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Unformatted text preview: Lecture 16 Wednesday March 2 EE 332 Semiconductor Devices Problem Assignment Monday Æ 5.9 omit parts d , h , and i Wednesday Æ 5.14, 5.19 s w qn J i G 3 10 let 2 − = − = τ τ for 5.14 useeq. 5.90 First PSpice problem is posted Regions of Diode I-V Curve Generation Current Proportional to 2 1 r V The number of thermally generated carriers is proportional to the number of impurities. As the depletion width W increases with the generation rate increases because there are more impurities in an enlarged W . Impurities with levels near the center of the gap are most effective. 2 1 r V Ideality Factor ( ) actor Ideality F , 2 1 1 / = ≤ ≤ − = n n e I I nkT qV Thus at low voltages, recombination in the depletion region is important and then the current is proportional to e V/2kT whereas at higher voltages we get the usual expression. The diode equation can be modified to account for these two regions as follows: ZenerEffect When negative bias is applied to a p-n junction and causes the n-conduction band to line up with the p-valance band, then electrons can tunnel from the p-valance band into the n- conduction band. This only occurs for small W requiring high doping. Restricted to few a volts. Avalanche Breakdown With large reverse bias, the electric field increases to where the velocity gained by an...
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- Spring '08
- rp, p-n junctions, Diode I-V Curve