Analog Electronics I DEE1233

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Analog Electronics IDEE1233

• Rosmadi Bin Abdullah
• A1-01-03

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Chapter 1 Basic Semiconductors

• - Materials Properties

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• Definition of atom
• Te smallest particle of an element that cannot
  further break down by chemical means.
• Composed of
• Protons
• Neutrons
• Electrons

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Bohr model theory

• Atom have planetary type of structure consisting
  central nucleus equipped with the proton and
  surrounded by orbiting electron.
• Proton are positively charged and electron are
  negatively charged.

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What we need to know about atom?

• Atomic number
• The atomic number is equal to the number of
  proton in an atoms nucleus.
• Distinguishes the chemical group characteristics.
• Electron shells and orbit
• Electron near the nucleus have less energy than
  the outer one
• Each electron orbits are grouped in shells
  (energy bands)

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What we need to know about atom

• Valence electron
• The farther the electrons from the nucleus, the
  higher energy it gets.
• The outmost electrons are in the valence shells
  and known as electron valence
• Strongly related defining chemical reaction,
  bonding structure and electrical properties
• Ionization
• Process of losing electron valence due to the
  electron valence absorbing the externally high
  amount of energy to be a free-electron.
• The previously departed atom will be charged
  positively and the receiving atom will be charged
  negatively.

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Number of electrons

• Maximum number of electrons (Ne) that exist in
  each shells of atom can be calculated as
• Ne 2n2
• where n(1,2,3,) is the number of the shells.
• Example Magnesium
• Mg (12) 2,8,2

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Element Properties

• Conductor
• Easily can conduct electrical current
• Least electron valence on the atom-loosely
  bounded
• Insulator
• Does not conduct electrical current under normal
  condition
• Most are compounds
• Lots of electron exist on the valence
  shell-tightly bounded
• Semiconductor
• Element that is neither a conductor nor an
  insulator but lies between the two element
• A material that is between conductors and
  insulators in its ability to conduct electrical
  current
• Easily affected by temperature and light energy
• Most of them have 4 electron valence on the
  valence shells-bounded in intermediate strength

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Semiconductor

• A semiconductor is a material whose resistance
  depends strongly on the applied voltage and
  temperature.

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Semiconductor

• 3 most used semiconductors carbon (C), silicon
  (Si) and germanium (Ge)

Carbon
Germanium
Silicon
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Energy bands

• Valence shells represents the band of energy of
  an atom
• Conductor bands
• Existence of electron valence. Where the electron
  valence become a free electron when acquire
  enough additional external energy.
• Energy gaps
• Energy differences between conduction bands and
  valence bands (define the require energy for
  electron valence to be a free electron).

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• Energy level increase as the distance from the
  nucleus increase

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Energy diagram for three types of material
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Energy band diagram for a pure (intrinsic)
silicon crystal with unexcited atoms. There are
no electrons in the conduction band (at 0 Kelvin).
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Covalent bonds
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Covalent bonds -octet rule

• The octet rule is a simple chemical rule of
  thumb, states that atoms tend to combine in such
  a way that they each have eight electrons in
  their valence shells, giving them the same
  electronic configuration as noble gas.
• The rule is applicable to the main-group
  elements, especially carbon, nitrogen, oxygen and
  halogens, but also to metals such as sodium or
  magnesium.
• In simple terms, molecules or ions tend to be
  most stable when the outermost electron shells of
  their constituent atoms contain eight electrons.

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Quiz

• Draw and define the Bohr model of
  6Nitrogen,12Magnesium and 47Argentum including
  its orbital name and existing electron valence
• Calculate the 32Germanium, 18Argon and
  40Zirconium maximum number of electron
• Describe the differences between conductors,
  insulators and semiconductors including their
  energy bands
• Why Germanium is less used than Silicon? Describe
  and illustrate.

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Chapter 1 Basic Semiconductors

• -N-type and P-type semiconductor

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Creation of electron-hole pair
At room temperature.
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Creation of electron-hole pair
Electron-hole pairs in a silicon crystal. Free
electrons are being generated continuously while
some recombine with holes.

• Electron-hole pairs in a silicon crystal. Free
  electrons are being generated continuously while
  some recombine with holes.

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FIGURE 1-13 Electron current in intrinsic
silicon is produced by the movement of thermally
generated free electrons.
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FIGURE 1-14 Hole current in intrinsic silicon.
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Doping

• Doping is the process of deliberately adding
  impurities to the crystal during manufacturing
  and increases the number of current carries
  (electrons or holes)
• Impurities extraneous elements
• Doping process create N-type and P-type of
  semiconductors

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N type semiconductor

• Doped with 5 pentavalent impurities
• E.g. Phosphorus (P), Arsenic (As), Antimony (Sb)
• 4 electrons used for covalent bonds with
  surrounding Si atoms, one electron will jump
  due to it is loosely bound by only small amount
  of energy needed to lift it into conduction band
  (0.05 eV in Si)
• Pentavalent impurity atom in a silicon crystal
  structure. An antimony (Sb) impurity atom is
  shown in the center. The extra electron from the
  Sb atom becomes a free electron

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N type semiconductor

• Pentavalent impurity atom in a silicon crystal
  structure. An antimony (Sb) impurity atom is
  shown in the center. The extra electron from the
  Sb atom becomes a free electron.

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P - type semiconductors

• Doped with 3 trivalent impurities
• E.g B, Al, Ga, In
• P-type semiconductor has mobile holes, very few
  mobile elecrons
• Also known as accepter atom
• Majority carrier hole
• Minority carrier - electron

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P-type semiconductors

• Trivalent impurity atom in a silicon crystal
  structure. A boron (B) impurity atom is shown in
  the center.

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Advantages of doped semiconductors

• Able to tune conductivity by choice of doping
  fraction
• Able to choose majority carrier (electron or
  hole)
• Able to vary doping fraction and/ or majority
  carrier within piece of semiconductor

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Chapter 1 Basic Semiconductors

• Diode model and voltage current characteristic
• -Diode biasing

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The basic diode structure at the instant of
junction formation showing only the majority and
minority carriers.
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Formation of the depletion region. The width of
the depletion region is exaggerated for
illustration purposes.
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Energy diagrams illustrating the formation of the
pn junction and depletion region.
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Diode forward bias.

• A diode connected for forward bias.

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A forward-biased diode showing the flow of
majority carriers and the voltage due to the
barrier potential across the depletion region.
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The depletion region narrows and a voltage drop
is produced across the pn junction when the diode
is forward-biased.
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Diode reverse bias
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Diode reverse bias

• The diode during the short transition time
  immediately after reverse-bias voltage is applied.

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Forward-bias measurements show general changes in
VF and IF as VBIAS is increased.
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V-I characteristic curve for forward bias. Part
(b) illustrates how the dynamic resistance rd
decreases as you move up the curve (rd
?VFIF?IF).
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V-I characteristic curve for reverse-biased diode.
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The complete V-I characteristic curve for a diode.
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Temperature effect on the diode V-I
characteristic. The 1 mA and 1µA marks on the
vertical axis are given as a basis for a relative
comparison of the current scales.
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Diode structure and schematic symbol.
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Forward-bias and reverse-bias connections showing
the diode symbol.
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The ideal model of a diode.
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The practical model of a diode.
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The complete model of a diode.
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Typical diode packages with terminal
identification.
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DMM diode test on a properly functioning diode.
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Testing a defective diode.
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Load Line Analysis

• Question
• - If the circuit of figure 1 has Vss 2V, R
  1kO, and diode with the characteristic shown in
  Figure 2, find the diode voltage and current at
  the operating point?

Figure 1 Circuit for load line analysis
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Diode characteristic
Figure 2 Load line analysis
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• Solution
• -Applying Kirchhoffs voltage law
• 
  --------------(1)
• -Substitute Vss 2V and R 1kO into equation
  (1).
• 2V 1k O x Id Vd
  --------------(2)
• Substitute Vd 0 into (2)
• This value is plotted as point B in Figure 2

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• Substitution of Id 0 and Vss 2V results in Vd
  2V.
• This value is plotted as point A in figure 2.
• Constructing the load line results in an
  operating point of Vd 0.7V ad Id 1.3mA as
  shown in figure 2.