Final discussion post.

Not sure is many people are still looking at this blog, but, just in case, here is a place to discuss the final if you like. Some people had trouble with #5. (Illuminated n-p junction and resistor..) Does anyone want to explain how to handle that? #6 as well.

Overall, I was impressed by how much people learned. Nice work!

Physics 156 Final. Wednesday, 12:00 noon

The final should provide an opportunity for you to show your understanding of semiconductors and metals. E vs k relationships play a big role. Where do they come from? Can you utilize them to calculate fermi velocity, fermi boundaries,…? Do you understand the significance of the Brillouin zone? Can you distinguish occupied and unoccupied states?

For semiconductors, the fermi energy is in an energy gap. Do you understand what an energy gap is and what the density of states as a function of energy typically looks like for a semiconductor? Special approximations can be used to estimate carrier density for cases where Ef is in a gap. Other approximations can often be used when Ef is not in a gap. The ability to recognize and distinguish those cases is important. Understanding the nature of those approximations, and what they rely on, is also important.

What is the essential nature and phenomenology of an n-p junction?

What role does shifting of the fermi boundary play in the conductivity of a metal?

Do you understand the origin of ferromagnetism?

I’ll post more here later. I just wanted to get the ball rolling and provide a place for questions and discussion here.
Added  notes: Perhaps it would be good to have a problem on illuminated n-p junctions. How do you feel about that? What about a ferromagnetism problem.
    It might be a good idea to test yourself with Fermi boundaries. You may wish to test your ability to identify where a Fermi boundary crosses the kx axis, realizing that the ky term is not zero when ky=0. (Same thing for the ky axis.)

Equations are show here: (What else do we need? I can't think of very many basic equations from the second part of the class.)

Conductivity of a Metal

Here is a video on conductivity of a metal that talks about the shift of the Fermi boundary and the electron speed. Please feel free to discuss and ask questions here.

Homework 7 solutions.

Here is a link. When you show a Fermi boundary, it is important to also show the extent of the (1st) Brillouin zone. The (1st) Brillouin zone is a domain in k-space in which each state can be found exactly once. Going beyond that would lead to encompassing some states more than once (over counting). The point of the Fermi boundary is to be able to specify which states are occupied (and which states are not occupied).

https://drive.google.com/file/d/0B_GIlXrjJVn4R09ISFh6Nl92NU0/view?usp=sharing