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Unformatted text preview: EEE 352Fall 2009 Homework 8 7.2 Calculate the built-in potential barrier, V bi , for Si, Ge, and GaAs pn junctions if they each have the following dopant concentrations at T = 300 K: (a) N d = 10 14 cm-3 , N a = 10 17 cm-3 , (b) N d = 5X10 16 cm-3 , N a = 5X10 16 cm-3 , (c) N d = 10 17 cm-3 , N a = 10 17 cm-3 . The built-in potential is give by (7.10) to be V bi = k B T e ln N a N d n i 2 The value for the intrinsic concentration is given in Table B.4, so that we find: Si Ge GaAs (a) 0.635 0.253 1.103 (b) 0.778 0.396 1.246 (c) 0.814 0.432 1.282 7.5 An abrupt pn junction at zero bias has dopant concentrations of N a = 10 17 cm-3 and N d = 5 10 15 cm-3 . T = 300 K. (a) Calculate the Fermi level on each side of the junction with respect to the intrinsic Fermi level. (b) Sketch the equilibrium band diagram for the junction and determine V bi from the diagram and the results of part (a). (c) Calculate V bi using Eq. (7.10), and compare the results to part (b). (d) determine x n , x p , and the peak electric field for this junction. From the Nanohub simulation, we find: (a) In the p-region, the valence band edge is at -0.137 eV and the Fermi level is at 0, while the intrinsic Fermi level is at 0.417 eV. Therefore, in the p-region, the Fermi level is 0.417 below the intrinsic Fermi level....
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This note was uploaded on 10/28/2009 for the course EEE 352 taught by Professor Ferry during the Fall '08 term at ASU.
- Fall '08