EE2 Physics for Electrical Engineers P r o f . B . J a l a l i W i n t e r 20 1 1 Practice Problem Set #2 ( No due date, for practice only ) 1. An abrupt p-n junction has 10 18 cm-3 donor atoms on the n-side, and 10 16 cm-3 acceptor atoms on the p-side. Take the diffusion lengths in the n and p regions to be 1.5 × 10-2 cm, and 9 × 10-4 cm respectively. If you need the diffusion constants, use the Einstein Relation, and look up the mobility in your text, or in Viswanathan’s notes. Calculate the overall pn diode capacitance/cm 2 , (a) at a forward bias of 0.5 Volts, and (b) at a reverse bias of 10 Volts. 2. Given that the critical electric field is 2 × 10 5 Volts/cm, calculate the breakdown voltage of a p-n junction with N A =10 17 cm-3 and N D =10 16 cm-3 . 3. An n-p-n transistor has an impurity concentration of 5 × 10 19 cm-3 in the emitter, 5 × 10 16 cm-3 in the base and 2 × 10 15 cm-3 in the collector. The base width, is equal to 2 μ m, thin enough for the Narrow Base Approximation. Once the minority carriers reach the collector they are swept away,
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