314-SampleProblems-F201000010 - the main valley to the...

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19. A p-n homojunction is doped uniformly w ith 10 donors per cm on the n-side, and 10 18 3 15 acceptors per cm on the p-side. The dielectric permittivity of Si , = 1 pF/cm. 3 (a) Sketch the energy band diagram, space charge density D , and electric field E as a n p function of x w ithin the depletion region, i.e. for -W < x < W . max (b) Given the built-in potential is 0.8 V, calculate the maximum electric field E and depletion w idth W under thermal equilibrium. (c) Repeat part (a) under a reverse bias of 10 V. (d) Suggest three applications for p-n junctions. 20. Consider the E-k diagram show n. (a) If this material is used in a light-emitting diode, w hat color light w ould be produced by the direct transitions from
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Unformatted text preview: the main valley to the valence band maximum? (b) Electrons recombining from the satellite valley dow n to the maximum in the valence band w ould give rise to phonon emission ( to account for the change in momentum or w avenumber k). Calculate 1 the w avelength of the phonon if k = 5 x 10 cm . 8-1 (c) Assuming the electron collision time remains the same, calculate the ratio of mobility for electrons in the main valley to that for electrons excited to the satellite valley. (d) Explain the physical origin of the current-voltage (I-V) characteristics show n in the sketch for a typical Transferred Electron Device (TED) or Gunn oscillator....
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