Band diagram of pn-junction diode at low temperature

In summary, the conversation is discussing the behavior of a pn-junction diode at very low temperatures where dopant ionization is completely frozen out. It is questioned whether the band structure will change and if the physics can still be described within an independent electron picture. The possibility of building a pn diode at low temperature and the location of the Fermi level in n/p-type semiconductors are also discussed. It is concluded that at very low temperatures, the carriers freeze out and the Fermi level remains at the energy where ne=1/2. It is also mentioned that in the degenerate case, complete freeze-out is not possible and that equilibrium may not be reached.
  • #1
Hi

What could be the band diagram of pn-junction diode at very low temperature where dopant ionzation is completely frozen out?

Would it still be like the band diagram at room temperature?
 
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  • #2
I don't think that the band structure per se will change very much. It is more a question whether the physics at low temperatures can still be described within an independent electron picture.
 
  • #3
DrDu said:
I don't think that the band structure per se will change very much. It is more a question whether the physics at low temperatures can still be described within an independent electron picture.

Thank you for the reply but if the band diagram doesn't change much, how can we describe the built-in potential since there is no mobile(ionized) charge present?
 
  • #4
Ok, so you are asking whether it makes a difference to bring two junks of p and n doped semiconductor at room temperature or at low temperature?
I was thinking of cooling a diode.
 
  • #5
DrDu said:
Ok, so you are asking whether it makes a difference to bring two junks of p and n doped semiconductor at room temperature or at low temperature?
I was thinking of cooling a diode.

We usually learn semiconductor physics based on the fact that dopant ionization is present.
The simplest doped device we can think of will be pn-diode. And we know analytically what the depletion width, built-in potential and band diagram will be with given temperature and doping (Na/Nd).

But let's think of the behaviour of such device at very low temperature where there are absolutely no mobile carriers (extra charge from donor/acceptor is not at all ionized).

Where will be the fermi level of n/p-type semiconductor?
Can we draw band diagram if we attach p and n type semiconductor to build a pn diode?
What is the built-in potential of pn-diode?
No mobile charge but can we still apply room temperature analysis?

These are the questions I have.
 
  • #6
But let's think of the behaviour of such device at very low temperature where there are absolutely no mobile carriers (extra charge from donor/acceptor is not at all ionized).
The carriers freeze out on each side of the space-charge region. Inside the space-charge region, carriers are "pushed out" by the built-in field, so you still have ionized impurities.

Where will be the fermi level of n/p-type semiconductor?
At the energy where ne=1/2. In semiconductor physics, the Fermi level is really the chemical potential term in the Fermi-Dirac statistics. The Fermi level does not move towards mid-gap when carriers freeze out (I think that's what you're thinking). Carriers freeze out because of the exp{(E-EF)/kT} term in the denominator of the FD statistics.

Can we draw band diagram if we attach p and n type semiconductor to build a pn diode?
If you do it at T->0K? Well, in the degenerate case, you will never have complete freeze-out anyway. But if there was complete freeze-out, you would probably never reach equilibrium. Remeber that the "Fermi level must be the same evrywhere" condition applies to equilibrium.
 

What is a band diagram of pn-junction diode at low temperature?

A band diagram of pn-junction diode at low temperature is a graph that illustrates the energy levels of the valence and conduction bands in a pn-junction diode at a low temperature. It shows how the energy levels change across the junction, and how the depletion region forms as a result of the built-in potential.

Why is it important to study the band diagram of pn-junction diode at low temperature?

Studying the band diagram of pn-junction diode at low temperature is important for understanding the behavior of the diode in different temperature conditions. It helps in predicting the diode's performance and optimizing its design for various applications.

What are the main factors that affect the band diagram of pn-junction diode at low temperature?

The main factors that affect the band diagram of pn-junction diode at low temperature include the doping levels of the p and n regions, the applied voltage, and the temperature. These factors influence the width of the depletion region and the location and shape of the energy bands.

How does the band diagram of pn-junction diode at low temperature differ from the one at room temperature?

At low temperature, the energy gap between the valence and conduction bands increases, leading to a wider bandgap in the band diagram. This results in a higher built-in potential and a narrower depletion region compared to the band diagram at room temperature.

What are the applications of the band diagram of pn-junction diode at low temperature?

The band diagram of pn-junction diode at low temperature is used in the design and optimization of electronic devices, such as solar cells, light emitting diodes, and transistors. It is also important in understanding the behavior of diodes in extreme temperature conditions, such as in space or in high-power applications.

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