The joining of both Ptype and Ntype materials is known as a PN junction' An understanding of the wor

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The P-N Junction

• The joining of both P-type and N-type materials
  is known as a PN junction. An understanding of
  the workings of this junction is critical to the
  development of your semi-conductor technologies
  knowledge including DIODES, AMPLIFIERS, and
  TRANSISTORS.
• When joined (P N) the conduction and valence
  bands partially overlap. The free electrons of
  the N-type material diffuse to the P-type
  material and fill the subsequent covalent bond
  holes. An energy release occurs as previously
  discussed. The net result is 1 positively charged
  N-type material (a lost electron) and 1
  negatively charged P-type material (electron
  gained) per diffusion.
• The amount of diffusion is dependant on the
  energy level differences between the PN type
  conduction bands.
• The area that becomes depleted of carriers, is
  known as the DEPLETION REGION. The ve area on
  the N side and the -ve area on the P side, form a
  Potential difference between the two sides.
  This is known as the BARRIER POTENTIAL. The
  barrier potential for silicon is approximately
  0.7 V and germanium is 0.3 V.

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n more negative 1 electron (aka n density
of of charge carriers.) p more positive 1
hole (aka p density of charge carriers.)
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The P-N Junction

• Biasing
• A PN junction becomes useful when we begin to
  control its depletion layer. By controlling the
  width of the depletion layer we can control how
  much current can pass through the device. This is
  due to the fact that the wider the depletion
  region becomes the higher the resistance. But
  firstWhat is current?
• Simplified, electron flow (or current) is the
  organized migration of electrons from atom to
  atom in a conductor or semi-conductor under the
  influence of some source of energy.
• Specifically, the electrical unit for current is
  the Ampere. One ampere is a rate of electrical
  current defined as one coulomb of electrons
  flowing passed a given point in every second,
  where
• A Ampere and C Coulomb
• 1A 1C/second or (6.25E18 electrons/second)
• Question - Why I for current as in EIR.
• Answer - I stands for Intensity of flow of
  current.
• Q1. How many electrons in a 1/4 amp?
• Q2. How much current is there 7.8125 E 17
  electrons?
• Q3. How many coulombs in 4 amps of current for 2
  seconds?

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The P-N Junction

• Biasing cont
• Q1. How many electrons in a 1/4 amp?
• A1. (6.25 E 18 )/ 4 1.5625 E 18
• Q2. How much current is there 7.8125 E 17
  electrons?
• A2. 1.25 E -1 A (1/8 A )
• Q3. How many coulombs in 4 amps of current for 2
  seconds?
• A3. 4 X 2 8 C
• What is Conventional Current Flow?
• A. Commonly used ve to -ve hole flow.
• What is Electron Current Flow?
• A. The correct flow of -ve to ve electron
  flow.

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The P-N Junction

• Biasing cont
• So, BIAS is a potential applied to a PN junction
  to control the width of the depletion layer. Two
  types of biasing modes are FORWARD and REVERSE.
• FORWARD BIAS
• Minimum DEPLETION REGION
• Minimum RESISTANCE
• Maximum CURRENT FLOW
• REVERSE BIAS
• Maximum DEPLETION REGION
• Maximum RESISTANCE
• Minimum CURRENT FLOW
• LETS START WITH
• FORWARD BIAS.

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The P-N Junction

• Forward Bias
• When an applied potential to the N-type material
  causes it to be more negative than the P-type
  material, the PN junction is said to be FORWARD
  BIASED When forward biased, there will be very
  little opposition to current flow. See figure
  1.14 (Page 14)

1. SW1 applies a negative potential in the N
material and electrons are pushed away toward the
junction in the conduction band. 2. Valence band
holes are pushed toward the junction by the ve
potential. 3. Once V is great enough, the
electrons will break through the depletion layer
and begin recombining with holes in the P type
material and conduction occurs. Thus VF gt Barrier
Potential.
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The P-N Junction

• Forward Bias
• TWO METHODS OF FORWARD BIAS
• 1. Apply a potential to the N type material such
  that it is more negative than the P type
  materials potential.
• 2. Apply a potential to the P type material such
  that it is more positive than the N type
  materials potential.
• Remember.
• N more Negative 1 electron (aka n density
  of of charge carriers.)
• P more Positive 1 hole (aka p density of
  charge carriers.)
• See figure 1.15 and 1.16 (page 15)

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The P-N Junction

• Reverse Bias
• When the applied potential causes the N type
  material to be more positive than the potential
  applied to the P type material, the PN junction
  is said to be Reverse Biased.
• During the reverse bias of a PN junction, the
  depletion region becomes much wider, the
  resistive value goes very high, and the junction
  current is reduced to near zero.
• See figure 1.17 (page 16). Next slide

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The P-N Junction

• Reverse Bias cont.
• TWO METHODS OF REVERSE BIAS ARE
• 1. Apply a potential to the N type material that
  makes it more positive than the P type materials
  potential.
• 2. Apply a potential to the P type material that
  is more negative than the N type materials
  potential.
• See figure 1.18 (page17)

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The P-N Junction

• Forward and Reverse Bias Comparison
• See figure 1.19 (page 17)

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The P-N Junction

• Bulk Resistance
• There is a slight opposition to current that is
  the net affect of the resistive values of both
  the P and the N type materials
• rb rp rn
• The typical value of is approximately 25 ohms or
  less.
• Dimension, doping material amounts and
  temperature all have a direct affect on the Bulk
  Resistance. This value is typically ignored in
  circuit calculations since very little voltage is
  dropped across it.
• REMEMBER THIS!
• N type material becomes ve charged when it
  looses a covalent band electron .
• P type material becomes -ve charge when it gains
  an electron into the covalent hole that was a
  part of the doping atom and part of the covalent
  bond of another atom (Si usually).