OK, here it is. Please post here regarding any questions, errors or ambiguities. This seems a little long, longer than I was hoping for. If you identify any questions that seem not so important-- that do not seem to have a point -- please post a comment on that here and maybe we can try to shorten it. Your thoughts are welcome. Please keep checking here for possible updates, corrections or clarifications.
* (problem 4 corrected, Saturday 8:40 PM)
https://drive.google.com/file/d/0B_GIlXrjJVn4aGJ6X25CaWowSDg/edit?usp=sharing
When is this due again?
ReplyDeleteTuesday at noon.
DeleteFor problem 2b), would you mind if we got a computer solution or would you prefer us to solve it with approximations?
ReplyDeleteapproximations. You can check them with a computer solution if you like, but please turn in a solution that uses approximations.
DeleteDoes the density of states equal zero at the edges of the conduction band in the equilateral DOS from problem 2?
ReplyDeleteProblem 2 was very interesting. I really liked it. Are there ever times where we approximate the CB as a triangular band as opposed to a constant band. You mentioned in class that the edge of the conduction band can be approximated as a parabola so I'm wondering if this is a way to approximate the band.
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ReplyDeleteIn problem number 5, you ask for a range of workfunction that would create an always on state. How many free flowing electrons at the interphase would be enough to consider the transistor to be "on"? I am thinking it might be around 10^15 but I really don't know.
ReplyDeleteAlso, is there any reason why you gave us a particular reason why you gave us the recombination time in problem 4, even though you did not give us the diffusion coefficient? Can I leave my answer in terms of tau or should I plug in numbers where I can?
Delete10^15 or 10^16 sounds reasonable.
DeleteI think I am going to have to fix problem 4. Thanks for pointing that out.
To solve number 5 numerically, wouldn't we have to know DOS or something that will lead us to the DOS? Unless I'm missing something, I don't think we have enough information as it is.
ReplyDeleteAlso, what do you mean by 1017 and 1015 on the extra credit problem?
"Also, what do you mean by 1017 and 1015 ..."
DeleteI don't think you have the correct version of the midterm. Try downloading again.
You can use the DOS from problem 1 (for 5) if you like.
@CK
DeleteI don't think so.
With D=10^22 and 10^15 as the n which allows significant current, we get a strange situation where n>10^15 everywhere just because mu is too close to Ec. Is this intended? This won't even function as a transistor because the semiconductor is conductive everywhere.
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ReplyDeleteTo determine an exact answer for #4b, don't we need to have the applied voltage?
ReplyDeleteNevermind.
DeleteI'm confused about 4. Where is x=0 on the semiconductor? d is the part where the two type meet; is x=0 the edge of the depletion zone? Then would < 0 be in between the depletion zone and the junction?
ReplyDelete" is x=0 the edge of the depletion zone?"
ReplyDeleteYes.
Is it reasonable to get preposterously huge current values for #6?
ReplyDeleteWould you like a numerical answer for number 4? I found an expression for the current density but it seems that there are a few perimeters that aren't given.
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