Fermi level change in semiconductors

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Discussion Overview

The discussion revolves around the behavior of the Fermi level in semiconductors, specifically focusing on the effects of replacing silicon (Si) with germanium (Ge) in a doped crystal lattice containing boron. Participants explore whether the acceptor level changes with the type of semiconductor used as a base and the implications of band structure differences.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the acceptor level of boron changes when replacing Si with Ge, suggesting that it may not change.
  • Another participant asserts that the band structure depends on the crystal structure and interatomic spacing, noting that the band gap for Si is twice that of Ge, indicating a dependence on the semiconductor type.
  • There is a repeated inquiry about whether the acceptor level will be higher or lower in Ge compared to Si, with a request for a general rule regarding this behavior.
  • A later reply suggests that there is no general rule of thumb for this behavior, especially in complex compound semiconductors, but references a 2003 paper indicating that hydrogen has a universal energy level aligned with the semiconductor's band gap.

Areas of Agreement / Disagreement

Participants express differing views on whether the acceptor level changes with the semiconductor type, and there is no consensus on a general rule for predicting the behavior of the acceptor level in different materials.

Contextual Notes

Participants acknowledge the complexity of the topic, particularly in relation to compound semiconductors, and highlight the importance of interatomic distance and band gap alignment.

Helena Wells
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TL;DR
Does the acceptor level or donor level change if we change the base of the semiconductor?
Suppose we have a crystal lattice of doped Si with dopant Boron atoms. The energy level of the holes of the Boron atoms are just some eV above the valence band of Si.

My question: If we replace all the Si atoms with Ge atoms will the acceptor level change or not? I don't think it will change but why not ask it? In other words, does the acceptor level depend on the type of semiconductor we use as base?
 
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The band structure is a product of the crystal structure (which reflects the structure of the base) as well as the interatomic spacing. The band gap for Silicon is twice that of Germanium and so yes it does depend. I believe the most important effect is the interatomic distance, but don't quote me..
 
So will it be higher or lower?Is there a general rule for it?
 
hutchphd said:
The band structure is a product of the crystal structure (which reflects the structure of the base) as well as the interatomic spacing. The band gap for Silicon is twice that of Germanium and so yes it does depend. I believe the most important effect is the interatomic distance, but don't quote me..
@hutchphd what are you studying/have you studied?
 
Long ago I did solid state theory...mostly surfaces and scattering from surfaces. I am now retired after doing optical, electronic, and systems design mostly for medical devices for 25 years . Also folks would occasionally hire me just for another novel look at a problem. I am a better engineer than I am a physicist...but I do love knowing the physics.
 
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Helena Wells said:
So will it be higher or lower?Is there a general rule for it?

I do not believe there is a general rule of thumb. Especially in complex compund semiconductors (like oxides and nitrides).
However in 2003, it was shown that hydrogen has a universal energy level provided that the band gap of the semiconductor is aligned according to unified scale (for example aligned with respect to vacuum level).

This is the paper that pointed this out:
https://www.nature.com/articles/nature01665
 
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