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Midterm Exam 1 Solutions 08

4 pts given during exam assume

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Unformatted text preview: sume , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , We have to look up four mobility values on the given mobility chart. Doing so, we find , , , , 1200 cm /V s 150 cm /V s 1200 cm /V s 450 cm /V s 0.622 iii) Find the ratio of the areal junction capacitances of these two p-n junctions when they are not biased (i.e., 0V). [4 pts] , Si , , 2 , , , Si 2 , 1 , , , , , Page 3 , , , , 1 , , , , , , 1.303 Problem 2 [25 points]: Bipolar Junction Transistor (BJT) a) The following two NPN BJTs have the same doping concentrations. The only difference is their base widths: BJT-A has a base width of 100 nm, while BJT-B has a base width of 200 nm. Find the ratio of their current gains. (If you give correct qualitative answer, i.e., which BJT has higher current gain and why, you will get half credit). [6 pts] E B C E B C Emitter: N-type, N d = 1018 cm −3 100 nm Base: P-type, N a = 1017 cm −3 200 nm Collector: N-type, N d = 1016 cm −3 BJT-A BJT-B , , , , , , , , , , , , , , 2 All of the other terms cancel because the doping (and therefore the mobility and diffusion constants) are the same between the two transistors. b) Consider the following two BJTs. They have identical dimensions and doping profiles, except BJT-A is NPN t...
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