314-SampleProblems-F201000011 - donors per cm on the...

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G 21. Consider a p-n junction in GaAs, w hich has a bandgap E = 1.42 eV, an effective density c of states in the conduction band N = 4.7 x 10 cm , and an effective density of states in 17 -3 v the valence band N = 7 x 10 cm . The electron affinity of GaAs is 4.07 eV. The p-side is 18 -3 doped w ith 10 acceptors per cm and the n-side w ith 10 donors per cm . 16 3 14 3 (a) Calculate the w ork functions of the p-type and the n-type materials. (b) Calculate the built-in potential of this junction. p n (c) Calculate the depletion w idths W and W on the p- and n-sides respectively. Why are they unequal? (d) Sketch the energy band diagram under a forw ard bias of 0.5 V, clearly labelling all energy levels and their relative locations. 22. The collector junction of a bipolar transistor has 10
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Unformatted text preview: donors per cm on the collector side 18 3 and 10 acceptors per cm on the base side. Assume the dielectric permittivity of the 15 3 semiconductor to be 1 pF/cm. (a) Is the transistor an npn or a pnp device? (b) Sketch and label the charge density D , electric field E and potential V w ithin the collector-base depletion region under zero bias. (c) Calculate the peak electric field and depletion region w idth under zero bias and 10 V bi reverse bias respectively. Assume the built-in potential V = 0.8 V. (d) What is the change in effective base w idth as the collector-base voltage is changed from 0 to 10 V? Does this improve or inhibit the performance of the transistor?...
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