BASIC Electronics (XEC02)
Syllabus
Semiconductor devices: Construction, working and V-I characteristics of diode,
Zener diode, Zener diode as a voltage regulator, LED.
Transistors: Introduction to BJT, FET, MOSFET; CMOS, working principle, and V-I
characteristics of Transistors, biasing of BJT circuits-fixed bias, emitter bias,
feedback bias, voltage divider bias, transistor as an amplifier
Operational amplifier: Introduction, applications: inverting, non-inverting
amplifier, unity follower, integrator, differentiator, summing circuit.
Introduction of logic gates and memory: ROM, RAM
• TEXT BOOKS
1. Introduction Electronic Devices & Circuit Theory, Boylestad & Nashelsky
2. Integrated Electronics: Millman & Halkias
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Application of Electronics
Electronics
Communication Defense Industry Medical Instrumentation
and Engineering Science
Radar Automatic X-Rays VTVM,
Guided Control Electron CRO
Missiles Systems Microscope Frequency
Coded Heating & Electrocardiogram Counter
Communicat Welding (ECG) pH Meter
ion Computers Electro Therapy
Line
Wireless Audio
Communication
Communication Systems
Telegraphy Radio Broadcasting PA Systems
Telephone TV Broad Casting Stereo System
Teleprinter Satellite Communication Record Players
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Classifications of Materials
I Metal Band Gap
II Insulator
III Semiconductor
• atom has discrete energy levels
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Energy Bands
• 2 atoms have doublet energy levels
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Energy Bands
• 3 atoms have triplet energy levels, etc.
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Energy Bands
~ Empty
EC
Ev
~ Full
• many atoms in crystal → energy bands
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Band Diagrams
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Semiconductor Materials
Atomic Structure
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Semiconductor Materials
Covalent Bonding
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Energy Band Diagrams
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Electrons and Holes
At T = 0K, all electrons are At T > 0K, thermal energy
bound in covalent bonds. breaks the covalent bonds,
No carriers are available for generating electron-hole
conduction. pairs. Now, carriers are
available for conduction.
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Types of Semiconductor Materials
• One of most important properties of a semiconductor
is that it can be doped with different types and
concentrations of impurities
• Intrinsic material: No impurities or lattice defects
• Extrinsic: doping, purposely adding impurities
– N-type mostly electrons
– P-type mostly holes
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Carrier Concentration at Thermal Equilibrium
• To calculate semiconductor electrical properties, we must know the
number of charge carriers per cm3 of the material
Fermi-Dirac statistics
• Distribution of electrons over a range of allowed energy levels at
thermal equilibrium
1 Probability that an available energy state at E
E E F
F( E) will be occupied by an electron at absolute
1 exp temperature T
kT
Mathematically, EF (Fermi Energy) is the energy at which f(E) = 1/2
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QUESTION: HOW MANY ELECTRONS / HOLES ARE IN THESE BANDS ?
Intrinsic Semiconductor (ni)
Electron Concentration:
Hole Concentration:
Electron Concentration (n0) = Hole Concentration (p0)= Intrinsic Carrier Concentration
Solve for the value of EF
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Extrinsic Semiconductor
To make semiconductors really useful, must introduce other means of
creating holes and electrons !!!
Doping = engineered introduction of other atoms to modify semiconductor
electrical properties
A. DONORS:
• Introduce electrons to semiconductors (but not holes)
• For Si, group V elements with 5 valence electrons (As,P, Sb)
N-Type Si
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Donor energy level
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B. ACCEPTORS:
• Introduce holes to semiconductors (but not electrons)
• For Si, group III elements with 3 valence electrons (B)
P-Type Si
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Charge neutrality
Notice what happens when we multiply together the n and p equations:
EF cancels out of product
further: The carrier concentration we had in the
pure semiconductor
n and p may no longer equal ni
As one increases, the other decreases to precisely compensate
Law of Mass Action
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Case1 : Intrinsic Semiconductor, = = 0
get: n0 = p0 = ni
Case 2: n-type semiconductor, >>
or ( - >> ni
get: n0 ≈ and p0 = /
Case 3: p-type semiconductor, >>
( - ) >> ni
get: p0 = and n0 = /
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Transport of Carriers
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Transport of Carriers
Carrier transport can be classified into two types:
Drift: Motion under an applied field
Diffusion: Motion due to a gradient of concentration
Most of the transport mechanisms considered classically (not
quantum mechanically).
Often, the both the drift and diffusion are adequate for many
situations and applications.
Carrier Transport: DRIFT of carriers in an Electric Field
Carrier Drift:
"Drift" = Net carrier movement induced by force (such as electric field)
"Carrier" = Mobile charge carrier = Conduction band electron / valence band hole
For a P-type (acceptor doped) semiconductor: p >> n
vp = µpξ, where µp is ‘hole mobility’ and ξ is the electric field
𝐽𝑝 = 𝜎𝑝 ℰ 𝝈𝒑 is Conductivity of Semiconductor
Total DRIFT CURRENT
(due to both electrons and holes in the same electric field)
Carrier Transport: Diffusion = Spontaneous
Rearrangement
SECOND POSSIBLE SOURCE OF CURRENT: Spontaneous redistribution of
carriers:
DIFFUSION of carriers At t=0, start with a blip of electrons
What happens at t > 0 ?
Obviously, it is going to spread out!
Combine these new DIFFUSION currents with DRIFT currents to get TOTAL
currents:
1. What are n and p in a Si sample with ND = 6 x 1016 /cm3 and NA = 2 x 1016 /cm3.
With additional 6 x 1016 of acceptors, what would be the result?
n = ND -NA = 4 x 1016/cm3
p = ni2/n = 5.6 x 103/cm3
With additional NA = 8 x 1016 /cm3
p = NA – ND = 2 x 1016 /cm3
n = ni2/p = 1.12 x 104 /cm3
2. A Si sample is doped with 1018 atoms/cm3 of boron. Another sample of identical
dimensions is doped with 1018 atoms/cm3 of phosphorus. The ratio of electron to
hole mobility is 3. Find the ratio of the conductivity of sample A to B.
p = pqµp
n = nqµn
p/n = µp/µn = 1/3
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Problems
1. Determine the conductivity of an intrinsic sample of Si at normal
room temperature. Given parameters for Si are μn = 1350 cm2/ volt-
s, μp = 480 cm2/ volt-s, ni at 3000K = 1.52 × 1010 / cm3, e= p = 1.6 ×
10 -19 C.
2. In a Si semiconductor at room temperature (3000k) the intrinsic
carrier concentration is 1.5× 1016 / m3. It is converted to an
extrinsic semiconductor of 1020 /m3. Applying mass action law for
the carrier concentration calculates the minority carrier
concentration.
3. For Ge, the mobility of electron at 3000 K is 0.38 m/(V.s). Using
Einstein equation determine the diffusivity of the electron.
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