ELECTRON
It is a stable elementary particle with a charge of negative electricity, found in all atoms
and acting as the primary carrier of electricity in solids.
ELECTRONICS
Electronics is the movement of electrons in a vacuum, gas, semiconductor, etc., in
devices in which the flow is controlled and utilized.
Electronics deals with electrical circuits that involve active electrical components such as
vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection
technologies.
ELECTRON DEVICES
An electronic component is any physical entity in an electronic system used to affect the
electrons or their associated fields in a manner consistent with the intended function of the
electronic system. Components are generally intended to be connected together, usually by being
soldered to a printed circuit board (PCB), to create an electronic circuit with a particular function
(for example an amplifier, radio receiver, or oscillator). Components may be packaged singly, or
in more complex groups as integrated circuits. Some common electronic components are
capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as
active (e.g. transistors and thyristors) or passive (e.g. resistors and capacitors).
ELECTRONIC CIRCUITS
Circuits and components can be divided into two groups: analog and digital. A
particular device may consist of circuitry that has one or the other or a mix of the two types.
, Analog circuits are constructed from combinations of a few types of basic circuits.
Analog circuits use a continuous range of voltage as opposed to discrete levels as in digital
circuits. The number of different analog circuits so far devised is huge, especially because a
'circuit' can be defined as anything from a single component, to systems containing thousands of
components.
Digital circuits are electric circuits based on a number of discrete voltage levels. Digital
circuits are the most common physical representation of Boolean algebra, and are the basis of all
digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are
interchangeable in the context of digital circuits.
UNIT I SEMICONDUCTOR DIODE
SEMICONDUCTOR
A semiconductor is a material which has electrical conductivity to a degree between that
of a metal (such as copper) and that of an insulator (such as glass). Semiconductors are the
foundation of modern electronics, including transistors, solar cells, light-emitting diodes (LEDs),
quantum dots and digital and analog integrated circuits.
DIODE
Diode – Di + ode
Di means two and ode means electrode. So physical contact of two electrodes is known
as diode and its important function is alternative current to direct current.
REVIEW OF INTRINSIC AND EXTRINSIC SEMICONDUCTORS
INTRINSIC SEMICONDUCTOR
An intrinsic semiconductor is one, which is pure enough that impurities do not
appreciably affect its electrical behavior. In this case, all carriers are created due to thermally or
optically excited electrons from the full valence band into the empty conduction band. Thus
equal numbers of electrons and holes are present in an intrinsic semiconductor. Electrons and
holes flow in opposite directions in an electric field, though they contribute to current in the
same direction since they are oppositely charged. Hole current and electron current are not
necessarily equal in an intrinsic semiconductor, however, because electrons and holes have
different effective masses (crystalline analogues to free inertial masses).
The concentration of carriers is strongly dependent on the temperature. At low
temperatures, the valence band is completely full making the material an insulator. Increasing the
,temperature leads to an increase in the number of carriers and a corresponding increase in
conductivity. This characteristic shown by intrinsic semiconductor is different from the behavior
of most metals, which tend to become less conductive at higher temperatures due to increased
phonon scattering.
Both silicon and germanium are tetravalent, i.e. each has four electrons (valence
electrons) in their outermost shell. Both elements crystallize with a diamond-like structure, i.e. in
such a way that each atom in the crystal is inside a tetrahedron formed by the four atoms which
are closest to it. Each atom shares its four valence electrons with its four immediate neighbours,
so that each atom is involved in four covalent bonds.
EXTRINSIC SEMICONDUCTOR
An extrinsic semiconductor is one that has been doped with impurities to modify the
number and type of free charge carriers. An extrinsic semiconductor is a semiconductor that has
been doped, that is, into which a doping agent has been introduced, giving it different electrical
properties than the intrinsic (pure) semiconductor.
Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the
electron and hole carrier concentrations of the semiconductor at thermal equilibrium. Dominant
carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type
semiconductor. The electrical properties of extrinsic semiconductors make them essential
components of many electronic devices.
A pure or intrinsic conductor has thermally generated holes and electrons. However these
are relatively few in number. An enormous increase in the number of charge carriers can by
achieved by introducing impurities into the semiconductor in a controlled manner. The result is
the formation of an extrinsic semiconductor. This process is referred to as doping. There are
basically two types of impurities: donor impurities and acceptor impurities. Donor impurities are
made up of atoms (arsenic for example) which have five valence electrons. Acceptor impurities
are made up of atoms (gallium for example) which have three valence electrons.
The two types of extrinsic semiconductor
N-TYPE SEMICONDUCTORS
Extrinsic semiconductors with a larger electron concentration than hole concentration are
known as n-type semiconductors. The phrase 'n-type' comes from the negative charge of the
electron. In n-type semiconductors, electrons are the majority carriers and holes are the minority
carriers. N-type semiconductors are created by doping an intrinsic semiconductor with donor
, impurities. In an n-type semiconductor, the Fermi energy level is greater than that of the intrinsic
semiconductor and lies closer to the conduction band than the valence band. Arsenic has 5
valence electrons, however, only 4 of them form part of covalent bonds. The 5th electron is then
free to take part in conduction. The electrons are said to be the majority carriers and the holes are
said to be the minority carriers.
P-TYPE SEMICONDUCTORS
As opposed to n-type semiconductors, p-type semiconductors have a larger hole
concentration than electron concentration. The phrase 'p-type' refers to the positive charge of the
hole. In p-type semiconductors, holes are the majority carriers and electrons are the minority
carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor
impurities. P-type semiconductors have Fermi energy levels below the intrinsic Fermi energy
level. The Fermi energy level lies closer to the valence band than the conduction band in a p-type
semiconductor. Gallium has 3 valence electrons, however, there are 4 covalent bonds to fill. The
4th bond therefore remains vacant producing a hole. The holes are said to be the majority carriers
and the electrons are said to be the minority carriers.
PN JUNCTION
When the N and P-type semiconductor materials are first joined together a very large
density gradient exists between both sides of the junction so some of the free electrons from the
donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in
the P-type material producing negative ions. However, because the electrons have moved across
the junction from the N-type silicon to the P-type silicon, they leave behind positively charged
donor ions (ND) on the negative side and now the holes from the acceptor impurity migrate
across the junction in the opposite direction into the region are there are large numbers of free
electrons. As a result, the charge density of the P-type along the junction is filled with negatively
charged acceptor ions (NA), and the charge density of the N-type along the junction becomes
positive. This charge transfer of electrons and holes across the junction is known as diffusion.
This process continues back and forth until the number of electrons which have crossed
the junction have a large enough electrical charge to repel or prevent any more carriers from
crossing the junction. The regions on both sides of the junction become depleted of any free
carriers in comparison to the N and P type materials away from the junction. Eventually a state
of equilibrium (electrically neutral situation) will occur producing a "potential barrier" zone
around the area of the junction as the donor atoms repel the holes and the acceptor atoms repel
the electrons. Since no free charge carriers can rest in a position where there is a potential barrier
the regions on both sides of the junction become depleted of any more free carriers in
comparison to the N and P type materials away from the junction. This area around the junction
is now called the Depletion Layer.
It is a stable elementary particle with a charge of negative electricity, found in all atoms
and acting as the primary carrier of electricity in solids.
ELECTRONICS
Electronics is the movement of electrons in a vacuum, gas, semiconductor, etc., in
devices in which the flow is controlled and utilized.
Electronics deals with electrical circuits that involve active electrical components such as
vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection
technologies.
ELECTRON DEVICES
An electronic component is any physical entity in an electronic system used to affect the
electrons or their associated fields in a manner consistent with the intended function of the
electronic system. Components are generally intended to be connected together, usually by being
soldered to a printed circuit board (PCB), to create an electronic circuit with a particular function
(for example an amplifier, radio receiver, or oscillator). Components may be packaged singly, or
in more complex groups as integrated circuits. Some common electronic components are
capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as
active (e.g. transistors and thyristors) or passive (e.g. resistors and capacitors).
ELECTRONIC CIRCUITS
Circuits and components can be divided into two groups: analog and digital. A
particular device may consist of circuitry that has one or the other or a mix of the two types.
, Analog circuits are constructed from combinations of a few types of basic circuits.
Analog circuits use a continuous range of voltage as opposed to discrete levels as in digital
circuits. The number of different analog circuits so far devised is huge, especially because a
'circuit' can be defined as anything from a single component, to systems containing thousands of
components.
Digital circuits are electric circuits based on a number of discrete voltage levels. Digital
circuits are the most common physical representation of Boolean algebra, and are the basis of all
digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are
interchangeable in the context of digital circuits.
UNIT I SEMICONDUCTOR DIODE
SEMICONDUCTOR
A semiconductor is a material which has electrical conductivity to a degree between that
of a metal (such as copper) and that of an insulator (such as glass). Semiconductors are the
foundation of modern electronics, including transistors, solar cells, light-emitting diodes (LEDs),
quantum dots and digital and analog integrated circuits.
DIODE
Diode – Di + ode
Di means two and ode means electrode. So physical contact of two electrodes is known
as diode and its important function is alternative current to direct current.
REVIEW OF INTRINSIC AND EXTRINSIC SEMICONDUCTORS
INTRINSIC SEMICONDUCTOR
An intrinsic semiconductor is one, which is pure enough that impurities do not
appreciably affect its electrical behavior. In this case, all carriers are created due to thermally or
optically excited electrons from the full valence band into the empty conduction band. Thus
equal numbers of electrons and holes are present in an intrinsic semiconductor. Electrons and
holes flow in opposite directions in an electric field, though they contribute to current in the
same direction since they are oppositely charged. Hole current and electron current are not
necessarily equal in an intrinsic semiconductor, however, because electrons and holes have
different effective masses (crystalline analogues to free inertial masses).
The concentration of carriers is strongly dependent on the temperature. At low
temperatures, the valence band is completely full making the material an insulator. Increasing the
,temperature leads to an increase in the number of carriers and a corresponding increase in
conductivity. This characteristic shown by intrinsic semiconductor is different from the behavior
of most metals, which tend to become less conductive at higher temperatures due to increased
phonon scattering.
Both silicon and germanium are tetravalent, i.e. each has four electrons (valence
electrons) in their outermost shell. Both elements crystallize with a diamond-like structure, i.e. in
such a way that each atom in the crystal is inside a tetrahedron formed by the four atoms which
are closest to it. Each atom shares its four valence electrons with its four immediate neighbours,
so that each atom is involved in four covalent bonds.
EXTRINSIC SEMICONDUCTOR
An extrinsic semiconductor is one that has been doped with impurities to modify the
number and type of free charge carriers. An extrinsic semiconductor is a semiconductor that has
been doped, that is, into which a doping agent has been introduced, giving it different electrical
properties than the intrinsic (pure) semiconductor.
Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the
electron and hole carrier concentrations of the semiconductor at thermal equilibrium. Dominant
carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type
semiconductor. The electrical properties of extrinsic semiconductors make them essential
components of many electronic devices.
A pure or intrinsic conductor has thermally generated holes and electrons. However these
are relatively few in number. An enormous increase in the number of charge carriers can by
achieved by introducing impurities into the semiconductor in a controlled manner. The result is
the formation of an extrinsic semiconductor. This process is referred to as doping. There are
basically two types of impurities: donor impurities and acceptor impurities. Donor impurities are
made up of atoms (arsenic for example) which have five valence electrons. Acceptor impurities
are made up of atoms (gallium for example) which have three valence electrons.
The two types of extrinsic semiconductor
N-TYPE SEMICONDUCTORS
Extrinsic semiconductors with a larger electron concentration than hole concentration are
known as n-type semiconductors. The phrase 'n-type' comes from the negative charge of the
electron. In n-type semiconductors, electrons are the majority carriers and holes are the minority
carriers. N-type semiconductors are created by doping an intrinsic semiconductor with donor
, impurities. In an n-type semiconductor, the Fermi energy level is greater than that of the intrinsic
semiconductor and lies closer to the conduction band than the valence band. Arsenic has 5
valence electrons, however, only 4 of them form part of covalent bonds. The 5th electron is then
free to take part in conduction. The electrons are said to be the majority carriers and the holes are
said to be the minority carriers.
P-TYPE SEMICONDUCTORS
As opposed to n-type semiconductors, p-type semiconductors have a larger hole
concentration than electron concentration. The phrase 'p-type' refers to the positive charge of the
hole. In p-type semiconductors, holes are the majority carriers and electrons are the minority
carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor
impurities. P-type semiconductors have Fermi energy levels below the intrinsic Fermi energy
level. The Fermi energy level lies closer to the valence band than the conduction band in a p-type
semiconductor. Gallium has 3 valence electrons, however, there are 4 covalent bonds to fill. The
4th bond therefore remains vacant producing a hole. The holes are said to be the majority carriers
and the electrons are said to be the minority carriers.
PN JUNCTION
When the N and P-type semiconductor materials are first joined together a very large
density gradient exists between both sides of the junction so some of the free electrons from the
donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in
the P-type material producing negative ions. However, because the electrons have moved across
the junction from the N-type silicon to the P-type silicon, they leave behind positively charged
donor ions (ND) on the negative side and now the holes from the acceptor impurity migrate
across the junction in the opposite direction into the region are there are large numbers of free
electrons. As a result, the charge density of the P-type along the junction is filled with negatively
charged acceptor ions (NA), and the charge density of the N-type along the junction becomes
positive. This charge transfer of electrons and holes across the junction is known as diffusion.
This process continues back and forth until the number of electrons which have crossed
the junction have a large enough electrical charge to repel or prevent any more carriers from
crossing the junction. The regions on both sides of the junction become depleted of any free
carriers in comparison to the N and P type materials away from the junction. Eventually a state
of equilibrium (electrically neutral situation) will occur producing a "potential barrier" zone
around the area of the junction as the donor atoms repel the holes and the acceptor atoms repel
the electrons. Since no free charge carriers can rest in a position where there is a potential barrier
the regions on both sides of the junction become depleted of any more free carriers in
comparison to the N and P type materials away from the junction. This area around the junction
is now called the Depletion Layer.
