Semiconductors - Flat band Diagram vs Equilibrium Diagram

[Marcin H]

Homework Statement

Homework Equations

Energy band diagram equations.

The Attempt at a Solution

This is more of a conceptual question, but this is the problem I am working on for reference. What is the difference between a flat band diagram and an equilibrium diagram? I know what they will look like by doing some googling, but I don't understand the difference between the two and what one tells us over the other. What are all the differences between them? Is the flatband diagram the diagram as soon as we bring our metal and semiconductor material together. Is that a snapshot of the moment they touch? And is the equilibrium band diagram after diffusion occurs? I am confused by the two in general and don't know what they tell us.

Here is what they will look like from googling:

I also, know how to find ФF, but that doesn't really help much with understanding these diagrams...

Edit* Also, how can we tell what regime the diagram will be in from the given information? How do we tell if it's depletion or accumulation or inversion?

 

[Lord Jestocost]

The flatband case prevails when the energy band diagram of the semiconductor is flat, which implies that no space charge regions exist in the semiconductor device. The equilibrium case prevails when the electrochemical potential (Fermi energy) of the mobile charge carriers is constant throughout the device.

See, for example, chapter 3 and 6 in: https://ecee.colorado.edu/~bart/book/book/contents.htm

 

[Marcin H]

The flatband case prevails when the energy band diagram of the semiconductor is flat, which implies that no space charge regions exist in the semiconductor device. The equilibrium case prevails when the electrochemical potential (Fermi energy) of the mobile charge carriers is constant throughout the device.

See, for example, chapter 3 and 6 in: https://ecee.colorado.edu/~bart/book/book/contents.htm

Thank you for the response. I still don't understand how accumulation, depletion, and inversion work. How can we tell if a device is in one of those regions? In the problem we are not given a gate voltage, which is how I thought we find out which region the device is in. How do we find the region without the applied voltage?

It kind of makes sense when an applied voltage is there, but I am still a bit fuzzy on that. [Here is what the book has](https://imgur.com/a/TT2ORAQ)

 

[Lord Jestocost]

Maybe, chapter 5 of Chenming Hu's "Modern Semiconductor Devices for Integrated Circuits" will be of help. You find it at https://people.eecs.berkeley.edu/~hu/Book-Chapters-and-Lecture-Slides-download.html