Thermal Velocity of an Electron?

Discussion in 'Homework Help' started by Lee_831, May 22, 2011.

  1. Lee_831

    Thread Starter New Member

    Nov 17, 2009
    6
    0
    Hi,
    Apologies if this has been asked before, I performed a search but didn't find much!
    Working on a textbook of semiconductor device physics, and have come across a formula for the thermal velocity of a hole/electron.

    It's listed as Vth = √3kT/m*
    Where m* is the effective mass.

    Now entering the data for a piece of n-type silicon as follows:
    k = 1.38x10^-23 JK-1
    T = 300K
    m* = 1.18Mo

    I work this out to be 1.02x10^-10, however the textbook answer is 1.08x10^5, which is nowhere near. :confused:
    Am I doing something wrong with the units or is something else off? I appreciate any help.
    Thanks,
    Lee
     
  2. jegues

    Well-Known Member

    Sep 13, 2010
    735
    43
    You are doing your algebra incorrectly, I was able to obtain the correct answer listed.

    V_{t} =\sqrt{\frac{3kT}{1.18m_{o}}} = 1.08 \times 10^{5}
     
    Last edited: May 23, 2011
    Lee_831 likes this.
  3. Lee_831

    Thread Starter New Member

    Nov 17, 2009
    6
    0
    Hi,
    Thanks for your quick reply, can you possibly suggest where I am going wrong? I am simply entering 3x300x1.38x10^-23, dividing that by 1.18 and then taking the square root.
    Thanks for your help,
    Lee
     
  4. jegues

    Well-Known Member

    Sep 13, 2010
    735
    43
    You have to divide by,

    1.18 \times m_{o}=1.18 \times(9.11\times10^{-31})
     
    Lee_831 likes this.
  5. Lee_831

    Thread Starter New Member

    Nov 17, 2009
    6
    0
    Sorry for the late reply.. Thanks everyone! Thought I was going insane.
     
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