Notes on the first midterm:
1. a) \( n \approx kT D_c e^{-(E_c-E_f)/kT} \: cm^{-3} = kT D_c e^{-9} = 3.7 \times 10^{17} \: cm^{-3}\)
1. b) \( p \approx kT D_c e^{-(E_f-E_v)/kT} \: cm^{-3} = kT D_c e^{-31} = 1.03 \times 10^{8} \: cm^{-3}\)
1. c) \(4\: eV \times D = 48 \times 10^{22}\) empty states in the conduction band.
4. I think one gets 2,100 nm for the length scale. Is that correct? Is that for a band mass of 1? It is interesting to notice all the parameters this does not depend on! (As well as the ones it does depend on (kT, tau, other tau and m)).
5. a) \(1 eV \times D = 12 \times 10^{22}\) filled states, that is, electrons, in the conduction band. (Because the Fermi energy is 1 eV above the conduction band lower edge. 1/4 of the conduction band is filled.
b) Here you can use the approximation. Why? (Post answer here in comments for extra credit.) \(p \approx kT D_c e^{-(E_f-E_v)/kT} \: cm^{-3} = kT D_c e^{-40} =\) Post number here in comments for extra credit.)
c) \(3 eV \times D = 12 \times 10^{22}\) empty states.
Feel free to comment, discuss and ask questions here. What problems did you like? What problems were you not so fond of...
I would like it to include HW 4. HW 4 is pretty short and interested. I would hate for it to get overlooked. We can discuss Tuesday. The ideal think might be to work on it before Tuesday and see if there are any parts where you get stuck.
ReplyDeleteSo, to speed things up and so you will be confident you are on the right track, you can ask me questions in the comments to HW 4, like:
ReplyDeleteIs this differential eqn correct?
Does the differential equation just involve p(x)?
Is this the right form for p(x)?
Is this the right length scale?
That way, if you get off track you can get right back on a good track quickly. I will post this also as a comment to the HW 4 post, and I am thinking that is the preferred place for this particular discussion. (About HW 4.)
Also, if you like, I can have office hours after class. Let me know if you would like to talk after class on Tuesday.
On the midterm tomorrow, there will be some problems where you calculate things, and also some discussion questions where you'd discuss things. On the discussion questions, be expressive. Don't hold back or be vague for fear of making mistakes.
ReplyDeleteAlso, for every problem assume that the density of states, temperature, band edge energies, band width, etc. is exactly the same as on homework 3.
There is a lot on both the biased and unbiased pn junction on the midterm. You will not have to calculate xd. I would focus a lot of attention on the last three videos and on HW 4.
ReplyDelete