# HW5 - Use Fermi probability to find out the number of...

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ECE331 Homework #5 (Due Friday, 5/9/2008) 1. Calculate values for the Fermi function f(E) at 300 K and plot vs. energy in eV. Choose E F = 1 eV and make the calculated points closer together near the Fermi level to obtain a smooth curve. Notice that f(E) varies quite rapidly within a few kT of E F . Show that the probability that a state E above E F is occupied is the same as the probability that the state E below E F is empty. (10 points) (Note: hand sketch is not acceptable) 2. An unknown semiconductor has E g = 1.1 eV and N c = N v. It is doped with 10 15 cm -3 donors, where the donor level is 0.2 eV below E c. Given that E F is 0.25 eV below E c , calculate n i and the concentration of electrons and holes in the semiconductor at 300 K. (20 points) (Hint: Not all donors are ionized.
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Unformatted text preview: Use Fermi probability to find out the number of ionized donors at 300 K.) 3. If n o = 10 16 cm-3 , where is the Fermi level relative to E i in Si at 300 K? (10 points) 4. Calculate the displacement of E i from E g /2 for Si at 300 K, assuming the effective mass values for electrons and holes are 1.1m o and 0.56m o , respectively. (10 points) 5. A new semiconductor has N c = 10 19 cm-3 , N v = 5 x 10 18 cm-3 , and E g = 2 eV. If it is doped with 10 17 donors (fully ionized), calculate the electron, hole and intrinsic carrier concentrations at 627 C. Sketch the simplified band diagram, showing the position of E F . (20 points)...
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