ece340Fall03HW6sol - ECE 340 Homework VI Fall 2003 Due:...

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ECE 340 Homework VI Fall 2003 Due: Monday, September 29, 2003 1. How long does it take an average electron to drift 0.1 mm in (a) pure Si and (b) Si doped with 6x10 16 /cm 3 donors at an electric field of 100 V/cm? Repeat for 10 5 V/cm. Assume that the electron effective mass m n *=0.26 m o . Solutions: (a) From the chart, the electron mobility for pure silicon is about 1350 2 / cm V Sec i , The drift speed of an electron is: dd vE µ = . The time of flight is: 1 8 0.1 10 7.41 10 . 1350 100 d dn LL tS e c × == = = × × (b), For Si with 6x10 16 /cm 3 donor, 2 790 / n cm V Sec = i 1 7 0.1 10 1.27 10 . 790 100 d e c × = = × × For 10 5 V/cm, from Figure 3-24, the velocity saturated at 10 7 cm/s, independent of doping and electrical fields. Actually if we assume the = still holds, then even for case b: 57 790 10 7.9 10 / d vc m s =×= × , which is large than the saturation speed. Therefore, for both cases: 1 9 7 0.1 10 11 0 . 10 d sat L e c v × = × 2. (a) Show that the minimum conductivity of a semiconductor sample occurs when n o =n i p n ) 1/2 .
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ece340Fall03HW6sol - ECE 340 Homework VI Fall 2003 Due:...

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