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# sol4 - ECE 440 HW4 Solutions Summer 2009 Thu 1(a A Si bar...

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ECE 440 HW4 Solutions Summer 2009 Thu, Jul 02, 2009 1 1. (a) A Si bar 0.1 cm long and 100 µm 2 in cross-sectional area is doped with 1x10 17 /cm 3 arsenic. Find the current at 300 K with 10 V applied across the length. To find current, use Ohm’s law. Since we already know the bias, all we need to do is find is the resistance (R) in order to solve for the current. Equation (3-44) gives resistance in terms of area, charge carriers, and mobilities. If we substitute (3-44) into Ohm’s Law, we get the following expression for current. Notice that this is the formula for the drift current which was derived in the text. Keep in mind that this expression is only valid if the drift velocity of the carriers is smaller than the saturation velocity. The saturation velocity is fixed for a particular material system. For Silicon, the saturation velocity is approximately 10 7 cm/s. First, we need to check that we are not in the saturation condition. For an electron concentration of 1x10 17 cm -3 , we can find an electron mobility of 700 cm 2 /V-s.

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• Summer '09
• Lie
• Condensed matter physics, carrier concentration, intrinsic carrier concentration, Si bar, saturation condition

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