physical electronics
DESCRIPTION
physics for engineersTRANSCRIPT
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PHYSICAL ELECTRONICSECX 5239
PRESENTATION – 01
C.R.M. ANTHONY4090621372014-01-10
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conductivity variation in semiconductors
It depends
on mainly two
factors ,
Atomic bond
Energy band
structure
conductivity
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Conductors
Conductors are generally substances which have the property to pass different types of energy.
Semiconductors
Semiconductors are solids whose conductivity lies between the conductivity of conductors and insulators. Due to exchange of electrons - to achieve the noble gas config-uration - semiconductors arrange as lattice structure. Unlike metals, the conductivity increases with increasing temperature.
Insulators
Insulators possess no free charge carriers and thus are non-conductive.
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Energy band structure
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Semiconductor energy bands at room temperature
Full valanceband
Empty conductionband
+e- +e- +e- +e-Energy
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ATOMIC BONDING
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Conductivity of Semiconductors
Consider the conductivity of a semiconductors
conductivity of a semiconductors = Charge of electrons & = Concentration of electrons & holes & = Mobility of electrons & holes Conductivity of electrons, = Conductivity of holes, =
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The variation of the drift mobility with dopant concentration in Si for electrons and holes at 300 K.
At room temperature T= 300 K. & Using the above graph conductivity of this sample at room temperature
= = 21.6//
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The temperature dependence of the intrinsic concentration.
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Intrinsic concentration == 1 ×
If Intrinsic ;
Using the above graph of (T) 1/T, we have:
1 × 1.9
= 526 K //
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Q7).
𝐵𝑧
𝐵𝑧
𝐼 𝑥
Y𝐵𝑧𝐵𝑧
𝐵𝑧
P e
𝐹 𝑦
𝐸𝑝
𝐸𝑒
𝐸𝑝P
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In the y-direction there is no net current, therefore ………………………………(1) ……………………………………………………….....(2)
There are driving forces activated on both electron & holes to drift along y axis. The net force experienced by the carriers…………………………………………..………(3)………………………………………………(4)Also, we can write the net force again as; ……………………………………….....(5) ………………………...............(6)Now we can equalize; (3)=(5) ………..….(7)& (4)=(6)…………………………………..(8)
P
e
−𝐹 𝑒𝑦
𝐹 𝑝𝑦
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Using above equation (7) & (8) substituting in eq(2) ,we can solve & obtain ;
Finally represent hole coefficient is; …………………………………(9)After that; ; Substituting the mass action law into Equation (9) we get; ……………………………………….(10)
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differentiation by n;
For maximize ; Resultant n is below which is leady for maximize ,
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Thank you!