314-SampleProblems-F201000004

314-SampleProblems-F201000004 - 17-3 v c e N = 7.0 x 10 cm...

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6. In the electron energy - momentum or E-k diagrams such as that sketched here, one finds the energy E and momentum p = (h/2 B )k allow ed for electrons in a semiconductor. Band diagrams such as that sketched on the right only show the allow ed energies. G (a) Estimate the band gap E for the semiconductor that the E-k relation show n. Is the gap direct or indirect? (b) Show clearly on both the figures the states in the valence band occupied by holes at room temp. (c) Assuming the lattice constant a = 0.4 nm, estimate the momentum change and energy change that must take place w hen an electron falls back across the gap (i.e. recombines) in this semiconductor. G 7. The compound semiconductor GaAs has an energy gap E = 1.42 eV, a conduction band c effective density of states N = 4.7 x 10 cm , a valence band effective density of states
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Unformatted text preview: 17-3 v c e N = 7.0 x 10 cm , and an electron affinity (difference betw een vacuum level and E ) P = 18-3 4.07 eV, all at T = 300 K. (a) Compute the hole concentration at 300 K if the material is intrinsic. (b) Compute the electron concentration at 400 K if the material is intrinsic. (c) If the GaAs is doped w ith 10 cm donors, caclulate the electron concentration 17-3 assuming full ionization of the donors. (d) For this doped, n-type GaAs of part (c), w hat is the concentration of holes at 300 K? F (e) Determine the location of Fermi energy E for intrinsic GaAs at 300 K. 8. The variation of resistivity D of intrinsic Ge w ith temperature is given by the follow ing table: T (K) 385 455 556 714 D ( S-m) 0.028 0.0061 0.0013 0.000274...
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