors
Conductorseasily allow current to pass through them.
Insulatorsdo notallow current to pass through them.
Semiconductorsare a group of material that posses the property of neither insulator nor good conductor, but somewhere in between Example of semiconductors are silicon(Si) and germanium (Ge).
Pure semiconductors are poor conductors, because the low number of free electrons. However, the resistivity can be reduced (so that it conducts more current) by putting in impurities into the pure semiconductors. The process of introducing a small amount of impurities (during manufacturing) into the semiconductors is called doping.
Types of semiconductors
Silicon And Germanium are the most important semiconductors used in the electronics industry
As the temperature of these materials is raised above room temperature, the resistivity is reduced and ultimately a point is reached where they effectively become conductors
As the temperature of a semiconductor is reduced below normal room temperature, the resistivity increases until, at very low temperatures the semiconductor becomes an insulator
A semiconductor normally are in the form of a crystal.
Properties Of Crystals
The structure of a solid substance have symmetric & non-symmetric arrangement of its atoms or molecules. Non-symmetric is termed amorphous.
In some crystalline substances, the imperfections in the molecular structure will confer additional properties on the material -luminescence, chemical or electrical effects.
Semiconductors are crystals of substances which exhibit electrical properties due to imperfections in their molecular structure.
Intrinsic Conduction
Although intrinsic conduction is taking place within the structure of the semiconductor crystal, there is overall electrical equilibrium, i.e. at all times there will be as many free electrons as there are holes.
Intrinsic conduction, because of its randomness, is not a useful property in a semiconductor crystal.
Two materials commonly used as semiconductor crystal are silicon and germanium.
A crystal of silicon is usually preferred as it has a lower level of intrinsic conduction.
Passive Components
Components in an electrical circuit which do not of themselves act to change or modify circuit conditions are termed ‘passive’.
Examples of ‘passive’ components, resistors, thermostats, inductors, capacitors, quartz crystal, silicon temperature sensors.
Quartz crystals are used in the form of a thin plate in resonant circuits and such circuits are used to produce oscillation.
Doping
The introduction of controlled quantities of impuritiesinto a semiconductors crystal when it is being formed can produce a crystal latticewith a predominance of electrons or holes.
The introduction of impurities into a semiconductors crystal (usually about one part in 1010parts) is termed ‘doping’.
The materials used for doping are selected so that their atoms will be combined into the crystal lattice without distortingit and that the required predominance of either electrons or holes is obtained.
N-type & P-type Materials
Adding extremely small amounts of impurities to pure semiconductors in a controlled manner is called doping.
Antimony, arsenic and phosphorus are called n-type impurities and form an n-type material when any of these impurities are added to silicon or germanium
Indium, aluminium and boron are called p-type impurities and form a p-type material when any of these impurities are added to a semiconductor