646s09hw11 - ELEG 646 ELEG 446 Nanoelectronic Device...

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Unformatted text preview: ELEG 646 ; ELEG 446- Nanoelectronic Device Principles – Spring 2009 Homework #11 - due Thursday, 7 May 2009, in class. 1. A p-n-p transistor with uniformly doped base, emitter, and collector regions has I E = 1.2 mA. Sketch the minority carrier distribution in the base when (a) the collector is shorted to the base, (b) the collector is shorted to the emitter, and (c) the collector terminal is kept open. 2. The emitter and collector regions of a Si alloyed p-n-p transistor are heavily doped, and the impurity concentration in the base is 10 15 cm-3 . Calculate the base-width that will make the avalanche breakdown voltage equal to the punch-through voltage. The punch through voltage is given by: V PT = qN D W Bo 2 /(2 ε s ) , where W Bo is the metallurgical base width. Assume that avalanche breakdown occurs when the maximum field strength in the depletion region becomes 5 x 10 5 V/cm. What minority carrier diffusion length and lifetime in the base are required to obtain a value of α = 0.95? Assume = 0....
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