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Construct a semilogarithmic plot

  1. Nov 20, 2006 #1
    How do you solve the following problems? Thank you for any inputs.

    1.Construct a semilogarithmic plot for Si doped with 2X10^15 donors/cm3 and having 4x10^14 EHP/cm^3 created uniformly at t=0. assume that tn = tp = 5us.

    2.calcualte the recombination coefficient alphar for the low-level ecitation described in problem 1. assume that this value of alphar applied when the GaAs sample isuniformly exposed to a steady state optical generation rate gop = 10^19 EHP/cm^3-s. find the stead state excess carrier concentration.

    3. For a 2cm long doped Si bar with a cross sectional area = 0.05 cm^2. what is the current ifwe apply 10V across it? if we generate 10^20 electron-hole pairs per second per cm^3 uniformaly in the bar and the lifetime tn = tp = 10^-4s, what is the new current? assume the low-level alphar doesn't change for high-level injection. if the voltage is then increased to 100,000V, what is the new current? Assume up=500cm^2/Vs, but you must choose the appropriate value for electrons.

    4. A 100 mW laser beam with wavelength = 6328 is focused onto a GaAs sample 100um thick. the absorption coefficient at this ewavelength is 2X10^4 cm^-1. find the number of photons emitted per second by radiative recombination in the GaAs, assuming perfect quantum efficiency. what power is delivered to the sample as heat?

    Thank you.
  2. jcsd
  3. Nov 20, 2006 #2
    Thank you for your help. I have another question about a Si sample that is uniformly optically excited at room temp.:
    A Si sample with 10^15/cm^3 donors is uniformly optically excited at room temperature such that 10^19/cm^3 electron-hole pairs are generated per second. Find the separation of the quasi-Fermi levels and the change of conductivity upon shining the light. Electron and hole lifetimes are both 10us. Dp = 12 cm^2/s.

    Thank you.
  4. Nov 21, 2006 #3


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    You're not supposed to just do people's homework for them. Just give a hint or a partial solution and only do that if they show their own work.
  5. Nov 21, 2006 #4


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    I'm locking this thread. kobetsai, as Orthodontist says, the PF homework forum guidelines are pretty clear about how to help people. Please re-read them to be sure that you understand. We are here as tutors, not as homework solution machines. davelandsman, as Ortho says, you need to show your work so far when you post homework questions.

    Welcome to PF to both of you. It can be a great resource when used correctly.
  6. Nov 21, 2006 #5


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    The complete solutions have been deleted, and I reopened the thread so you can get proper help with your homework.

    As berkeman stated, we offer HELP, not complete answers. Handing someone a complete solution will not help them understand the subject and learn how to do it themself. If you do not know a way to prompt them in the right direction without giving away the complete answer, please don't respond.
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