Question about semiconductors' holes.

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    Holes Semiconductors
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Discussion Overview

The discussion revolves around the concept of holes in semiconductors, particularly their presence during the photoelectric effect, their characteristics, and their effective mass. Participants explore the behavior of holes in different materials, including metals and semiconductors, and the implications for electric and magnetic fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether holes are present in metals during the photoelectric effect, suggesting that holes are typically associated with the valence band in semiconductors.
  • One participant explains that holes are effectively positively charged vacancies in the valence band and can carry current, while noting that in metals, the vacancy left by a conduction electron does not behave as a localized hole.
  • There is a discussion about the effective mass of holes, with one participant stating that it varies by material and providing an example of silicon having a heavy hole effective mass.
  • Participants express uncertainty about the characteristics of holes compared to electrons, particularly regarding their behavior in electric and magnetic fields, noting that holes flow in the opposite direction to electrons.
  • Clarifications are sought regarding the term "mobile yet localized," with participants discussing the meaning of localization in the context of electrons and holes.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the presence of holes in metals during the photoelectric effect, and there are differing views on the characteristics and effective mass of holes compared to electrons.

Contextual Notes

The discussion includes varying definitions and interpretations of terms like "mobile" and "localized," and the effective mass of holes is noted to depend on the specific material properties, which are not fully resolved.

Freeze3018
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I know holes are made/present after electron leaves its place but are holes present in metals during photo electric effects?

what is the mass of a hole (if it has any)?

what are its characteristics are they exactly opposite of electron ( i mean its behaviour in electric and magnetic field ) ?
 
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When calculating the dynamics for a crystal in an applied field, you need to include the contribution from every band. Using a derivation from solid state which I can't quote exactly, you can show that you can solve for the motion by considering the evolution of the occupied states (the electrons), or equivalently, the unoccupied states (the holes). You choose one convention for each band because otherwise you would be counting twice. Conceptually, the holes are only useful in the valence band where almost all states are occupied. But if you wanted to, you could treat the conduction band as a huge number of holes as well.

In the normal usage, holes are in the valence band and electrons are in the conduction band. Their properties depend on the band structure, and in general, will not be exact opposites of each other. Electrons and holes can have very different effective masses in some materials.
 
Freeze3018 said:
I know holes are made/present after electron leaves its place but are holes present in metals during photo electric effects?

what is the mass of a hole (if it has any)?

Gravitational or inertial?
 
Freeze3018 said:
I know holes are made/present after electron leaves its place but are holes present in metals during photo electric effects?

A "Hole" typically refers to a vacancy left in the valence band that is mobile yet localized, so that it acts as an effective positively charged object free to move around and carry current. If the photon in the photoelectric effect knocks an electron out of the valence band (typical in semiconductors), then, yes, it will leave a hole. This effect is used in photodiodes. If the photon knocks a conduction electron (as is abundant in metals) out of the material, it does not leaves a hole, because the vacancy it leaves behind is not localized and does not act as a pseudo-particle.

Freeze3018 said:
what is the mass of a hole (if it has any)?

It depends on the material. The hole is assigned an effective mass based on how it moves about under forces, which differs by material. For instance, Silicon has a heavy hole effective mass of 49% the mass of a totally free electron.

Freeze3018 said:
what are its characteristics are they exactly opposite of electron ( i mean its behaviour in electric and magnetic field ) ?

Holes are positively charged and have different masses than electrons. This means they will flow the opposite direction as electrons under an applied field.
 
THnax chrisbaird but what do u mean by "mobile yet localized"
 
Localization means that an electron/hole is associated with an atom/molecule. Don't quite get what is mobile + localized.
 

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