Physics of semiconductor in light and dark

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Discussion Overview

The discussion revolves around the physics of semiconductor behavior when exposed to light, particularly focusing on transitions between energy bands (valence band to conduction band) and surface states. Participants explore concepts related to superband gap transitions, charge movement, and the implications of these processes in light and dark conditions.

Discussion Character

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

Main Points Raised

  • Some participants describe the transitions occurring in semiconductors when illuminated, including the movement of electrons from the valence band (VB) to the conduction band (CB) and surface states (SS).
  • There is a mention of the conditions required for superband gap illumination, specifically that the energy of incident light must exceed the band gap energy.
  • Participants discuss the concept of surface states and their role in electron transitions, noting that electrons can move from SS to CB and from VB to SS under certain energy conditions.
  • One participant emphasizes the importance of charge movement in altering band bending, which can be monitored using Surface Photovoltage (SPV) techniques.
  • Another participant questions the clarity of the original inquiry, suggesting that the question is too broad and lacks specificity.
  • There are differing views on the nature of charge movement, with some arguing it is a change in energy state rather than physical movement.
  • A suggestion is made to refer to a specific paper for further insights on the topic.

Areas of Agreement / Disagreement

Participants express various interpretations of the processes involved, with some agreeing on the definitions of VB, CB, and SS, while others challenge the clarity and specificity of the original question. The discussion remains unresolved regarding the exact nature of charge movement and the physics behind the observed phenomena.

Contextual Notes

Some participants note that the original question lacks specificity, which may hinder a focused discussion. There are also unresolved aspects regarding the definitions and implications of energy transitions in semiconductors.

Who May Find This Useful

This discussion may be of interest to those studying semiconductor physics, particularly in the context of light interactions, energy band theory, and surface phenomena in materials.

quantum world
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Hi all,
when we shine light on semiconductor surface with white light, superband gap transition occurs (VB to CB). Also we have surface state (SS) too, so there is probability of transition from VB to SS and SS to CB as well. The time transient of this surface is similar to charging of a capacitor (in light) and discharging of a capacitor (in dark). Could someone explain physics of this process?
 
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quantum world,

when we shine light on semiconductor surface with white light, superband gap transition occurs (VB to CB).

Could you define "VB" and "CB" and explain what the superband gap transistion is?"

Also we have surface state (SS) too, so there is probability of transition from VB to SS and SS to CB as well.

What is "SS", and how does it relate to the statement above?

The time transient of this surface is similar to charging of a capacitor (in light) and discharging of a capacitor (in dark).

What surface?

Could someone explain physics of this process?

What process? I doubt if anyone will even try. The question is too broad, ill defined, and not specific enough.

Ratch
 
VB=valence band CB=conduction band

when the energy of incident light, hf≥ band gap energy, super band gap illumination takes place.

The surface between a semiconductor and vacuum or gas is referred as a free surface or just surface.

The termination of periodic structure of semiconductor at its free surface or the bonds that are free at surface may form surface localized electronic states within semiconductor band gap is called surface state.

The electrons from ss can move to cb if incident energy hf≥ ( Ecb - Esurface state )

The electrons from vb can move to ss if incident energy hf≥ ( Esurface state - Evb )
 
quantum world said:
VB=valence band CB=conduction band

when the energy of incident light, hf≥ band gap energy, super band gap illumination takes place.

The surface between a semiconductor and vacuum or gas is referred as a free surface or just surface.

The termination of periodic structure of semiconductor at its free surface or the bonds that are free at surface may form surface localized electronic states within semiconductor band gap is called surface state.

The electrons from ss can move to cb if incident energy hf≥ ( Ecb - Esurface state )

The electrons from vb can move to ss if incident energy hf≥ ( Esurface state - Evb )

So exactly what is this "physics" that you want an explanation for?

Zz.
 
Actually the movement of charges from cb to vb or from ss to cb or from vb to ss due to illumination, changes the band bending which is monitored in Surface Photovoltage (SPV) technique. Actually physics is hidden there so I want to be clear about that.
 
Try with Optical Detection of Surface States in Ge Phys. Rev. 144, 749–751 (1966)
 
quantum world said:
Actually the movement of charges from cb to vb or from ss to cb or from vb to ss due to illumination, changes the band bending which is monitored in Surface Photovoltage (SPV) technique. Actually physics is hidden there so I want to be clear about that.

The actual "movement" of charges?

Isn't that like asking the "movement" of an electron when it makes an atomic transition?

There is no "movement" here. It is a change in the energy state! The conduction band and valence band are not two separate locations.

Zz.
 
For a general explanation of how orbital electrons can absorb energy
from light, try reading the first few sections here:

[note that sometimes electrons just jump energy bands, other times they can actually
be ejected from the material.]
http://en.wikipedia.org/wiki/Photo-electric_effect
 

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