F2010_ECE132_Quiz2_Fri

F2010_ECE132_Quiz2_Fri - ECE 132 Quiz 2 Name...

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Unformatted text preview: ECE 132 Quiz 2 Name __________________________ October 15, 2010 This question will check your knowledge of compensation when a semiconductor is doped with both acceptor and donor atoms. Recall that a donor dopant creates one or more states filled with electrons at some energy level ED within the bandgap. An acceptor dopant creates states which can accept electrons at a different energy level EA within the bandgap. In the figures below, Silicon has been doped with a Group V element with concentration ND and energy level ED. At room temperature almost all of the donor atoms are ionized (ND+ ≈ ND). Then three samples of this material were further doped with 3 different elements which can accept electrons, all with the same concentration NA but different accepter energy levels: EA1, EA2, and EA3. Assume that ND > NA » ni. The thermal energy kT has been identified relative to the conduction band to help you. kT Ec ED Ec kT ED Ec kT ED EA3 E v (1) EA1 EA2 E v (2) Ev (3) 1) What is the concentration of conduction band electrons (n0) before the acceptor dopant is added? 2) For each of the three cases, is n0 = NA, ND, NA+ND, NA‐ND, or ND‐NA? Give a reason for your answer. You will not need the Fermi function, look at the problem intuitively. • Case (1): • Case (2): • Case (3): ...
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