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Semiconductor physics Questions

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shaikss

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Hi,

I have few queries regarding the below Qs.

1. How does the fermi level vary with distance under both equilibrium and non-equilibrium conditions? Is it constant or varying under equilibrium and non-equilibrium conditions?
My query>> Fermi level vary with temp. But I am not getting how to analyse how fermi level changes w.r.t distance.
2. what happens to fermi energy level when temp is increased in n-type semiconductors?
My explanation>> When temp is increased, donor electrons move from valence band to conduction band and so is the fermi level. At the same time, when the increase is temp is very high, there is a point where the affect of doping is neglible when compared to affect of increase in temp. So, the fermi level moves more deeper into the forbidden energy and so fermi level approches mid level of the energy gap and becomes intrinsic. Is this correct? Or had i missing something in my analysis?
3. When donor impurity concentration is increased, what happens to fermi level position?
My explanation>> Fermi level varies with doping concentration. fermi level moves towards the conduction band edge in case of N-type semiconductor and towards Valence band in case of P-type SC. Am I wrong at any point?
4. As the temperature is increased from 0 K, what happens tothe mobility of a moderately doped semiconductor?
My explanation>> Mobility increases to certain level afterwards it starts decreasing.

Please let me know whether my analysis is correct and correct me if I am wrong at any point.
Do tell me how fermi level vary with temperature.

Thanks!
 

As the temperature is increased from 0 K, what happens tothe mobility of a moderately doped semiconductor?
Click to expand...

Generally two scattering mechanisms affect the mobility of electron and Hole
Lattice Scattering and impurity scattering
Lattice Scattering due to vibration of lattice due to temperature ,and proportional to Absolute temperature
therefore mobility should decrease as expected .

But Impurity Scattering is dominant at lower temperature .

---------- Post added at 20:57 ---------- Previous post was at 20:51 ----------

h**p://ecee.colorado.edu/~bart/book/book/chapter2/ch2_7.htm
 
blooz said:
Generally two scattering mechanisms affect the mobility of electron and Hole
Lattice Scattering and impurity scattering
Lattice Scattering due to vibration of lattice due to temperature ,and proportional to Absolute temperature
therefore mobility should decrease as expected .

But Impurity Scattering is dominant at lower temperature .

---------- Post added at 20:57 ---------- Previous post was at 20:51 ----------

h**p://ecee.colorado.edu/~bart/book/book/chapter2/ch2_7.htm
Click to expand...


Hi,

Thanks for your explanation. Can you please let me know about the below query?

How does the fermi level vary with distance under both equilibrium and non-equilibrium conditions? Is it constant or varying under equilibrium and non-equilibrium conditions?
 

shaikss said:
T
How does the fermi level vary with distance under both equilibrium and non-equilibrium conditions? Is it constant or varying under equilibrium and non-equilibrium conditions?
Click to expand...

Equilibrium
- fermi level is constant

Non equilibrium

there will be a gradient in Fermi level due to the drift and diffusion of holes and electrons
so we use a Quasi Fermi level concept

Quasi Fermi level
h**p://en.wikipedia.org/wiki/Quasi_Fermi_level

The new Fermi level that describes the population of each type of charge carrier (electrons and holes) in a semiconductor separately when their populations are displaced from equilibrium. This displacement could be caused by the application of an external electric potential, which injects electrons and holes, or by exposure to light



---------- Post added at 11:06 ---------- Previous post was at 11:05 ----------

h**p://www.tf.uni-kiel.de/matwis/amat/semi_en/kap_2/backbone/r2_3_2.html
 
blooz said:
Equilibrium
-There is no gradient in Fermi level ,that is fermi level is constant

Non equilibrium

there will be a gradient in Fermi level due to the drift and diffusion of holes and electrons
so we use a Quasi Fermi level concept

Quasi Fermi level
h**p://en.wikipedia.org/wiki/Quasi_Fermi_level

The new Fermi level that describes the population of each type of charge carrier (electrons and holes) in a semiconductor separately when their populations are displaced from equilibrium. This displacement could be caused by the application of an external electric potential, which injects electrons and holes, or by exposure to light



---------- Post added at 11:06 ---------- Previous post was at 11:05 ----------

h**p://www.tf.uni-kiel.de/matwis/amat/semi_en/kap_2/backbone/r2_3_2.html
Click to expand...

Thanks :)
 

some solid state physics lectures
about crystal structure ,Lattice Vibration
h**p://www.physics.udel.edu/~bnikolic/teaching/phys624/lectures.html
h**p://hyperphysics.phy-astr.gsu.edu/hbase/solids/sili.html#c4
 

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